Small cracks or holes in plaster can be filled with patching plaster or a setting-type joint compound such as Durabond 90, which sets in 90 minutes. Because joint compound is softer, sands easily, and sets slower than patching plaster, it’s easier to work with. Setting-type joint compounds (also known as hot mud) are also better for patching than drying-type joint compounds, which just aren’t as strong. Note: To ensure a good bond, strip paint from the surfaces you’re patching and sand the adjacent areas lightly before applying compound.

Small cracks in plaster are repaired by stripping surface paint, cleaning loose plaster, and under­cutting the cracks slightly with a knife or a small, sharp-pointed lever-type can opener (also called a "church key”) Undercutting allows the patching material to harden and form a key that won’t fall out. Before patching, wet the exposed plaster well and brush on a PVA (polyvinyl acetate) bon­der such as Plasterweld® or Elmer’s White Glue® to bond the patch to the old plaster.

Over the crack, stretch a length of self-adhering fiberglass mesh. Then use a taping knife to spread the patching material into the crack. Leave the first coat of joint compound a little rough so the second adheres better. After lightly sanding the
first coat, apply the second, feathering it out to blend-in the patch’s edges.

When the patch dries, sand it lightly with fine, 220-grit sandpaper, wipe it clean, allow it to dry thoroughly, and prime the patch with an oil – based primer.

Large cracks often accompany sections of bowed or sagging plaster, which have pulled free from the lath behind. If the plaster is sound— not crumbling—you can reattach it to the lath using type-W drywall screws and plaster washers, which fit under the heads of the screws. A screw gun is good for this operation.

However, before you attach the screws, mark their locations on the plaster, and use a spade bit to countersink a hole ‘/ in. deep for each washer.

Sunk below the surface of the plaster, the screw heads and washers will be easy to cover with patching compound.

Place screws and washers every 8 in. to ‘0 in. on both sides of the crack and anywhere else the plaster seems springy and disconnected from the lath. Once you’ve stabilized the crack in this man­ner, scrape, tape, and fill it, as described earlier.

Small holes the size of a removed electrical out­let are easy to fill if the lath is still in place. Remove any loose plaster, brush out the debris, wet the lath and the surrounding plaster well, brush on a PVA bonder, and trowel in patching material. Leave the first coat a little rough, let it dry well, and apply bonder again before trowel­ing in a second, smooth coat.

Patching I Cracked Plaster

Cracked plaster often means that it has pulled free from its lath. Use screws and plaster washers to reattach it, countersinking them so they’ll be easier to patch.

Patching Holes I in Plaster

If plaster lath has been cut out, replace it before patching the hole. Insert and secure a small section of wire lath with a wire looped around a pencil, as shown. Twirl the pencil to draw the wire lath tight to the back of the plaster, then fill the hole with two coats of patching plaster. Unwind the wire and snip it when the first coat is hard.

If the hole has no lath behind it, you’ll need to add some. Scrape the loose plaster from the edge of the hole. As shown in "Patching Holes in Plaster,” on p. 373, cut a piece of metal lath larger than the hole and loop a short piece of wire through the middle of the lath. Then, holding the ends of the wire, slide the lath into the hole. To pull the lath tight against the back of the hole, insert a pencil into the front of the loop and turn the pencil like an airplane propeller until the wire is taut. The pencil spanning the hole holds the lath in place.

After wetting the lath and surrounding plaster, spread a rough coat of compound into the hole. When the coat has set, unwind the wire, remove the pencil, and push the wire into the wall cavity. The hardened plaster will hold the metal lath in place. Trowel on the finish coat.

Large holes with lath intact should be partially patched with a piece of drywall slightly smaller than the hole. Because a hole with square corners is easier to patch than an irregular one, square up the edges of plaster, using a chisel or a Dremel tool with an abrasive wheel. (Wear goggles.) Be careful not to cut through the lath. Use type-W drywall screws to attach the drywall to the lath behind, stretch self-adhering fiberglass mesh tape around the perimeter of the patch, and apply joint compound or patching plaster as described earlier. For best results, the drywall should be slightly thinner than the existing plaster, so you have some room to build up and feather out the patch.

As an alternative, pegboard is a dandy sub­strate for such patches because you can cut it easily with a jigsaw to fit irregular holes. Hold a sheet of!4-in. pegboard over the plaster, eyeball and trace the shape of the patch through the holes in the pegboard, and screw the pegboard to the lath—textured side out. The patching plaster will ooze through the holes in the pegboard and harden in the same manner that plaster keys into the spaces between lath strips.

Joint compound is a marvelous medium for texturing a drywall patch or matching the texture of existing plaster. All that’s needed is a little ingenuity.

► For a stippled plaster look, place joint compound in a paint tray, thin it with water till it is the consistency of thick whipping cream, and roll it onto the wall or ceiling using a stippled roller. Don’t over-roll the compound, or you’ll flatten the stipples.

► Create an irregular "splatter" texture by thinning the compound to a heavy-cream consistency, sucking it into a turkey baster and squirting it onto the wall.

► For an open-pore, orange-peel look, use a stiff-bristle brush or whisk broom to jab compound that is just starting to dry. Jab lightly and keep the bristles clean.

► To achieve the flat but hand-tooled look of real plaster, apply the compound in short, intersecting arcs. Then knock down the high spots with a rubber-edged Magic Trowel®, as shown.

► If you’re trying to duplicate a slightly grainy but highly finished plaster surface, trowel on the topping coat as smoothly as possible and allow it to dry. Then mist the surface slightly and rub it gently with a rubber-edged grout float.

You can achieve the irregular, hand-tooled look of plaster by covering drywall with joint compound applied in tight, intersecting arcs. Because of its crack-resistance, use 90-minute or 120-minutes setting-type compound. It’s okay if the drywall isn’t completely covered.

I

PLASTERING

1. If casing, baseboards, or floors are already installed, cover them with paper and tape to protect them from plaster splatters.

2. Mix the plaster to the consistency of soft – serve ice cream before ladling it onto a mason’s hawk. For skim-coat plaster, follow the manufacturer’s mixing instructions, which typically recommend adding 12 qt. to 15 qt. of water for each 50-lb. bag of plaster.

3. To prevent cracking, cover blueboard seams with self-adhering mesh tape. Load your trowel from the hawk and…

the gaps in the lath and becomes a mechanical key when it hardens.

3. Trowel on, then roughen the brown coat after it has set slightly.

4. Trowel on a finish, or white coat, which becomes the final, smooth surface.

In the old days, plasterers often mixed animal hair into scratch and brown coats to help them adhere. Thus old plaster that’s being demolished is nasty stuff to breathe. The finish coat was usu­ally a mixture of gauging plaster and lime, for uniformity. Scratch coats and brown coats were left rough and were often scratched with a plas­terer’s comb before they set completely, so the next coat would have grooves to adhere to. Finish coats were quite thin (Иб in.) and very hard.

Lath can be a clue to a house’s age. The earli­est wood lath was split from a single board so that, when the board was pulled apart (side to side), it expanded like an accordion. Although metal lath was available by the late 1800s (it was patented in England a century earlier), split wood lath persisted because it could be fashioned on-site with little more than a hatchet. By 1900, however, most plasterers had switched from lime plaster to gypsum plaster, which dried much more quickly. And about the same time, plasterers began using small paper-coated panels of gypsum instead of wood or metal lath. Called gypsum lath or rock lath, the panels were so easy to install that they dominated the market by the 1930s. But time and techniques march on. As mentioned earlier, after World War II, drywall all but replaced plaster as a residential surface.

I Keying Plaster to Wood

This plaster cross section shows how the scratch coat of plaster oozes through the lath and hardens to form keys, the mechanical connection of plaster to wood.

To finish drywall, seal the panel joints with tape or cornerbead, then cover them with joint com­pound. Typically, three coats of compound are applied in successively wider coats and sanded after each application. The first coat, usually a high-strength taping compound, embeds the tape. The second coat should be a thin layer of topping compound or all-purpose compound that you feather out to hide the joints. With the third coat, you feather out the compound farther, creating a smooth, finished surface. (See "Joint Compounds,” on p. 358, for more about these materials.)

First coat. Fill nail holes or screw dimples in an X pattern: One diagonal knife stroke applies the compound, and the other stroke removes the excess.

If you use paper tape on the joints, apply a swath of taping compound about 4 in. wide down the center of the joint. Press the tape into the 1. Before applying paper tape, cover the seam

center of the joint with a 6-in. taping knife. Then with an generous bed of joint compound apply compound over the tape, bearing down so you remove the excess.

If you use self-sticking mesh tape, stick it directly over the joint and apply the bedding compound over it. In other words, don’t apply a bed of compound first. Mesh tape must be bedded in setting-type compound, as explained earlier in this chapter.

AN ORDERLY

All that raw drywall can seem a bit overwhelm­ing, so here’s a taping and mudding sequence that starts easy, so you can become comfortable with the tools and materials:

► Screw and nail holes

► Bevel-edge joints (the long edges of panels)

► Butt-edge joints

► Outside corners

► Inside corners.

Have a pail of clean water and a sponge handy so you can rinse your taping knives periodically. They glide better if they’re clean. Keep the job site clean, too: If you drop a glob of compound on the floor, scrape it up and discard it so you don’t track it around the house.

a 10-in.-wide taping joint knife and feather out the seams roughly 8 in. to 10 in. wide. After applying the compound, smooth it out with an even wider blade—say, a 14-in. trowel.

As you’ll learn when working with joint com­pound, the lower the angle of the blade and the less pressure, the easier it is to smooth and feather (spread out) the mud. The greater the angle and pressure, the more compound you’ll remove.

This is easier to do than explain. Because butt – end joints are not beveled, they’ll mound slightly at the center of the seam. That’s okay. Use a 10-in. taping knife to build up the compound on both sides of the joint, feather out the edges, and then smooth the center. Consequently, butt-end joints may need to be wider than bevel-edge joints.

You may often need to feather butt-end joints 16 in. to 20 in. wide.

When this second coat is dry, sand with 150-grit to 220-grit paper. A pole sander will extend your reach and enable you to sand longer without tiring, but don’t sand too aggressively or you’ll abrade the paper face or expose the tape. Easy does it.

Third coat. The third coat is the last chance to feather out the edges, so use a premixed, all­purpose, drying-type compound, which is easy to thin out and sand because it has a fine consistency and dries quickly. Although premixed compound will be the right consistency, it’s okay to add a little water to thin it even more.

Because the third coat is only slightly wider (2 in.) than the second coat, you’ll be applying a relatively small amount of compound. Use a 12-in. trowel, with a light touch. Some pros thin this coat enough to apply it with a roller, and then smooth it with a trowel, so there are no trowel marks when they’re done.

Hand-sand the final coat, using fine, 220-grit sandpaper or a very fine sanding block. Shining a strong light on surfaces will highlight the imper­fections you need to sand.

Wrap up. If you intend to texture the surfaces, the third coat doesn’t need to be mirror smooth. Even so, don’t scrimp on the second coat, or else the joints may be visible through the texture

To give yourself the greatest number of deco­rating options in the future, paint the finished drywall surface with a coat of flat, oil-based primer. It will seal the paper face of the drywall and provide an excellent base for any kind of paint or wall covering.

DRYWALL REPAIRS

To keep solutions concise, let’s divide drywall repairs into four groups: nail pops and surface blemishes; fist-size holes through the drywall; larger holes; and discolored, crumbling, or moldy drywall. Any repair patches should be the same thickness as the damaged drywall.

Popped nails and screws are generally a quick fix: Drive another nail or screw 1 h in. away from the popped one to secure the drywall. If it’s a popped screw, remove it and fill the hole. Cover both the old hole and the new screw with at least two coats of joint compound. If it’s a popped nail, don’t try to remove it; drive it slightly deeper to dimple the drywall.

When a piece of drywall tape lifts, pull gently until you reach a section that’s still well stuck. Use a utility knife to cut free the loose tape, cover the exposed seams with self-sticking mesh tape, and apply two or three coats of compound—sanding lightly after each. Drywall repair kits with precut patches are available at most home centers.

To repair drywall cracks, cut back the edges of the crack slightly to remove crumbly gypsum and provide a good depression for a new filling of joint compound. Any time the paper face of dry – wall is damaged, cover the damaged area with self-adhering fiberglass mesh tape. Then apply three coats of joint compound. Because the repair area is small, it doesn’t matter what type of compound you use, though setting-type com­pounds are preferred.

Small holes in drywall are often caused by doorknobs, furniture, or removed electrical out­let boxes. Clean up the edge of the hole so the surface is flat. Then cover the hole with self­adhering fiberglass mesh tape. (Better drywall repair kits have metal-and-fiberglass mesh tape.) Use a light touch when applying the first coat of joint compound, pushing the mud through the tape, but don’t press so hard that you dislodge the mesh.

Mechanical drywall taping tools are commonly referred to as Bazooka® tools, after a popular brand, and they can be rented, usually for 2 weeks at a stretch. The suite of tools includes a taper that applies tape and com­pound simultaneously, as well as finishing tools, various head attachments, and flat boxes for taping seams.

These tools are great for larger jobs, creating uniform, flat surfaces that need little sanding. "You can put tape and mud up almost as fast as you can run," notes one pro. Most rental com­panies supply a video on how to use these tools, but taking a class in addition isn’t a bad idea.

Give the repair three coats of compound, feath­ering out the edges as you go. Take it easy when sanding. Especially after the first coat, the tape frays easily. By the way, there are precut drywall patches for electrical outlet boxes, which save time.

Large holes should be cut back till you reach solid drywall. Because mesh tape and compound will probably sag if the hole is much wider than 4 in., holes larger than that should be filled with a patch of drywall roughly the size of the dam­aged area. These patches need to be backed with something solid, so they’ll stay put.

The easiest backing is a couple of furring strips cut about 8 in. longer than the width of the hole and placed on both sides of the hole. To install each furring strip, slide it into the hole and, while holding it in place with one hand, screw through the drywall into the wood. Screws will pull the furring strips tight to the back of the drywall. Then cut the drywall patch, place it in the cutout area, and screw it to the strapping.

Cover the edges of the drywall patch with self­adhering mesh tape, fill the screw holes, and apply joint compound—three coats in all. Here, a setting-type compound, such as Durabond® 90, is a good bet because it dries quickly and is unlikely to sag. The more skillfully you feather the compound, the less visible the patch will be.

For holes larger than 8 in., cut back to the centers of the nearest studs. Although you should

have no problem screwing a replacement piece to the studs, be sure to back the top and the bottom of the new piece. The best way to install backing is to screw drywall gussets (supports) to the back of the existing drywall. Then position the replace­ment piece in the hole and screw it to the gussets, using drywall screws, of course.

Discolored, crumbling, or moldy drywall is

caused by exterior leaks or excessive interior moisture. Be sure to attend to those causes before repairing the drywall. Excessive moisture is often due to inadequate ventilation, which is especially common in kitchens and baths. Leaks around windows and doors are often caused by inadequate flashing over openings.

If the drywall is discolored but solid, and if you’ve remedied the moisture source, wash the area with soap and water, allow it to dry thor­oughly, and prime it with white pigmented shel­lac or some other stain-resistant primer. The same solution works for minor mold on sound drywall.

However, if there’s widespread mold and the drywall’s crumbling, there’s probably extensive mold growing inside the walls. You’ll need to rip

out the drywall and correct the moisture prob­lems before replacing finish surfaces. In extreme cases, you’ll need to replace the framing. Chapter 14 covers mold abatement at greater length.

Plastering

This section is limited to plaster repairs because applying plaster takes years to master. The tools needed for plaster repair are much the same as those needed for drywall repair: a screw gun or cordless drill; 6-in. and 12-in. taping knives; a mason’s hawk; and a respirator mask, if you’ll be removing or cutting into plaster. There’s a lot of grit, so wear goggles, too. The tools and tech­niques for plaster are similar those needed for stucco, discussed in Chapter 7.

ANATOMY OF A PLASTER JOB

Traditional plastering has several steps:

1. Nail the lath to the framing.

2. Trowel a scratch coat of plaster onto the lath. The wet plaster of this coat oozes through