Tile FAQ’s

The list below contains some of the most commonly asked questions I get about tile and installation methods. For each one I have included a (very) short answer.  I already have, or will have in the future, a post about every one of these. If that post already exists there will be a link at the end of the answer.

I will continue to add to this page as the questions come up. If you have a question just leave a comment at the bottom and I’ll include it on this page.

Just click on the question to view the answer.


What type of grout should I use for my tile?

It depends on the tile and the size of the grout lines. Read this: Using the correct type of grout

How large should my grout lines be?

It depends on the tile size and the look you want. Read this: How large should grout lines be?

Can I fill my cracking grout with more grout?

Maybe. Read this article for a more complete answer: Filling grout lines with more grout

Are there any “magic” products available to remove stains from your grout and tile?

No there are not. One of the closest things to magic that you can buy is oxygen bleach. It is not bleach! It's a slight misnomer. This is the main ingredient in products like oxyclean. It works very, very well to clean grout. More information: How to clean grout

Does grout help stabilize tile, hold them in place, or make them stick better?

No it does not. (Epoxy grout is different) Read this: Does grout stabilize tile?

Are tile, stone or grout waterproof?

No they are not. Read this: Is tile waterproof?

Can I install my tile without grout lines?

No, you should not. Read this: Tile with no grout


Can I install floor tiles on my shower walls?

Yes you can. Read this: Floor tiles on a wall


Will sealing your tile and grout make it waterproof?

No! It absolutely will not.

Should I seal (or re-seal) my tile and grout?

If you would like it to be easier to clean then yes, you should.

Setting Materials

What should I use to set my tile?

It depends on where you are installing the tile. Read this: Proper setting materials for tile

Are mastic and pre-mixed “mortar” acceptable to install tile on a floor or in a shower?

No they are not. Read this: Proper setting materials for tile


Does my floor have to be level before I install tile?

No it does not. Read this: Does my floor have to be level for tile?

Do I need a waterproof membrane for my shower walls?

Yes, a membrane of some sort is required. Read the article for the different types. Read this: Preparing a shower wall for tile

Can I simply stick tile to the drywall in my shower or the plywood on my floor?

You can but it won’t last – so no. Read this: Preparing a shower wall for tile or this: Installing backerboard for floor tile


Should I use grout or caulk in the corners of my shower?

Technically? Caulk. Realistically? It depends. Read this: Caulk or grout in corners?

If you have any suggestions or questions please feel free to leave a comment.

Genoveva V

Hi, first of all “Thank you” so much for sharing all your great information. I wish I had found your site a couple of weeks earlier as I have already installed the Hardy boards directly to the existing metal beams. I did use hardy board seam tape and cemented all the seams prior to install the 9″ x 12″ tiles using TEC INVISION UNIVERSAL ADHESIVE. I plan on sealing the grout in hopes this will help with some water proofing. My concern is the existing shower floor is concrete with a cast iron drain. I will be using your instructions for the shower floor and have decided to use the Rubber Membrane method however the existing drain flange although corroded has weep holes. I have attempted to remove the metal drain with out success. So I have figured out two options one I cut the drain out from the inside to remove the entire piece and replace with a Kerdie – more work more time more money or two if I can cement over the weep holes and proceed with my Pre-slope, Rubber Membrane, Deck mud and tiles to get a water proof shower floor? PLZ HELP! p.s. I’m a 54 yr old female who has worked side jobs in construction and tiling for over 20 yrs. Full complete showers were very few. This is actually a labor of love for my sister and although she lives in a luxury condo in WPB FL. when I did the tear down they had just used green board for the shower walls so I did upgrade them by installing hardy board I just feel bad that I did not make them 100% water proof …Any info on this issue would be greatly appreciated…After all I wouldn’t want my two little doggies to burst into flames :( Thanx again ;)



Do u have any comments on “Fix a Floor” sold on-line by Home Depot. Its recommended for hollow or loose tiles,



When I was applying the Unmodified thinset over the kerdi, it seems to skin over quicker than all the other times that I have tiled using modified thinset. Is this common and is there any tricks to keep it from “skinning over” before the tile gets pushed against it? It was not abnormally hot or dry in the room, I misted it with a spray bottle and worked fast but still had issues. Doing around 5′ square section at a time…



Hi Roger,
This website and your books have been very helpful. I need some advice before I start tiling my shower. My niches are built, waterproofed with Kerdi membrane and ready to tile. I had originally planned to use bullnose tile on wall around niche edges, overlapping the tiled sides of the niche sidewalls with the bullnose. This fit my planned tile layout . Then I decided that I would like to use Rondec instead, but just realized that this will set the tile surrounding the niche back 1/4 inch, making the niche 1/2 inch too wilde for the surrounding tiling plan. Is there a way I can shim the niche side tiles in 1/4 inch each? Sides are each one cut-to-fit tile. Or should I cancel or return the order of Rondec and stick with the bullnose?
Thank You so much.



Hi Roger,

I’m getting ready to tile a tub surround. My plan was to use regular drywall thoroughly coated in Redgard. But…I read the article you wrote on installing Redgard on shower walls. You are recommending a cement based backerboard. Why does this matter assuming the Regard makes the whole thing waterproof?

Thanks again for all of your help!



any breach in your systemand the drywall and it turns to mush, then hello all new tile job…. condesendation from behind, leaks from above, plumbing elbow let’s go, shower valve kicks an o ring… drywall becomes mush.



Hi Roger,

I purchased your topical waterproofing manual, and plan to thoroughly read it several times this weekend with some tasty beverages. I am going with the Kerdi-Line Drain (linear). I have a question that I did not see the answer to skimming your manual. Of the two available grate heights, 3/4″ and 1-1/8″, which should I order? I’m thinking 3/4″ because of the slope, but only want to order this one time.

38″x72″ shower, using 12×24 tiles most likely, unless wifey finds something else she wants.

Thanks for your time,




Hi Roger – Doing a new bath and ran out of SLC on a small part of the room. Did the run to the store, Mixed quick by eye (not a good eye) and dumped probably more than a needed.

Now that’s dry that corner is higher than everywhere else. It may be somewhat flat (you can see/feel where the pour ended) but that area is where I am putting the kerdi shower tray (32X 53)

Should I try to fix it with more SLC (just where the tray will go)? or do it with extra thinset when laying the tray down or something else? from tip to tip it’s probably a 1/2 drop.




Hi Chris,

You can level the kerdi tray with thinset as you set it.



Will do. Do you suggest I apply the thinset directly on the low spot and then back butter the tray?



Hi Roger,

I discovered your site while doing research on putting ditra heat membrane down over plywood subfloor. I am redoing our kitchen and want to install heated floors with the ditra heat membrane. We are using 12″ x 24″ porcelain tiles. My question to you is…what thinset should I use to adhere the ditra to the subfloor and what thinset should I use for adhering the tiles to the ditra? I was also told that I should fill the ditra waffles in first then do the tiles the next day. Any advice would help on the way you would do this.

btw your site has been very helpful.



Hi Rory,

Over plywood you need modified thinset beneath the ditra, and unmodified between the ditra and tile. You can fill the waffles first, it does make it easier to work over it. It isn’t necessary, though.



I purchased your “Creating a Traditionally Waterproofed Shower” manual to help me get my project started because I’m going with a shower pan liner, but I want to use Redgard instead of plastic for the walls.. Mainly because I have a window in my shower and I want to ensure a waterproof seal around it.

I want to make sure I will be doing this correctly: After installing the durock, leave a 1/16″ to 1/8″ gap between the changes in plane and caulk with silicone between them. After applything thinset only between the gaps on the flat seams in the same wall, not the corners, I can then apply regard to all corners and surfaces of durock to create my moisture barrier? My concern is if this will allow the walls to move still and not crack the tile or split the regard?

Awesome instruction manual, I greatly apprecite it! Thanks!




Hi JW,

After you get the corner gaps filled with silicone you need to tape and mud all your seams. The flat seams get filled with thinset, then taped over and smoothed, the corners also get taped and smoothed with alkali-resistant tape and thinset – over the silicone. The silicone allows for ‘swelling’ expansion in the corners, the tape and mud tie all the walls together so they can not move in different directions. Once all that is cured you redgard everything. The alkali-resistant mesh tape you use when taping and mudding holds it all together so it will not move and split the redgard.



Hello Roger,

I recently asked you about the Plasma grout, and that point I don’t think you had used it yet. Have you since used it, and if so, what are your thoughts on using Plasma for:

1. 12×24 travertine tile on a concrete floor (1/16 inch or 1/8 inch grout line?)
2. 3×6 glass tile (subway) and 6×6 glass (arabesque) on a concrete wall (1/16 inch grout line) — glossy finish glass tile (concerned about scratching)
3. 4×8 glazed ceramic tile on a concrete wall (1/16 inch or 1/8 inch)
4. 2×8 ceramic subway tile on concrete wall (1/16 inch)
4. 12×12 inch Carrara marble herringbone mosaic sheets on a shower floor (1/16 inch grout line) – (concerned about staining of tile by grout)
5. Ceramic pennyround sheets on shower floor (what size grout line advisable?)

Is a hybrid urethane grout like Plasma prone to yellowing in sunlight?
If the Plasma may be troublesome for some of these installations, am I safer just sticking to Laticrete cementitious (sanded and unsanded for glass) grouts?

Thank you very much.



Hi LS,

Yes, I have used it. It will work for all your listed tile installations. It will not scratch the glass. If the grout is darker than your marble then seal the marble before grouting. Same goes for regular cementitious grout.

It will not yellow in sunlight, it is uv stable.



Hello Roger,

Thank you very much for your help, and for taking the time to answer so many questions. Much appreciated.

Best Regards,


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