Mastic for Ceramic Tile for Shower Walls?

sailormassAugust 4, 2012

Hi, all--Thanks for giving me such great advice over the past few days. I have another question. In my master bath, I am having a four by four tiled shower. I've chosen a three by eight tile that is a ceramic faux travertine. Looks great so far--tile installer has only just started.

Here's my question: the installer comes very highly recommended by a couple of wise, experienced, honest friends who are quite knowledgeable about tile.

The installer himself, who works with his son, has thus far seemed very expert, very sincere, very honest. I am wondering, then, why, when I returned home the other day, the son had started the job and I noticed he'd used TEC Double Plus Ceramic Tile Adhesive. It's my understanding that this is mastic and mastic is not the best choice for tiling shower walls, etc. It's my understanding that thinset is the thing to use.

Of course, I plan to ask the installer first thing Monday morning, but, in the meantime, can anyone think of a reason why an reputable and honest installer not concerned with speed but definitely concerned with craftsmanship might use this mastic instead of thinset?

I've attached a pic of the tile and the pattern being installed, in case that is relevant info.

Thanks for your help!

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Sorry--Size of tile is 3 x 6, not 3 x 8, in case that makes a difference. Thanks!

    Bookmark   August 4, 2012 at 11:04PM
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NEVER any mastic in a wet area. Mastic is an organic adhesive and WILL re-emulsify in the presence of water. You need a MORTER (sold in bags) and preferably a latex-modified morter.

    Bookmark   August 5, 2012 at 6:09PM
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Thanks, stone tech--I'm going to get this straightened out first thing in the morning.

    Bookmark   August 5, 2012 at 6:58PM
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Glad to help. Better fixed now than later....

    Bookmark   August 5, 2012 at 7:58PM
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Sophie Wheeler

Just because he's done projects for others doesn't mean he's done them correctly. And the product that needs to be used here is thinset not "mortar". Mortar is for laying brick and stone, not tile.

The biggest thing you should verify is how the shower pan and walls was constructed to be waterproof. If he's using mastic for the walls, I shudder to think what he's done for the pan and the wall waterproofing.

    Bookmark   August 5, 2012 at 8:26PM
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Thinset is a type of mortar.

    Bookmark   August 5, 2012 at 8:35PM
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Most manufacturers approve their mastics for shower walls but not for shower floors. But that's the manufacturer.

My preference, as well as the preference of most others on this forum, is that while mastic is approved by the manufacturer for use in shower wall applications, I prefer to use thinset.

Understand that mastics are organic adhesives. Mastic simply dries out and hardens. It undergoes a physical change, which can easily be reversed, versus a chemical change, which cannot. When exposed to water or a moist environment for lengthy periods of time, mastic could absorb water and re-emulsify; it will soften. The bond between tile and substrate can be lost. That's why it's approved by the manufacturer for shower walls which get intermittent wetting, versus shower floors which can have standing water.

As others have written, thinsets are inorganic, they are portland cement based products. Portland cement undergoes a chemical cure when mixed with water. It doesn't simply dry out. It undergoes hydration, a chemical reaction, and becomes something different. The water in the portland cement based mix is "chemically consumed" in the reaction. It doesn't simply "evaporate away" like the drying process that mastic undergoes. Once thinset cures, it is what it is. Wet it, dry it, soak it, dry it, it's still rock hard and the bond between tile and substrate remains intact through repeated wet/dry cycles.

Soak a ball of cured thinset in water, it'll be wet, but it'll remain rock hard. Soak a ball of dried mastic in water, it'll turn to mush.

Anything "premixed" and "ready to be applied" that is sold in a resealable plastic bucket? No matter what the label says, it's organic mastic. It is not a "thinset" even if labeled so. It can absorb water and re-emulsify.

This is not a thinset. It is not a mortar. It is an organic adhesive:

Manufacturers have obliterated the meaning of "thinset". Technically "thinset" refers to an inorganic cement-based product designed to be used in a "thin layer" to set tile.

"Thinset" comes in dry powder form.

"Mastic" comes premixed in resealable buckets.

Here's a tidbit from REC regarding their product. Note that is is not waterproof. It's waterresistant.

So what to do, what to do...

If they used the mastic on the tiled shower floor, that's a no-no.

Mastic on the shower walls of an occasional-use residential shower (versus an often-used commercial shower, like a gym)? It's considered acceptable by some and by the manufacturer...but many consider it to not be a best building practice.

Mastic anywhere in a steam shower? No way.

My personal opinions regarding its use:
-not in showers
-not in tub surrounds
-not on floors
-not on countertops
-not for porous stone due to staining/bleed through issues
-yes to decorative (no moisture) installations
-yes to decorative backsplashes

Blah. Information overload. Good luck with your project.

    Bookmark   August 6, 2012 at 11:50AM
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Wow--I owe everybody a big apology--the tile setter is in fact using thinset. He had just been storing rags, trowels, etc. in thick empty mastic pails--this is truly the case--glad I didn't come down hard on him when he got here.

I'm so sorry I asked advice when I was mistaken, but I very much appreciate everyone's help!

    Bookmark   August 6, 2012 at 12:50PM
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Hopefully you impressed him with your knowledge :)

    Bookmark   August 6, 2012 at 6:56PM
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