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02-12-2010, 01:53 AM
We're planning to replace the vinyl in our kitchen and bathrooms with porcelain tile. My question has to do with the subfloor. Our home was built in 1960 and has this amazing solid wood tongue and groove subfloor. It's supported by probably 40 or so concrete pillars under the house.

Here's a picture of a section I had to cut out to get access to an area under the house that was blocked by since-removed HVAC hard pipe.

With a subfloor like that, what's the thinnest underlayment I can use for tile on the floor?

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02-12-2010, 02:19 AM
you are going to have to put some plywood over that. Tile doesn't like solid wood, too much expansion/contraction. I believe 1/2", but it may be 3/4", someone else will have to chime in there, too late to remember right now.

After that you could go with 1/4" cbu or ditra, then tile.

Dave Taylor
02-12-2010, 03:16 AM
That is a nice lookin' wood subfloor but..... Gregg has it right.

A dimensioned lumber subfloor like you have has way to much individual board movement to maintain a solid ceramic covering.... so it should be covered with a minimum 1/2" plywood of type I (exterior gluing) that has no face grade greater than "C".

Question though.... what exactly is the joist structure that supports this subfloor like..... or..... are the 40 or so concrete pillars under the home it?

02-13-2010, 01:23 AM
Thanks for the replies.

The house has a typical foundation with a crawlspace. The 40 or so pillars are under the house adding support for the weight of the subfloor and the solid hardwood floors throughout the place. The boards are solid wood, but they are tongue and groove, so the expansion and contraction is meant to happen laterally.

I need to put 1/2" plywood down then. So here come the noobie questions. Is OSB a better choice? How would I secure the cementboard to the plywood?

Dave Taylor
02-13-2010, 01:55 AM
Joshua asked:
Is OSB a better choice? How would I secure the cementboard to the plywood?

OSB is not a better choice.

Carefully follow the manufacturer's installation instructions for the cement board (CBU) of your choice.

Typically, imbed the CBU in a thin spread of thinset and fasten it to the floor using a recommended screw type like "Backer On" before the thinset sets.

What kind of joist structure is beneath this subfloor?
This joist structure will make a difference on how you proceed, or not.

02-25-2010, 05:05 PM
So my subfloor is 2" thick solid tongue-and-groove redwood or maybe fir. The joists are 6.5" tall and 3.25" wide. The joists are 4' apart. Each joist is supported every 4' of it's length by a concrete footer.

The deflection calculator doesn't take that distance and the pillars into account and I haven't found a calculation that I can do manually yet, so I thought I'd ask here. Is this floor going to be strong enough for porcelin tile?

02-25-2010, 05:21 PM
Is this the same floor as in some of your other threads, Joshua?

Those Left Coast floor structures are well known here and Injineer Bob has run the numbers for us. I'm presuming you mean a "nominal" thickness of 2" and if the boards are Fir, you need only add half-inch plywood and you're OK for ceramic tile, providing your support posts for the beams are no more than about seven feet apart.

If the boards are Redwood, we need to chat with Bob on it, I'd think.

My opinion; worth price charged.

02-25-2010, 05:43 PM
Yes, same floor.

I just remembered I have access to a cutaway of the subfloor (the one in the picture is covered by a storage unit) and remeasured and the subfloor is exactly 1 3/4" thick.

I don't have a lot of experience with fir, but this looks a lot like redwood.

And thanks for the reply.

02-25-2010, 05:47 PM
OK, I've combined one other thread here, Joshua. If your other threads are about this same bathroom project, I can bring the others in here, too. Best to keep it all together so folks can see what you're working on and what's been previously asked and answered.

There is no photo in the other thread, either, though.

02-25-2010, 05:52 PM
Sounds good, thanks.

So I can probably use 1/2" plywood. Will I need anything over that like cement board or do I just tile over the plywood?

Brian in San Diego
02-25-2010, 05:56 PM
You'll need a tiling substrate like Hardiebacker or an uncoupling membrane like Schluter Ditra installed over the plywood. Tiling directly to plywood is not for the faint of heart and requires very strict accordance to the process to be successful. We discourage DIYers from attempting it.


02-25-2010, 06:45 PM
We're considering adding heating under the floor. Any difference between Ditra and cementboard as far as that's concerned?

02-25-2010, 06:50 PM
By "under the floor" do you mean under all you have now, or under the tile installation only?

02-25-2010, 06:56 PM
It would just be to heat the tile.

02-25-2010, 07:20 PM
You need to check the installation instructions for the heating system you intend to use. If it's an electric type, you can usually install directly to your plywood subfloor. I would then recommend installing Ditra over the filled wire system and then tile.

My opinion; worth price charged.

03-17-2010, 11:35 PM
Getting very close to the day I start the remodel.

So my last major concern is the threshold. As you can see from the cutout, on top of the 2" thick subfloor throughout the entire house except the bathrooms and kitchen have that 1/2" oak hardwood.

The bathrooms right now have 1/4" of what looks like particleboard and then a layer of laminate.

If I have to put down 1/2" of plywood, then thinset, then 1/2" cementboard, then the heating wires, then thinset, then floor is going to be over 1 1/2" thick isn't it?

So my question is, do they make threshold transitions that steep and is this fairly common and is there anything I can do to lessen the height of the floor?

03-18-2010, 04:47 AM
First off, you remove the partical board and laminate. That gives you about 3/8". 1/4" backerboard is fine for your floor, no need for the 1/2" stuff. Heat mats are about 1/8", and your tile is usually 3/8" thick, but could be less. I see about a 7/8" to 1" height differential, and yes, a transition can be made for that.

If you want flush floors, you'll have to remove the existing plank subfloor and install plywood. Much more work.

03-18-2010, 06:17 PM
Since I haven't tiled before I'm not sure how much height the thinset will add to each layer.

Brian in San Diego
03-18-2010, 06:58 PM
Under the backerboard, next to none to about an eighth. Under tile about 1/2 the height of the notch.

03-19-2010, 11:59 PM
I have 12x12 porcelin tile that's 3/8" thick. What size notche trowel should I use? And is there a formula? If it's based on the thinset manufacturer's recomendations, then what type of thinset will allow me to use the shallowest notches?

Tool Guy - Kg
03-20-2010, 12:04 AM
For a floor application, a 1/4" x 3/8" x 1/4" notch trowel would be the first trowel I'd grab. I'd install a few tiles with them and pull a couple back up to see if I was getting at least 80% thinset coverage below them...and adjust the trowel size up or down accordingly.

But details are important. Where is this being installed and is it interior or exterior? Do you already have a thread going on for this project?


03-20-2010, 02:02 AM
Well, ya, I got this thread going, but I thought this would make a nice general discussion that could help other people looking for answers specific to notched trowel size. I did a quick search and didn't find any threads about it.

Maybe one of you guys could write something up. How to select notch size and notch shape, etc.

My particular project is a bathroom.....tile going on the floor and walls.

03-20-2010, 08:10 AM
Joshua, we prefer to keep all the project questions on a single thread where possible (see post #9). "General discussion" threads don't work well here in the Advice forum. We do have those about technical issues in the Professionals' Hangout where all visitors are welcome.

The object of the notched trowel is to achieve the best coverage on the back of each tile. Flatness of substrate, flatness of tile, method of notching the mortar, consistency of mortar, brand and type of mortar, and a number of other factors can influence what will work best in any given situation. No one-size-fits-all formula I'm aware of.

Goldstein's post #21 is a good place to start.

My opinion; worth price charged.

03-20-2010, 05:57 PM
Just finishing my parts list

I'm thinking of hardibacker for the floor because in it's 1/4" form it feels stiffer and denser. I'll use wonderboard for the walls because it looks easier to blend in with the green drywall already in the bathroom.

I understand I need the "backer on" screws for securing the backer to the plywood. I'm attaching the plywood to the subfloor, not the joists. 1) Am I also attaching the backberboard to the plywood and not the subfloor?

2) What type of screws should I use screwing the plywood into the subfloor? I know it will be covered in thinset, so I'm guessing it needs to be a particular material or coating.

3) Is there a certain tape meant for joining backberboard or for going under thinset or is standard drywall tape all there is?

4) As far as expansion gaps. I leave them between the plywood and backerboard and around the perimeter of the room and against the already in place shower floor. But I only fill in the very top gap with silicone caulk, right?

03-21-2010, 09:03 AM
1. Yes.

2. Any coated or plated decking screw will suffice. Homer has DeckMate in their fastener isle. Those are useful.

3. Yes. It must be alkali-resistant mesh tape. It will say it's for backerboard use. Do not use what you find inna sheetrock isle unless it's misplaced there.

4. Don't unnerstan the question.

My opinion; worth price charged.

03-21-2010, 04:09 PM
Thanks again.

Those Backer On And Rock On screws are too long then. If I have 1/2" playwood and 1/4" backerboard then I only need about a 5/8" or 3/4" screw.

Should I use them anyway, or is there a different type that will work?

03-21-2010, 04:35 PM
Joshua, I can't imagine a situation where a fella'd wanna attach a CBU to nothing but a half-inch plywood. If you're doing that, you're very likely doing something wrong. Do tell.

Your fasteners for your CBU want to penetrate at least 3/4" into frming for a wall or all the way through your subflooring for a floor installation. A little long is OK.

My opinion; worth price charged.

03-21-2010, 10:07 PM
Cool. Can you change the title of this thread to "Joshua's Beginner DIY Bathroom Questions".

Thanks for all the advice and comments.

Tool Guy - Kg
03-21-2010, 10:27 PM
Got your title request taken care of. :)

03-22-2010, 06:26 AM
As far as expansion gaps. I leave them between the plywood and backerboard and around the perimeter of the room and against the already in place shower floor. But I only fill in the very top gap with silicone caulk, right?You can leave the perimeter gap empty if you want. If you want to caulk, you can caulk the plywood to wall gap or the backerboard to wall gap, or both. I would leave it all empty, or fill with backerrod and caulk the tile to wall joint, if that joint was visible.

03-22-2010, 12:26 PM
Backer rod looks perfect.

A few questions on aligning and setting the tile.

1) They sell those little 1/8" spacers that looks like this
and some that look like this and fit in the corners

Will I find one significantly easier?

2) When setting my first row of wall tiles, should I set the lowest row of tile and just use one of those 1/8" spacers to keep a gap at the bottom by the shower or tub? Do I need to let that row dry before expanding upwards?

3) I know I need to leave a gap in the corners of the shower. Should it be 1/8" or 1/4"

4) For grouting a 1/8" space, is it alright to use one of those pastry bag things or is there something better?

5) And, for cleaning up the grout lines, is there a tool to shape them or is it just the sponging off action that gives the grout its shape and level?

Houston Remodeler
03-22-2010, 05:30 PM

Time for some decaf buddy ... I got tired just reading that post :neesie:

1- The soft spacers in the upper picture are better for lower quality tiles that aren't the exact same size. They are more forgiving as you can squish them a little and make up for a larger sized tile or a lumpier wall for example. The hard spacers as in the pic are better for rectified tiles or realllllly flat walls. You can't see through the hard spacers so if your joints are off a tad, you can't see it. I use both spacers, depending on the job.

2- You can use a ledger board and start with the second row of tiles OR use a hard spacer, like a small paint stirrer. They bridge several tiles and give a flatter edge to the bottom row that individual spacers can't give, plus they don't squish from the weight of the ascending rows. If you use soft spacers on the tile to tub joint, they may get stuck in place after having been squished so hard you can't get them out. Plus you then have a smaller gap than planned.

3- 1/8 is a nice touch. 1/4" is allowable, but I prefer a small tight even joint. It shows craftsmanship and care. :usflag:

4- Use a rubber float. The pastry bag will be far more trouble than its worth.

5- To shape the joints; wait the right amount of time, wipe with a dampened sponge that isn't too wet or too dry, and wipe flat and smooth in a circular motion, but not too hard. This is really something you have to do to learn. Wiping in the same direction as the joints will wipe out more grout, wiping across the joints will leave more behind. Excess water can lighten the grout. Excess water can weaken the grout. Excess water makes the job physically easier, but don't fall into the allure of the shortcut. Use a good sponge, they cost about $2 each pictured below. Get 3 or 4. Have a second person rinsing them out for you in a 5 gallon bucket. As far as I know, no one has lost an eye tossing damp grout sponges back and forth.

05-11-2010, 04:36 PM
Tore the bathroom apart over the weekend. I'm heading out today to get the supplies for prepping the floor so we can tile this weekend. What took so long was waiting until I had enough time to tear out the old HVAC hard pipe from under the house to get more use from the dumpster.

Like most people I'll be using hardibacker on the floor. I'll also need some plywood. I know to leave a gap and to tape the hardibacker. How about the plywood underneeth?

Also, we'll be leaving the shower base in place. Should I leave the same size gap next to it as I do along the walls? Or should it be smaller so I can caulk it?

Brian in San Diego
05-11-2010, 07:38 PM
1/8" gap between plywood panels as well as hardiebacker panels. 1/4" between plywood and/or tile from immoveable objects. You can probably "cheat" a little bit with the tile but you need to keep a gap in there for expansion.

05-11-2010, 08:22 PM
Thanks very much.

Is there plywood tape out there or should I leave the gap exposed?

One last thing before I go shopping. I'm leaving these expansion gaps so the plywood can expand under different humidity levels and shift gracefully as the house settles and whatnot. But the subfloor is 2" thick solid wood tongue-and-groove which they installed the way they did for the same reasons. If I screw down the plywood to the subfloor, I'm leaving gaps for the plywood to shift, but I've also just effectively tied the subfloor together so it can't do what it was meant to do anymore. And then I'm screwing the backberboard onto the plywood. I've now got three layers all of different material that will expand and contract in different ways at different times. I don't know. I'm trying to wrap my head around how this expansion is meant to work in light of everything being screwed together.

Houston Remodeler
05-11-2010, 08:28 PM
When you screw wood to wood, it all expands and contracts at the same rate, as one big unit.

The CBU gets well attached so that it doesn't flop all around the place, like an old thin wood floor does, which would crack the tiles, break the bond, and ruin the floor.

Plywood tape:lol1: Thanks for the belly laugh. Good one. Nearly had me for a moment. :postitbg:

05-12-2010, 03:35 PM
I assure you I'm still too new to be making jokes....or using emoticons. :twitch: I know there's no such thing as plywood tape, but should I use masking tape or drywall tape or something to cover the gaps?

Also, for my purposes ditra would work the same as hardibacker, right? I'm starting to think I may take that route instead. Fewer screws in the subfloor plus the uncoupling effect.

Houston Remodeler
05-12-2010, 03:43 PM

Just ignore the plywood seams. There is no "treatment"

Ditra is an excellent choice over plywood. Use a quality modified thinset and you are good to go.

06-11-2010, 03:43 PM
So I decided to use Ditra instead of CBU. Of course, it took a month to get it from tile-experts because they were backordered.

Anyway, I couldn't find any premium unmodified thinset at Lowes or Home Depot. I called the place we bought our tile from, Bedrosians, because I remembered they had a nice little contractor store in their warehouse. I called the lady there and asked for a premium unmodified thinset, she thought hard about it and then asked me what it was for and I explained I was going to use a Ditra underlayment. "Oh, well we carry Ditra-set". LOL. So I go from SOL with the big box stores to best case scenario. I'm picking up a few bags this afternoon and start tiling tomorrow.

I keep rechecking that I have everything covered. Every question I come up with, I can think of an answer I got from this thread or different threads here on the forums So thank you all very much for the answers and advice. If it comes out good I'll post picks. If it's a disaster, I'll start a new account under a pseudonym and start a thread on demoing a bad install. :)

Brian in San Diego
06-11-2010, 04:36 PM

Just to make sure we are clear on one point. You would use the Ditra Set to set tile on top of the DItra. To install the Ditra on your plywood subfloor you need a thinset conforming to ANSI A118.11. (That would be a modified for use over EGP.) Versabond fits that bill. You do not want to use Ditra Set to attach the Ditra to the subfloor unless you use an approved latex additive. (I think I'd go with's usually around $15 a bag.)


06-11-2010, 05:30 PM
Ya, I got it. The Ditraset manual recommends adding D-L36 to Ditraset for installing Ditra.

06-12-2010, 05:17 PM
My hardwood store closed early, so I'm heading to Lowes or Home Depot soon.

The type of plywood I'm looking for is AC BC or CC. I'm assuming this is because we want a C side facing up because it will be a rougher, but not too rough, surface for the thinset to adhere to. Is that correct? Because the only exterior grade plywood I found at Home Depot was CDX. Haven't checked Lowes yet. Is exterior for sure the way to go or would I want tongue and groove flooring plywood as an alternative?

06-12-2010, 06:19 PM
Joshua, the grade of the plywood is the face grade designations, the AC, BC, etc. You're looking for those grades in an exterior glue plywood. Most anything you find in a big-box store in those grades is gonna be EGP, but look at the grade stamp for the designation EXT or Exposure 1.

You want to install it with the better grade up, but it really doesn't matter much. All T&G plywood designated as flooring grade or similar is gonna be an EGP.

You do not want CD plywood.

My opinion; worth price charged.

06-12-2010, 06:50 PM
Thanks. HD actually has no face ratings on their plywood, so I have no way to know. I haven't bought wood outside of a lumberyard in a while, so I had no idea they were doing that. I even asked a guy who wanted to know if I had an questions. :) They had sturd-i-floor which looked okay but was tongue and groove and, upon reading about it at home, is rated CD.

I know I was told not to use OSB? But how about Advantech? It's that stuff that has a waterproof resin in it.

06-12-2010, 07:00 PM
Well, I got no eye-dee where you are, Joshua, but Homer's in my area carries plenty BC and some AC and such. Also have CD, of course.

Anything that says Sturd-I-Floor on it is quite suitable. Not sure where the confusion lies, but that's not gonna be a CD grade board.

Nothing at all wrong with OSB that's rated for subflooing, either, and Advantech is a good choice. I prefer plywood for the second layer of subflooring, though.

Lotta good options out there.

My opinion; worth price charged.

06-21-2010, 02:18 PM
Prepped the plank subfloor. Ply is down. Floor feels solid. Ditra is cut. Tile layout is determined. All tools and materials are on hand to tile.

I realized after laying down the plywood, that I'm going to have to cut the door jambs. I obviously don't want those below the level of the tile.

Question 1. The jambs weren't the only thing I noticed. The toilet flange is the same level as the tile set on the ditra when I dry fit everything. Once I add the thinset, it will be probably 3/8" below. At Lowes I saw both an extra thick wax ring and this Fluidmaster gasket thing ( Would either route be preferrable?

Houston Remodeler
06-21-2010, 02:23 PM

There are hard plastic extender rings. Get one, silicone it down, you'll be fine.

07-07-2010, 04:10 AM
Thanks. That's exactly what I needed.

I just completed the dry fit and got all the cuts done. Looks amazing and I'm looking forward to the tiling. BTW, tiling your bathroom, it turns out, is 90% not-tiling your bathroom.

The latest challenge. The toilet flange sits in the middle of a tile. So far I've broken 5 tiles and one carbide bit.

First I drilled a hole and tried a jig saw with a diamond blade. That never had a prayer even with a backer for the tile. Tried setting the tile down onto a tile saw with the guard removed for a plunge cut. As soon as the blade made it through, there was a crack. The next three tiles met their demise under the diamond blade of my newly purchased angle grinder. Same story, I can score the tile deeply but as soon as the blade makes it through to the other side, even clamped to some plywood, there is a snap.

I have a pair of nippers and am fully amenable to nipping the entire 8" diameter, but I can't even get enough of a hole to be able to work the nippers.

Do I have any other options?

07-07-2010, 05:14 AM
Joshua, cutting a 8" hole inside a 12" tile doesn't leave a lot of strength in the tile for rough handling. Consider cutting the tile in half, then making half circle cuts. The joint will fall under the toilet, or at worst, will show only in the back.

BTW, use diamond cutting blades, bits, etc for porcelain. Keep the cutter and tile cool by keeping some water flowing. For hole saws, some guys cut a sponge to fit inside the saw, then keep the sponge wet. Support for the tile is a must, as well as a light touch.

Houston Remodeler
07-07-2010, 06:38 AM

Try this:

1- Mark the tile where it will be cut on BOTH sides of the tile
2- Coat the back side of the tile with fast setting epoxy, the kind you find in the dual syringes at Home Burrito. I like gorilla glue.
3- Embed a square of kerdi or similar on the backside, smooshing it into the epoxy.
4- let that set until its rock hard. You should be able to see the markings on the rear side of the tile through the kerdi
5- Cut tile as normal
6- bottom pic shows the hole getting smoothed out

We once had a large hole to cut in the very corner of a 12x24 rock hard porcelain tile. This worked well for us.

07-10-2010, 10:32 PM

Well, I still have to grout and caulk and put up baseboards and door frames, but, still, the tile is down. It looks pretty darn straight and there's only one intersection I know of where the four corners don't line up perfectly (one is off by maybe 1/24") but it's to the side of the toilet between it and the vanity, so I'm hoping it isn't noticeable.

As for the closet flange, I gave up trying to get the hole in the solid tile. The hole was too close to the edge. After the 10th tile I gave up and split one tile and cut the half circle in each. Turns out the grout joint will be completely covered by the toilet in the front. LOL. What a waste of time and money.

I was a little concerned about my choice of trowel. I went with the Schluter recommended size for tile over Ditra, but I probably could have used an extra 1/8 of an inch for better coverage. The tiles I picked up where suctioned on really well, but a couple had 60% or so coverage. I backbuttered those an put them back. Part of the problem was a very slight bow, roughly 1/12", in the floor that I didn't catch until I put down the plywood, for which I was counting on the thinset to be able to level. I was pressing down the tile with a 4' Stabila level to make sure everything was flat and level, so it was probably the lower sections that didn't get 80%+ coverage. Next time I'll go slightly deeper on the trowel notch if my floor isn't completely flat.

I think I nailed the thinset consistency though. I got it a teensy bit thicker than mayonnaise.

I'll follow up in a couple days with pics of the whole process. Thanks again a TON to everybody who's been offering guidance on this project.

07-11-2010, 01:12 AM
Already have more questions.

The grout. I used 1/8" spacing between my tile. Should I use sanded or unsanded grout? Any particular brands to consider?

07-11-2010, 02:43 AM
I'd use sanded for 1/8" joints.

07-11-2010, 08:17 AM
Me, too.

07-11-2010, 02:35 PM
I may go to the tile store and check out the millions of brands and colors they offer. But Lowes carries sanded Laticrete, Spectralock, and Keracolor. HD only carries Polyblend.

Any reason to go with regular sanded Laticrete over Spectralock?

07-20-2010, 02:27 AM
Here is the subfloor after I ripped off the vinyl and the particleboard and all the square nails and staples.

I laid down 1/2" plywood, nice exterior grade stuff. Plenty of decking screws.

Here is the Ditra down. I got those cuts pretty went down in two sheets and the scraps went in the closet. Yes, I cleaned up those thinset spots once they dried....somehow I got a glob of thinset on my shoe towards the end.

Here is the tile all down. Because I was doing this solo, I did a dry run and got all my cuts done. Still, flying in the face of wisdom, I started with the doorway because I needed to have those tiles and the ones in those rows perfectly straight. I put down a faint blue chalk line and used a straight edge along it to keep those first two rows of tile straight. Using the shower as an island, I was able to get past them to lay the rest of the tile.

The grouting was extremely physical. I run half-marathons, but I was dripping sweat before I finished this small bathroom. I think I did a good and thorough job of packing the grout. We went with Spectralock in an almond shade and it looks fantastic. One container of AB and C covered the entire room and had some left over. My wife took over to do the grout cleanup. We finished the water rinse tonight and will give it a couple days before finishing the room and then starting on the wall tile.

Again, many many thanks to everybody assisting me with this project with your answers and advice.

Dave Taylor
07-20-2010, 03:41 AM
Very nice Josh.

Thanks for the pics. :---)

07-24-2010, 09:13 PM
Okay, so the latest crisis.

Above the vanity was a large frameless mirror that I removed when I demo'd everything else. It was held on with some nasty black glue. The glue wasn't coming off without tearing the drywall--and taking with it the green moisture guard, so I thought I'd go ahead and just replace that section of drywall. It would also be an excuse to see what the interior of the wall looked like, since it lies between both bathroom and we wanted to see what condition it was in because the other bathroom has some warping on the floor. And I've never done drywall so it would be fun.

I cut a 28" strip across the wall where the glue was. Everything was bone dry and looked really good. The wall is made of 2x6 redwood. Super. Except that that wall had been the first to go on and I wasn't going to be able to slip into the corners and properly secure the drywall. So I decided to cut the sections on the adjacent walls just to the first stud and replace those sections too. On the interior adjacent wall, no problem. The exterior adjacent wall uncovered what may be an issue.

For some reason, they only taped the fiberglass insulation along the sides of the studs and not at the top or bottom. I have a hard time believing this was unintentional and if it's been like this for 50 years and only this much mold and dust has accrued, then maybe there was some reasoning to it. On the other, as I understand it, the vapor barrier on an exterior wall needs to be completely sealed.

I know this is a tiling forum and not a construction forum, but I'm sure you guys have encountered things like this and can at least let me know if this looks like a problem or not.

07-24-2010, 09:30 PM
Joshua, it's helpful when folks pewt some information in their User Profile, such as geographic location. Helps in situations like figgerin' out what your climate is and how significant any insulation issues might be, eh? :)

That looks to me like a typical (read, sloppy) batt insulation installation. But everything in your walls looks clean and dry and nothing I see is setting off any alarms.

Patching sheetrock, by the way, doesn't really require going all the way to any particular joist or area. In fact, it's frequently easier to make a patch if you don't get real close to any joist at all. Just use some sort of backing strips (I favor rips of plywood) and screw into those strips through the existing sheetrock and then through your patch. Can fix large or small areas that way and often more quickly than trying to get the cuts over the center of a stud.

My opinion; worth price charged.

07-24-2010, 10:45 PM
Thanks, I'm sure I'll use that technique. I've used popsicle sticks to patch small holes before....that's more or less the heavy duty version of it. In fact I may do that for the shower walls in this bathroom.

But, in this case, this glue was all over the place. I'd have ended up patching half the wall.

I'm inclined to just patch it and move on. I did multiple mold tests around the house for the heck of it last year, and nothing showed up. Still, I can shake this feeling that as soon as I screw the new drywall over this stuff, Mike Holmes is going to wake from his slumber in a cold sweat and anxiously stare out the window.

07-25-2010, 12:25 AM
I was checking and they were saying for places like Sacramento that are a mixed-dry climate, you actually want moisture in the wall to be able to evacuate from either side of the wall. We get real real hot and pretty cold here, so a complete vapor barrier on either side of the wall would effectively trap moisture during either Winter or Summer depending on which side of the wall you placed it.

The wall and roof assemblies in this building are “flow-through” assemblies, with some degree of vapor permeability in all components of the wall and roof. This bi-directional drying is the preferred approach in Mixed-Dry climates. The most common exterior rigid insulation used in this assembly is expanded polystyrene, a semi-vapor permeable sheathing.
Reference (

So, as I thought, it looks like they did this intentionally and this amount of mold over the course of 50 years is a side-effect of limiting it.

07-28-2010, 02:08 AM
I had a home inspector come in because we found evidence of a very small leak above the shower, once I removed the drywall. He determined it was coming from the shake roof where the sun had dried and virtually turned to powder, a large portion of the shingles on the southern facing side of the house where the bathrooms are.

Nothing really bad, just some mold in some of the fiberglass and some wear on the exterior house wrap. We've cleaned and then sanitized it.

Here's my question. He recommended, since the exterior house wrap has some holes in it, to coat the inside of the wall cavities behind the shower with Redgard. Makes sense since the other option is to remove the stucco and re-apply the house wrap. My question is, does this sound okay if I'll be using Kerdi on the shower? Two moisture barriers sandwiching the wall cavity? For this reason should I apply the Redgard just to the wrap paper and not go up the inside of the studs with it?

Houston Remodeler
07-28-2010, 06:10 AM

Me thinks that's a bad idea on several fronts. I'm gonna guess you have plywood under that siding? If you do then you are going to rot out that siding faster this way. Leaks on the outside need to be fixed.... on the outside.

And the moisture sammich thing too.

07-28-2010, 12:57 PM
Oh, the leak will be fixed. The wall is bone dry right now, there's just dried mold in there from last Winter. We have a few months before we'll be seeing any rain and we'll have the roof replaced or repaired by then.

The issue the Redgard is addressing is the tears in the house wrap which will allow vapor into the wall cavity unless they are patched. I could patch the holes with tape, but the Redgard seems like it would be a longer-term solution. I just questioned his recommendation or hitting the inside of the studs with it too.

Houston Remodeler
07-28-2010, 02:19 PM
I know they make tyvek tape. I keep some in the shop. Pretty cheap stuff. It seems like ordinary tape with a logo on it. Not sure if its anything different but why take the chance over a buck or two?

07-31-2010, 07:48 PM
I checked the Schluter website and it mentions you can apply over drywall without taping the joints. In fact, it says if you did tape the drywall that you need to go over it with a latex primer, so, to me, it sounds more ideal to not tape the drywall.

But I couldn't find any info on whether to cover the screw heads with some joint compound or leave them exposed too. Anybody know?

07-31-2010, 07:54 PM
Leave them exposed

07-31-2010, 08:11 PM
Your thinset mortar will fill them just fine, Joshua.

07-31-2010, 10:37 PM

Latest update is that we cleaned the small amounts of mold and sanitized it. I patched the holes in the house wrap with gorilla tape and put new insulation in. I put the drywall up for the shower and used 2" drywall screws about every 5" along every stud. I also had a large section of drywall to replace where the mirror used to be and just finished patching it, taping it, and putting down the first layer of joint compound.

Because I didn't add a skim coat and primer to the new drywall for the shower, it's about 1/16 lower than the surrounding drywall and there's one side where the Kerdi will overlap the old and new drywall. Is that a problem or can I compensate for it at tile time? I guess I can tear the old stuff out, but it's only a few inches wide. Not sure what I was thinking other than that I wanted to leave the stuff by the door frame and window frame alone.

Oh, and it should really be relayed to the general FAQs for tile that when using a Shop Vac, it should be considered mandatory to use a HEPA filter. Drywall dust is too thin for normal filters. I found that out the hard way the first time I did some cleaning up. The new filter traps all that stuff. Expensive at $30 from Lowes but reuseable and it will save you from dusting your master bedroom.

08-01-2010, 06:27 PM
Good idea on the filter. I bought 2 extra hoses and I keep the shopvac outside running the hose in the window.

So nice and quiet and dustless

08-02-2010, 08:15 AM
Because I didn't add a skim coat and primer to the new drywall for the shower, it's about 1/16 lower than the surrounding drywall... If you are using larger tiles (say, 4" or bigger), you can deal with it as you tile. If you are using smaller mosaics, skim coat the low areas with thinset, then tile after the skimcoat has cured.

08-02-2010, 11:08 AM

After posting that I realized how silly it sounded, so I ripped off the old drywall and put new stuff up. But it's still slightly higher than the other sheets, so it has to do with the studs. The tile is 8x12.

It's good to know I can do a skim coat as that would really be the cleanest.

08-02-2010, 03:12 PM
Oh, real quick. Skim coat before or after the Kerdi?

Houston Remodeler
08-02-2010, 03:51 PM
Either or, your choice. some under and some over may be easier to do than build up all at once.

08-06-2010, 02:14 PM
I used thinset to get a nice skim coat on the lower areas and things look much better.

I'm already looking ahead to the wall tile. This is a corner shower. In the corner where the tiles meet, do you want to run one wall of tiles all the way to the corner or should I leave a gap at the corner on both walls and fill the corner with caulk?

Brian in San Diego
08-06-2010, 04:20 PM
In the corner where the tiles meet, do you want to run one wall of tiles all the way to the corner or should I leave a gap at the corner on both walls and fill the corner with caulk?You never want to stop the tile against an immovable surface. Keep a small gap off the wall and then keep the distance between that tile and the tile from the opposite wall the width of your grout joint. Then caulk that joint.


09-06-2010, 09:59 PM
Well, the past month was a nogo for tile. We bought a dual sink vanity because this is a master bathroom. But, of course, our current vanity had only one sink. I tore open the wall again and once I saw the drain was blocked by a drain from the adjacent bathroom, I hired a plumber to reroute the drain. After a lot of research, I felt confident I could handle the supply lines so I redid the supply lines myself using PEX with ProPex fittings. I had to go under the house to unscrew the galvanized pipe to get it out of his way first and once I saw what those 60 year old pipes looked like inside, I decided it would be worth investing in the Uponor PEX tool to clean this up soon. Then there was putting the drywall back up, taking care of the seams, priming, and painting.

Put the vanity in today which meant I could finally install our nice new Toto toilet. Got it installed without a hitch thanks to the advice here about the flange extension and, ya, you can't see the tile I split to cut the hole for the flange.

I understand I'm doing this all backwards, but my priority all along has been to get our second toilet back. Living with three girls will make that a priority....even if two of them are little.

So tomorrow, the bottom row of tile goes up in the shower. The wall still has about a 1/8" slope inward toward the bottom. How thick a layer of thinset can I safely place under the tile?

Brian in San Diego
09-06-2010, 10:09 PM
Regular thinset can probably withstand a "build-up" of about 1/4-3/8" under the tile so with only a 1/8" difference you should be fine.

09-10-2010, 03:01 AM
I got the first row up. Using Ditraset, how long do I need to wait before I do the rest of the shower?

Brian in San Diego
09-10-2010, 08:50 AM
Are you using a ledger board and starting with the second row? If so, you can keep on tiling. The ledger board will hold until the thinset is set on anything you tile in a day. After 24 hours you can remove the ledger but I left mine in place till near the end.

09-10-2010, 02:18 PM
I just laid the first row of tile. I had the tile resting on top of spacers on top of the ledge of the shower base.

Is 24 hours good enough or should I give it 48?

Brian in San Diego
09-10-2010, 03:13 PM
I'd say keep on tiling. If everything was done correctly on the first row, 24 hours is plenty of time for the thinset to cure.

09-12-2010, 01:43 AM
Shower tile is done, but I made a nice mess in the process. I'll clean it up and take some pics.

We'll be sampling grout tomorrow. I also just realized I'm going to need to use 3 different colors of silicone caulk. :cry: :bang: :twitch:

09-12-2010, 11:48 PM
Like I mentioned earlier in the thread, because the bullnose pieces for this tile were all 3" wide, I didn't want to run them along the top because I didn't want it to look like a frame or something. I also didn't like the idea of ending the tile against the ceiling and wanted to add crown moulding to the room I managed to find some really thick PVC crown molding at Lowes that I ran around the entire room. That's where my tile ends.

Obviously I still have a lot of thinset to scrape out from the grout lines. I just gave up using a manual grout saw because it was too scary running that thing so close to the edges, so I'm going with a thin screwdriver and a custom abrasive pad I've fashioned.

There is a 1/8" gap there in the corner, it's just slightly off to the side and hard to see from this angle.

Having a couple guys come in this week to give me quotes on the shower doors.

10-18-2010, 11:56 PM
Quick update. Picked out the granite for the countertop Saturday. There's a great place here in Sacramento where they stock remnants. They even have an online inventory with pictures and prices that is updated instantly. They also have some full slabs and, as they did for us, they'll cut a side off for you and you pay only for what you need plus a small fee. We got crazy beautiful Tuscan Gold granite for $19/sqft. I'm having that fabricated this week.

We're stuck on the shower walls. We have a fantastically standard neo angle base that is 17.5" on each side and 25" for the door, but I can't find a single shower enclosure anywhere that will fit it. It's the shower base from the previous shower. It was so solid and level, I didn't want to mess with it and try to lay down a mud or a schluter floor or anything. Now, it turns out, it would have been much easier to mount frameless doors with tile.

01-11-2011, 02:26 AM
Got the granite fabricated and installed. Picked out and installed the fixtures. Then we picked out mirrors and lighting. And, finally, I found a great local supplier for shower doors and got a new neo angle enclosure.

I plan to install the shower this weekend and then the bathroom is done and I'll snap picture or maybe post a hi-def video tour.

I've run into another question I couldn't find any answers for by searching.

I'm caulking the shower now. I bought caulking to match the grout for the corner where the two walls meet. I bought almond to match the walls for the outside edge to match the paint color. And I bought white to match the base tray. I would like to have caulk on the bottom edge of the lowest row of tiles be white to match the base. That's going to mean running the grout-colored caulk in the corner once the white dries. Will that point where the two caulk lines meet be a weak point or does silicone caulk stick to its dried-self just fine?

01-11-2011, 05:40 AM
Silicone will stick to dried silicone well enough.