Basement and Crawlspace FAQ: Foundations

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Loose Sills

I live in California in a house built in 1926. The mudsills are not bolted to the poured concrete foundation. If what I read about earthquakes is true, I’d better get them fastened down. I’ve been told that there’s no simple way to do this. How can I secure them without jacking up the whole house to get the bolts in?

For those not familiar with the term, the mudsill, or sill plate, is the lowest member of an exterior wood-frame wall, which rests on the foundation and supports the joists and upright portions of the frame. The term mudsill originated from the procedure of correcting irregularities in the top of the masonry foundation by embedding the sill in a layer of grout or fresh mortar. Normally, this sill is anchored to the foundation wall.

I agree that you should fasten the mudsill to the foundation. In the event of an earthquake, the house could slide, shift or even overturn. Because of the limited space, installing anchor bolts in the top of the foundation would be difficult and costly. Jacking up the house is not a practical solution and not recommended. I suggest that you have an ironworks shop fabricate iron angle brackets. The brackets should have a small spike on the short end which can be hammered into the sill plate to prevent sliding. By mounting brackets on all of your house exterior walls, you will adequately secure the structure. Specifications as to the bracket size and spacing will depend on your locale. So, check with a licensed professional engineer in your area specializing in structural design.

Serious Seepage

When it rains, I have a leak in my foundation wall along a cold joint that runs around the foundation’s perimeter. The joint is the result of pouring the concrete on two different days. To fix this and make the wall more attractive, I thought of troweling a portland cement/sand mixture over the wall, hut will it stop the seepage?

SEAM IN FOUNDATION

A cement stucco can improve the wall’s looks, but won’t stop the leak. The surest (and most expensive) fix is to intercept the water before it gets to the wall with drainage, then undercut the crack with a masonry saw or chisel, and seal the seam inside and out. A less expensive fix is to patch only the seam’s inside face.

There are at least three choices of patch material: hydraulic cement, epoxy patch and flexible joint sealant. You can buy hydraulic cement in hardware stores. However, you will probably have to order the epoxy patch. Joint sealant may be sold at home centers or it can be ordered.

Hydraulic cement is simply troweled into the widened crack. Epoxy patch is troweled on both sides of the wall, though the seam is widened only on the wall’s outside. If the leak is serious, you could patch the seam, as shown, and install copper-tubing stubs that form injection ports. Thin epoxy is injected through the tubes, which are later pinched shut, cut off and covered.

Joint sealant is squeezed into the enlarged seam after the seam is wire brushed. Apply butyl rubber, silicone or (preferably) polyurethane joint sealant using a caulk gun. If possible, on the inside, mask off along the seam and brush on a pourable (also known as self-leveling) joint sealant between the pieces of tape. You can temporarily repair the joint by just wire-brushing its inside face and brushing on joint sealant.

Floor Slab

The concrete floor of our basement is constantly covered with a powder-like dust and nothing that we have tried prevents it, including applying a concrete sealer several years ago. Vacuuming and mopping helps for a week only. Any ideas what this would be and how can we get rid of it?

The condition that yon describe is called dusting. According to the Portland Cement Association, the dust consists of fine particles of concrete aggregate (sand and stone). The particles form a thin and loosely bonded layer on the concrete’s surface. Movement across the concrete breaks the particles loose and stirs them into the air.

Several things can cause this, such as using a concrete mix with a low cement content or one that contains too much water. It may also result from improper finishing arid installation, such as subjecting the concrete to freezing temperatures before it has cured, allowing the concrete to dry too rapidly or troweling it smooth while it’s still so wet that water is standing on the surface.

One way to correct the dusting is to grind off the thin layer to expose the solid concrete underneath. This, however, may not be very practical in your home. Another method is to apply a chemical surface hardener that contains either sodium silicate, commonly called water glass, or a metallic fluosilicate (such as magnesium and zinc fluosilicate). These products are available at construction supply companies.

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Updated: Saturday, December 24, 2016 16:29