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Project Difficulty:
Moderate
Estimated
Project Time: 2 days
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Safety goggles
Wire brush
Bristle brush
Neoprene rubber gloves
Water and bucket
Acid etching compound
Cold chisels (various sizes)
Double-faced sledgehammer
Shop vacuum
Hydraulic cement
Pointed trowel
NIOSH-approved respirator
Wide nylon paintbrush
Sealant
Hawk
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Although there may be no obvious signs of drips or leaks in your basement, moisture can still find its way through masonry (concrete) walls, resulting in a musty odor or even mildew. Concrete is not waterproof, and sealing the walls from the inside is good prevention but will not fix a serious water problem.
Before sealing a masonry wall, patch any obvious cracks with hydraulic cement until the whole surface is flush with the wall.
Waterproofing sealants are sold under a number of names, including cement paint, waterproofing paint, basement paint, and concrete waterproofer. Most contain a mixture of portland cement and synthetic rubber that, when brushed on, will stop slow seepage through walls. For a sealant to work, it must be applied to a clean surface, preferably one that has never been painted. (The sealant can still do a good job if all the old paint is completely removed.) After applying the sealant and allowing it to dry, finish the job with a coat or two of good latex paint.
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1.
Clean the Wall Surfaces
Using a wire brush and wearing safety goggles to prevent eye injury, scrape off any loose mortar and dirt. Wash off grease with a degreaser or detergent recommended by the waterproofing product manufacturer. Wear neoprene rubber gloves to protect your hands (Fig. 1). Then vacuum the walls to remove any remaining dust and dirt.
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2.
Remove Efflorescence
Efflorescence is a harmless white deposit that sometimes forms on concrete or concrete-block walls from the water-soluble salts within the masonry. It collects on the surface and can prevent the waterproofing material from bonding properly to the wall. An acid-etching compound (such as a ten percent solution of muriatic acid) dissolved in water and applied using a stiff bristle brush, will remove efflorescence. Be sure to wear safety goggles, neoprene rubber gloves, long pants, and a long-sleeved shirt while working with the solution. Follow the manufacturer's instructions and apply the solution carefully. (Make sure you have plenty of ventilation.) Then rinse the wall with clean water to neutralize the acid, and allow the wall to dry thoroughly. (Fig. 2)
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3.
Prepare Cracks and Holes
Wearing safety goggles, use a cold chisel and a double-faced sledgehammer to undercut each crack and hole, forming a "key" that will provide a suitable shape (wider on the inside) to which the hydraulic cement can adhere. Chip out all damaged concrete, creating a crack about 1/4-inch wide and about 1/2-inch deep. If you run into any reinforcing steel, then you will have to keep chipping, getting to a depth of about 1 inch behind the steel. Then vacuum any loose dust and dirt. Hydraulic cement is very effective in sealing cracks, even wet ones; as it hardens it expands a little and locks tightly to a properly prepared crack. (Fig. 3)
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4.
Apply Hydraulic Cement
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Using a pointed trowel, mix a small amount of powdered hydraulic cement with water in a bucket until the cement begins to thicken a bit. Thoroughly wet the area of the crack with water.
Place the cement on the hawk and hold the hawk against the wall in front of the crack. Using the pointed trowel, pack in the cement, working from bottom up. Pack it a little past the surface, and then scrape off the excess with the edge of the trowel, letting the loose cement fall onto the hawk. Discard the excess. Trowel the area smooth immediately. (Fig. 4)
If the crack is leaking water, chisel the crack wide enough to accept a short length of tubing or hose at the base of the crack. As most of the water will now drip through the hose, the pressure around the crack will be reduced, making it easier for the hydraulic cement to set without being washed out.
Now mix the hydraulic cement, put it on the hawk, and trowel it in, as above. Pack it tightly around the hose. Let it all set. Meantime, while the water continues to drain into the pail, prepare a plug for the hose location by molding a plug out of pasty hydraulic cement into the shape and size of the hose you are using. When the new plug starts to dry and holds its shape, pull out the hose in the wall and push in the plug to just a bit below the surface. Trowel over hydraulic cement until smooth.
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5.
Plug Other Water Problems
Check for water seepage at wall and floor junctures. If you find cracks, open the spaces with a cold chisel and double-faced sledgehammer, as in Step 3, and then apply hydraulic cement, following the instructions in Step 4. (Fig. 5)
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6.
Apply the Sealant
After the hydraulic cement has cured and the wall is dry, seal the walls using a sealant. Follow the instructions that accompany the product, work in a well-ventilated area, and wear neoprene gloves and a NIOSH-approved respirator. Use a wide, nylon paintbrush to apply the sealant; for thorough coverage, be sure to dab it into the pores of the masonry (Fig. 6). Let the first coat dry as per manufacturer's recommendation, and then apply a second coat. After the second coat has dried, finish the wall with a coat or two of latex paint.
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