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Flooring and Carpeting/Offgassing from mastic used for a backsplash


QUESTION: My husband installed a glazed subway tile backsplash a month ago and used Tec Double Duty mastic as the adhesive and Tec Powergrout. The mastic has been offgassing ever since and making me ill. My husband doesnt want to tear it out and so we have been using Afm Safecoat mexeseal on the grout to try and stop the offgassing. So far I haven't noticed a change in the offgassing, can the mastic offgass right through the glazed tile, is there something else we can do to stop it? He didn't put the mastic on very thick and waited a week before he grouted it, is there something else we can do for this? Thanks for any help you can give us.

ANSWER: Forgive my tardiness Debbie, life a little crazy lately...

   Ok so this issue of outgassing seems to have a life of it's own and while the possibility of a short term odor is not unusual a long term one (your case) would be considered a rarity. Typically mastic will chemically kick in just a few hours after the material has been covered, and certainly within the 24-36 hours after install would be free of any noticeable odor being present. You mentioned that your husband didn't "apply it too thick" so what size trowel did he use? If a standard 3-6" subway tile was employed a 1/8" V-notch trowel would have been fine for installation. In years past I have used as large as a 1/4" square notch trowel to apply the adhesive if the subway tile had a more primitive design that required more adhesive to securely hold it to the sub-strate. Also if a week was past prior to grouting there should be zero smell left to detect. Mastic by itself needs only about 15-20 minutes to "skin over" once combed out for install to be dry to the touch so to have the tile installed and grouted in place would force me to look elsewhere for the source of odor. At this point Debbie I would consider pulling off a few pieces of the installed tile to check on the cured adhesive that lay behind it. Mastic can indeed take a few days to "cure" out and become an inert solid securing the installed material. Sealing is unlikely to help much in my opinion other than do what its intended to do which is to protect the grout from staining. It is within the realm of possibility that the mastic perhaps was a bad batch manufactured without either the proper amount of chemicals to produce a satisfactory adhesive or missing a certain portion of the ingredients to cause it to not cure/set as expected but you won't know until you pull off some pieces of tile to inspect whats going on behind it. With things being a month old the mastic adhesive should be properly cured and dry giving off zero odor. Try this and see what you find out and come back and let me know what you discover. Again Debbie sorry for my tardy response, feel free to return anytime...

Perry V.

---------- FOLLOW-UP ----------

QUESTION: Thank you for your response, I don't know if I can get my husband to check a few tiles or not he said it will be terrible trying to get them off the wall without tearing up the drywall. Anyway our tiles are 6 x 8 so s little bigger than a regular tile, he just figures it's taking longer than usual to cure but I'm to the point of just taking it all out and be done with it. I did look at the spec sheet for this Tec Double duty mastic and it has a lot of Vocs in it and petroleum chemicals in it so I'm thinking this is our problem. Are you familiar with this product at all and do you know if others have had problems as well. Thanks for you help.

Welcome back Debbie....

   I didn't see what size notch trowel your husband employed for the install which might help a little if I knew. The larger the notch the more adhesive that is going to need to because the subway tile is a larger format (6 x 8") more adhesive was likely required to ensure an adequate bond to hold the tile. For this kind of install I will typically flat skim the wall I am covering and simply comb the back of each tile that way I can control the amount of adhesive needed to put it together. If the mastic is "still outgassing" then that would also mean that the cure hasn't happened yet and the tile is likely to be fairly easy to pull from the wall. Just cut out the grout from the joints of a sq ft. of material from the end of the install and pull them from the wall. If the mastic is still curing they will come off straight away. This will make it clear if there is an issue with the odor you are objecting to. I have never used Tec Double Duty Mastic but nearly all standard mastic is oil based (petroleum)and voc's will be present, it's not like paint where it is now a growing standard to reduce them. Ok Debbie I hope this helps, feel free to return anytime...


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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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