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I'm turning a one car garage into an office and want to paint the floor. I bought some Behr concrete paint, and the guy at Home Depot insisted that I have to put down a layer of primer first.

Do I really? This garage may have held a car a long time ago, but the floor doesn't look greasy at all. I'm not going to be parking a car in here, it's going to be an office with pretty light wear and tear. Also, I'm lazy, so I'm willing to gamble on this unless it's really stupid.

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Just asking ... why are you not putting a boarded and insulated floor in? I'm assuming because the garage floor is at the same level as the house floor, I'm also assuming you have an internal door to the garage. – Antony Scott Sep 25 '11 at 0:08
I'm in southern California so no real reason to insulate. I've got an internal door to the room. Also, I like the look of painted concrete - going for an industrial loft feel. – Jon Galloway Sep 25 '11 at 0:10
I painted some concrete steps using a 1-part epoxy floor paint, probably the same as what you're using. I didn't prime. Looked good at first but 3-4 months later, the paint is flaking and peeling pretty badly. I'll be redoing with a primer when the weather warms up. It might take a lot of work to get enough of the paint up that I'd be able to prime. So in short -- prime. Don't repeat my mistake! – Shimon Rura Jan 24 '12 at 4:22
up vote 13 down vote accepted

Probably yes. And probably an oil based primer unless the can says otherwise. On top of that a concrete primer if they exist. If you don't prime then you run the risk of the paint peeling, especially since garage floors are so smooth. Plus you might run through way more paint than you think and need to get more since concrete is so porous, it will soak it up like a sponge. You don't have to of course, but how much is the paint vs primer? If paint is more get the primer as well. And get an extension pole for the roller and everything will go fast.

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+1 for "porous" – Antony Scott Sep 25 '11 at 12:09
Always use primer if the paint specifically demands it be used. Proper primer for the substrate is created to bond to the substrate, seal and protect it. Paint is created to bond to primer. Skip those steps for failed DIY paint jobs and amateurish results. – Fiasco Labs Aug 31 '14 at 17:34

I would say you definitely need to prime, as it's really sealing the concrete so that any paint you do apply doesn't soak in too far. I painted my garage floor 8 years ago (or thereabouts) and it was in great condition (as good as when I first applied it, apart from the exposed edge at the front) right up until earlier this year (when we converted it into a proper room with a boarded and insulated floor, hence my earlier comment). I didn't experience any peeling and only needed one coat of paint. I can't remember what I used, but it was paint specifically for painting concrete floors, light grey in colour. I do remember that the primer was clear, and was meant to soak into the floor and "seal" it ready for the paint.

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You really should prime anything you are going to paint. It's the 'glue' that holds the paint to the surface.

For concrete, and for "going for an industrial loft feel" I'd suggest that you also consider an acid stain instead. It's a lot more forgiving in its application and, IMHO, is the key factor in an industrial loft.

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I painted a concrete floor several years ago and I used a coat of primer and a coat of paint. I choose to do it so that the paint wouldn't peel/chip as easily. It has lasted very well. It's a workout area and gets a lot of use.

I know Behr has the Premium Plus line that contains the paint and primer in one. Not sure if they have it for concrete paint though.

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Yes, you need to prime. Not just with any primer, actually -- there are specific primers for priming porous masonry surfaces, and you need to use one of those. On top of that, you need to follow the directions, which typically will include cleaning thoroughly with a chemical like trisodium phosphate. If you just try to apply a latex/acrylic house paint straight to the concrete, it will fail in snort order and taking it back up will be a pain in the butt.

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Look at the instructions on your concrete paint and do whatever they say. If Behr doesn't recommend primer but you do it anyway, you'll be asking this paint that's specially designed to bond to concrete to bond to primer instead, which it might not do as well.

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I found I could get away with outdoor latex primer when resurfacing concrete with a thin layer of sand mix. I have also grown the technique using masonry screw drilled and placed into broken concrete which was then primed when Iwas faced with broken corners and edges of significant size. None have failed and it has been years. This was done at a multi apartment building I bought and remodeled.

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