Advice on painting cement walls

[keyuhui]

Hi,
I was wondering if anyone out their has any experience painting concrete walls that could help me out. I live in China and have been trying to paint the walls of the apt I'm renting. The walls are concrete, coated by some kind of semi-glossy substance (not sure what is is...it's not quite like typical drywall mud.) Anyway, about 1-2 hours after apllying the first coat, patches of paint started peeling off. I scraped them down and continued painting other areas. Later I noticed the peeling had continued. What did I do wrong? I'd appreciate any in-sight anyone might have. Thanks.

[Patricia]

If the concrete has been "treated" you probably cannot paint it. We have concrete floors which were treated just after being poured. In order to paint the floor, we had to hire someone to bring in a machine that would cut through the shelack to raw concrete so that the paint would stick. Before this, the paint would just peel off within hours of painting them. I doubt you want to do this in an apartment and I am not sure you could it on walls anyway. Sorry.

[HayZee518]

Painting over concrete

Not sure about the composition of your concrete but if the mix has more sand in it than portland cement it will, it will continually flake off over time. The adherent bond of aggragate, cement and sand hasn't been monitored for strength. Scrap off as much of it as you can, then use tri-sodium-phosphate to wash the walls. Use a scrub brush, rinse and let dry. Then apply a concrete sealer. Thoro-seal is a portland cement based product that will coat the wall. Then when this is dry you can use an oil based paint to finish the wall.