Plastic provides vapor barrier in crawl space

Q: My house is built on a crawl space, like most of the houses in my area. Only part of the dirt floor of the space is covered with plastic. Do I need this plastic cover and if so, what thickness do you recommend?

A: The plastic cover or vapor barrier is definitely needed, especially in a dirt-floor crawl space. Without a vapor barrier, moisture will migrate to the surface of the soil and eventually cause serious problems in the crawl space, including mold and possibly structural rot.

The plastic should cover the entire floor. Use the thickest plastic sheeting you can find – at least 6 mils thick. The cover needs to be durable because it will probably have to withstand some traffic in the crawl space without tearing.

Several sheets are usually needed, and they should be overlapped by 18 inches or more at the edges, then taped in place with strong duct tape. The ends of the sheets should lap up the walls at least six inches; hold them in place with adhesive caulk. You can also put some bricks or lengths of pressure-treated wood to hold the plastic in position.

In most regions, the crawl space should also be well ventilated to help keep moisture from condensing. But in regions where relative humidity is very high in summer it is often best to close crawl-space vents to keep out the highly humid air, which can condense quickly in the cooler crawl space.

If in doubt about ventilation, consult building-code officials in your area.

Q: We have wide pine overhangs all around our 56-year-old house. Over the years they have become mildewed and splotchy. The overhangs now have a clear finish, but painters have suggested power washing it and painting. Do you have any suggestions?

A: If it is a choice between a clear finish and paint, I think painting is most practical. Clear finishes do not hold up well outdoors, and require regular maintenance to keep them looking good.

However, you can get a good appearance and cut maintenance way down by covering the overhangs with vinyl or aluminum soffit panels. These panels only need occasional cleaning.

The initial cost would be higher than painting, but you should come out ahead in the end by eliminating periodic repainting.

Q: The concrete steps to our front stoop have settled over the years and there is a two-inch gap between the riser of one of the steps and the stoop.

Neighbors say the steps have been that way for years, so the settling is apparently over. I can’t afford new steps and am looking for a less-expensive cosmetic solution. Can you help?

A: You should be able to fill the gap with concrete mix, sold in bags at any home center or hardware store. The gap is apparently in a vertical surface so the problem will be to keep the concrete mix in place while it sets up.

Find a board long enough to sit on the step and cover the gap. Mix a batch of concrete big enough to fill the gap and pack it into the gap with a small trowel. If the concrete starts to fall out when you get near the surface of the riser, use the board as a dam to hold it in place.

When the gap is filled and smoothed, prop the board in position with some bricks or concrete blocks while the concrete sets up. The patched area should be allowed to cure for a couple of months before you paint the steps with a high-quality porch and floor paint.