First time thinset user

[highschoolhank]

I am tiling a kitchen backsplash using porcelain tiles approximately 6" x 24" applied horizontally. The tiles are a bit over 1/4" thick. The substrate is sound sheetrock though the surface has some roughness due to what I think is some old, dried out contact adhesive.

I'd like some recommendation on the thinset to use and the size of notched trowel. Although a pro would presumably apply the thinset to a big area and set several tiles, since this is my first time using thinset and large porcelain, I was planning on back buttering the individual tiles and just setting a couple to start with. There will only be about 20 tiles in total. Will back buttering work?

I will have a ledger for the first course of tile. Assuming I mix the thinset to the proper consistency should I need to take other measures such as taping to hold the tile to the substrate while the thinset dries

[Carbidetooth]

Hank, clean the wall with TSP, maybe rough it up a bit with 80 grit if glossy and you're ready to go.

Custom's Versabond is available at HD and will work just fine. 1/4 x1/4 square notch trowel should work, but pull first one back off to check for coverage. I often back butter tile on backsplashes. On small areas, it's just easier than trying to comb the wall. You'll be surprised at the immediate holding power of thinset, I doubt you'll need tape.

On backsplashes I set right off the countertop...no ledger. I'm assuming c-tops are level? Typically use 1/16" spacer and build up from there. Space at countertop to backsplash caulked with color matched acrylic or silicone.

[highschoolhank]

Thanks Carbidetooth!

One more hitch I just ran into. There is a side wall 24" front to back that will also be tiled. I found that the sheetrock there has a significant front to back dip (about 1/4"). Since the tiles will run horizontally the tiles would sort of bridge it, so I'm building the wall out some with joint compound, a bit at a time. Will the thinset stick OK to unprimed drywall? How much of a gap do you think it is permissible to leave?

[cx]

Welcome, Hank.

1. I don't have any problem with setting tile directly to drywall or drywall mud on a kitchen backsplash. Some folks recommend a paint primer first. I don't think it's necessary.

2. None.

My opinion; worth price charged.

[Carbidetooth]

CX told you what you need to know.

Not a necessity, but I like primer on finishing compound, but care less about it if setting compound. I also like to paint first if possible 'cuz I'm better at finishing grout than cutting in with a paintbrush.

[cx]

Let me second the "painting first." I always want the wall primed and painted with at least the first coat of color before I tile up to it.

[highschoolhank]

I'm just using the pre-mixed all purpose joint compound. Thanks for the painting tip!

[highschoolhank]

Sorry to be a nervous Nellie here, but the closer I get to actually starting the job the more anxious I am about using thinset. From just about everything I have seen online I should not use mastic, but if drying time is not an issue (I'm in no hurry to do the grout) and given the tile size, etc. do you think mastic would work OK?

[Steve in Denver]

Originally Posted by Hank

There is a side wall 24" front to back that will also be tiled. I found that the sheetrock there has a significant front to back dip (about 1/4"). Since the tiles will run horizontally the tiles would sort of bridge it, so I'm building the wall out some with joint compound, a bit at a time. Will the thinset stick OK to unprimed drywall? How much of a gap do you think it is permissible to leave?

Originally Posted by CX

2. None.

I'm not sure I followed this - I'm thinking the question about the gap was related to the dip? and CX's answer was saying that you want to fill the dip fully so you get full contact with your adhesive between the tile and the substrate...

But to make sure there isn't any confusion about other possible gaps, you DO want a gap where the tile transitions to the counter, cabinets or in corners. I started my first row of tiles supported by 1/8" spacers resting on the counter. These gaps allow for the inevitable movement...caulk or silicone goes in the gaps to finish it off...grout tends to crack in those expansion joints.

[highschoolhank]

Steve, thanks for jumping in.

The gap and the dip are related and I understand what CX is saying. I also understand that I need to have a small gap between the countertop and the bottom of the first course, as well as those other transitions that you mention.

[cx]

Didn't realize I left room for confusion there, Steve (I understood perfectly). Thanks.

[gwrussp]

Hank, from what I've read elsewhere on this forum they (the tile gods here) have said mastic is even ok on kitchen backsplashes but what I've already read here is that mastic requires air to dry being organic and larger tiles like yours mean it's harder for it to dry in the center.

Before I fired my contractor his "tile" guy was using mastic on 4x12 subway tile in our bathroom (complete no-no despite manufacturer's claims). I found that even after a full week of drying time when the tiles were pulled off the mastic in the center was still very wet like it just came out of the bucket. I was not impressed at all with mastic based on that experience so for large tiles I'm thinking you are better off with the thinset. It's cheaper too. Just my opinion though and I'm no expert.

[Houston Remodeler]

A quailty mastic such as Omnigrip works well for smaller sized tiles as mentioned, as well as very soft bodied tiles.

Mastic shrinks as it dries so it isn't good for leveling out a lumpy surface. Thinset is the only choice in that case.

Mastic can stain natural stone. Use thinset there too.

Mastic and glass don't mix.

[highschoolhank]

Russ and Paul, you have convinced me that mastic won't do it.

I really appreciate all of the feedback!

[highschoolhank]

Another question.

I'll have very small grout lines (1/16 inch) and the grey color of the VB thinset I'm using would be perfect for the tile. Can I just fill the grout lines with the VB thinset?