Question: How do I waterproof a basement from the exterior?
In general, the main method of waterproofing the outside of a building foundation is two-fold. First, move water away from the foundation area. Second, apply a waterproofing layer to the foundation itself.
1. Move Water Away from Foundation
The most common method of moving water quickly away from a foundation is to trench out an area 1 foot by 1 foot below the surface of the earth next to the foundation. This is a best-case scenario; sometimes, you may have to go as deep as 3 feet.
Next, install a perforated drainage pipe and cover with gravel; this is also known as a french drain. Be sure to slope the backfill away from the house.
2. Seal Foundation Wall
Before installing the drain and backfilling it, you should first apply waterproofing materials to the outside of the foundation walls about half-inch thick. This is a method called parging. It's important to remember the parging is not the ultimate waterproofing technique. It is only preparation. Only after parging do you lay down the actual waterproofing material such as epoxy or other materials specially made for foundation waterproofing.