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Discussion Starter · #1 ·
My bathroom walls are cinderblock and they need to be patched with concrete (aka scratchcoat) to make them plumb (see pic in message from 10 min ago). However, my understanding is that raw cinderblock can suck the moisture out of the concrete before it has a chance to set properly. So you're supposed to coat it with something.

So I asked the paint guy at Dome Hepot and he recommended this:

http://i.imgur.com/puJ6ZdT.jpg

Behr
Premium Plus
Multi-Surface Primer & Sealer

It claims to be ideal for masonry. But it's not entirely clear if it is ok to actually do masonry on *top* of it. A contractor did another wall in something that looked clear. This is pure white so I'm worried that it's not really the same thing. Will concrete adhere to this Behr Multi-Surface Primer Sealer?

If no, what is the correct primer for cinderblock so that it can be covered with concrete?
 

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Do you think there might be a way to moisturize the block before you apply a leveling layer?
 

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Concrete & Masonry
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The guy at HD doesn't know his a$$ from fat meat, don't listen to him. That can't be top coated with mortar. All you really need, do to how rough the walls are, is water to get the surface damp. If you really want to use something, a bonding agent (HD carries Sika brand here in the concrete aisle) is good.
 

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Discussion Starter · #5 ·
If you really want to use something, a bonding agent (HD carries Sika brand here in the concrete aisle) is good.
Can you be more specific? I see Sika additives but my understanding was that there was something that was like a sealant that is applied with a roller or brush? This is supposed to help new concrete adhere to the old surface.

I am going to be adding some strips of wood as guides and for support when applying the top coat. It's a fairly large surface that will be thick in some spots. So to make sure everything is plumb and square and to help carry the weight I'm going to use construction adhesive to add some wood strips that can be knocked out afterward. So a bonding agent / sealant might help the construction adhesive (heavy duty liquid nails).
 

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Concrete & Masonry
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Can you be more specific? I see Sika additives but my understanding was that there was something that was like a sealant that is applied with a roller or brush? This is supposed to help new concrete adhere to the old surface.

I am going to be adding some strips of wood as guides and for support when applying the top coat. It's a fairly large surface that will be thick in some spots. So to make sure everything is plumb and square and to help carry the weight I'm going to use construction adhesive to add some wood strips that can be knocked out afterward. So a bonding agent / sealant might help the construction adhesive (heavy duty liquid nails).
http://www.homedepot.com/p/SikaLate...C-_-NavPLPHorizontal1_rr-_-NA-_-202521398-_-N

Adding a sealer before another coat of similar material will never aid in adhesion, quite the opposite actually...........
 

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Discussion Starter · #7 ·
http://www.homedepot.com/p/SikaLate...C-_-NavPLPHorizontal1_rr-_-NA-_-202521398-_-N

Adding a sealer before another coat of similar material will never aid in adhesion, quite the opposite actually...........
Great. The last contractor painted something onto one of the walls. It dried clear and has a dull sheen. So now mortar won't stick to this as well?

I'm not sure I understand this product. The documentation describes using it as an additive and the graphic on the front of the bottle shows it being poured into mix. But the documentation also says it can be used as a primer:

"Primer (for acrylic coatings only): Apply undiluted SikaLatex® R to prepared concrete
substrate using brushes, rollers, soft brooms, or spray. SikaLatex® R must be tack-free
(film formation) prior to coating. Estimated coverage on a CSP-3 prepared surface is 300
sq. ft./gal. SikaLatex® R primer may be applied up to 24 hours ahead providing the area
is kept dry and clean."

So this means it can be used "for acrylic coatings only" as in latex paint? Rats.

Part of that wall is going to need screen to cover voids next to pipes so perhaps I should screen the entire wall now?
 
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