Do it Yourself Basement Waterproofing
Basements often have damp problems, because they are, at least partly, below ground level. For a basement with concrete floors and walls, it is quite possible to deal with this problem yourself. (A brick-lined basement is not covered here.)
Rising damp in the floor can be treated by sealing the floor with polyurethane. You apply this at a rate of 1 litre for every 4sq metres and you need to apply three coats. (Manufacturers say 1 litre for every 5, but in practice, you need more than that, at least for the first coat!) First you must make sure that the floor is swept clean. (The sealant will not work with an oily surface so if your basement is actually your garage, you have a problem!) You will need: stone chisel and lump hammer, a bricklayer's trowel, a soft long handled broom to spread the sealant, not a stiff bristly nylon one.
If the basement is really wet, try to get it as dry as you can before starting. Put in a de-humidifier or a heater for a couple of days first.
Deal first with minor holes, that is, ones through which there is NO active water entry.
Minor Cracks and Holes
Mix 5 parts sharp sand to 1 part urethane and just enough water to make it hold together â€“ too much water will give you a weak mix. Clean out any loose material and prime the holes with urethane; give it a few minutes to become sticky and then fill the holes, smoothing the surface with your trowel. Leave them overnight to dry.
Water Entry Cracks
Check for any cracks in the surface through which the water is actually entering . Get on the safety gear â€“ goggles, ear-protectors, gloves. Enlarge the cracks with a stone chisel (you need to whack the chisel with a lump hammer â€“ wear goggles and ear protectors) and then clean out all the loose material. Mix some quick-drying hydraulic cement with water into a putty like consistency â€“ only do enough for one crack at a time. Make sure you are wearing rubber gloves and warm the cement between your hands between your hands. Press it down into the crack. Hydraulic cement dries within a few minutes and expands as it dries, so press down on it with a trowel until it is dry.
Join Between Floor and Wall
In the same way as you did for the water entry cracks, you need to use hydraulic cement between the floor and the wall. With the stone chisel, cut a small trench, about 2cm deep and wide, the whole way along the join and fill this with hydraulic cement, following the instructions given above. The filling should be angled so that it forms a join between wall and floor.
When you are satisfied that you have done all the preliminary work and that all the cracks have been dealt with, check the surface â€“ if it is still very wet, use a fan heater at full blast to try to dry it a bit â€“ the first coat of polyurethane needs to be able to penetrate the floor. You are going to apply three coats and they all need to be done in one day, so don't start this late in the afternoon!
Apply the first coat with the broom and as soon as it is dry enough to walk on, apply the next coat. This must be done within three hours. Follow the same procedure for the third coat.
Leave the floor to harden for four days or for a week if you are intending to cover the floor with carpeting or any form of tiling. This should be quite possible, provided that any adhesive you are using is suitable for a non-porous surface. If you intend to lay a permanent floor covering, such as ceramic tiles, it may be wide to wait for a month or so in order to check that your sealing has been 100% perfect.
If the walls of the basement are also showing signs of rising damp, you can treat them in the same way, but using a decorator's wallpaper paste brush instead of a broom, and they will then be able to take a coat of emulsion paint. Make very sure that you are wearing goggles if you intend to treat walls â€“ an eyeful of polyurethane is very definitely not what the doctor ordered!