Carpentry Q&A Archives

2005 CARPENTRY Q&A ARCHIVES

Here are some helpful tips from Mark Feirer, the author of Carpentry & Building Construction.

Q What can be done to conceal cracks that appear between molding and a wall or ceiling surface?

A Many carpenters and painters prefer to caulk these joints with siliconized acrylic latex caulk. It is easy to apply, paintable, and fairly flexible.

For more information on molding, please see Chapter 35 of Glencoe’s Carpentry and Building Construction © 2005 by Mark Feirer.

Q Why is it important to keep the mudsill at least 8" above grade level?

A This minimizes the formation of rot in the edges of the floor structure. The mudsill is the framing member located closest to the grade level, so it is particularly prone to decay. If the mudsill isn’t kept at least 8" above the grade level, here’s what happens. As the sill decays it becomes soft, and then the ends of the joists sink. The situation gets worse when damage extends into the rim joist and the ends of the floor joists. As the weight of exterior walls bears down on the rotten wood, the floors sink. Most houses have a center beam that supports floor joists at the middle of the house. As the outermost portions of the floor system sag, this beam often remains unaffected by rot and continues to support the central areas of the floor at the correct level. This is why floors in an older house often tilt downward towards the outer walls.

For more information on framing, please see Chapter 19 of Glencoe’s Carpentry and Building Construction © 2005 by Mark Feirer.

Q What is the correct way to install a ceiling fan?

A A ceiling fan should not be connected to any standard ceiling electrical box. It's not the electrical load of the fan that's the problem--it's the fact that a fan is heavy and it spins. According to electrical codes, a paddle fan shall not rely solely on the electrical box for support. There are several specialty boxes that solve this problem. One type incorporates steel straps that support the box between two adjacent rafters. Others use a system of steel plates arranged so that the weight of the fan is supported directly by a single rafter. Both approaches prevent the box from twisting out of position because of the vibration and torque (twisting force) that a fan generates, and they eliminate the possibility of fastener failure.

Q How can I make wood trim fit tightly against a brick chimney?

A Wood can be “scribed” to fit against an irregular or uneven surface. You'll need a simple compass (the type with a pencil in one side and a pointed metal leg on the other), and either a coping saw (for thin trim) or a jigsaw (for thicker trim). Narrow jigsaw blades, sometimes called scroll blades, are the best for cutting along irregular lines.

Hold the trim as close to the chimney as possible while still keeping it plumb. Then tack it in place temporarily with finishing nails. Now set the compass to the same distance as the widest gap between the chimney and the trim—generally at a grout joint. Hold the legs of the compass horizontally, and draw it downwards starting at the top of the chimney. As the point of the compass follows the irregular surface of the brick, the pencil will trace a matching contour on the wood. When you've traced the entire length of the column, remove the trim and cut along the pencil line. When you put the trim back in place, the cut edge should match the brick fairly well, though you'll probably have to adjust the fit with a file or a utility knife to make it perfect.

For more information on molding, please see Chapter 35 of Glencoe’s Carpentry and Building Construction © 2005 by Mark Feirer.

Q Snow sliding off a roof sometimes damages rain gutters. Is there any way to prevent this?

A As snow and ice slide off the roof, they'll slam right into the outside edge of a gutter that is not installed correctly. The abuse eventually causes the gutter to sag. On a properly installed gutter, the outermost edge of the gutter should be slightly lower than the edge of the roof. In other words, a straightedge resting on the shingles shouldn't touch the gutter. Otherwise, every snow pile that slides off the roof will put pressure on the gutter and may eventually rip it loose.

Q Why does wood molding sometimes separate from the ceiling after installation?

A There are several causes of this problem. For one, it typically takes a while for new framing to "dry out" enough to stop shrinking. How long this takes depends on how green the wood was to begin with and how much exposure the rooms have had to the drying effects of central heating. It is not unusual for this process to take a year or two. Another possible problem lies in the molding itself. If a wide molding is made of solid wood, rather than a composite material, it will expand and contract with seasonal changes in moisture content. The amount of expansion is typically greater across the width of trim than along its length. A third possibility is related to installation. Unless carpenters install backing for the molding, there isn’t much meat to nail into where the walls run parallel to the ceiling joists. Also, if not properly secured, the wood is free to move around.

For more information on molding, please see Chapter 35 of Glencoe’s Carpentry and Building Construction © 2005 by Mark Feirer.

Q What is the best way to paint new plaster walls?

A Painters often recommend a primer-sealer as the first coat on plaster. A good product will accomplish several things: It will even out the porosity of the surface to help produce an even sheen of finish paint, provide a vapor barrier to minimize the passage of water vapor into the walls, and provide a surface to which paint can readily adhere. Some painters feel that oil-based primers generally do all of these things better than latex primers. You should be able to use either oil or latex primers beneath oil or latex finish paints--just be sure to allow ample drying time, especially with a latex finish over an oil primer. Latex eggshell finish paints are by far the most popular choice for walls because they're washable without appearing too glossy. And the lower the sheen, the more forgiving the paint will be in accommodating minor wall imperfections.

For more information on plaster, please see Chapter 40 or for more information on painting, please see Chapter 41 of Glencoe’s Carpentry and Building Construction © 2005 by Mark Feirer.

Q Is it possible to make a house soundproof?

A Making a house soundproof would be very expensive, and the work is generally suitable only for sound studios. However, there are ways lessen sound transmission. To reduce noise generated inside the house, consider such things as carpeting over hardwood floors or replacing plastic drain pipes with cast iron. Reducing noise generated outside the house is more difficult. The most cost-effective strategy is to eliminate "flanking paths." These are air spaces between building materials that allow sound waves to enter the house unobstructed. You can eliminate many of these paths simply by weather-stripping doors and windows. Because they are denser than spring-bronze weather stripping, felt and EPDM rubber products are the best weather strips for blocking sound. Pull out the caulking gun to seal other flanking paths, such as the gaps around hose bibs and wiring penetrations. Basically, any place you'd seal out air or water offers a potential pathway for sound.

For more information on soundproofing, please see Chapter 39 of Glencoe’s Carpentry and Building Construction © 2005 by Mark Feirer.

Q What causes condensation?

A Warm, moist air that touches a cool surface will cool. Because cool air can't hold as much moisture as warm air, beads of water (condensation) will form on the outside of the cool surface. This process is sometimes described as “sweating.” It sometimes occurs on cold-water supply pipes in basements. More often, it appears on the exterior surface of toilet tanks during the summer, particularly if the water is supplied from a well. The cold water chills the tank and causes warm, humid room air to condense on the outside of the tank. Hot, humid climates aren't the only ones that suffer from condensation problems. The same process happens in cold climates, when warm, moist air inside the house hits the relatively colder surface of the window glass in the winter.

For more information on moisture protection, please see Chapter 14, page 249 of Glencoe’s Carpentry and Building Construction © 2005 by Mark Feirer.

Q What is slab jacking?

A Concrete slabs can sink if they are poured on improperly compacted fill or on soil loaded with organic material. Another cause in older houses is a broken water or sewer pipe that washes away the fill beneath the slab. Slab-jacking (also called mud-jacking) is a technique that calls for drilling a series of holes through the sunken slab, then pumping quick-setting grout (concrete without gravel) into the holes. Hydraulic pressure lifts the slab as the grout fills voids in the soil. When the grout hardens, it supports the slab in its new position and the application holes can be patched. The technique can be used on any slab concrete slab in good condition, including driveways, sidewalks, and patios.

Q How can I seal a caulking tube for later use?

A Caulking tubes hold about 10 oz. of material, but rarely does anyone use exactly one tube. There always something left, and that means sealing up the tube for reuse later. Some tubes come with caps that screw on, but most don't. Some carpenters seal the nozzle with duct tape, stick a 16d nail into the tip, drive a small screw into the tip, or screw on an electrical cap. Even then, a plug of caulk will eventually solidify in the tip. Maybe someday manufacturers will make caulking tubes with removable tips so the plug of dried caulk can be pried out from the base end of the tip. Until then, try this. Drive a long, slender drywall screw deep into the nozzle and into the dried plug, then pull out the plug as you withdraw the screw. If that doesn't work, a long, narrow flatblade screwdriver, the kind that electricians use, does a passable job of coaxing out the plug. If that doesn't do it, just cut the tip off a little bit to make the hole a little larger.

Q What can I do if a wall must be framed between an existing floor and ceiling?

A The best way to frame a wall is to assemble it flat on the floor and tip it into place. However, in some cases walls must be framed between an existing floor and ceiling. A wall built exactly as tall as the distance between finished surfaces won't always tip into place--it's actually slightly taller when measured diagonally across its thickness. You could make the wall a little short and then shim it into place, but there's a better way: Rack the wall to get your clearance. This method uses simple geometry. Turn that rectangle of a wall into a parallelogram to reduce it's height just enough for you to get the clearance you need. Once in place, push the wall back into a rectangular shape, and it'll snug up to the ceiling just right.

Q When I use OSB for sheathing, which side should I use?

A Oriented-strand board (OSB) is inexpensive and relatively strong and is often used for wall sheathing. Unlike plywood sheathing, one side of OSB is smooth and the other is a little rough. From a structural standpoint, it doesn't make any difference which side faces up. But if you were a roofer climbing around on a newly sheathed roof, which side would you rather be walking on? For added safety, the lightly textured side offers a bit of extra traction.

On the other hand, there's another issue to consider if the OSB has tongue-and-groove edges. The T&G profile is not symmetrical, so the sheets must be oriented correctly for the joints to match. With those panels, look for the "This Side Down” stamp and be sure to follow that direction.

Q What can I do to solve gutter drainage problems when the downspout drains into piping that runs below grade?

A Gutters collect water falling on the roof and direct it to downspouts. When downspouts appear to drain into the ground, they are actually sending water through an underground system of 4" diameter plastic pipes. These pipes often drain into a drywell, sometimes called a catch basin. This is often a pit filled with pea gravel that allows water to percolate slowly into the surrounding soil. Sometimes drainage pipes lead to a municipal storm sewer system or simply to "daylight,” a point lower than the house where water can flow out of the pipe at grade level.

Unfortunately, all sorts of things can happen to the underground drain pipes over time. Sometimes they're choked by dirt and leaves collected by the gutters or by roots from nearby trees. If that happens, they can sometimes be cleared by working a hand auger (plumbing snake) into the pipe until it hits the blockage, then using a metal detector to find the end of the snake. The area around the blockage must then be dug up to clear the blockage. Using a power snake to clear the blockage isn't an option because the process can destroy lightweight plastic pipe that's often used for drainage.

In daylighted systems, something may be blocking the discharge end of the pipe. That's not hard to resolve--as long as you can find the end of the pipe. It's also very common for vehicles driving over a lawn to crush drain pipes, particularly when the ground is soft. Concrete trucks are the worst offenders, and crushed drainage pipes are often an unintended consequence of pouring a foundation for a new addition. When installing drainage systems, some contractors use heavy-duty Schedule 20 pipe. It's very crush resistant and doesn't cost much more than standard Schedule 40 drainage pipe. If it saves a homeowner from having to dig up a crushed pipe in five years, it's worthwhile.

If a drywell is involved, most of the time the drywell itself has clogged rather than the pipes leading to it. A drywell is often just a steel drum with holes poked in it, buried a few feet below the surface. Or it might be nothing more than a hole filled with rocks. Either way, the drywell eventually silts in and no longer works as a drain. It must be replaced. A 50-gallon sectional plastic catch basin is easy to transport and install. After digging a pit, assemble the catch basin, lower it into the pit; then connect the drain pipes to it. Wrap the basin with landscape fabric to keep silt out; then surround it with pea gravel to encourage water dispersion.

For more on gutters and downspouts, see Carpentry & Building Construction, Chapter 31, section 31.3.

Q What can I do to prevent concrete dusting?

A Dusting is a weak surface layer of sand-rich cement paste that turns powdery when it dries. Dusting is caused by troweling concrete while surface water is still present. This can also make the concrete scratch easily.

In many cases the water source is rain, but the same results can occur even in dry weather. Water in the concrete mix naturally rises to the surface after the slab has received the first two finishing steps: screeding and bullfloating. The next step, troweling, shouldn't occur until after this water, called bleed water, has evaporated.

If a slab has been rained on, take steps to remove the excess water. You might be able to sweep off the excess with a long trowel, or you can drag a garden hose across the surface to skim off the excess. But if you missed that chance and are faced with a dusting problem, all is not lost. You should be able to coat the floor with one of various types of floor sealers. These products bind the surface layer into a harder, more durable layer that won't dust.

Some concrete finishers use a deep-penetrating acrylic sealer to solve dusting problems. The surface must be pressure washed first, then allowed to dry before applying the product. However, a sealer can make the surface slippery. It may be necessary to add a bit of sand if the problem surface is being used as an exterior walking surface.

For more on placing concrete slabs, see Carpentry & Building Construction, Chapter 15.

Q What’s the best way to install interior trim on a series of small windows that are located side by side?

A The best way to solve a complex problem is to simplify it. In this case, start by visualizing all that glass as one big window rather than many small ones. How would you trim it? Just like a regular window, using one continuous length of head (top) casing and two lengths of side casing. At the bottom you could install a single sill and apron, or you could continue the casing to "picture frame" the windows. The casing between each window should be a single piece. Some finish carpenters would make these individual pieces from thinner stock than the head and side casing. This would create a slight reveal that might help to make the outer casings more dominant visually.

Q What is Type X drywall?

AType X drywall is a fire-resistant type of drywall that is sometimes called “fire code” drywall. It costs somewhat more than standard drywall. In residential construction, Type X may be required by code on the wall separating an attached garage from the house.

What makes Type X more fire-resistant than standard drywall? It is denser than an equal thickness of standard drywall. It also contains two additives that make it less likely to disintegrate in a fire: glass fiber and vermiculite. The fiber reinforces the sheet, and the vermiculite prevents it from shrinking when it gets hot.

Using 5/8" Type X drywall on a 2x4 wall instead of standard 1/2" drywall increases the wall's fire rating from 35-40 minutes to a minimum of 1 hour. A fire rating is a gauge of how long it would take fire to cause a wall to fail, based on laboratory tests.

Q What can be done to prevent wind from causing a chimney to backdraft?

A The traditional method is to top the chimney with a bluestone slab that sits atop four short pilasters, or legs. They are usually made of mortared brick. The slab prevents wind from blowing smoke straight down the chimney.

A different approach is sometimes used in coastal areas exposed to high winds. At the top is a simple device made of sheet metal. It pivots automatically to shield the windward side of the chimney while exposing the leeward side. Think of how a weathervane works, and you'll get the idea.

Q Does a polyurethane finish have to be completely removed before a wood floor can be refinished?

A No, and there’s a good reason to avoid a complete refinishing when possible. Even a careful sanding by a refinishing professional removes some of the wood surface, and that reduces the floor's life. Unlike sanding, screening a floor with 120-grit abrasive mounted on a buffer scours off a bit of the finish. This prepares it for a new coat. Once the entire floor has been screened, it can be refinished. Prior to screening, the floor should be cleaned to remove any wax, grease, and dirt. After screening, be extremely thorough in eliminating dust before you recoat the floor.

Q What causes a floor finish to wear unevenly?

A Any floor or floor finish wears most where it's walked on most. The kitchen is the busiest room in a house. It is typically the target of more spills, stains, and subsequent mop-ups. So it's no surprise that floor finishes in a kitchen require more maintenance than finishes elsewhere in the house. Other high-wear areas are hallways and entrances to rooms. To get more life out of any finish, put a throw rug at the main entrance to collect finish-destroying grit.

Q How do I determine the causes of excess moisture in a basement?

A If a house is new, the moisture may be related to the concrete curing process. If this is the case, it should subside within the first year. In an older house, seepage or condensation are the usual culprits. Use duct tape to adhere foot-square patches of aluminum foil to various locations on the basement walls and floor. Check them in a day or two: water droplets on the underside of the foil indicate moisture seepage through the concrete, while droplets on the exposed surface suggests condensation. Sealing the walls with a cement-based paint can sometimes cure seepage. Reducing humidity in the basement can cure condensation.

Q How are cantilevered decks framed?

A A cantilever is a horizontal beam supported only at one end. Typically, this occurs when floor joists are extended through an exterior wall to support a small deck. Cantilevers must be carefully designed to support the loads placed on them. However, one rule of thumb for a cantilever is this: For every foot the deck extends outwards from the house, the supporting joists should extend two feet into the house. Cantilevers are suitable only for relatively small decks, such as an observation deck off a master bedroom. Also, it's important to properly flash the area where the joists penetrate the siding so that water has no chance to enter the structure. Finally, be sure that the exterior wall immediately below the deck can handle the extra loads.

Q Where should the plumbing shutoff valve for a bathtub be located?

A A shutoff valve for a sink can easily be located in the supporting cabinet, but there's no obvious place to park a shutoff valve for the tub and shower. The plumbing is often buried in a wall, making access awkward. The best solution is to include a small, unobtrusive door or hatch on the back side of the wall. In other cases, shutoffs may be located in the basement on the supply pipes leading to the tub.

Q What are the advantages and disadvantages of earth-berm construction?

A The basic idea of a berm is to use the earth's mass to insulate part of the house from cold and hot weather and to isolate it from winds that might sweep unrestricted across the landscape. The berm can also dampen noise transmission to the house. From a construction standpoint, a bermed house isn't much different than a house with a walkout basement. In both cases, the success of the house will depend upon how carefully the buried wall was built and on how thoroughly the builder provided for proper drainage and ventilation. Other issues affect this type of construction: fire safety and ventilation. Building codes require that all bedrooms have a window large enough to be used as a means of escape in case of fire. Natural ventilation in a house is also important, but this is not always easy to do with earth-berm construction.

Q Do codes allow rigid insulation to be used on walls or ceilings in a house?

A Building codes require that foam insulation exposed to the interior of a building must be covered by a non-flammable surface, such as 1/2-inch drywall. In some cases, such as when rigid foam insulation is used as part of a roof assembly, codes might allow it to be covered with plywood sheathing. However, always check with your local building inspector to determine the most suitable installation details for rigid foam insulation.

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