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CallMeVilla 08-23-2011 01:16 AM

Wall Tile Over Painted Wallboard?
Here is an odd one: Been asked to tile (6x6) over cement board on an exterior wall. No problem until they said they had painted the wallboard!

How should I prepare the board? Angle grinder with a sanding disk or wire disk? I plan on using unmodified thinset . . . is that the strongest?

oh'mike 08-23-2011 07:10 AM

Not so good----Grinder with a wire wheel to scuff well----unmodified with liquid additive is the strongest-Kerabond and Keralastic by Mepei is a good example.

A high quality modified thinset should do it.

Bud Cline 08-23-2011 12:20 PM

What brand is the cement board?:)

BlueStoneFloors 08-24-2011 09:59 AM

Yeah just scuff or sand any sheen off of it. Not a big deal painters are routinely ahead of us on jobsites and they always overspray. Don't use unmodified mortar, your situation needs latex modified mortar. All tile-concrete board installations use modified.

JazMan 08-24-2011 10:07 AM

I want to see the answer to Bud's question.


Bud Cline 08-24-2011 03:46 PM


I want to see the answer to Bud's question.
So does Bud.

What brand is the cement board?:)

adam_withrow 08-29-2011 06:24 PM

either keralastic or granirapid are WAAAAAY stronger than unmodified thinset

other than that, you can use a drywall sander if you really want to. just knock the sheen off. make sure you get any loose dust away in the process. as long as the paint is well-bonded, the mortar will be too.

i used to do a lot of tile on military bases, and in the name of things looking right for the people with the funny hats, a lot of mistakes like that were deliberately made all of the time.

Bud Cline 08-29-2011 06:32 PM

Keralastic is a brand of thinset? Why am I so confused?:)

adam_withrow 08-29-2011 06:46 PM

Keralastic is a polymer reinforced thinset offered by mapei. They also sell the liquid latex that you add instead of water.

IT IS STRONG! if you have some spooge left over after setting a lot and you don't get it within 24 hours, it is almost impossible to break off with a 5 in 1

Bud Cline 08-29-2011 06:55 PM


Keralastic is a polymer reinforced thinset offered by mapei.
Yow I know that, :yes: I was trying to be gentle with you.:)
It wouldn't hurt for you to mention that Keralastic would be mixed with unmodified thinset to complete the thinset concoction.

adam_withrow 08-30-2011 11:35 AM

man, i did that once on fort carson, and my boss freaked out! i tried to say, "don't worry about it, man" and he wouldn't have it.

i'm glad to hear someone else say it. i wish he was on this forum.

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