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Flooring and Carpeting/osb subfloor and Ditra


Hello Perry. I am about to tile and was going to use ditra for and underlayment. I have two concerns. With your experience is Ditra okay to use over OSB? I have heard it both ways. And my other concern is deflection. The subfloor is 3/4" OSB and the joist are 16" on center, 12" tall, with a span of 10 feet. So I think i'm okay.  The joist are engineered and didnt know if that made any difference. Once again, THANK YOU for your help.

Thank you for your question Eric,

    There is often a contrast in what is claimed (for protective purposes) and what is done in the practical World. Initially there was a concern with Ditra being installed over an OSB substrate mainly because if you think about it OSB is a "particle board" of sorts only very large "particles" if you will...follow me? Particle board (sawdust and glue basically) had dreadful consequence when tile was installed over it back in the early days and it didn't take very long to discover this huge problem. Because Builders (certainly all Production Builders) have taken to OSB in lieu of plywood for the obvious reasons. Custom Builders still, more often than not, employ traditional plywood for their substrates knowing that it is superior by far to OSB. That being said time has proven that Ditra works well over OSB and is done daily as a natural course of installations given todays construction practice. So...additionally Eric, your sub-structure is good and adequate for your task ahead. Many Builders have increased the span to 19.2" so that they can save a few dollars by having to purchase a couple extra floor joists. I wish they didn't do that but the market has changed and price point is key to todays market. Some Builders have even spread out the joists to 24" O/C which can only be covered by carpet and vinyl and even that not without incurring the "deflection" that was concerning you. To be honest here our Industry Standard for sub-floor structure really calls for a "two layer" assembly of 5/8" plywood with the second layer lay crossway to the layer below over the joist assembly that you currently have. This would make for the kind of support that "NO ONE" does any longer but if they did it would make for the kind of "feel" that is totally unknown to modern day buyers. Under the circumstances, and your current conditions Eric you are good to go with your install, and Ditra will help to control any deflection that may occur. That's it I hope this helps you with your project, feel free to return anytime....

Perry V.

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Perry Vellenga


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? 33 years this August 2012/ 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., Now involved in Residential new construction covering all types of interior finishes and designs.


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, Lane Bryant,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..

My response's are published all across the Internet and picked up by multiple Interior Design sites and Industry related web sites where people have questions...

too many most of which don't count...

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