Before you get in the car to purchase that waterproofing compound, you will want to assess the basement wall and the source of the seepage. Almost all of water problems in a basement are due to cracks or holes in the basement wall or floor, so it is imperative that you first fix these aberrations.
Hairline cracks can be filled with the waterproofing mixture you will apply to the whole leaking area. If the crack is larger than an eighth of an inch, clean it out and then patch it before applying the waterproofer. Take the patch material (consisting of one part cement, two parts sand and enough water to stiffen the mix) and force it into the cracks with a trowel or putty knife.
There are two choices when it comes to coatings for your basement. Premixed liquids, either water or oil based, are like a heavy paint. You just brush them on. Users say that there is little difference between the two in efficacy but the water based compound is an easier cleanup and does not produce noxious fumes that can come from the oil based product. In fact, some users have had to vacate their homes due to the intense smell.
The other option is powder that is mixed with water or some kind of bonding agent to the consistency of pancake batter. These containers of powder can run over 50 pounds and have a tendency to leak the powder into the air when trying to get the cover back on. And you better work fast, as the mixture can set up rather quickly and defy spreading on your wall.
Under tests, the powders were found to be poor relatives to the already mixed liquid compounds. In fact, reviewers say the premixed UGL Drylok Waterproofer, either oil or water based, is the premiere application, withstanding four times the hydrostatic pressure than other brands with a very convenient application. Sears Acrylic Wall Paint and Quikrete Masonry Coating did not waterproof as well.
Once you have your cracks sealed, and your waterproofer purchased, make sure you read the application directions carefully. Some products require the surface be unpainted, so a sanding and stripping job may have to precede application. The wall should be dry and free of mildew (get out the bleach and add to water in a one to four proportion and scrub it on the moldy wall). In fact if your walls have a tendency to mildew, you might want to add to the wall a final coat of paint with a mildew resistant additive.
Apply the mixture starting at the bottom of the wall (where there is greater hydrostatic pressure) with a stiff brush and force the compound into the wall, filling every pore that water could seep through. And once you have one coat on, do some "safe side" labor and add another coat...two or three may be more expensive but they will save in the long run by keeping the moisture at bay.