Ask the Experts – Coverings 2012 edition


What is the association’s recommendation as far as a trowel size to use when installing an 18”x18”x3/8” ceramic tile? Do I need to back-butter the tile? I am installing on 1/4” Durock placed over 3/4” plywood subfloor over radiant heat.


For an 18”x18” tile, you should use a medium-bed thin-set mortar. You will probably need a 5/8”x3/4” loop-notch trowel to get the proper 80% coverage for interior dry areas. Back-buttering is always a good idea to improve coverage.

– Michael Whistler, NTCA Symposium presenter


We need an installation method for installing Daltile 2”x2” mosaic tile in a roll-in shower room. The architect has had us use a cleavage membrane (#15 felt with wire lath) at all floor areas where we’re using mud. The building floors are a concrete plank. There is also a drain outside of the shower area in the space where the toilet and sink are. The rooms outside the shower will get wood flooring with wood sleepers below (approximately 2” total). There is no need for a saddle between the shower and the toilet and sink area. The high points should be around the perimeter of both areas, and most importantly at the entry into the shower area, which acts as the high point for both areas. We would use waterproofing. What do you suggest?


To follow is a drawing that shows common installation procedures for curb-less shower systems to retrofit an existing shower with ADA-approved wheelchair accessibility. No saddle or threshold that a wheelchari need negotiate will have a change in elevation of more than 1/2”, and no two elevations shall occur closer than 5’.
This can be used with a cleavage membrane along with reinforcing wire but will increase the mud bed thickness from 1/2” to at least 3/4” at the thinnest locations for residential; 1-1/4” for commercial. This may require raising the floor outside the shower 1/4” to 3/8” to meet the wheelchair accessibility recommendations. This is a common practice but is not yet available in the TCNA Handbook. The NTCA Methods and Standards Committee is currently working on submissions related to barrier-free and curbless showers for the Handbook.

– Gerald Sloan, NTCA training director

Ask the Experts – April 2012


If a tile installer damages things in my home, should he fix them?  As a result of this tile installer’s sloppy work, my arcadia door (where the tile comes up to) now drags and squeaks. Before installation, no problems for 20 years. He also scraped the metal track of the door so I will have to paint the metal. He told me I could take care of both things myself. Shouldn’t he????


This is a fair question, and addresses whether you have a quality contractor. I was a contractor for many years. I assume that the door now rubs and squeaks because the new tile is higher than the old flooring, so the door now scrapes along its bottom. This is an issue that needed to be discussed and decided before work commenced. Our company would seldom modify doors, but there were times when we would subcontract a carpenter (if the door was wood) to cut the bottom of a door. But this was always discussed during bid time, so the client knew there was an additional expense.

As far as damage to other finishes, we always repaired or fixed things we messed up. But then, we were one of the top companies in our area, not the cheapest, so our reputation on customer satisfaction and ethical dealings was of utmost importance to us.

Michael Whistler, NTCA Symposium presenter

Ask the Experts – March 2012


What is the best way to handle a situation with a general contractor (GC) on a job I am just starting? I remember from the NTCA Symposium you had some good points on how to deal with incorrect specs and GC’s.

It is on above-ground concrete (steel framing and decking) with 1/4˝ deep saw-cut joints cut every 10’ or  so. I recommend a full coverage membrane installation over the saw-cut joints; GC wants to go partial to save money. Tile will be 16˝x32˝ porcelain.


This is a good question, and begs some questions from my end. Do you want to use an anti-fracture membrane so you can offset movement joints away from their current positions? Are you hoping to be able to eliminate some of the joints by using the membrane? Is this installation a running bond or is it a square grid pattern?

There is new industry language re: above-ground concrete that says you should revert to the more stringent 10´ to 12´ maximum distance between movement joints, so maybe your saw-cut joints should just be followed up through the tile. There’s also language that says you should never cover any type of construction joint, including saw-cut joints. Any joints in the substrate should follow up directly through the tilework with a soft/movement joint above. If you decide to offset or ignore these joints, you will definitely be taking a large risk.

I took a firm stance after a couple of failures. I gave documentation showing that soft joints were industry requirements, and tried to educate the owner, design pro or GC that the tilework needed room to move. If we came to loggerheads on the issue, I would not proceed until I had direction, IN WRITING, to do the tile installation against industry and my standards. But realize that even with such a document, you are still at risk. In the event of a failure, the court will rule against you saying that as the professional you should have known better.

– Michael Whistler, NTCA Symposium presenter

Ask The Experts, Sept 2011

I am a consumer in Oregon currently going through a complete bathroom remodel. We are currently at a standstill with our contractor due to tiling issues; I am hoping someone can help me to make sure I understand code and tiling processes correctly.

We are using a general contractor. The entire bathroom was gutted, new plumbing, electrical and total new tile on floors and walls; everything new. We have a contract and he is to do all the tiling.

My understanding is that the tile should be completed, meaning: all tile, grouting, cleaning of grout and sealant should be finished before anything is installed in the bathroom. The contractor has not finished grouting where the walls and floors meet and has not done any cleaning and sealing of tiles. But he has gone ahead and installed the vanity as well as toilet and shower fixtures. We are concerned that since he has installed these items without finishing the grout and sealing of the grout, any water that gets behind the shower fixtures and the vanity can cause damage.

We believe he needs to take out the vanity and the plumbing/shower fixtures that have grout running behind and under them for the tile to be completely sealed. He says he is not going to do it. If he had finished all tiling work before installing these items we’d have no problem.

I am hoping this note can help ease your mind. Yes, grouting and cleaning any grout residue from the tile surfaces should be completed before installing fixtures. Where the wall tile meets the floor tile, or where tile meets a tub, should NOT be grouted. This area needs to be filled with a flexible sealant (like silicone caulk) to allow for the slight but certain move- ment that will be occurring at those changes in plane.

Sealers are typically misunderstood by consumers. You understand correctly that tile and grout are not waterproof. But the waterproof- ing (or moisture barrier) is actually designed into the substrate, or the system used BENEATH the tilework. Even if the system were not tiled, the waterproofing would not allow water to damage your structure. The best sealers are the ones that allow moisture or vapor transmission, or breathability. Sealers are not (and should not) be a waterproofing or moisture barrier. Sealers are NOT required in any tile installation, and at best should be looked at as an add- on product that allows the migration of smaller water molecules, but stops the larger dirt and oil molecules from getting a firm grip onto the surface, allowing greater ease of cleaning. Therefore, sealing is good if using a quality sealer, but not required.
To your question about the toilet and vanity being installed before the sealer, I hope the previous explanation lets you understand that since the areas beneath these permanent fixtures are protected, and never will need cleaning, there is not really any need to seal the tile and grout where they reside.

Michael K. Whistler
NTCA Workshop Presenter/Technical Consultant

Ask The Experts


I have a house built in 1985 built with a 250 square foot room that has a good 3/4-inch plywood subfloor on wooden joists. It feels solid, level, and no bending when walking. I wish to install slate tiles and intend to add 1/2-inch of plywood to the subfloor. In the corner of the room was a fireplace which I’ve demolished and will replace with a wood stove. The fireplace had a 6-inch thick cement pad under it which is higher than the plywood surface in the rest of the room. I wish to make the whole floor at one level, so I’m lowering the cement with a demolition hammer, to the level of the 1 1/4-inch subfloor. Can I transition from slate on 1 1/4-inch mixed plywood to slate on cement, or would it be safer to cover the whole floor with the same layer before tiling?
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