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Flooring and Carpeting/Concrete Floor Prepping


QUESTION: I recently made a newbie mistake of using Killz to address mildew and molds issue on the bathroom floor after ripping the vinyl off from the concrete slab.

Home Depot guys told me I need to strip off the "paint" but does Killz qualify as paint? It feels more like a primer than paint. Anyway, can I use the Mapei thinset designed for painted concrete surface?

What would you suggest that I do?

ANSWER: Thank you for your question John,

     I understand your concern with this but the truth is Kilz is a primer and really doesn't have the ability to hold fast to a substrate that is intended to have tile installed over. Paint by itself has bonding ingredients in it that help it to "stick" to the surface it is bonded to. So I would just get a floor scraper (the kind that uses a 4" razor blade) and remove the Kilz, it shouldn't come up very hard as you will see. This will also help you to understand and be happy that you didn't install your tile over this material. If there were a legit painted surface you would still need to "prep" the surface of the paint before you could proceed with an install so either way you are going to have an additional layer of labor to get to where you need to be prior to installing tile...ok? Thats it John I hope this helps you with your project, feel free to return anytime...

Perry V.

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

QUESTION: Thank you, Perry! I am so glad I waited for you to reply. And you are right, it is a primer and not paint...and easy to come off since I scraped a test area with the exact kind of scraper you mentioned.

How about the latex additive to mix with the mortar instead of using water? That's more for a painted surface (as suggested) but would it hurt if I use after scraping off the primer?

Kindly advise at your soonest convenience.

Welcome back John,

    I'm glad I could help with your project. Back in the day before the latex blending was already done for us we purchased the "liquid glue" in 5 gallon pails. We were treading in unknown territory with this concoction and even though there were defined parameters for the mix rate there was the temptation to add "just a little more" because if a little was good we bet that more would be better. Back then it was pretty expensive for the cocktail but we didn't care. I even got used to using a "green thinset" for my installs because that is what the color of the thinset became after we added the latex. We learned that we were simply wasting a lot of product and money with our outlandish mixing rates. When the modified thinset first came out we were really concerned that this new product didn't turn green when we mixed it up thinking that now we may be placing ourselves at warranty didn't happen. The now modern modified setting materials is blended at ideal mix rates and confidence in the product has never been stronger. If you are looking to help with the bonding process then let me suggest that after you remove all of the suspect Kilz that you simply do an acid etch of the surface as this will clear out some of the cement pours allowing for a more positive bond with the tile. Save your money John and just use the latex modified pre-mixed thinset for your install, it will be enough. Thanks for the nice rating as well, as that is our "payment" for lending our service that we love to do. Come again any time...


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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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