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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 > Back from the Bahamas...Different Floor Problem

Flooring and Carpeting - Back from the Bahamas...Different Floor Problem

Expert: Perry Vellenga - 10/31/2009

Question
Firstly, thanks for you "best kept secret" on my other floor...it worked like a dream! Pity anyone who needed to remove the metal lathings after we were done!
I have a second floor 3/4" T&G (pressure treated), staggered joints, 12" wooden I beams on 12" centers, spaced joints, glued and screwed 4" on edges and 6" for the rest, max span anywhere 8' on concrete filled cinder block steel re-enforced walls below, well within L720 limits. Good so far!
I needed 3/4" build-up to match a stone staircase height...a second plywood underlayment was to be laid per MIA stone tile specs
Learning (tongue in cheek) from my first problem floor...instead of a second layer of "pressure-treated" plywood, my carpenter over thought the problems with the first floor and on his own substituted 1/2" Durock, but instead of setting in thinset (because sub floor was pressure treated)...he used liquid nail and screwed it down 4" on edge, 6" spaced for the rest. I gained some but not all of the needed height and I suspect defeated the entire purpose of a thinset installed CBU. I know the best answer was your "secret" but as I say this was a decision made while I was off island WITH my tiler. BTW...still within L720 limits by far!
I am still 1/2" low, with some leveling to do. The tiler says that the CBU solved the adhesion issue for thinset on PW and since the floor didn't need additional stiffening that the best solution is to cover it in Ditra to pick up the 1/2" (1/8" thinset + 1/8th" Ditra). Can this be done? What is the consequence of having the CBU installed as mentioned?
The tiler said to first use a bonding agent and use self leveling concrete for the low spots, then thinset and lay Ditra...does this make sense? Why not use bonding agent for the rest of the CBU before the thinset?
Finally...my tiler says the CBU joints would normally be taped and thinset filled for conventional tile laying (sans Ditra) but is unsure if that should be done with the Ditra or whether the thinset for the Ditra should be worked into the joints. He asked if there was a difference in how wood joints and CBU joints should be treated in regards to filling or being left void when it comes to Ditra.
BTW, being from Jamaica, he has never seen Ditra until now and is a huge fan. He may not be up to speed with new US products but man can he lay straight and level tile. Poetry in motion, 400 sq/ft solo in a day (including mixing thinset)using string/level and square. A ray on sunshine on this cloudy day.

Answer
Hey Michael,

Most of the "unseen" consequence for flooring installations is generated from inadequate sub-floor assembly...your assembly does not suffer from this problem. So as the "freestyle" underlayment assembly you have going there is a lot happening here. That being said If you don't have the available funds then working with a 1/2" shortfall (if I were the guy) could be made up by fancy trowel work and additional setting material...no problem. Now if you "have" the Ditra then it wouldn't hurt to work it into the assembly as the benefits that it offers is never detrimental. Keep in mind though that you are only going to gain a 1/4" not a 1/2" from that portion of the assembly. Plywood as an underlayment is far more prone to expansion and contraction than cement board. Typically though the taping is the same. I have "experimented" over the years with a "personal" method of addressing this fact by keeping the recommended 1/8" joint spacing between the plywood sheets and simply "caulking" in this same joint with a quality caulking which fills the joint itself but allows for movement when temperature and humidity is creating the pressure below...follow me? Now the thinset was combed out over the Ditra afterwards just like normal and onward we go. Of course the cement board "must" be taped as you are attempting to "copy" an actual muddy floor install so the "fill and tape" process recommended should be adhered to. Now Michael, the suggestions I have just made to you are my own. The NTCA would "poo poo" some of my methods as they fall outside of accepted scope of work, but for me some jobs need a solution more than they need a formal approved/accepted method. You must have quite an operation going on there Michael, sounds like fun. I hope these off kilter suggestions help you with your project...always welcome to return.

Perry

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