Battling a wet basement from the inside

Leaky foundations are the bane of one's existence for a large number of homeowners. Whenever possible, the best way to cure the problem is from the outside.

There are times, though, when it is very difficult - and sometimes even impossible - to do so. Such conditions may include: heavy planting of shrubs, healthy perennials or ground cover along the foundation; the presence of plants that are valuable or difficult to move without the risk of losing them; plants which will suffer having their shallow root system covered with additional dirt; or simply not enough room to work safely, if at all, with the needed machinery or to store materials. These are all reasons that make outside waterproofing undesirable.

This does not mean, however, that the only recourse for the unfortunate homeowner is to set everything he or she stores in the basement on pallets or put concrete blocks under the washer and dryer (as I have seen done in desperation).

The problem can be solved from the inside in several ways.

But one thing that should never be done with a block foundation is what most people think of doing first, and what is most often advertised by various manufacturers and merchants. Concrete blocks should never be waterproofed from the inside unless an escape for any water that might accumulate is provided.

I have seen several examples of this being done with catastrophic results. The cores of the blocks can fill with water, which evaporates and invades the exterior walls and the attic of the structure. The worst case I have seen involved a four-unit apartment structure built in sand (which one may consider as the safest environment) that had to be evacuated.

The interiors of these units had turned black from mold growing on the walls and ceilings. The heavy smell of excessive moisture in enclosed spaces was quite uncomfortable. The doors and windows were swollen and dripping. The roof sheathing had also suffered. In other words, the apartments were unlivable, and the tenants had moved out long ago to save their furnishings and health.

There are several approaches to dealing with basement leakage from the inside:

• An underslab system

• An above-slab system with open drain

• Above-slab system with concealed drain

Underslab system

If, for some reason, you wish to conceal the drainage system, there are two ways to achieve it.

If the leakage is coming through cracks in the floor and at the joints of walls and floor, it usually indicates hydraulic pressure under the floor is such that it is causing the water to rise to a level above the slab.

If you know for sure, or can ascertain by a trial cut or hole, that there is a substantial crushed stone bed underneath the slab, the stone bed can be used as the drainage bed, and all you may need is a sump equipped with a quality submersible pump.

However, if there is no good draining stone bed, or if it is determined that the water is coming through the walls above the slab, (this is more likely with a block foundation), the slab needs to be cut and removed, from the foundation walls to approximately 1 foot back along the entire perimeter.

The material below the cut in the slab should be removed to a depth of about 12 inches from the top of the floor. Place a couple inches of egg-size crushed stones in the bottom of the trench and a 4-inch perforated plastic pipe over it.

Lead the pipe to a sump placed strategically where outside drainage makes the most sense. The pipe need not be sloping; water seeks its own level.

Drill or punch holes in the inside faces of concrete block foundation walls between the webs just above the footing to allow for drainage.

Complete the backfilling of the excavation with stones, making sure you cover the top of the footings with a layer of stone as the conduit to the stone bed. Place removable strips of plywood wrapped in plastic against the walls with their tops at the level of the top of the concrete patch and use them as a screed when you patch the concrete. Remove them when the concrete has set enough to do so. These will provide a narrow slot for water that may come through the walls to be able to reach the drainage system (the belt and suspender approach).

You may want to slope the concrete patch slightly toward the walls, just in case there is so much water that it spills onto the slab. This should help keep the water from spreading over the entire floor.

If you are in a high radon area, you should investigate a radon mitigation system that will suck the gas out from under the slab and discharge it over the roof.

Above-slab systems

If leakage is occurring through the walls of your basement, or through cracks in them, as opposed to coming up from below the slab, or if you do not wish to go to the hassle of installing an under-slab drain, you can use an above slab drain system, either an open drain or a concealed one.

An open system is well-suited to an unfinished basement.

It can be done in one of several ways. The most commonly used, in my experience, and the most difficult and unsightly to accomplish, is to build a cement curb on the slab a couple of inches from the base of the walls.

Another method that, if carefully done, can control and direct water to a sump is to set a curb made of pressure-treated wood in a bed of polyurethane sealant a couple of inches away from the walls. You probably should use 2-by-4s ripped in half with the ripped side up. Caulk the joints between pieces with the same sealant also.

The area of the concrete to receive the caulk should be thoroughly cleaned and, if it is very slick from hard troweling, it should also be etched with muriatic acid. Muriatic acid is very corrosive, and you should use it with care with full eye and skin protection, and you should not use any metal tools or bucket with it.

In my opinion, however, the best method is to use vinyl guttering with its back cut off on a table saw, using a blade installed backward, as recommended by the vinyl siding industry for cutting this type of product. This will leave the bottom of the gutter, which is what you will set on the sealant's beads.

Treat the concrete as detailed above and lay a couple of thick beads of polyurethane sealant on it when you are ready to lay the gutter sections.

Next, join the sections of gutter with their couplings and caulk them thoroughly (a couple of sheet metal screws or pop rivets may be useful). Let them set for a day, and then set the bottom of the sections of gutter in the sealant, pressing them down with a piece of wood.

They terminate, of course, at the sump.

Above slab with concealed drain: This method may be preferred in all cases, but is certainly the method of choice when the basement walls are finished.

If the walls are not paneled or drywalled, and you have selected the pressure-treated wood system, simply cover the pieces already set in place with another piece of pressure-treated wood. You may want to use a 1-by-4.

Or you can set a 1-by-3 (from 1-by-6s ripped in half) on edge against the pieces already set on the concrete floor, and cover them with eased-edge pressure-treated deck boards slightly overhanging for looks. If there is a possibility that water may be running down the walls, nail roofing nails into the edge of the wood cap facing the walls, leaving a quarter-inch or so of the shank sticking out as a way to create a narrow space for water to run down into the concealed gutter.

If you have selected the vinyl gutter system, simply turn it over and set the turned edged top of the gutter in a single bead of sealant with the bottom section against the walls. If water seepage through the walls is anticipated, place a few aluminum or stainless steel nails as spacers between the walls and the top of the gutter.

If the walls are paneled or drywalled, simply cut the finish at a point determined to be the top of the gutter and set the gutter underneath it.

In my experience, polyurethane sealant is, by far, the best caulking material to use. I have used Sikaflex-1a for nearly sixty years in some pretty esoteric ways (such as to reset ceramic tiles on ceilings and to repair shoes), and it has surpassed any other sealants or adhesives recommended by manufacturers. Sikaflex-1a is a product of Swiss origin. There are also U.S.-made polyurethane sealants. You will usually find them only in waterproofing and masonry supplies stores or large concrete providers. They are used extensively in commercial and industrial construction.

You can also have a waterproofing contractor install fiberglass gutters at the base of the walls, leading to a sump and pump. These gutters are more attractive that homemade ones, but be prepared for a hefty bill. These contractors will also install sump pumps.

• Henri de Marne was a remodeling contractor in Washington, D.C., for many years, and is now a consultant. His book, "About the House," is available at www.upperaccess.com. His website is www.henridemarne.com. Email questions to henridemarne@gmavt.net, or mail First Aid for the Ailing House, Universal Uclick, 1130 Walnut St., Kansas City, MO 64106.

© 2015, United Feature Syndicate Inc.