How do I build a deck footing that will stay
put?
Click Image to enlarge.
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?
Click Image to enlarge.
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
Click Image to enlarge.
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
