To answer some of your questions, our crawlspace is enclosed with concrete backer board, not poured concrete or masonry blocks. Why? We couldn't afford any other option. Mr. Clow, our concrete guy, suggested using backer board since it is basically bug proof and weather proof. We spent roughly $1,000 for enclosing our crawlspace including labor. The other options we considered ran between $8,000 to over $20,000. We consider the concrete board our semi-permanent temporary solution to sealing our crawlspace. Except for the bottom couple of inches, all of the concrete board will be above grade.
Our interest in painting the board it two fold. One, it will look better painted. Two, paint hopefully will keep the board from wicking-up moisture when it rains. Periodic exposure to water tends to stain the board and it is not an attractive look. No one wants to look at an old woman who has pissed herself, right?
I'm thinking about using Drylock, a latex "waterproofer" for masonry, which is produced by a company called UGI and sold at Lowe's. From what I've read, I need to sand-off or otherwise remove any paint, dirt, etc, and then paint on two coats of the stuff. I'm thinking about spraying a bead of Good-Stuff foam along the bottom of the board where it meets the concrete perimeter foundation. I'm hoping this will keep water from getting under the bottom edge and seeping up the concrete board.
I'm hoping this will seal the backer board. What I'm trying to figure out is whether I can paint over the Drylock with exterior, waterbased paint. Or, should I prime the Drylock and then paint? Or, is just a waste of time?
As long as the Drylock keeps moisture from seeping up and under the exterior paint, I figure it ought to work. If it doesn't keep the moisture out, it's just a matter of time before the exterior paint will start to blister and peel.
Any thoughts about how well this will work? Or, do I just need to buy a gallon of the stuff and play mad-scientist?