Advice needed on SLC installation [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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06-25-2019, 02:04 PM
Hi all,

New member here.
Thanks to all the experienced members that contribute to this forum, I have researched and created a work plan for a small bath remodel. The immediate task is to get the floor ready for my porcelain tile installation. I have already done the calculations using the deflecto and am confident that the subfloor structure is adequate. I originally considered using durock on top of the 3/4 t&g subfloor, but now plan to use self leveling compound due to some flatness issues.

I am hoping some of you can give advice and suggestions on the following plan:

Fill any holes with plastic wood filler
Fill any seams with silicone caulk
Install a dam around the perimeter with self adhesive foam insulation (Frost King or similar) and any openings such as toilet flange, heat vent. How wide should the foam be to provide the required isolation from the wall?
Prime subfloor with LevelQuik latex primer
Install metal lath with galvanized/stainless staples every 6-8". What size staples are recommended?
Spray additional primer over metal lath
Mix LevelQuik RS with an egg beater type mixing paddle for 2 mins
Spread SLC - per Custom needs to be min of 1/2" thick over single layer plywood (I am using a single layer of 3/4 T&G). Will a push broom work okay? Floor area is about 64 sq ft.
Wait 24 hours and apply RedGard. Not sure if this step is necessary but included it as it has been mentioned several times on the forum for crack protection.
Install tile when RedGard is cured (12 hrs?)


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06-25-2019, 04:41 PM
Looks like you have it pretty well covered. Only thing I would advise is to use a flexible rake instead of a broom to pull the SLC into position....then use a flat trowel to feather out the edges....:gerg:

06-25-2019, 07:49 PM
Thanks for the quick reply Laz.

When you say flexible rake, is that like a steel tine lawn & leaf rake?

Also a few points of clarification on my questions:

What is the recommendation for how wide the foam should be around the perimeter? I thought I read 3/4" somewhere in the forum.
Is a 1/2" long staple adequate for fastening the lath?
Do you think the RedGard is a good idea?

Thank you.

06-25-2019, 08:44 PM
I think 1/4" foam is ok.
Spiked shoes leave no divots so you can walk on it. I think a metal leaf rake or regular rake would work ok. But the bought a spiked roller.
Mark the perimeter of the room as it doesn't self level perfect. It's best to hit your marks as you go.
Sounds like a 6 bag or more job. It's nice to have a helper. Mix 2 bags at same time with two drills , then pour and helper goes to make the other batches.
I don't think the lathe needs primer. If 1/2" Staples hold the lathe that should be fine.

06-25-2019, 09:12 PM
Welcome, Mike. :)

If this is your first time using SLC, I'm gonna recommend you stay away from the rapid setting product and use instead the LevelQuick ES product. Especially if you'll be working alone.

My opinion; worth price charged.

06-26-2019, 05:23 AM
Teddy - thanks for your helpful suggestions.
I've not heard of a spiked roller before, but I see a Spiked Screeding Compound Roller on Amazon. Looks like it was made for this kind of application and is about the same cost as a rake. I also like your idea of marking the target levels.
I have seen the use of spiked shoes on some videos - I am hoping I can find some that strap on to my (rather large) shoes.
Six bags sounds about right based on the manufacturer's tables - will need to enlist a helper. I agree it will make it much easier.

CX - thanks for nudging me towards the ES product. I had been going back and forth with my thinking and I think it will make for a less stressful job!

Does anyone think the RedGard would be a worthwhile step?

06-29-2019, 12:31 PM
Before I move forward with installation of the SLC, I want to consider some alternatives. My concerns with SLC include the extra weight (vs Durock), the potential for something to go wrong, and the feeling that it is overkill for my project. The tiled area of the floor is 8’ x 6’.

Possible alternatives

Use ¼” Durock installed over a bed of thinset applied to the ¾ T&G subfloor. I am thinking the thinset would fill any depressions enough to make it acceptable for tiling (assuming tiles in the 13-15” range). This was my original plan (I already have the ¼” Durock)
Use a product such as MAPEI Planipatch or Henry 547 Patch & Skimcoat to level out the dips in the subfloor. Then apply the ¼” Durock in a bed of thinset as above and tile over the Durock.
Use LevelQuik only in select areas to fill in dips. Apply ¼” Durock as above and tile over the Durock.

Any comments on these alternatives would be very much appreciated. Thanks.

Tiger Mountain Tile Inc
06-29-2019, 12:37 PM
If it were me, I would switch over to Ardex Liquid Backer Board or Cusom Level Tech(?) which neither requires lath and both can go down to 1/4 inch. (LBB down to 1/8").

I think Ardex wants all seams and gaps filled with Feather Finish. Not sure how Custom wants it done- maybe the caulk?

The thickness of the foam is not an easy thing to gauge. It's not unusual to have an inch of foam around a toilet flange. I use sill seal (window section of the home improvement store) for around the perimeter. You can cut it, or fold it in half, for a 1/4 inch and staple it around. The foam that you've described should work fine too.

For pouring the SLU, it's not as easy as it sounds. At least, it's not as easy to get flat as it sounds. Once the floor is covered in the leveler it's hard to know where you are "at" with the depth. Is it too deep? Is it deep enough?

I like to use screws and screw them into the subfloor as a gauge of height. Then when you are spreading the leveler over the floor you'll know what height you want to hit.

The smoothing tools and prickly rollers are nice but not easily available and not something one usually wants to purchase for a one-time event. I used to use a squeegee before I bought proper self-leveling tools.

Also, cleats are wonderful. Being able to walk back on the floor and smooth things out is key. If you have heated floors then you can't have metal spiked cleats.

The trouble areas are where the two batches meet. One batch is drying at a different rate than the other.

Self leveling isn't as easy as it sounds.

clifton clowers
06-30-2019, 12:54 AM

Also, for cleats, I found some on Amazon for $20. They were definitely worth the investment.

06-30-2019, 03:48 AM
Very good post Clifton in your thread. My buddies drill would have died or caught fire. So we only used it for the first double batch. We had water fill lines on our buckets and 4 ready to go. We mix with a timer. I imagine different paddles would make a difference. I used my egg beater style. 4 square bands of 5/16-3/8" rod. My cheap drill has been a workhorse more than I can believe. I think it's a Firehawk or some off brand. If a drill died half way through a pour it would be a disaster. Also we ran around plugging a couple leaks on a full bathroom pour. When they say run a bead of caulk around the baseboards they are not joking. I did a test pour where I had 3/8" dip in about 4' more than specified for vinyl plank flooring. Only 2 bag 2 batch job. I learned 2 mistakes. It doesn't like to flow to a feather edge like Clifton mentioned and I should have used a scree but it looked so shiny and level. (After this poor I ordered the spike shoes and rollers) And isn't it called self leveling!! #2 i made mistake of pouring 2 ND batch on top of first. it would have been much better if I had poured one batch on half the spot and the second batch on the other half. I also had a low spot going into a storage room doorway nearby and I spent a lot of time trying to stop it from flowing that way. I should have put a dam across that door and poured three bags and leveled them all with the scree since it was across the narrow canyon of only four to five feet. And I made things worse with my delay in calling for batch #2, it would have been so much better if I had poured half the floor. It's best to pour and level with the spiked roller as you go. I used a foam squezee some and it works ok but leaves marks. That don't go away like spikes do. The spiked roller and shoes work so well until it starts getting too thick. There's a video where they are pouring an industrial pour in a hallway and one man is pouring large batches and the other man is using the spiked roller back and forth in the hallway. It was amazing how much the spiked roller will push the leveler around and leave no Trace when it's freshly mixed SLC.
My 3 rd floor was a much larger poor but had feather edges on three sides which are a pain in the ass. it also had a low valley that wandered off into a low but flat enough corner that I did not want to fill. Number 2 pour was in the bathroom and it was almost a complete room except for one 3 by 3 corner. it's so much easier when you are flowing it against a wall or a blockade at a doorway without feather edges.

06-30-2019, 08:50 PM
Thanks all for the tips on working with SLC and the potential pitfalls.

I only plan to do this once and I might be lucky enough for it to go smoothly. However, because of the possible problems a novice might encounter, I am interested in also considering these other alternatives:

Use ¼” Durock installed over a bed of thinset applied to the ¾ T&G subfloor. I am thinking the thinset would fill any depressions enough to make it acceptable for tiling (assuming tiles in the 13-15” range). This was my original plan (I already have the ¼” Durock)
Use a product such as MAPEI Planipatch or Henry 547 Patch & Skimcoat to level out the dips in the subfloor. Then apply the ¼” Durock in a bed of thinset as above and tile over the Durock.
Use LevelQuik only in select areas to fill in dips. Apply ¼” Durock as above and tile over the Durock.

Thoughts on these other methods would be appreciated. Thanks!

06-30-2019, 09:01 PM
Mike, if you plan to use a CBU as your floor tiling substrate you must install that first and do any flattening or leveling over that. You don't want to use any of those flattening or leveling products first and then install your CBU. Those materials will not tolerate the mechanical fasteners you need for the CBU.

My opinion; worth price charged.

07-01-2019, 05:19 AM
Thanks CX.

Are the products I mentioned (MAPEI Planipatch or Henry 547 Patch & Skimcoat) appropriate for application on top of the CBU, or are there others that work better for building up any gaps?

07-01-2019, 07:45 AM
I think either of those products would be fine, Mike, but if in doubt, read the manufacturer's installation instructions. If still in doubt, contact the manufacturer's tech services people. CBU is not usually included in anyone's list of suitable substrates on accounta the product manufacturers can't tell just what your CBU might be nor how it might have been installed. But if it says it's suitable for use over concrete and wood substrates, you can be confident it'll be suitable for use over a properly installed CBU.

My opinion; worth price charged.

07-02-2019, 05:57 AM
Thanks again CX.

I did notice that the data sheets do not call out CBU specifically as an acceptable substrate. Good to know that CBU are still okay.

Fast eddie part deux
07-02-2019, 07:36 AM
Mike ... if are still buying tools ... this is a great opportunity to go to that much maligned source ... Harbor Freight ... and buy a cheap 1/2" slow speed drill to mix the slc.

07-02-2019, 01:08 PM
I was told to mix the SLC at high speed just don't en-train any air.??
ALso I read where the water is just right if a small bead of water forms at the vortex. I guess it means the particles all have a mating H2O. I got this every batch,.

Tiger Mountain Tile Inc
07-02-2019, 07:14 PM
It can get a bit confusing. You install the levelers first if you are putting a membrane over them. However, if you want to use cement board then install that first- then use the levelers.

08-07-2019, 03:02 PM
Just noticed your replies from July - sorry for the late response. Didn't get an email to let me know you responded. Anyway, thanks all for the advice.

Ed - I have a 1/2" drill on order from Harbor Freight and it should be here Friday.

I got wet feet about the SLC - it just isn't in my comfort zone, so I am using 1/4" Durock as a bonding layer for the tile and will use leveler over the CBU if required.

I plan on using the Durock brand screws to fasten down the CBU to the 3/4 T&G floor (with thinset over the plywood).

Are the Durock screws the best to use, especially on the 1/4 CBU? I have used these screws when I fastened the 1/2 CBU in the tub alcove and had to be very careful to minimize the cracking and crumbling. Read somewhere on the forum about someone using a different screw that was better. Any opinions on this? Any particular technique to avoid cracking along the edges (USG says the screws should be between 3/8 - 5/8 from the edge)


08-07-2019, 03:35 PM
Mike....make sure you embed the panels in thinset...mixed on the "loose" side just before you screw them down....

08-07-2019, 05:02 PM
Thanks Laz.

I plan to use Versabond polymer modified and will make sure to mix it somewhat loose.

08-24-2019, 02:17 PM
Finally got the Durock thinsetted and screwed to the subfloor. Major accomplishment in what has become a 1.5 year project. (yes, my wife is still talking to me!). After taping the joints I will be ready to start tiling.

Is there a need to wet the Durock before laying the tile? I read that this should be done for Hardie backer (I think) but haven't run across the same advice for Durock. The Durock technical sheet does not mention this, but thought I would check in with the pros.


08-24-2019, 02:30 PM
Mike, it won't hurt anything to wet it down. I wouldn't flood it, just wipe it with a wet sponge before spreading thinset. It's okay for it to be damp, you don't want it shiny wet. Being damp will buy you a little time when setting the tiles.

08-24-2019, 02:41 PM
Thanks Davy. Easy to do and a little bit of insurance.

08-24-2019, 07:40 PM
It also helps to get the dust off the surface when you wipe it down.

08-25-2019, 01:05 PM
Thanks Kevin - that makes sense. I am glad to have these tips before I start to lay the tile.

A couple of questions regarding laying the tile.

I have been planning to match the top of the tile (13x13 porcelain) to the top of the hardwood in the adjoining hallway. The top of the tile without mortar (just laying on the Durock) to the top of the hardwood is 3/8". Because of variations in flatness across the floor of about 1/8" or so, it looks like my mortar thickness could be 1/2" in some areas. To achieve this height I am planning to use Mapei Ultraflex LHT mortar. Is this a sound plan? If so, what size trowel is recommended? I only have about 50 sq ft, so I don't think any extra effort on my part would be a problem. But I want to make sure there aren't any issues with the plan.

Is it the norm to caulk the interface between the floor tile and bottom of bathtub or should this be grouted? I From what I can read, it looks like caulk, but I do see some installations that use grout.

Thanks in advance for any advice.

08-25-2019, 02:18 PM
1. Mike, looks like you're in the area of "unless you need additional height" that all the manufacturers of CBU explain when they recommend their thinner panels for floor installations. Half-inch Durock would seem to have fit your needs much better than quarter-inch material.

You can, of course, try to make it up with an LHT mortar, but I think you're in for a very rude awakening, even with only 50 square feet to tile.

2. With only one exception (shower drain grate) the ceramic tile industry recommends a flexible sealant between ceramic tile and anything that is not ceramic tile. That would be especially true of a floor/tub junction.

My opinion; worth price charged.

08-25-2019, 02:30 PM
Yes, why did you use 1/4" rather than 1/2". To late now but I should put it on my profile.
Screw the adjoining surfaces meeting. Install it right and deal with a transition piece. For 3/8" there are many transitions that will work. They will be forgotten in a few weeks.

08-25-2019, 03:57 PM
Thanks, CX and Teddy for your review of my flawed plan. I am sure you have saved me quite a bit of grief down the road.

Why didn’t I use ½” Durock? That’s a great question. I will say that once the ¼” Durock was installed I was surprised at the distance to the top of the wood floor. This project has been going on for so long that I completely forgot that I was originally considering a larger tile with 7/16” thickness. All of my calculations were based on this thickness, but I forgot to update the calculation when I changed to the current tile at ¼” thickness. A pro did my master bath and he matched the wood floor AND had a heating mat under the tile. It seemed so easy! (guess that’s because he is a pro).

I believe in function over form and wouldn’t gamble on having issues down the road by doing something outside of acceptable methods. I am sure the transition piece will be fine – and as you say, forgotten in a few weeks.

Thanks again!

Tiger Mountain Tile Inc
08-25-2019, 07:34 PM
It won't make much difference, but I like to flip the tile upside-down and measure the height that way. Sometimes you're measuring the sloped shoulder of the tile when you have it face-up.

Also, you might think about adding an uncoupling membrane such as Ditra to the top of the cement board and that should put you within a range to make the heights work. Yes, it's more money but it might save you from messing with a transition.

08-25-2019, 07:39 PM
Certainly not too late to remove the CBU and replace it with the thicker version, either. Yeah, big PITA, that, but might still be the best option.

My opinion; worth price charged.

08-26-2019, 05:27 AM
Thanks again for the suggestions.

Today my plan is to experiment with a couple of different trowel sizes to get an idea of where I will end up height wise relative to the wood floor. I know the transition strip will work and I assume it is acceptable practice in the industry and not just a band aid for mistake in matching the two heights (is this true?).

Jim, the uncoupling membrane is an interesting idea, but I am not sure if that will use up too much of the height delta and not leave me with enough room to accommodate possible variations in the flatness across the floor. CX, ripping the 1/4" out would be a last resort due to the time and effort required. Is there a concern that the transition strip would not be a good solution?

08-26-2019, 05:34 AM
In a perfect world both floors planes will match in height but in the remodeling world things are rarely perfect. Hence the transition strips - they're used all the time and if executed well are perfectly acceptable.

And for what it's worth, Mike, I've been working my MBR remodel for well over a year and a half. ;)

08-26-2019, 08:01 AM
Is there a concern that the transition strip would not be a good solution? Not for me. I always presume I'll need something at such junctions in remodeling work.

08-26-2019, 12:10 PM
the unknowns that are required to get surfaces to match up are to numerous in most cases. What about when the hardwoods are sanded 1/8" for refinishing? I think transitions are normal. i think 1/2 x trowel yields like .18-.2" thickness
1/4" gives like .1" if trowel is held at 90 degrees it should yield 50% but at 45 degrees it is 70.7 % of the 50% 90 degrees trowel angle doesn't work very well . and near a wall you cant do close to 90 due the the handle.
In my shower floor I had the dilex-eke 125 size on the floor and needed to match that. 1/2 " x 1/2" trowel wasn't enough so I resorted to adding 1/4" x 1/4" on the back butter of the tiles then I got enough thinset for what I needed. to much is better than not enough.
These transitions do require you to pick the best one and design around them... some metals ones go under the tile... some on top of everything but also some and custom made ones will need a 3/4" gap to contact the subfloor between the surfaces.

08-26-2019, 01:36 PM
Did some testing today on 1/4 x 3/8 and 1/2 x 1/2 trowels.

Holding the trowel at 45 deg I got about 1/4" of mortar consistently, which leaves me with about a 1/4 transition with the thickness of the tile included. I did backbutter, but not excessively - mainly to fill in the indentations on the back of the tile. I also got 100% coverage on the three trials that I did. This would have been a very enlightening test to run before I started the project. I can see now that getting to a 1/2" of mortar would have been very difficult. Thanks to CX and Teddy for steering me away from that nightmare.

I plan to use the 1/4 x 3/8 - didn't see an advantage to using the 1/2 and it didn't hold the ridges well in some areas - probably because I was mixed a little thin.

Good to know that transitions are pretty normal. (and the point about the issue when the hardwood is refinished is real). I did take a look today and see that depending on the type (as Teddy points out) I will need to plan for it before placing the tile at the doorway.

Dan - I can appreciate your pain with your year and a half MBR project! I was supposed to have this project done last fall (started beginning of 2018). New goal is to at least have the toilet installed for guests on 9/7, which means the floor needs to be done.

Thanks again for all of the help!

08-27-2019, 01:45 PM
Thinking ahead..

Is there an issue with grouting a section of the floor one day and finishing at a later time (a few days or so)?


08-27-2019, 02:03 PM
I probably would not if you are using a traditional powdered grout. Too much variations in mixing style, water content, etc.

I would not worry at all if you are using something like the Mapai "Flexcolor CQ" as the colour consistency is second to none. Different day installs remain true.

08-27-2019, 03:01 PM
Thanks Laz,

I will be using Mapei but was thinking more of the powdered product. Any technical drawbacks to the ready mixed Flexcolor CQ? I have avoided ready mixed products in general because I was under the impression that they were inferior to the powdered products.


08-27-2019, 03:24 PM
Mike, not at all inferior. Let not your heart be troubled. Yes, it DOES set up a bit quicker, so only do perhaps 5-10 sq. ft. at a time and clean it up in a circular motion with a clean sponge....then wipe it diagonally with a clean sponge. You might need to use a microfiber cloth to buff it out after ten minutes or so....but, trust this, it will come out awesome. :gerg:

08-27-2019, 07:44 PM
Mike, the Flexcolor sets up faster on the face of the tiles but stays wet in the joints. One reason I avoid it. The color does stay consistent but be careful or you'll wash the joints out too low. Also, depending on the texture of your tiles, A fiber cloth might work but sometimes you may have residue left on the face that would need to be cleaned off after the grout sets.

08-27-2019, 09:43 PM
Thanks Laz, Davy.

From what I have read online, some people love it and others think it is a bit difficult to work with. I do see though that quite a few first-timers have had good success as long as they pay attention to the quirks.

I have a small area in total, so working slow and paying attention to the issues you mention seems workable.

08-28-2019, 10:04 AM
Davy is spot on. It sets up so fast in thin layers on tile. Like 10 mins. But joints stay flexible and mushy for a long time. I worked with the flex color 3D which I think is similar it is hard to not wash out the joints to much. I think you need a hard square fine grain sponge so you can wash tile tops close to grout line but not touch it. Even using white scotch brite pad on end of 1 " putty knife. Yiu can actually touch the joints with you finger to move lumps around under the non sticky surface layer. Then 10 mins after that go back and wash grout joints better.

08-28-2019, 11:25 AM
Worth mentioning that the CQ pails come with a firm, square edged sponge included. Less problem with pulling the grout out...

08-28-2019, 11:46 AM
I was just going to post that the 3D came with this nice square firm sponge like the type I'm talking about it also came with a very small white Scotch-Brite pad . The tail is on the less than half full of grout and it's amazing that the Pell the grout in the pale did not dry out even after weeks because this the seal seems so poor on the top flap. I did try to keep the plastic on top. I swear this is almost some type of living animal that knows when it's out of the box and when it is supposed to dry. I would definitely suggest you make a little story board with scraps and practice on a few joints and not on your actual floor

08-28-2019, 12:32 PM
the cq stuff dries so fast. when the instructions say to do a small area and clean it before you move on, it is no joke. I would stick to a 3x3 foot section at a time, cleaning it before it can dry.

08-28-2019, 03:48 PM
Good info on the grout - thanks. I like the idea of practicing on some scraps first to get the hang of it.

I started laying the tile today and already have a question.

After about two hours I was becoming concerned that the mortar might be getting old, even though the stated pot life is 4 hours. Because of this, I took up the last two tiles laid and scraped the mortar off the tiles and the CBU. I am going to work on this again later this evening at which point the remaining mortar residue will be drying/dry.

Is it okay to re-lay these tiles tonight or should I wait until tomorrow. The mortar seems crumbly and I don't get a good feeling that it would bond well to the new mortar.


08-28-2019, 08:07 PM
Scrape off all you can and if anything is still wet, wipe it off with a wet sponge. A little dampness in the CBU won't hurt anything.

08-28-2019, 08:16 PM
Thanks Davy.

I decided to work in a different area tonight and will reset the tiles removed tomorrow.

08-28-2019, 09:13 PM
I hope you did as Davy suggested before you moved to the next area, Mike.

08-29-2019, 07:55 AM
Yes CX - I immediately scraped the mortar from the CBU and tiles. Didn't wipe the CBU, but this morning the surface looks solid/stable.

08-29-2019, 02:08 PM
I've had some tiles that I pulled at the end of a mortar batch. 2 hours is potlife I get. I was weighing my powder and measuring water. I was using cold Utah water and Its probably 60 f in summer. I noticed a difference in pot life if my mortar bag was in the sun. I actually started to put my next up bags inside the cool basement. I scraped mortar off tile backs and a quick wipe with a wet sponge. I was surprised that I could sponge the residue off and clean the tile like new the next day. I guess thin layers and a bit of excess water kills the mortar.
I have also mixed up a new batch and started right where I left off.

10-28-2019, 01:00 PM
Happy to say the floor tile is finished and I am pleased with the results. The Mapai Flexcolor CQ grout was easy to use and the color matched the areas that were grouted ahead of time.

I ended up with a transition height from tile to wood floor of 1/4". I am considering making a custom transition piece. Let me also say that the transition piece will in no way detract from the appearance of the job and is much more practical than trying to make the tile end up at the same exact height. Thanks to all for the advice on this phase of the project.

Next I will be working on the tub alcove. I would really appreciate some comments on the plan:

The tub alcove uses 1/2 Durock on the walls. The CBU is installed 1/4" above the tiling flange and sits proud of the flange (towards the drain side).

Kerdi band will be used to seal the CBU to tub transition. Kerdi fix will be used fill the 1/4 gap and fasten the band to the tub. The band will be attached to the CBU using a modified thinset.

RedGard will be used to waterproof the CBU.

The above is based on the advice I could find in the forms. I am hoping for some clarification on a couple of points, though.

There is a conflict between the thinset recommended for the Kerdi band (un-modified thinset) and the recommendation of modified thinset for the tile over Durock. I see several mentions of using Versabond lightly modified thin set for the band. Understanding that it will void any warranty with Schluter, are there any other cautions when using Versabond (or other unmodified thinset) for the Kerdi band? I would use a better quality modified thinset for the tile itself.
When applying the RedGard, does it also get applied over the KerdiBand or only in the areas above the band?

Thanks in advance for your help!

10-28-2019, 01:55 PM
Kerdi band will be used to seal the CBU to tub transition. Kerdi fix will be used fill the 1/4 gap and fasten the band to the tub. Definitely use the Kerdi Fix to attach the KerdiBand to the tub's tiling flange, Mike, but I'd make no effort to fill the gap between the flange and the CBU above it. In fact, I'd make an effort not to fill that gap.

1. You're gonna violate somebody's rule as you've noted. Use the modified mortar to bond the KerdiBand to the CBU.

2. There is no applicable rule, but I'd lap the RedGard onto the KerdiBand a couple inches.

My opinion; worth price charged.

10-29-2019, 05:17 AM
Thanks CX. I appreciate your advice on this.

What is the reason for not filling the gap with Kerdi fix?

10-29-2019, 08:43 AM
The object is movement accommodation. Why would you want to fill the gap with anything at all? The waterproof membrane will provide the waterproofing over the gap. I suppose you could fill the gap with a flexible sealant, but it would serve no practical purpose.

My opinion; worth price charged.

10-29-2019, 09:06 AM
Makes sense - thanks again.