Joe Ferrante was the kind of subcontractor that I always try to seek out. His experience over the years has taught him a different way to set tile that is not the norm but extremely effective. I have used his technique on many jobs and it always produced excellent results. After tile board He would thinset the seams with fiberglass tape and then skim coat the entire board with modified thin set. When you thinset the seams typically there is a slight hump, so the skim coat evens the surface out and makes it flatter. This skim coat has to dry properly. He then set the tile with latex mastic. If you have any reservations about this technique, I would not use it. When you work for an Architect you will have to submit all materials for their review and they will typically submit your methods and materials to the manufacturers who make the materials. The manufacturers will have a prescribed method for using their products, and they will not guarantee any other way except their way. If you don't follow their recommendations and the job fails, then you are responsible for the fail. I have found many times that the manufacturer may know a better way but will not say so because it may take more skill than the average installer has. Liability is the key issue, don't fight it unless you are willing to take responsibility for the whole job.

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.

Wait till the counters are in then get sample tiles to make sure you like it. After you get the tile for your project, make up a sample board of the tile you choose using double stick tape. Pick one or more grout colors that you might like, then mix up a small batch and grout the sample board(s). LET IT DRY (overnight, as it will lighten up). Then see if you like the color for your kitchen. We ended up picking the 5th color we tried. Good luck!

The very first thing you do is verify deflection and how it relates to chosen tile material's rating. You must look at the whole thing from structure> Joist> underlayment> subfloor before even talking about cement board and crack isolation. You are asking such novice questions id be careful and do A LOT of homework. DIY is great and you may pull it off but get the correct process and information involved so you dont waste your time and materials. These forums are loaded with bad information more added daily.