Is regular flat paint OK as a primer on concrete walls?

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Old 01-12-12, 10:22 AM
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Is regular flat paint OK as a primer on concrete walls?

I have a new garage with cinder block walls and I want to paint the interior white.

I received a 5 gallon bucket of flat white paint for FREE and I was wondering if I can use that as a primer for the semi-gloss I am going to put as the final coat. Will that work OK?

I see conflicting information out on the web, most indicating I should use a primer/sealer. I do not have to worry about moisture so that is not a factor. I'm just hoping I can use the FREE paint.
 
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Old 01-12-12, 12:50 PM
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Welcome to the forums!

You could use that paint by itself but the problem is that unpainted block tends to really suck up the paint. It's quite possible you could use up all your 'free' paint and have the block look like it needs another coat of paint.

How much block do you need to paint? You might get by with 'thinning' block fill [primer for concrete/cinder blocks] with some of the 'free' paint so you won't have to buy as much block fill primer.
 
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Old 01-12-12, 02:27 PM
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I'm no expert...but primer is designed to stick to a surface, seal it (in some cases) and provide a surface for the topcoat to stick to.

That said...I used some latex flat exterior paint to semi-cover up some exposed concrete block when we tore down a dilapidated shed. No primer or anything...just rolled it over the exposed grey block. That was almost 5 years ago and it's still well adhered and doing what it was supposed to. This is out on a fence that gets direct sun in 110 degree heat in the winter, occasional heavy rain during "monsoon" season and the other side of the fence is bare block.

Personally, I'd probably use it, but a block fill type paint would help seal and fill all those little voids and holes and give you a smoother finish.
 
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Old 01-12-12, 03:20 PM
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I answered this earlier - wonder where it went

oh well, let me try again

The problem with not priming the block is the raw block will suck up the majority of the paint. It's possible that you can use up all your paint and have the walls looking like they need another coat

I'd suggest buying some blockfill to prime with. You could get away with 'thinning' your blockfill with some of your 'free' paint but I'd want the prime coat to be at least half blockfill. Paint applied over raw block will hold up fine but it needs the blockfill to fill the pores and make the block look painted. The coarser the block, the more it needs the blockfill. On the exterior, blockfill also provides some measure of waterproofing.
 
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Old 01-12-12, 06:33 PM
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I'm less concerned about cover and more about adherence. I expected to go at least two coats anyway, so if the flat paint will work acceptably (not peel off in 3 years or anything) and act as a decent base coat then I'm good.

So; no fears of using the flat paint as a "primer" (of sorts)?
 
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Old 01-13-12, 02:06 AM
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Oh...the garage is 43x22x12 so I approximated 1134sq ft (accounting for no windows and the garage doors on one face)
 
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Old 01-13-12, 04:13 AM
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Most paint will adhere fine to raw cinder block so I don't think adherence will be an issue. Paint usually covers about 400 sq ft per gallon on slick surfaces but raw cinder block might only get 200 sq ft per gallon - so it might take all your paint for 1 coat.
 
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Old 01-13-12, 04:32 AM
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That meets my expectations for coverage anyway. I put some up on one wall and much of it got absorbed right in. Even so it really brightened the wall, and therefore the room, up quite a bit.

Thanks for your help!!
 
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