What is the first step to finishing drywall?

A paste of gypsum powder and water that fills seams around sheets of drywall

If you want to learn more, please visit our website finishing drywall for beginners.

Not to be confused with spackling paste

For plaster of paris, see Plaster-of-Paris

For pipe joint compound, see Pipe dope

Kitchen renovation spackling to cover holes and tape between sheetrock boards Drywall with joint compound applied.

Joint compound (also known as drywall compound, drywall mud, joint cement or mastic) is a white powder of primarily gypsum dust mixed with water to form a paste the consistency of cake frosting, which is spread onto drywall and sanded when dry to create a seamless base for paint on walls and ceilings.[1]

When used for new walls, joint compound effectively eliminates blemishes from the surface of drywall, such as fasteners, damage, or drywall tape. Joint compound is used to finish gypsum panel joints filled with paper or fiber joint tape, corner bead, trim and fasteners, and to skim coat. It is also convenient for patching holes, bumps, tears, and other minor damage to existing walls. In North America, troweling joint mud on gypsum panels is a standard construction technique prior to painting wall and ceiling surfaces.

Joint compound type and formula selection forms part of a drywall system that can be finished anywhere from a level 0 to a level 5, where 0 is not finished in any fashion, and 5 is the most pristine.[2]

A similar compound is used in sprayed-on textural finishing for gypsum panel walls and ceilings that are pre-sealed and coated with a joint compound. Until the last century, several different plasters such as veneer plaster and "plaster of Paris" have been used in similar ways to joint compounds as fillers or for decorative purposes since ancient times, and the actual make up, and working properties of these compounds is much similar.

Comparison with spackling paste

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Joint compound is comparable and contrastable with spackling paste.[3] The similarities and differences are discussed at Spackling paste § Comparison with joint compound.

Supply forms

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Ready-mix joint compound is a pre-made joint compound of drying type only designed for fast application and easy maintenance. The compound is a complex combination often including water, limestone, expanded perlite, ethylene-vinyl acetate polymer, attapulgite, and other ingredients.

Powdered

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Powdered joint compound is mixed with water immediately before use. Powdered drying or setting-type compounds are available in similar combinations and consistency as the ready-mix. This type of joint compound is commonly referred to as "hot mud" due to the exothermic reaction that takes place when the powder is mixed with water.[4]

Types

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Drying

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Drying-type comes in ready-mix or powdered form. Drying-type joint compounds are vinyl based and harden by evaporation. Drying-type joint compound is usually more forgiving than setting type joint compound and can be used for as long a period as needed while not dry or frozen. Drying-type compound and all materials should be used at temperatures above 55 °F (13 °C).[5]

Setting

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Setting type comes only in powdered form and are mixed with water immediately before use. Setting-type joint compounds are plaster of paris based and harden by chemical processes and evaporation rather than solely evaporation, giving it an advantage in filling holes and gaps that would take many days to dry out with shrinkage cracks if using the drying type compound. Another advantage to setting-type compounds is that after curing, they do not soften when wet. Thus, they are better for moist environments, such as bathrooms.

Setting type compounds are available in setting times ranging from 5 to 300 minutes and finish characteristics from tough and well bonded to soft and easy to sand. After setting any leftover cannot be resaturated and reused. All tools in contact with setting type joint compound must be very clean, or the compound may be set up prematurely. Setting type compounds can be used at temperatures down to 45 °F (7 °C).[6]

Special formulas

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Lightweight

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Lightweight joint compound formulas weigh 25-30% less than conventional joint compounds due to ingredient changes and allows for easier sanding.[7][8]

Reduced dust

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Reduced dust formulas cause the dust particles to clump together, falling out of the air sooner than regular formulas, thus reducing airborne dust.[9]

Moisture and Mold

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Moisture- and mold-resistant formulas are available.

Tapeless

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Want more information on skimming stainless steel? Feel free to contact us.

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Tapeless drywall joint compounds can be applied directly to the joints without either paper or fibreglass mesh tape. Eliminating the taping steps can save about 30% of labour time for finishing drywall joints.

Tapeless setting joint compounds are either reinforced by chemical glues or fibers.

Tapeless drying-type joint compounds can be mixed with a fiber additive which can be mixed into conventional drying-type compounds to create tapeless joint compounds.[10]

Fire rated penetrations

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Firewalls, walls built to slow the spread of fire, with penetrations fill the gap around the penetration with fire safing material (fire wool) and the surface around the penetration is sealed with an additional 1⁄2" - 1" thick fire-rated joint compound that dries red in color.[11][12] Drywall systems without penetrations can obtain ASTM C475 fire ratings using conventional joint compound at the seams.[13]

Usage

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Mudding is usually done in three layers, with the sheets of drywall to be mudded usually having tapered edges to provide space for the thickness of the tape and mud at the seams. Correct type of mud selection is essential for the first and last layer, though an all-purpose compound may be adequate for all coats. Some drywall professionals use setting type mud for the first coat and a drying type for the thinner finish coat.

Three main joint compound layers/coats:

1. Bedding coat or taping coat where the mud is applied to seams and corners and paper joint tape is pressed into the mud (if using a fiberglass mesh tape the self-adhering tape is applied to the joints first, and the mud pressed through the tape). The mud used here needs to adhere well and be strong and is called a taping compound; typically met by all-purpose compound.
2. Filler coat where the tape is covered and roughly smoothed
3. Finish coat or topping coat which is very smooth. A topping compound is soft, smooth and easy to level and sand.[14] Some finish coat sanding is usually required to get a smooth surface.

Workers applying joint compound to drywall.

Joint compound is the primary material used in the drywall industry applied by a tradesperson called a "drywall mechanic," "taper," or "drywall taper."[15] The flexibility and plastic qualities of joint compound make it a versatile material both as a sealer or finishing coat for wall surfaces and in decorative applications ranging from machine sprayed texturing to hand-trowelled or even hand-crafted sculptural finishes.

Applying and sanding joint compound is messy work, and finished surfaces, such as floors and air handling ducts, must be covered.

Pockmarks

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Pockmarks are defects caused by air bubbles which form after the joint compound is applied, due to the inability of moisture to be absorbed into the surface under certain surface conditions:

• already painted
• layer of grease
• layer of cigarette smoke
• drying-type compound applied over a dense, setting-type compound.

The moisture exits through the finished surface, making bubbles that dry as pockmarks. The bubbles can be reworked while the compound is drying to attain a smooth surface. Although additives exist to reduce pockmarks, additive use is discouraged by drywall manufacturers as they reduce bonding, so they should not be used on the bed coat.[16] Pockmarks may be created intentionally to mimic certain rough wallpaper textures.

Health concerns

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Construction workers mixing or sanding drywall joint compound are often exposed to high concentrations of dusts containing talc, calcite, mica, gypsum, and in some cases, respirable silica;[17] which have been associated with varying degrees of immediate eye, nose, throat, and respiratory tract irritation. Prolonged exposure over time to breathing the dust from drywall joint compounds may cause persistent throat and airway irritation, coughing, phlegm production, and breathing difficulties similar to asthma. When silica is present in the drywall joint compound, workers may also face an increased risk of silicosis and lung cancer.[18]

Prior to 1977, joint compounds often contained asbestos fibers to enhance cohesiveness.[19][20] Exposure to friable asbestos increases the risks of various severe health conditions, including cancer. In 1977 the Consumer Products Safety Commission banned wall patching (joint) compounds containing asbestos.[21]

For the reasons above and possibly others, constant use of a respirator is recommended by almost all drywall compound manufacturers and is required by some labor authorities.[18]

See also

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• Spackling paste – Any of a class of pastes that fill small holes in walls and ceilings
• Plaster-of-paris
• Plasterwork – Construction or ornamentation done in plaster or a similar material
• Calcium silicate – Chemical compound naturally occurring as the mineral larnite

References

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Project details

Skill

1

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5

Easy

The sheets are heavy and a bit unwieldy, especially when covering the ceiling

Cost

$8 to $10 per half-inch x 4×8-foot sheet

Estimated Time

6 to 8 hours

While hanging drywall takes a little muscle, getting the drywall ready for paint or wallpaper requires finesse. The goal here is simple: Make the joints between drywall panels disappear so that walls and ceilings are perfectly smooth.

Is It Hard to Finish Drywall?

The process isn’t com­plicated. It takes just a few tools—a small and a large drywall knife and a swivel-head pole sander—to finish drywall. Here, Paul Landry, of P.L. Drywall in Waltham, Massachusetts, shows us how to mud and tape drywall, using premixed joint compound (a.k.a. “drywall mud”) and drywall tape.

How to Finish Drywall Step-By-Step

1. Drywall Finishing Steps Overview

Gregory Nemec

The tricky part is learning how to properly bed the tape and feather out the compound to an imperceptible edge. “First time out, you’ll probably get more ‘mud’ on the floor and on your clothes than you do on the wall,” says Landry, who finished the walls at This Old House‘s recent TV project in Man­chester, Massachusetts.

Sanding is the other key skill. Joint compound is soft, so the challenge is to avoid removing so much that you risk fraying or tearing the paper tape. “Be patient,” Landry advises. “Even beginners can do a fine job if they take their time.”

2. Stir compound and prep surfaces

Allen Penn

• Cut band on top of the bucket with a utility knife or tin snips and pry off lid.
• If there’s water on top of the compound, chuck a mixing paddle into a ½-inch drill. Mix at slow speed until water is blended and compound is smooth. If there’s no water, the compound is ready to use.
• Look for any screwheads poking above the drywall surface and drive them until slightly recessed.
• Tear away any loose or torn paper from drywall (especially at corners and cut edges) to prevent bits from ending up in the compound.

3. Cover joints and screwheads

Allen Penn

• Using 5-inch knife, fill mud box halfway with compound.
• Load the edge of the knife blade with about 2 inches of compound.
• Starting in one corner of the room, force the compound into the joints between sheets. When they’re completely filled, hold the knife at a 25-degree angle to the surface and smooth out the compound in a single pass.
• Scrape excess compound off knife and into mud box.
• Fill screw holes with a swipe of a compound-loaded knife.
• When all the joints and screwheads on a wall or ceiling are filled, go to Step 4.

4. Apply paper tape

Allen Penn

• Unroll 3 feet of tape from dispenser, but don’t tear it off.
• Center tape over seam and, using fingers, gently press into the fresh compound.
• Unroll and bed tape into rest of joint.
• At the end of the joint, place the knife edge perpendicular to the tape face and tear.

5. Smooth tape

Allen Penn

• Starting halfway along the joint, hold the 5-inch knife against the tape at a 25-degree angle to the wall.
• Pull knife to one end of the joint in a single stroke, smoothing the tape and pressing it firmly into the compound.
• Scrape excess compound from the blade into mud box.
• Return to the starting point and repeat in the other direction. (This technique prevents tape from pulling off wall.)
• Repeat Steps 3, 4, and 5 on remaining walls or ceiling.

6. Tape Inside Corners

Allen Penn

• Using a 5-inch knife, fill the seam and cover 2 inches on either side of the corner with compound.
• Cut a piece of tape the full length of the corner; crease it in half lengthwise. With knife, gently push into corner.
• Starting in the middle, draw the knife along the drywall, smoothing the tape on one side of the crease. Skew blade 45 degrees to squeeze out excess mud.
• Run knife in the same way on the opposite side of the crease. Finish by smoothing back to the starting point.

7. Cover outside corners

Allen Penn

• Make sure the metal corner bead on outside corners is nailed or clinched every 10 inches. Straighten bends, if necessary, with corner clincher (see tools and materials above)
• Using the 5-inch knife, smear one side of bead with compound. Repeat on the other side.
• Holding the blade against drywall and bead at the same time, run the knife down the corner, smoothing the compound in a single stroke. Repeat on the other side.
• Let compound dry overnight.

8. Sand the first coat

Allen Penn

Pro2Pro Tip: Don’t try to sand out indentations or craters; these will be filled by subsequent coats of compound.

• Check that compound is uniformly white, which indicates that it is dry. (Wet areas appear darker.)
• Sand inside corners with corner sanding block.
• Sand all other surfaces using a pole sander with medium-grit abrasive. Apply gentle, even pressure. Sand only enough to smooth rough areas; don’t sand down into paper tape.
• Feel for rough areas and sand as needed.

9. Apply second and third coats

Allen Penn

• With the 10-inch knife, scoop up 2 inches of compound. Then scrape off 2 inches worth at each end of the blade.
• Apply compound to all joints and screwheads, then smooth it in a separate pass. Allow to dry overnight.
• The next day, sand with fine-grit drywall sandpaper.
• For third coat, load entire edge of 10-inch knife with compound and apply to joints and screwheads as before. Smooth to an imperceptible, feathered edge.
• Let dry overnight, then sand as before. Wipe all surfaces with a damp cloth to ready them for priming.

Tools

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