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Discussion Starter #1
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?
 

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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.
 

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Tile with Style
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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.
 

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

Jaz
 

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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.
 

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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
 

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Tileguy
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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.
 

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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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