Painting new cement requires cleaning the area thoroughly to help bonding. But don’t use an etcher before painting fresh cement. And don’t paint too soon after it is poured.
How old is the cement? Depending on the dryness of the basement and the age of the repaired cement it may be too soon to paint. The lime or moisture in new cement can weep if it is still curing. This condition may prevent your paint from bonding. Do not paint over concrete less than 30 days old.
Before painting, rinse the repaired area with plenty of clear warm water. This will dissolve the surface salts and allow the paint to more effectively bond to the cement. After rinsing, let the surface dry completely. In some damp basements this could take up to five days or more. Use a dehumidifier if you have one. If your thermostat has a fan switch, set the fan to run continuously for several days. Circulating the air will allow you to continue your project sooner.
A mild etcher improves the bonding ability of paint to old concrete. Cement etcher can be too aggressive for use on new concrete. I use it on greasy, dirty, or very smooth concrete before painting. Use an etcher only if the surface is going to make adherence difficult. Avoid getting etcher on the new concrete.
Some sealers are meant for ‘stand alone’ protection and are not to be painted over. A variety of sealers contain silicones that prevent the paint from bonding. Ensure the success of your project by reading the use restrictions carefully on both the paint and sealer products.
More than one year ago we painted the bare concrete in our new store with Plytex Porch and Deck enamel. We used no sealers or etching, and it looks great, especially considering the abuse our floors endure. Our only prep-work was to wash the floor with a solution of T.S.P. (trisodium phosphate), rinse well, let dry, and paint.
A sandy or gritty condition indicates the cement could be a little weak. If the repaired area is ‘dusting’ when you rub your hand over it, consider a prime coat of enamel floor paint thinned 10% for better penetration. Another fine product for sealing masonry before painting is Waterlox Tung Oil. Good luck and remember, don’t paint over a damp surface.