# Mastic over drywall for kitchen tile backsplash??



## angus242

jarvis design said:


> And, I do not let anyone tell me what to use...but maybe thats just me!


:thumbup:


----------



## moorewarner

Here is the post game wrap-up.

Did bring in that tile guy and had him try the white modified thinset. It was Mapei glass tile thinset, and it didn't work well. It was drying fast and powdering up and not giving good adhesion to the Hardibacker.

So we both set about gathering more info. I called the place that sold it and got that either modified thinset or "wall glue" or mastic could be used. He talked with an older tiler that he initially started with who said he was familiar with the process we were using and said the Hardibacker was absorbing the moisture causing the thinset to dry to fast and powder. He said he had a job upcoming to install an identical tile and he would be using mastic. He said the hardibacker absorbing moisture would prevent the mastic from staying wet and developing mold.

So what was used was mastic. I will post pics soon of most of this job including the tile.

So any thoughts on the use of mastic or the reasons for the thinset failure or the other tilers words?

if so I would be glad to hear them. Either way this fish is in the can now and nothing left to do but learn from it.


----------



## angus242

I wouldn't really say thinset failure. I would say bad prep. Maybe the thinset wasn't properly mixed. Mapei has picture instructions on the back of each bag. Easy to follow, maybe that didn't happen. Whenever setting thinset over a CBU, I always spray a little bit of water to get moisture into the substrate so the thinset isn't prematurely evaporating.

Hardi is used for flooring applications all the time with thinset over it without issue. I don't think it was a material failure. :no:


----------



## iHandy

angus242 said:


> I wouldn't really say thinset failure. I would say bad prep. Maybe the thinset wasn't properly mixed. Mapei has picture instructions on the back of each bag. Easy to follow, maybe that didn't happen. Whenever setting thinset over a CBU, I always spray a little bit of water to get moisture into the substrate so the thinset isn't prematurely evaporating.
> 
> Hardi is used for flooring applications all the time with thinset over it without issue. I don't think it was a material failure. :no:


Again to underline what Angus says:

The thinset needs water for its chemical reaction to set. Too much water and the bond is weak, too little water and the bond is weak. Mixing the correct amount of water is important. Then ensure that any porous substrate is saturated with water so that it doesn't suck the water out of the thinset, causing a weak bond.

Cheers,


----------



## moorewarner

angus242 said:


> I wouldn't really say thinset failure. I would say bad prep. Maybe the thinset wasn't properly mixed. Mapei has picture instructions on the back of each bag. Easy to follow, maybe that didn't happen. Whenever setting thinset over a CBU, I always spray a little bit of water to get moisture into the substrate so the thinset isn't prematurely evaporating.
> 
> Hardi is used for flooring applications all the time with thinset over it without issue. I don't think it was a material failure. :no:


Yeah, I asked and he said he followed the instructions exactly.:whistling

The pre-wetting of the Hardi is a good idea and one he didn't do. Honestly he was predisposed toward the Mastic so I don't think he was inclined to problem solve or think through a solution other than that. Maybe the phone call to the older tiler was bs as well, who knows.


----------



## moorewarner

*Update with pics*

This is why I tend to shy away from subs. So I think this guy did a fair job, not to many errors, he didn't totally hose me but he actually said to me that his work was "perfect", his word.

sigh...

I told him if he thought it was perfect he wasn't looking hard enough, that applies to everyone and every job.

So my major issue is the electrical boxes sticking out about in 1/8 of an inch from the wall, gotta get dealt with, by me, of course.

My gripe is those boxes were set to his requested depth, then as he is doing the tile work after the first one rather than stopping and coming to get me and saying "oops, I should have told you shallower, what do you want to do?", he just keeps on going.

So now I have to grind these boxes down with the glass tile right there instead of resolving it and then him tiling.

I am just usually so disappointed in how others work that I just avoid it and say fook it I'll do it myself.

Whatev, here are some pics.


----------



## angus242

Perfect is in the eye of the beholder??????

I just read on this forum somewhere yesterday that tiling was easy. If it's _so _easy, how come I rarely, if ever, see a job done correctly or at least aesthetically pleasing????? 

As you already know, that job is less than perfect. How hard is it to keep everything horizontally level? :blink:

As for the outlets, _never _let the tile guy tell you what they should be. Unless it's some ridiculously thick material, just have the drywall rings flush with the substrate (1/2"). You can just use longer screws. I carry 2" #6-32 in my tiling box for that very reason. If your tile guy is not thinking beyond just his work, he is making it much harder for anyone else that comes in after him to finish things off properly. 

When I tile around outlets, I go to the detail of making sure the cover plate screws have access. Nothing worse than seeing a new backsplash and the plastic cover plates are bulging because the screw has no where to go


----------



## Tinstaafl

angus242 said:


> Unless it's some ridiculously thick material, just have the drywall rings flush with the substrate (1/2"). You can just use longer screws.


This is one place I constantly see tile and slab guys violating the NEC.



> *314.20 In Wall or Ceiling.* In walls or ceilings with a surface of concrete, tile, gypsum, plaster, or other noncombustible material, boxes employing a flush-type cover or faceplate shall be installed so that the front edge of the box, plaster ring, extension ring, or listed extender will not be set back of the finished surface more than *6 mm (1/4 in.)*.
> 
> In walls and ceilings constructed of wood or other combustible surface material, boxes, plaster rings, extension rings, or listed extenders shall be flush with the finished surface or project therefrom.


Happens most often when adding tile or a slab to an already existing "finished" wall, and it would admittedly be a serious PITA to reset those New Work boxes. But technically, it's a code violation. You should be using an extension ring.


----------



## angus242

Tinstaafl said:


> This is one place I constantly see tile and slab guys violating the NEC.
> 
> Happens most often when adding tile or a slab to an already existing "finished" wall, and it would admittedly be a serious PITA to reset those New Work boxes. But technically, it's a code violation. You should be using an extension ring.


Tin, I never use thicker than 1/4" material for a back splash. Hell, most floor tile is only 5/16".


----------



## Tinstaafl

angus242 said:


> Tin, I never use thicker than 1/4" material for a back splash. Hell, most floor tile is only 5/16".


I knew that was going to be your response. :laughing:

I also know that you're fully acquainted with what I'm talking about. :thumbsup:


----------



## angus242

Tinstaafl said:


> I knew that was going to be your response. :laughing:
> 
> I also know that you're fully acquainted with what I'm talking about. :thumbsup:



Good point on bringing up the issue, though. I suppose my version of "ridiculously thick" can be mistaken. :sad:

Tin set it straight! :thumbup:


----------

