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About Perry Vellenga
Expertise
Ceramic Tile/Marble. I can answer questions about floor preparation, tile selection, layout questions, performance of products, expectations of finish, compatabilities, questions about grout and epoxies, evaluating an installer, asking the right questions to check competence...more? 30 years this August 09'/ many years in commercial application from exterior finishes to Mall store fronts/ interior finishes like floor packages in stores inside Malls examples: The Limited, Lerner/NY, Lane Bryants, Bombay Co., ect...

Experience
I worked in an exclusive field of floorcovering called "Tenant Development" which is by invitational bid only, by way of a National bid list. These are large floor packages usually over 3500 sq. ft. of 18" x 18" Marble and Granite and many other types of Marble and sizes. They are specialty stores where the floor package can cost upwards of $50,000 for one store. I have also done "Structure" stores and J. Riggins stores, Express and Body Shop stores where wood flooring is used. Presently work for a National Flooring Company in the Residential new construction arena that covers most interior design elements..Granite Slab tops/wood flooring both job finished and prefinished ect..

You are here: Experts > Style > Interior Decorating > Flooring and Carpeting > What type of thinset can be used?

Flooring and Carpeting - What type of thinset can be used?

Expert: Perry Vellenga - 11/1/2009

Question
Help...once again Perry.
I just read your answer to Larry G regarding your preference for modified thinset and color choice.
I have 1/2" Ivory Cream travertine chisel edge tiles to be laid on a variety of substrates and the thinset I have is a latex modified gray Bonsal 500. Par for this course, it is not economically viable to send back and wait for white given freight costs and duty issues here in the Bahamas.
The vast majority is to be laid on a concrete sub-floor so I prefer the bonding characteristics of a modified thinset even though the drying time may be longer before grouting.
All showers, tub surrounds, back-splashes (raw browning or CBU underlayment) to use Kerdi and 2 smaller wood floor areas 1 with mortar bed and the other with CBU underlayment are to use Ditra membrane.
As you know Schluter has a definite stand on thinset. Unmodified thinset only except for wood substrates and only to bond the membrane to the wood underlayment. Apparently this is due to the fact that modified thinset needs to air dry as opposed to hydrate set and the waterproof membrane retards drying.
My tiler has never used any Schluter products before.
Assuming Schluter warranties are a non-issue here and you always recommend following manufacturer's recommendations...I want to step outside the box and use modified thinset regardless.
Given that I am using stone and not a less porous ceramic or porcelain tile, aside from slower drying times, what else could likely go wrong by using modified thinset front and back of the membranes regardless of the underlying substrate described?
Any tips for keeping the gray thinset from causing horrendous problems with the ivory tile?

Answer
Hey Michael,

Working in a Tropical climate the ambient humidity is going to be significantly elevated for a Ditra install. Schleuter, just as any "Frontline" Manufacturer would, is going to be careful to stress ANY suspected pitfall that may involve their product to be done a certain way. This is especially true with ALL adhesive Manufacturers in particular, and for the obvious reasons...that being said I have NEVER heard or seen where a guarantee has ever been followed up on or a warranty pursued in this scope of work and I've been doing this a long time. So what to do. I now work in Colorado and while the claim is to use a modified thinset layer only for plywood and a standard thinset is all that is needed for the setting layer over the Ditra I have always used the modified thinset for "both" the Ditra and the Tile layer. If I were installing in a basement then a standard thinset is just fine and a modified layer not necessary, more of a cost savings issue really for me. It would also be true for a simple cement slab on grade. The only caveat' I would maintain there would be the use of a "White" thinset over grey...(I'm getting to that)... but over a cement board or plywood underlayment I use a modified adhesive. Also the Manufacturer recommends a 3/16" "V" notch trowel but for me it is not enough to give me comfort so I always use a 1/4"x 1/4" square notch over a "keyed" substrate...follow me? When it comes to "production" installs there is seldom time to allow a curing day (or two). I would suggest that if you have the luxury then use it to dispel the jitters over using a modified adhesive for the bonding layer. This will give/lend positive time for things to evaporate out naturally prior to getting after the install process...especially when you have a couple hot days to spend fishing or skiing or working on your tan (I used to have one a number of years ago). Now I DO have a solution to the grey thinset beneath the light colored Stone problem. It came from when I had decided to use "ONLY" white thinset and I had some grey left over to use (I used to purchase thinset by the pallet to save money). I would use the grey thinset for the actual setting bed and then have a second bucket of white thinset mixed up to backbutter or skim the "back" of the tile only and then set it down into the setting bed. The white skim coat isolated the back of the tile from the darkening grey thinset and you could move on like "normal". As I have mentioned before Michael...sometimes a practical solution is better than a restrictive approved method. We do live in the real World where sometimes thinking outside the box is necessary to help a confusing scenario or a worried customer. Ok, that's it. I have enjoyed the exchange Michael and another opportunity for "Perry's Tile Solutions" Esq. ;-)
Feel free to come again anytime...

Perry

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