Backer Board Moment Has Come - A Little Help [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-07-2015, 07:52 PM
Well, I started this bathroom remodeling project in October. It's been a journey! I've made mistakes, corrected them, sometimes two or three times and I've learned a lot in the process. With the plumbing, electrical and drywall almost done, I am at the point I need to put up my Hardie backer board.

I've read, re-read and studied and I understand the backer board stops 1/8 above the lip of the tub. I am putting in a new tub, and secured it with stainless steel screws and washers as required. I found out today that the lip of the tub on the backside was bowed out in the center causing it to hit the center wall studs 1/4 sooner than the ends. I had shimmed the ends not catching that.

I "think" I can bend the lip of the tub out the same on the ends and eliminate those shims. Does this sound reasonable? The tub is already plumbed and I would hate to have to move it.

If I put the backer board 1/8 above the tub, how are the washer and screws covered? Does the tile drop over them?

Also do I need additional blocking along side the bottom lip of the tub. I have seen some people suggest that, others not.

I am looking at purchasing RedGuard so I don't plan to put the vapor barrier behind the backer board. I understand you paint that on with two coats after doing the mesh and thinset over the joints.

Am I on the right course? Any helpful thoughts for this novice in this area would be appreciative. I've done a lot of DYI stuff in my life, and helped many; but in this area I am a bit edgy since it is my first time.

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02-07-2015, 08:05 PM
First, a comment - since there's a riser coming out of the valve and it's a 3-handle one, unless you've added an add-on antiscald valve in that circuit, it does not meet today's code, and an inspector would fail it upon inspection!

It depends on the size of the tile you are planning. YOu need at least 60% or so of the tile supported by the wall, and more is nice. You could add some thin shims, and then the cbu would clear the washers and screwheads and be able to come down further without issues. Your tiling flange seems to end a bit shy of the end of the tub - it will be important to be VERY careful and accurate about your waterproofing. Note, 1/2" HardieBOard is thinner than 1/2", so you have a little playing room when matching up with drywall.

02-07-2015, 10:27 PM
Welocome, Thomas. :)

In addition to Jim's comments, I'll say that what you really need to do is shim all those walls such that your Hardibacker can cover the inside of the tub's tiling flange down to within a quarter-inch of the horizontal surface of the tub.

You really didn't want that plywood on the one wall, but if you shim over it for the backerboard you may be OK.

If all that requires that you make some sort of transition where the backerboard meets the existing drywall (I presume) outside the shower, so be it.

My opinion; worth price charged.

02-08-2015, 07:53 AM
Thank you very much for the helpful and quick response. I read the comments two or three times making sure I can digest it all. I am a rookie at this and sort of a perfectionist, hence the overkill with the plywood. I actually figured --at the time I first put it up--it would provide an easy place to nail/screw the backer board on.

1. It doesn't hurt the situation does it? My problem was the was short 2.5 inches with the new tub, so I had to fur out the wall with 2 x 6's and added the half inch plywood to make up the rest.

2. While the valves are new, the faucet and plumbing on that side is basically the same as before except some modification's to accommodate height. Figured as the house is 45 years old, I was grandfathered in. I'll look into what and where a antiscald valve can be installed in the circuit. That is a new one.

3. The tub's tiling flange is the tub's lip as I have been calling it correct? Speaking of it, I discovered late yesterday from all appearances that the reason I had to shim the back ends of the tub's tiling flange is because the center of that flange was bent out and hit the wall studs first. Hence the ends of the flange on the backside, which were not, I shimmed. I put a level along it yesterday and clearly saw that problem. I am still trying to decide what to do there, as I thought about bending it back and seeming then If the ends would not need to be shimmed?

4. I actually dreamed this question it seemed. How does one handle the tub ends toward the front where it drops to the floor. Do I cut the backer board so that a narrow strip covers the 3 7/8 gap near the bottom sides of the tub. That would require cutting the entire piece the depth of the tub minus the bottom edge. That would also require me to add that equivalent amount at the top.

My wife is a very patient person, but with four members in the family, she keeps the pressure on me to get this back in operation, if nothing more than to get the second commode back in operation.!

02-08-2015, 07:59 AM
I knew I would forget this question.

Based on your statement, "Hardibacker can cover the inside of the tub's tiling flange down to within a quarter-inch of the horizontal surface of the tub," are we saying I should put the backer board OVER and down the tub's tiling flange.

Not just above it? I think I have read some have suggested an 1/8 above the tiling flange. Not trying to open it to debate, but looking to make sure I understand what you are saying.

Houston Remodeler
02-08-2015, 09:11 AM
1/8" over works too . If you get the cbu over the tub flange, it often bows out and throws the wall out of plumb unless you furr out the studs.

See pics below

02-08-2015, 09:15 AM
You can stop the cbu above the flange (depending on the tile size), but many people prefer to have it come down over the flange, and to keep it from bowing out, you need to either notch the studs or shim them.

FWIW, with a remodel, you MUST bring the parts you change up to current code. That valve, even though they may still sell them, does NOT meet today's codes. Once you remove the old one, you lose any grandfathered approval, and it does NOT make any sense to keep it there. It will complicate your plumbing enough if you had to put in an anti-scald device separate from your valve, not counting the required maintenance access, that you really must replace that valve. You can get multiple handled devices, if you really want to. One 'system' that I've had good luck with is the Delta R10000 rough-in valve body which supports three different types of control depending on the version you choose along with the trim: single handle pressure-balanced; two handle, volume, temp; two handle volume, thermostatically controlled. ANy of those types will fit into the rough-in valve and could be changed at a later time should you change your mind ( like the thermostatically controlled versions).

There are two aspects of containing water: water proof, and vapor proof. Most of the liquid applied waterproofing materials are not great vapor proofers, and as a result, with a solid backing like plywood behind it, the ply could end up damp from condensation.

02-08-2015, 09:23 AM
Thank you again all for your feedback. I am digesting it all.

Of course the headache with putting in a new valve as you suggest is the center stud in the wall. I would have to remove it, but I've done worse at this point. I would need to remove the tub and you wouldn't believe how hard it was to customize the drain.

I am slowly accepting the idea though. I always try to do the right thing and have a firm motto of thinking of the guy behind me. In this case, the next homeowner if and when I sell this house.

BTW, here is a picture of the tiling flange which I 'believe' is bent out. If you can see in the picture with the level, the gap is much smaller at the end then in the center. The result is the tub flange is needing to be shimmed at the ends and not at the center.

I think I have three options but I am open to more:

1. Try to bend the flange in at the center. Maybe tricky.

2. Notch out the two studs at the center whereby the rest of the tub will meet the end studs. This would result in the flange at the center falling under the notched stubs at the center. Any problems with this?

3. Return the tub with all the pain of getting it out and unplumbed from below. The drain was custom built out of Schedule 40 PVC.

Is it ever easy? :-)

Houston Remodeler
02-08-2015, 09:24 AM
You can't bend the flange or the pan. Shim the studs.

02-08-2015, 11:57 AM
Even if the studs are true and the problem is with the tub? I take it then shim the outside stubs then to accommodate the tub's issue.

Makes sense, only question with that is the flange will not be aligned up evenly with the top edge of the backer board. In other words, the center will be further towards the back of the backer board since they are not shimmed and the ends will be further up.

Maybe I am overthinking this. Probably a common occurrence to the pro's who run across this on occasion. To someone like me who maybe runs across it once in a life time, it's a mental hurtle to overcome. :-)

02-08-2015, 04:51 PM
If you shim the studs so that you can bring the cbu down over the flange to near the horizontal ledge of the tub, I doubt you'd notice the curve, and then, you can keep your wall nice and flat and plumb. Wouldn't be hard to test...put something on the tub ledge to prevent it being scratched, and just set a sheet of ply or cbu or something up there and look.

02-09-2015, 12:15 PM
Thank you everyone. Looks I have to do some more destruction before I move forward. Need to study on how to install the valve.

Ca you tell me if this is true today? "Basically if you cover the walls as you have them now with a moisture proof drywall and seal the joints with the appropriate mud, youíre ready to tile. You donít need backer board. Backer board is used on the floor to keep it from flexing. On the walls, it is a great big overkill. Itís not needed. And itís really not a true waterproofing method. It just happens to be dense enough, so it mostly works. But if water gets to it, it will hold water and destroy itself just like drywall will. The drywall is easier to work with than backer board as well. Very few of the professionals are using backer board anywhere. Most are using drywall and Schluter products for waterproofing. But proper drywall with epoxy grout will waterproof almost as well as Schluter and no backer board is needed."

Should I return my Hardie board or is the above not accurate?

02-09-2015, 12:27 PM
Thomas, if you'll visit our FAQ you'll find a brief tutorial on how best to post quotes here on the forums and to properly attribute them. Very simple once you see it. :)

Don't know where you found that statement, but it's mostly silly in my view and completely inaccurate. The only parts that have any basis in fact are that CBU is not waterproof and that one of Schluter's products can be used over drywall in a wet area.

My opinion; worth price charged.

Houston Remodeler
02-09-2015, 12:27 PM
Sentences 1 through 7 are false. 8 is correct. 9 and 10 are false. 11 is true. 12 ,13 and 14 are false.

02-09-2015, 12:28 PM
Sounds to me like someone had an overdose of orange Kool-Aid! :D

IF you are planning on using Kerdi it may be an acceptable substrate, little up for debate yet! :)

Otherwise sheetrock has no place as a tub surround. :shake:

02-09-2015, 12:44 PM
Thank you. I am taking this all to heart. Originally the plywood was there because I was going with a "plastic" tub and surround (stability and gave me the half inch I needed.) I later changed my mind not understanding that leaving it there for tile would be a problem.

I just have to figure out how to best get the tub and plywood out and new valve in there with the least amount of damage to my new walls. On the front, the tub's edge is just inside the drywall. Something is going to have to give. :bonk:

Thank you all.

02-09-2015, 05:54 PM
The premise of drywall as a backer in a wet area relies on the consideration that, when a topical waterproof sheet membrane is applied, anything behind it is technically in a dry area (like your window in a wall - you have drywall all around it or drywall underneath your roof, especially on a cathedral ceiling). More than one sheet membrane manufacturer allows building a shower area using drywall (gypsum board) as the backer. Using it in other wet circumstances is just plain foolish, though.

02-09-2015, 07:35 PM
Just an update. Tonight after work I removed the old shower valve, faucet and shower head stem. Capped the lines until I figure how I put in the proper balancing valve.

Still mulling how I can get the plywood out. Have the remove the tub to do that and that is where I am putting my brain power to work.

Can I ask a question here? If the plywood is an issue because it 'could' get wet and rot, how is it the studs don't face the same potential problem. Both are wood and both could face the same 'potential' issue.

Just asking so I can learn.

02-09-2015, 10:05 PM
My opposition to the plywood is the possibility of it warping and effecting your tile installation. If you're gonna fur out the CBU and your furring strips are over your studs, it may not be much of an issue at all. Just not a place to introduce a potential problem when the material serves no useful purpose.

My opinion; worth price charged.

02-09-2015, 11:51 PM
If you wish to retain that mixing valve, you'll need an external pressure balance valve, or some other device approved that will meet the anti-scald requirements that have been in effect for quite a number of years now. The easiest way to do that is to buy a modern tub/shower valve that has it built in. ON most, that is built into the cartridge, but on some, it's a separate pressure-balance spool valve. Keep in mind that if you do put in a separate one in line, you need to provide a means to service it - a door or removable panel. For this reason, few people go to the trouble of using one, they don't sell a lot of them, and as a result, they tend to be expensive over having one built into the valve.

02-10-2015, 01:04 PM
I am taking your advice and pulling out the plywood tonight. Figure I will cut it almost even with the tub, remove most of it, and from the now exposed back cut an opening to get a handle hold and left the tub over the remaining plywood. Will get my son to help lift the other end.

Called the tub manufacteur. They told me to notch the stud or two where the flange bows out. Said it's somewhat common due to the manufacturing process. He's telling me to put the backerboard above the tile flange.

I believe the majority on this site think it should go over. Over to 1/4" above the flat, horizontal edge of the tub. Am I right?

02-10-2015, 01:22 PM
1/4" is what I see all the time. The point is that they shouldn't is needed for expansion.

02-11-2015, 07:51 PM
Progress Update.

I have followed through with the advice here, and while it took some major effort w/o removing the tub, I pulled the entire plywood sheet out from behind the tub.

I have also notched out the two center studs that hung up the tub from going all the way against the wall. It now touches both ends of the back wall studs.

Couple advice questions.

1. Should I put short horizontal blocks along the back side along the same side as the flange. I've seen that mentioned, is that for the backer board to have more placed to secure?

2. The wall where the plywood was, was a combination of 2 x 6's and that 1/2 "plywood. Both are out at the moment, but I need 2.5" inches to reach the back of the tub tiling flange on that side. Should I just offset the 2 x 6's a 1/2" further forward {leaving a 1/2" gap at the very back of them).

3. I understand to have the backer board hang over the tub flange, I will need to shim out all the studs. Is the practice to just cut those shims out of pieces of 2 x 4's? How far should these long shims extend over the tub flange? I assume they will be pretty slim.

Anything in looking at these pictures I need to be working on?

Thank you.!

02-13-2015, 06:27 AM
The weekend is here! Any thoughts on my posted questions earlier this week?:wohoo:

Houston Remodeler
02-13-2015, 06:35 AM
1- you can, it doesn't hurt

2- You can but I would put 1/2" filler like plywood or drywall then screw through from the other side to help keep the studs from twisting

3- use drywall shims (hard cardboard) or sister studs.

02-13-2015, 09:24 AM
1) vertical studs would be better where possible (picture number 2, for example). When not possible or easy, as with your valve wall, the horizontal studs should lay flat. If they bend, they will tend to bend toward one of the faces, you don't want them bending toward or away from your backer board.

2) What Houston Remodeler said. If you can't get to the other side, put in some blocking near the middle to keep the studs from rotating.

3) sister studs are a good alternative to shims, especially since you are shoring up the walls now anyway. Relatively cheap and really easy. If you are going to make shims, you should rip down some strips of plywood, of the desired thickness, into 1 1/2" wide strips, and use those. Plywood won't split when you screw or nail through it, unlike regular wood. Use some construction glue for a better bond to the studs if you want to.

The shims do not need to extend down in front of the tile flange. in fact, that would be bad, as it would create a wick for water. Just put them on after you have the tub all pulled up to the wall, starting just above the top edge of the tiling flange. I say after the tub is in, because then you will know how thick the shim really needs to be.

02-13-2015, 12:47 PM
Great thank you. Sister studs for #3. I take it those are 2 x 4's screwed along side vertical studs, but brought out to the edge of the tiling flange so that the backer board hangs over tiling flange, but a 1/4" above the flat side of the tub.

On the back wall with those cross pieces that will not work, other sides it could. If my understanding is right. Last night I removed all cross pieces where the valve is going.

On the side block pieces, to be clear, I run them biggest flat side facing out towards me right?

Again thank you!

02-15-2015, 07:54 AM
I purchased two valves, one Moen and one Delta. Seems pros and cons to each for a DIY'er. Delta has a bracket that is flat on the back so mounting it to at horizontal 2 x 4 is straightforward. The plastic plasterguard helps align it up to the finished surface and has a +/- 3/8 tolerance. It has the universal valve in the box. It was $30 cheaper and the manual and instructions seem to reflect that. It doesn't mention connecting to CPVC, but a transition piece should allow for that.

The Moen {posti-temp}puzzles me on the valves mounting holes. They are forward from the back making screwing it evenly a bit awkward. The rounded portion of the valve keeping it from sitting flat on any 2 x 4. It has a round plaster guard. The online videos give a person the impression it should be installed from the back of the tub/shower, and after the backer board and tile are up. The manual is more clear and pristine with illustrations on valve height and shower head height. It mentions all four plumbing materials including CPVC.

1. The biggest question I have is I know my backer board thickness {Hardie "1/2"}, but how do I compensate for my tile thickness. Do I have to know that before I put either one of these valves in? I've read in more than a few places installers have gotten the valve installed to far or not enough when the homeowner purchased a house.

2. Is one valve easier to work with than another besides the price difference of $120 to $91. Moen vs. Delta.

3. With installing new studs on this side with the valve, flush with my 1/8" thick tub tiling flange, I should not need to shim the studs, but am able to go right over the flange? I am thinking 1/8" is nothing for the backer board to be screwed over, is that correct?

I have a long weekend and the wife is gone so it would be an ideal time to turn the water off and install it. Valentines came and went and her bathroom was not ready. :-(

02-15-2015, 08:29 AM
I don't know which one is best or easiest to work with. The plumber I use like Delta over Moen. But, the next plumber will like something else best. Sometimes it's best to go ahead and temporarily install the trim so you can figure out the correct depth.

02-15-2015, 11:35 AM
Wonderboard was developed to take the place of conventional mud walls that had been the only surface to install tile over for, I assume, "a long time".A large number of these mud walls are extant and functioning "just fine". In all cases, these mud walls with their attendant wire and scratch coat and mud coat are constructed so that the 1/4 inch ceramic tile sits flat on the tub base. This can only occur if the mud coat surface itself sits ON the tub base in front of the tub/tile flange. The mud wall should have never have been constructed with a scratch/mud construct "resting on" the tile flange. and then some caulking or cement filling the gap before the tile is installed. The developer of Wonderboard understood this and all his and other like products developed since 1975 have done is eliminate the wire,scratch and mud coats. It really is no harder than that to understand. Ipso facto, I do not care how you get there shims or furring or whatever; The cement board 1/2" or 5/8" must front to back sit entirely IN FRONT of the tub flange if you want a leak proof installation. Tape and membranes and caulking to enclose and isolate a joint that is there because the board is not laid within the confines of the inner perimeter of the tub flange are superfluous and subject to failure over time. This lesson applies to a copper pan for a shower stall as well. The board sits within the confines of the pan. Period.

02-15-2015, 12:48 PM
Yes, the tile does need to sit on the drain side of the lip. That's one of the good things about mud work. It's thick enough to get out over the tub lip. I never knew that placing the scratch coat on the tub lip was wrong. I have yet to see a problem with doing it that way.

02-15-2015, 04:03 PM
Yes, the scratch can go on the lip with no problem. I was a bit too emphatic in emphasizing that you want as much of the mud coat in front of the lip as you can and that then its full waterproofing capacity is realized. And to get in the habit of thinking of a wonderboard installation in the same way as a mud installation. But that the mud install is the Gold standard and all other methods must be judged by it. Cement board and the following imitators over the years are all great, BUT keep in mind they are all intended to be standins for wire-scratch-mud. The more things change the more they stay the same.

02-15-2015, 05:30 PM
Bookie, While I'm very much in favor of having the mud or CBU entirely on the drain side of the tub's tiling flange, so long as the moisture barrier or waterproofing membrane is on that side of the installation it will meet the requirements and function well enough.

02-15-2015, 08:26 PM
Interesting comments as my bathroom tile previously was mud and wire. It was blue, and it had a hairline crack across the middle. Being concerned about water getting into the crack and the tile being dated, I figured for future resale I needed to act.

I have to laugh. Two friends of mine told me I could chisel off my tile and redo it. I now know their tile was on drywall or backer board of some sort. Their tile came off in complete, intact pieces. Mine broke on the very first one!

I found out quickly what a mud tile job consisted of. It took several days to bust it all out with a 5lb sledge; tough as it was with the wire mesh behind it. I filled my son's entire pickup with it!

--On this membrane, vapor barrier concept. If plastic or roofing felt goes behind the backer board, down to the tub flange and over it, how does the potential water get out if it ends up being caulked down at the end? Seems like it would be trapped above the caulk or other sealing product.

02-15-2015, 08:46 PM
It's easy to think that water will be pouring thru the CBU and tile and then running down hill against the moisture barrier. I don't think it's like that at all. There's just not that much water that gets thru there at a time. It's just a little dampness is all.

A few weeks ago I tore out a 2 coat mud shower and when I got it all down I could see thru the wall to the back side of the other bathroom wall. It was also a mud job without a moisture barrier. I could see the mud mashed thru the lath from the back side and see under the tub. I looked carefully at the studs for traces of moisture. There were no traces what so ever. I talked to the homeowner and they told me that their 2 kids used that tub surround every day for over 20 years. I know that all showers aren't like this. I do think that a CBU wall will soak in more moisture than a mud wall but I still don't see a lot of water getting back there like we would think. Even with no moisture barrier, it usually takes years for moisture to get to the studs.

02-16-2015, 04:56 PM
Great thank you. That makes sense.

Almost have my new valve in. It must be an art knowing how far to place it so it ends up flush with the finished surface. Thankfully I have access from both sides.

One guy on YouTube strongly suggests a 2 x 4 brace against the back wall is the proper distance for Moen and Delta valves once screwed to it. Mount the valves to it and it should be the right measurement to be flush with the finished wall. Sounds too good to be true?

I assume #30 roofing felt is ok to use as strips to shim with if necessary.

02-16-2015, 05:43 PM
Its true, I install Delta valves like that no problem.
Install your valve then place a piece of backer and tile over studs to check.

02-16-2015, 06:28 PM
Drywall shims work nicely, too.

02-16-2015, 07:12 PM

Unable to find drywall shims at Home Depot or Lowe's. Never heard of them before this forum. Pretty neat little item.

Going from CPVC to the brass fittings on my new Moen valve. Which is better?

--Sharkbite 90's or Chief Sioux CPVC to Brass fittings?

I am making progress with my wife out of town and being able to turn the water off!

02-16-2015, 07:17 PM
CPVC to Brass fittings, because the shark bite 90's may not end up were you need them.

02-22-2015, 08:48 AM
I was going to put my valve in Saturday, even figuring out the exact location distance wise from a mock-up; but then thought, probably the walls need to go in first. So I finished up the rest of the tubs back wall studs I had removed when I removed the plywood as seen in an earlier picture.

So my studs are all up, tub is secured, drained connected and I reckon since I need to shim my studs to get the CBU over the flange, I should wait on the valve {shimming might make a difference.}

But a really simple question.

1. Shimming the studs {about 3/8 - 1/4"} all the way to the top with Hardie backer board the first 5 feet, and the last feet with green drywall is going to cause quite a bump from the green board to the rest of the 1/2' drywall.

Is that a common occurrence and one just has to feather it out with drywall compound that much?

It looks like the Hardie backer board is about 1/8" thinner than the drywall it will bump up against so the bump against the drywall isn't nearly as much.

2. Even though I extend out from the tub about 5 inches, I should still use thinset for taping that Hardie transition to the drywall?

Thank you. Slow, but sure.

02-22-2015, 10:03 AM
Very common in remodel using CBU adjacent to drywall. Sounds like you've got a lot to build out and I'd recommend you consider adding another layer of 1/4" drywall or finding some sort of trim for your tile to cover the change in thickness. If it's only at the top you have that problem, you might wanna consider running your CBU all the way to the ceiling. You can either tile all the way up or skim with drywall mud and finish like the other walls.

On the walls adjacent to the shower with only the difference in thickness of the materials you may be able just to tile to that joint and hide it or, again, find a tile trim to hide the problem and call it a feature.

Outside the tile/wet area you can finish the joints with whatever works best for your application.

My opinion; worth price charged.

03-01-2015, 06:38 PM
This weekend I finally was able to tackle whether I could go over the flange or just above the flange. Everyone's advice has paid off!

By purchasing lattice shims, notching the studs, adding sister studs, I believe I have been successful in assuring I can go over the flange, down to a 1/4" above the tub horizontal portion.

Also it appears I will be over the drywall plane by only 1/8." This will be in the dry area.

1. Ok to use drywall compound at that seam or should I use what? I see mastic mentioned and thinset? Not sure what is for what application. {I can research that if necessary, not trying to be lazy in asking.}

2. I take it 1/16" off on one stud isn't significant in nailing Hardi backerboard to that stud?

3. I purchased 1 5/8" Back-On screws. I see Hardi suggests using 1 1/4." Can I assume I am ok to use what I bought; especially since I used 1/4" shims on the back wall?

4. Am I reading this right with Hardi backerboard, you can use either side but the preferred side is the smooth side? I am doing tile.

5. Redguard is fine with tile and won't affect the adhesion?

6. I really desire to avoid adding extra blocking along tub and above. I am hoping with Hardi backerboard that is really over kill. True?

Thank you all!

03-01-2015, 07:12 PM
Not sure I'm fully understanding some of your questions, but............

1. Not sure what seam we're talking about, but see post 42 above.

2. Again, not sure, but 1/16th" shouldn't make any difference in nailing anything.

3. Yes.

4. James Hardie recommends you use their printed pattern as a fastening guide so that would be the side to which you'd tile.

5. Mmmm, adhesion to what?

6. I would definitely want blocking at the top of the tub, but above that I wouldn't think it necessary.

My opinion; worth price charged.

03-01-2015, 08:01 PM
Thank You!

1. Seam I am referring to is where the Hardie backerboad meets the drywall.

2. My Hardie Backer board 500 1/2" doesn't have any printed pattern or nail guide on it. I've looked and saw others refer to that, but also got the impression they discontinued printing that.

3. I was just questioning with Redguard on the Hardi backerboard if it would affect how well the tiles adhere to it. Probably overthinking it on that one.

4. Ok on the blocking. Was sort of hoping the Hardi board would be ridged enough without them. Getting those blocks lined up and screwed in with my shims will just make it a chore.

03-01-2015, 08:23 PM
Because cbu, and especially HardieBacker, is so absorbent, I think they recommend diluting the RedGard and using that as a primer before the 'normal' coats - carefully read the instructions.

You really should pick up a wet film gauge (they're cheap, often only a few dollars at a good paint store), as with all waterproofing membranes like that, getting the proper thickness is critical for proper operation. Too thick is as bad as too thin. One reason why I like sheet membranes verses liquid ones. Give two people the same material and the same brush (or roller), and their coat thickness can vary significantly. YOu really do want it between the min/max, and to check, you need that gauge.

03-02-2015, 07:10 PM
I drive right home by a Sherwin Williams so I will pick up one of those wet film thickness gauge. Never used one before though I have painted a lot in my life.

I sort of looked into those sheet membranes. HD and Lowe's doesn't stock them in house and they appear very pricey online. They do seem highly recommended though some suggest they are a bit tricky to use.

I called Hardi backer board today for kicks during lunch. Before I could finish my first sentence, the guy said, 'either side, doesn't matter.' Caused me to chuckle.

I'll pass on what else he shared just for reference. Vapor barrier not required for their product---check you local codes. Additional blocking not required for Hardie 500 as long as 16 oc. Screws good with 1-1/4".

Again I had to laugh. He was so direct and to the point.

03-02-2015, 10:01 PM
Most of the manufacturers of CBUs will tell you that waterproofing is optional. Well, 'cept maybe CBP for their Wonderboard, where I think they still correctly require a moisture barrier for wet area installations.

But the ceramic tile industry still requires a moisture barrier behind the CBU or a direct bonded waterproofing membrane on the face for any installation in showers or tub surrounds.

My opinion; worth price charged.

03-03-2015, 01:32 PM
You are right of course. At this point I am still leaning on waterproofing with Redguard.

Last night I might have discovered a problem with my Hardiebacker. While on my exercise bike of all things, I looked down the row of boards at the 4 ft end and noticed a wavy pattern. Got off the bike and put a solid metal level to them and while the bow side will flatten out, the small wavy parts do not.

Waves look to be about 1/16 to 1/8". I searched online and found two posts related to this problem. One on this website and forum which CX even addressed! Warping/Wavy/Uneven Hardiebacker!?

Am I just being overly cautious with this and over thinking it? Should I return it. I tend to thing the product should be completely flat.

03-03-2015, 03:45 PM
It should be flat.

03-05-2015, 12:52 PM
Found out I had to add some 2 x 4's on the left and right side of tub if I am going to add shower doors. One side is done, other side tonight. I only have an hour or so each night to work on this project.

If I want to have a towel rod on the backside, is that something that gets glued onto the tile or should there be some horizontal board on the back side?

I am re-thinking RegGuard because it looks like I would need 2 gallons or $100 worth. I already have the plastic 6 mil. If I go with the plastic, I assume the holes made by the backerboard screws is not significant?

The plastic goes over the flange, is pressed against it by the backer board, and then trimmed? Put some sort of shield behind it when cutting it so as not to scratch the tub?

The backerboard edge and the plastic edge at the tile flange then gets caulked with 100% silicone?

Both plastic and backerboard 1/4" above the horizontal edge?

Do I have it right?

This weekend I hope to get the backerboard up and the greenboard in above it.

Thank you as always

03-05-2015, 02:56 PM
When you have several questions in one post, it helps to number them. Otherwise we'll miss some and cause confusion. :)

If the towel rod is mounted with screws, then it's always best to have some blocking behind it. When mounting with screws inside the shower, it's best to fill the screw holes with silicone to keep moisture out. If you're just using plastic behind the cement board, you can skip the silicone.

The 1/4" gap between the tub deck and CBU should be left open.

Don't waste the extra money on Green board. You'll do better to spend the money on a better quality paint, or a primer coat.

03-05-2015, 08:15 PM
I just ran across another post on this forum that is throwing me for a loop.

After finally deciding to go with the backer board over the tub lip, it seems John Bridge agrees with a comment by Netty to stop above the tub lip.

The specific comments are on thread lines #12 and #13 on the post entitled "space between tub and cement board."

Working all week to get the backer board to go over the tub lip as most here have suggested, this adds a bit of apprehension to my equation. Especially since it does seem to address doing so due to movement.

Am I reading that post wrong?

03-05-2015, 08:38 PM
Thomas, while it is possible to stop the CBU above the tub's tiling lip, especially when using a moisture barrier behind the CBU, I recommend always having the CBU fall entirely on the drain side of the tiling flange. That also works with the moisture barrier behind the CBU and works more effectively with direct bonded waterproofing membranes.

If you stop the CBU above the tiling flange and plan to use a direct bonded waterproofing membrane, you need to use either a sheet-type membrane or use a reinforcing fabric with a liquid-applied membrane.

My opinion; worth price charged.

03-05-2015, 09:18 PM
Thank you!

So can I assume this whole "movement" issue is a bit over hyped and not really a problem? Outside of the in-line drywall plane arguement, the "movement" arguement was the only other justification to keep the CBU above the flange I read.

I appreciate everyone patience with me on this. I have already used what I have learned to help others and hopefully as others go down this path, the information on this thread will aid them as well.

03-05-2015, 10:52 PM
Not sure what movement argument you're referring to, Thomas, but you do, indeed, need to provide movement accommodation between your wall and your tub. Shouldn't be any argument about that.

03-06-2015, 06:48 AM
Perhaps I am confused about this whole movement thing. Several sites including this one refer to it. The for example had this to say,

If you have a tub or shower base you will also want to stop the backerboard about 1/8 inch above the lip. You do not want to run the board over the edge of the lip because it will cause the backerboard to bow out and your wall will not be flat. It will also allow the tub or shower base to move a bit Ė itís attached to the wooden studs as well. Tubs also move when they are filled with water. You need to allow for that movement.

My tub directions clearly state it must be secured to the wall studs by stainless steel screws and washers. As pictured earlier I have done that.

In that light, I am not sure what movement we are supposed to be allowing for. In my case the tub or walls would move together due to being fastened together.

Add on now the backerboard, if it hangs above the flange, they obviously don't affect each other with any movement. They go their separate ways.

If it hangs over the flange, I reckon the CPU and tub flange could rub each other during any movement.

Above I was told not to caulk the gap at the bottom of the CPU and the tub so that would not affect any movement.

So when we speak of movement, what are the experts referring to when they speak of providing for movement and or its associated problems?

I mean if you add tile and caulk the bottom of the tile to the tub, then you have bonded the tile to the tub and how does that work out with movement?

03-06-2015, 08:03 AM
the movement comes from the fact that different materials expand at different rates when the temperature changes. We're talking about thousandths of an inch here. That's enough to crack grout or even stress the bond between thinset and substrate (doubtful but possible).

Rubbing is really not a concern. Putting the CBU in front of the tile flange is definitely the easier thing to do, and gives you many times better odds that you don't get water behind the tub flange.

Also, I'm going to have to disagree, at least partially, with Floor Elf. If you put a lot of weight in the tub, and it is installed incorrectly, then it may flex down a bit. However, if you put support under it when you installed it, as you are supposed to, then a stiff floor will prevent all but the very slightest downward movement. You're also supposed to install a 2x4 horizontally to act as a little shelf underneath the edge of the tub to keep the edge supported.

03-06-2015, 10:32 AM
While I agree with Roger (your Tile Elf ( about the need to provide movement accommodation between tub and wallboard, I do not agree that stopping the wallboard above the tiling flange is the better way to do that. If your wallboard will not fall on the inside of the tiling flange without interference, we generally recommend shimming the studs in that area to provide clearance.

I concur with Gerry's recommendation above.

And keep in mind that when we talk about movement in ceramic tile installations, we're not talking about the components packing their little suitcases and moving to the neighboring town, we're talking very small increments of movement and they are always present and active.if you add tile and caulk the bottom of the tile to the tub, then you have bonded the tile to the tub and how does that work out with movement? That's why the industry recommends that gap be filled with a "flexible sealant." There will be movement there and you need to allow for it.

My opinion; worth price charged.

03-06-2015, 12:35 PM
I feel better from what you both have shared.

My tub does have a full stringer running the entire length of the tub edge and the tub came with a fully insulated base. I put down brand new 3/4 plywood, perfectly level and secured every six to 8 inches with 2.5" hex shank deck screws. Below that is 1/2 plywood.

The studs I either notched or shimmed so that the CPU goes over the tub flange and a very small gap exits so it does not bow out at all.

So I think I am ready to put up the CPU this weekend!

1. To be clear, no caulk needed with tub edge to cpu {1/4" gap}
2. To be clear, caulk tile edge to tub.

03-06-2015, 12:44 PM
1. Correct.

2. That's the industry recommendation. I don't like it much, but if some gaps are created in the sealant bead to allow for drainage, I'm not as much opposed. You will not find that in tile industry recommendations.

My opinion; worth price charged.

03-06-2015, 07:29 PM
Your #2 comment makes perfect sense to me. If it is completely sealed, it begs the question how any trapped water gets out from behind the tile or CPU board if the vapor barrier is behind the CPU board.

Thank you.

03-06-2015, 07:36 PM
Thomas, those panels you're putting on the walls are Cementitious Backer Units, CBUs. :)

03-07-2015, 07:16 AM
LOL! I work full time in Information Technology too. Guess I naturally gravitate to 'central processing units' rather than 'cementitious backer units.' I know I definately feel at this stage more confortable working with them!

Appreciate the clarification on the acronym though; it took me quite awhile to figure out exactly what those letters meant.

I tackle breakfast first today, then 'cementitious backer units.' :clap1:

03-07-2015, 12:53 PM
I know this is a silly question to someone who has used these CBU boards and Block-On screws.

With my impact driver, I have driven three into the board. Hard to get them at a perfect angle so that they are completely flush all the way around. In trying to get them past the surface all the way around, it creates a little ridge of material around the edge. I've been lightly scraping it so it is smooth.

1. How perfect do these screws have to be flush with the surface?

2. Ok to go beyond the surface in order to get the entire screw head flush with it? Again, unless they are driven perfectly square, it is hard avoid having one side a bit further out until you keep screwing it in.

As I shared, on the three I have done so far, I took a slight scraping to skim off the raised material left from drilling in the screw.

Maybe a mute point when the tile mortar is placed over the entire board?

03-07-2015, 02:16 PM
Now I'm suspecting you have actual intent to confuse here, Thomas. :D

Is it possible that you are using Rock-On screws rather than "Block-On" screws?

It is necessary that your screw heads, of whatever brand and type, do not sit at all proud of the CBU surface. It is also necessary, according to the CBU manufacturer, that your screw head not sink excessively into the surface of the panel and reduce the pull-through strength.

If you're not getting your screws perpendicular to the face of the panels, all I can suggest is that you do better, eh? Worst case you might try pre-drilling your holes if necessary, but you should, with a bit of practice, be able to start your screws squarely most every time. If you must set them a tiny bit deeper sometimes to get the head flush with the surface, do that. But don't make a habit of setting them too deep.

As for the mushrooming around the edges of the screw heads, it's easy enough to just pass quickly over all of'em with a rub-brick when you're all done to remove any such material.

My opinion; worth price charged.

03-07-2015, 04:47 PM
Back Hardi board panels are up, side pieces are cut. But now a noticeable problem.

Front Hardi board panel sticks out beyond the drywall plane a good 3/16."

I worked so hard to get all those new studs and boards over the tiling flange on that side too!

At this point in my thinking I am tempted to do:

1. Move the studs back enought to get on-plane.
2. Place 6" Flashing Tape across front tiling flane and onto studs.
3. Move Hardi backer above tiling flange and secure.

I am thinking the front of the shower will get the least amount of water running across it anyway.

Sometimes I feel like I am working against a stacked deck!:bang:

03-07-2015, 05:17 PM
My bad; I am using Buildex Backer-On.

Ok, so the screw head should be completely flush with the Hardi backer. In other words, if I were to rub a putty knife over them, they should not snag at them?

Peerless Tile
03-07-2015, 06:11 PM
correct...even if counter sunk a bit.

03-07-2015, 07:36 PM
Thank you, that is what I ended up doing and which worked the best. I pre-drilled and counter-sunk them. If I had to do this for a living I reckon I would find a better and faster method.

Going to quit for today and let myself re-group on how to best fix my over the plane issue with my one side almost a quarter of an inch out.

Thank you all. This site and members have kept me sane on this once in a life-time project.!

03-12-2015, 11:56 AM
With advice from my friends, I have a work-around for the tub flange issue on the front side. I have shimmed out the drywall a bit and now the backerboard will work over the tub flange.

I have an issue I need recommendations to make this work perfectly.

There are five studs on the right side of the tub, extending out several good inches beyond the tub area and up against the drywall.

Three studs are new and align well. Two more studs were already there and the drywall is attached to the last of the two on the right.

The studs near the drywall are not even and I am thinking the easiest way to do it since they taper up as well as being uneven with each other, is to use some sort of 'leveling' compound over the two.

By running a putty knife along the three even studs, I could fill the unevenness of the last two with 'something' and it should allow for the backer board to align nicely with the drywall.

Is anyone familar with anything that can fill a gap that varies like this and which will stick to studs. The Hardi backer will go over this edge which is well beyond the tub water area.

I was wondering about Durham Rock hard or some other putty.

Once this angle is resolved, it is put my valve in and screw in this last board.!

03-12-2015, 03:29 PM
Shave the protrusions back with a handplane. You can fill in depressions with drywall shims (think paper tablet cardboard backer), heavy stock paper, wood, and just about anything else that isn't compressible and can take a nail, screw, or a few staples. Use a long straight-edge (level works) to check the vertical and horizontal planes to ensure things are as flat as you care to get them.

Otherwise, replace the studs.

If it were me, I would pull the studs out, joint one side flat, glue a rip of plywood to the freshly jointed side and then re-rip the stud back to 3.5". But I'm guessin' you don't have a jointer or maybe even a table saw. :) In that case, replace the studs with a new ones...carefully culled from the stack to ensure it is straight, no huge knots, no bark, and no center pith on the stud. If possible, find a quarter-sawn stud. There are about 3 or 4 of them per stack. :D Finally, get kiln-dried studs...they will tend to stay straighter than the real wet stuff.

Bottom line, your framing needs fixed. :yo:

03-13-2015, 12:00 PM
It was painful last night. In order to follow your advice and rip those two studs out, I had to tear into my neatly done drywall. Not wanting to butt joint this, I just ripped out all 10 feet of the new drywall I had put up.

Back to the studs on one side.

So while I have a love - hate relationship for doing this, the fact is I can definately make CX happy by getting the tub flange over the tub. Indeed, with new drywall going up all across, I can maniuplate the studs to make the seam between the backer board and drywall perfect.

Hindsight is 100% I should have put in the backerboad first then the drywall.

Getting lots of experience doing most of this stuff twice. :dunce:

Peerless Tile
03-13-2015, 06:31 PM
Seems like your on the right path now...Tackle that valve and post up some pics. The good folks here will get you where you need to be.

03-22-2015, 06:22 AM
Yesterday I finished walling everything in and setting the valve. Additionally, pressure tested the valve water connections and no leaks. Here are two recent pictures.

Without everyone's help I couldn't have made it, especially one member of the forum who went the extra mile with his advice. I am very grateful.

I am opting out to have the tile work done by a professional. I have already reached out to him and am very confident he will do a great job.

Again, very thankful for this forum and the members who have been extremely patient with his novice!

03-23-2015, 11:50 AM
Should I take it as a good or bad 'sign' no one is commenting on my progress in the pictures?

I know some installs I have seen had the CBU board go all the way to the top of the wall. I didn't for several reasons.

1. That is the height my bathroom was before when it was a mud job. The mud and tile ended at the same height as is the other bathroom which is a mud job.

2. The CPU ended perfectly at 5' feet buying four sheets.

3. The shower head will extend well into the area surrounded by CBU.

4. I will be using oil-based primer on the green board.

5. My tile will go above the CBU board and above the shower head a row or so.

I wasn't trying to be cheap with the CBU board in other words. Redguard or Keri is going on the CBU according to my professional installer. I understand Keri would be best.

03-23-2015, 11:53 AM
I would recommend you not infer anything, Thomas. Some of us rarely comment unless we see a question to which we feel qualified to respond. :)

03-23-2015, 12:42 PM
I'll bite.

What's CPU?

What's Keri?

Looks like a nice clean job thus far. Look forward to the tile. :)

05-11-2015, 05:32 PM

Here is the final product minus the final plumbing fixtures: valve cover, shower head, and tub spout. What do you think? I opted to let a professional do the tile work. My wife is counting the days now till she can use the bathroom again. :-)

Tiger Mountain Tile Inc
05-11-2015, 07:02 PM
Looks great to me! :tup2:

05-11-2015, 08:42 PM
Wonderful job.

05-12-2015, 05:47 AM
Thank you. We think he did a good job too!

Do people seal sanded grout anymore? I was advised not, but my best friend insists I need to because of the sand being porous. Seems on the Internet there are varied opinions. My friend is coming out of town here Friday and I wanted a good answer either way I go.

Tiger Mountain Tile Inc
05-12-2015, 08:41 AM
If it's cement grout I would seal it. :)

05-12-2015, 10:33 AM
Sealing the grout will help make it easier to keep it clean and hopefully stain free. What kind of grout did you use?

05-12-2015, 10:51 AM
Sanded grout. That is what the bag is labeled. Didn't look to close at it, but I can tonight if need be.

My friend who is coming over this weekend feels the sanded grout being porous {water gets through it easily] should be sealed to prevent or reduce that problem. He says Epoxy grout you don't have that problem.

BTW, is it hard to pull one tile up a bit to level it with another? I've got my eye on one piece that could use an adjustment.

Thanks for the feedback and compliments. My wife keeps being excited every time she looks in on it. Good to be almost done!

05-12-2015, 11:31 AM
Well, technically, tile and grout are both porous. This is why they are not relied upon for waterproofing...that is someone else's job.

I guess I was asking if it was a cement based grout, or epoxy grout, or urethane but it sounds like cement so sealing is a good idea.

If your thinset has cured for 24 hours or longer, moving the tile might be pretty difficult and you could break it.

05-12-2015, 05:08 PM
The grout name is Laticrete 1500 sanded grout.

I revisited that one piece of tile and I am fine with it the way it is. The juice isn't worth the squeeze.

Any recommendations on what type or brand to use as a sealer? I've never done it before.

05-13-2015, 04:34 PM
Usually you'll be safe if you stick with Miracle, Stone Tech or Auqa Mix sealers. Each one has a natural sealer that is probably what you would want. I like the Miracle 511 but the others will also work.

05-16-2015, 05:34 AM
I picked up the grouter sealer you recommended above. Thanks!

Which brings me to an observation / question.

On my hands and knees sealing the grout, I observe some of the tiles are not lined up across their neighbors evenly by 1/8." Having not walked on the floor with my bare feet, I had not noticed this, but this morning I can in places feel a slight ridge between the two.

In my smaller tiled bathroom 6 x 6 tiles, this isn't observable. Is this normal with 12" tiles? I know the floor was just about perfectly level so I am thinking it is the variation in the thickness of the adhesives used under the tiles.

I am ignorant on what is acceptable, good or great job as well as lean perfectionist, so am I setting the bar in my mind too high? I put a 4' level across a section and a 1/8' gap runs between end to end. I see on the Internet some people call it lippage.

Again, pardon my ignorance in questioning this. I really just want to know for knowledge sake. They say a dumb question is one never asked. As you saw, it looks great.

05-16-2015, 06:03 AM
All batches of tile vary a little in thickness and size, some more than others. Plus, the thinset thickness you applied can vary a little also. If you grout the joints too low, it can make it look even worse. Some differences are acceptable but a high tile can be replaced if it bothers you too much. 6 inch tiles will flow with an uneven floor better than larger tiles.

07-06-2015, 06:58 PM
Do I need to caulk around my tub if the backerboard and tile are over the tub flange? For some reason, I didn't get around to doing that and thought I read there was some debate or need for doing so.

BTW, here is the finished project completed a few months ago.

Houston Remodeler
07-06-2015, 07:58 PM

Yes: to keep the water from going over the edge of the tub along the tile, to keep out dirt, and to make it look neater.

07-06-2015, 08:02 PM
Some of us still argue against caulking that tub/tile joint, Thomas, unless you at least leave some weep holes in the caulking.

Tile industry standards call for that joint to be filled with a flexible sealant.

Up to you.

My opinion; worth price charged.