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Ask Handyman

By Travis Larson

From The Family Handyman

How do I build a deck footing that will stay put?

A footing that will heave

Q I’m replacing my old deck with a new one, complete with new footings and posts. One corner of my old deck would move up several inches in the spring and back down as the weather warmed, but it never quite settled to the previous level. What causes this weird seasonal levitation, and can I prevent it when I build my new deck?

Phillip Morgan Hayward, WI

A Your deck has a bad case of “frost heave-osis.” In the winter, the ground freezes from the top of the soil downward. The depth of frost penetration depends on the soil type, the severity of the winter, the amount of water in the soil and the depth of an insulating blanket of snow. The frost depth varies by region. In frigid Minnesota, the frost depth is 42 in., whereas a warmer state like Missouri may have a frost depth of only 1 ft. When you contact your local building department to get your building permit, ask what the frost depth requirement is and the required size and shape of the footings. Then dig the footing holes so that the bottoms of the footings are at or below the frost depth.

The mechanics of frost heave are complex, but here’s a quick primer. Water in the surrounding soil collects and freezes into thin layers of frost called “ice lenses.” When water freezes, it expands about 9 percent—think of how ice cubes are domed above the original water level in the ice cube tray. Ice exerts a pressure of about 50,000 lbs. per square inch—enough force to lift even a large building. A puny little deck on inadequate footings doesn’t stand a chance. The reason buildings and decks don’t always return to their original height is that surrounding dirt sometimes fills in under the footing while it’s lifted.

Heavy clay soils don’t drain well, so they tend to have more frost heave problems than sandy, well-drained ones. But even if footings are deep enough, ice lenses can latch onto the rough surfaces of wood and concrete and lift footings and posts from the side. That’s why concrete piers poured in waxed cardboard tubes and smooth wooden posts work well for below-grade support.

Here’s how to get a solid, frost-proof footing:

• When you pour concrete footings, hold the cardboard concrete form tube about 12 in. up from the bottom of the footing. Do this by nailing the sides of the tube to the center of a tic-tac-toe grid of 2x4s at the top of the hole. Then dump concrete through the tube into the bottom of the hole. After the wide part at the bottom of the hole has filled, the tube will fill too.

• Flare the sides on concrete footings so the footings will resist heave in harsh winters when frost penetrates especially deep. Greater width at the bottom will also distribute weight over a larger area.

• Mound soil around the posts after the backfill settles to direct runoff water away from the post.

A concrete postscript:

If you’re pouring more than a few footings, order premixed concrete from a ready-mix company. You’d be shocked at how many bags of concrete mix you’d have to mix by hand to fill a form tube.

Figure concrete volume by multiplying the height of the post and column in feet by the radius of the tube in feet squared times 3.14. Divide the total by 27 to get the cubic yardage you need to order. Add extra for the wide footing bases.

What causes the mysterious soot marks on my walls?

Q In my bathroom, little black spots seem to mark the locations of all the drywall fasteners. My wife burns candles, and I say that’s the reason. She says, and I quote, “Then how come we don’t have marks in the other rooms where we burn candles?” I’ve learned over the years I’m usually wrong—but I’m having trouble giving this one up.

Gregory Rusert, Ballwin , MO

A You’re right this time, but try not to gloat too much. Candles produce a lot of soot—especially candles in jars, scented or oil-burning candles, and candles with low-grade waxes or long wicks. If you wash the walls, you’ll probably see that the area around the fasteners has soot too, just not as thick. The metal fasteners attract more of the soot particles than drywall, particularly if they’re on a cold, outside wall. Add to that a small, enclosed, humid room that contains more contaminants for longer periods.

You can lose the marks by scrubbing the walls and repriming them with a stain-killing primer such as BIN or Kilz, then repainting. But the same marks will probably reappear with the same romantic practice. Keep the soot to a minimum by buying high-quality, unscented candles. Keep the wicks trimmed and the candles out of containers.

Which PVC fitting should I buy?

Q I recently went to a home center to get PVC pipe and fittings for roughing in a new bathroom in my basement. I found two styles of fittings, one with smooth surfaces and the other with flanges wherever the pipes join into the fitting. No one there seemed to know which one I should use. Are they for different purposes? Which should I buy?

Tom Gamello, via E-mail

A You should buy the ones with the hubs (what you call flanges). They’re designed for drain waste vents (DWV). The other type is for pipes that carry water under pressure. Called pressure fittings, they’re used in homes for some types of groundwater heating systems and swimming pool plumbing. The fittings are thicker and stronger and allow the pipe to penetrate farther into the fitting to reduce the chance of failure. Using pressure fittings for drain waste vents won’t meet code in most areas.

P.S. People who make cool stuff out of PVC pipe (lawn furniture, for example) like to use pressure fittings for their clean, neat look.

Two super plaster repair products

Repairing sagging plaster

Repairing cracked plaster

Q I’ve got some loose plaster in my living room. To repair it, do I need to chip out all the loose stuff, or is there a simpler alternative?

R. Moore, Newark, NJ

A Plaster sags from ceilings or bulges from walls when the plaster keys embedded around the wood lath break loose. To repair it, you’ve got two choices. You can break out all the loose stuff and replaster the area—not a do-it-yourself project. Or, you can stabilize the sagging plaster by using plaster washers (see left photo) to pull it back up against the lath. Plaster washers don’t always work, but they’re cheap so it’s worth a shot.

First, locate the joists or studs and mark their location in the loose area. Push up the loose plaster and place 2-in. screws and the perforated plaster washers into the joists or studs about every 6 or 8 in. The convex washer will flatten as the screw tightens. If the plaster has a rough surface, you may need to first scrape the surface to get the washer to lie flat. Next, secure the loosened field to the lath between joists with more washers. Finally, skim-coat over the washers with drywall joint compound. It may take several coats and extra effort to create a smooth finish or mimic the existing texture.

If you have solidly attached plaster with cracks spider-webbing through your walls and ceilings, you can stabilize and coat the entire surface with another product—sheets of fiberglass mat. One such system, called Nu-Wal, costs about 44¢ per square foot. With it, you simply roll on a latex-like base coat, embed the fiberglass mesh, and roll over it again. This method essentially gives your plaster walls a new flexible skin so non-structural cracks won’t reappear. Plus, it acts like a vapor barrier, keeping moisture from migrating into the wall, and it’s approved for lead paint encapsulation on interior walls.

[Before making repairs, be sure to solve the moisture, settling or other problems that caused the cracking or sagging.—S.S.]

Buyer’s Guide

Plaster Repair Washers: Lee Valley Tools, (800) 871-8158, item No. 67Z-2001. $3 for a pack of 10.

Nu-Wal Restoration System, Specification Chemicals, (800) 247-3932, www.spec-chem.com. Ask for the installation video.

Contributing Editor • SAM SATTERWHITE

Art Direction • BOB UNGAR

Photography • BILL ZUEHLKE, RAMON MORENO & MIKE KRIVIT

From The Family Handyman - January 2001