Tuesday, March 8, 2011

How-To: Drywall Finishing (Part IV)

A six-inch knife is recommended. Spread joint compound on and smooth it down, watching for scratch marks and air bubbles. Don't build. any more than you have to and keep corners square and neat. Make sure the joint compound is filled all

the way to the bottom, if the area is getting a window seal. The inside of the window needs to look good, since it’s always well lit. Almost all builders check inside the windows. If you are doing a second coat, and they need a third coat, it would be worth your while to skim it again. They dry fast and can be coated again easily.

Skim the sides of doorways with a twelve-inch knife in the same way as you did the outside of the windows. The inside of the doorways and ends of walls have a lot of joint compound in the narrow center, and it normally needs to be filled quite a bit on the second coat. The insides of doors, like the insides of windows, catch light and usually need a third coat. Closet doorways aren’t as important as the doorways between the kitchen and dining room, of course. While coating metal and butts that go to the floor, be sure to carry the joint compound to within an inch from the floor. Avoid leaving globs of joint compound at the bottom. This area needs to be kept neat, or it can interfere with the floor molding.

Three different situations occur with flat joints:

Situation 1. Your first coat was done with an eight-inch knife, and you don’t need a wide joint. In this situation, use a ten-inch knife for the second coat.

Situation 2. Your first coat was done with a ten-inch knife. In this situation, use a twelve-inch knife for easy covering.

Situation 3. Your first coat was done with a twelve-inch knife, and you need a wide joint. In this situation, overlap each side two inches.

No matter how the joint is coated, when you’re skimming, it needs to be pulled off straight down the middle so your knife straddles the joint recess. Then pull the sides off with one stroke down one side and back on the other. By pulling joint compound off the center, you will be able to see all the high and low spots. If the area needs building on one side or the other, build accordingly. If the area will be getting only two coats, you will need to be careful and neat. If the area will be getting three coats, you can build it correctly now. (See Figure 6-31.)

Two different situations occur when applying the second coat to both sides
of angles:

FIGURE 6-31 Second coating flat joints

After putting the joint compound on the joint, pull knife straight down the middle, going in one direction. Feather edge on top side; then, coming back , feather the other side. Turn knife over and smooth it down if needed.

Situation 1. The first coat was done with joint compound. In this situation make sure the center is dry. Otherwise, the joint compound will roll up in the center

Situation 2. The first coat was done with quick set, so you don't have any drying problem. In this situation, the second coat will be a tight skim done with a five or six-inch knife. While skimming the joint compound off hold your knife out with its side edge running along the center and braced against the other side. When you did your first coat, you skimmed off the same side first. On this second coat, reverse the procedure, skimming off the second side first. This way, if you have a crack to fill, you will be sure to fill both sides. If you used a soft joint compound on the first coat you will have to be careful when holding your knife straight out. When you use adjacent wall as support, you can cut a groove into the soft joint compound. In this case, you might have to make yourself a knife with straight sides simply by taking an old knife and cutting its sides down straight.

The second side is done exactly the same way as the first side. Hold the knife out and let the side edge ride against the other side for support. Be neat, as this method has only one coat. You will need to spend some time on it to get it exact. Any flaws can be sanded out. If the angle from the first coat isn’t dry yet, don’t bother coating the second side. It will only make a mess.

Use the same procedure as you did for the second coat. Nails around doors don’t have to be coated this time unless they are fairly deep and you think they might show after the framing is in. Avoid having to come back just to coat a nail. You may have places where the rough edges have caught the knife and caused ripples. These areas need to be coated crossways. Unless the hangers have dimpled the nails too deep, this should be your last coat, so be neat and overlap any edges.

If the first coat was done vertically, the second should be done horizontally. This way, you will be sure to fill any ridges and imperfections. Skim off tight across the middle first, as this always needs to be filled.

Apply the second coat to the fur down with a twelve-inch knife in the same way you did the first coat. Overlap by a couple of inches and pull the joint compound off loose so it can build where it needs to. Refer to Figure 6-24 for review.

The areas around pipes and bathtubs need to be skimmed tight.


Any patches where the tape had to be overlapped should be coated the opposite way from the first coat. All bad places need to be coated both ways.

I If the walls will be painted with enamel, you will have to be very neat with the third coat. You will need a tight skim with no sanding. If you sand a joint it will be smoother than the paper covering the drywall, and the joint will show up. Therefore if you plan to use enamel paint, sand very well now so the joints can be skimmed tight and smooth without sanding.

Sand butt joints and metal the same way you sanded them in preparation for the second coat. The wall should be smooth all the way to the bottom. Cut away the globs, or the trim won’t be neat.

Angles won’t need another coat unless you have problems. If you have coated one side at a time, you can now skim both sides if they need it.

Nails won’t need another coat unless they were very deep. You can tell if they need another coat by looking at a wall that has a window at one end of it This wall will show every flaw.

Any joint that has flex bead used on it must be sanded very carefully. Take care not to sand the paper edge on the joint compound.

Receptacle boxes and flats must be sanded lightly. Joint compound should be cleaned out of receptacle boxes.


The joint compound for the third coat needs to be fairly thin because you will be skimming everything off tight. The goal is to fill any shallow joints, scratches, or nicks left from other coats. Doing this will cut your final sanding time by about 70%.

If you have an untrained helper, you can utilize this person’s time in the following way. Have your helper roll the joint compound on the joints with a paint roller. Then, you follow and skim it off tight. Do not let the person rolling on the joint compound get too far ahead of the person skimming it off, because the edges dry quickly. The purpose of this technique is to produce a smooth job and to eliminate edges. If you do it right, you won’t have to use sandpaper at all. You should have two buckets, one to roll the joint compound from and the other to empty your pan into. Before reusing the joint compound, you will have to mix it up again to eliminate globs and make it easier to skim off smoothly. This method enables your untrained help to be more productive.

A twelve-inch knife is recommended, since almost all butt joints need to be coated crossways. This is to eliminate the ripples in the joint compound caused by an unsteady knife. All receptacle boxes, butt joints, flex bead joints, and bastard angles need to be coated crossways.

The butts are always the first thing to coat, since they require the most drying time. If a butt joint still needs to be built a little, it might dry in time for you to skim it crossways again before you leave. Butts along the bottom of the wall have a common mistake: globs of joint compound on the bottom next to the floor. Eventually, you will have to clean this up, and it’s better to do it now. Scrape off this joint compound and coat crossways if needed. The trim must fit flush against the wall.

In the kitchen, a receptacle box is often close to the door, which is wrapped with metal corner bead. This is a problem area. See Figure 6-32 for tips on how to coat this. Use a twelve-inch knife and coat it sideways.

Outside corners where flex bead was used will need to be coated sideways for the third coat.

Spread joint compound to overlap previous joint compound slightly, and skim it off tight. Always pull the knife along the recess to make sure it is filled in. Then skim off each side with the same stroke of the knife. Skim one side while pulling the knife one way, and then turn your knife around and pull off the other side on the way back. Save strokes where you can.

Switch box next to the metal corner bead-wrapped doorways usually are a problem area because the flat joint dead ends at the doorway, and the metal is filled vertically So this time coat is cross ways.

The angles should be finished, unless you have a problem angle with a wide crack that needs to be filled. If anything, coat problem bastard angles crossways with a twelve-inch knife. If you have coated one side at a time, you should have both sides coated now. If at you have used quick set, you can follow the directions from the second coat for angles. Just hold the knife out from the wall so the angles will be square and the edge of the knife wont slide back into the recess. Hold the knife out straight from wall and skim.

If a third coat is necessary for the receptacle boxes, coat them in the direction most needed.

Many people think that anyone can sand, but this is not true. Only a trained person should finish sand because this stage needs to be done right. This is your final product. See the next post or the chart in Figure 6-33 for the type of sandpaper you should use for each type of final coating. As you sand, keep an eye out for ridges, knife marks, and scratches. Also watch for problem spots such as the bottoms of butt joints, doorways, and end walls where the joint compound comes all the way down to the floor.

When sanding butt joints, be careful not to sand into the tape. If the butt joint is coated right, the tape will be close to the surface. If you do sand into the tape, coat it over with joint compound again so it won’t stick up and show when painted. Watch for ridges and scratches. Always check the bottoms next to the floor. Scrape off any globs of joint compound and coat crossways to fill any deep ripples.

When sanding metal, the edges of metal that are showing should be free of joint compound. When the metal is clean and shiny, it will look good, saving you a lot of trouble later.

Inside windows need to look neat. You should scrape off any joint compound against the metal window. As you do this, take care not to scratch the metal or the window.

When sending bastard joints and 45° joints, be careful not to sand into the paper edge of the metal edge tape.

Flats are usually the easiest to sand. Watch for any knife marks and ridges where a piece of joint compound on the wall has caught the knife and caused a ridge.

When sanding corners, do not sand into the center. If you push the sander into the center, the side of the paper on the sander will cut into the adjacent corner. If something is in the center or small pieces of joint compound are left on it, the best thing to do is to fold up a piece of sandpaper and run it down the center. A second option is to keep a corner on your sander worn (if you are using a hand sander) and use only that corner-not the side. Don’t try this with a pole sander
because you don’t have good control over it. A third option is to just carry a knife and run it down the center to knock off any pieces of joint compound.

To sand nails, simply run the sander around the edges.

Before sanding receptacle boxes, clean joint compound out of the inside; it will fall out with just a little help. Sand the area smooth, being careful not to sand into any tape, which should be close to the surface. It’s a good idea to take a utility knife and cut out the boxes that were taped. Sometimes, an electrician might pull the tape up while trimming the box. You don’t want to have to come back and fix it.

In tub and shower units, the edges next to the joint compound should be cleaned off. Scraping with a knife or a sander will scratch into the fiberglass. The best way to clean the fiberglass is to wet it, let it sit a few minutes, and then lift it off with a knife.

Plaster is easy to clean if you wet down the area that needs to be cleaned. After three or four minutes, the plaster softens and is easy to remove.


Before you sand, you need to know how the walls will be finished. In preparing this job for the painter (or for yourself, if you will be painting it), you will need answers to the following questions:

  1. What kind of paint will be used?

  2. What kind of texture, if any, will it have?

  3. How will the job be done-with spray or with a roller?

Some painters need to see sand marks into the paper or they aren’t happy. This is why you need to talk to the painter before you sand, if possible. Ask the three questions and discuss the kind of job the painter prefers. The painter can give you a lot of trouble, so it is in your own best interests to get along. If the painter isn’t sold on your job, you will probably have to come back and fix it.

There are two painting methods for smooth walls: spray painting and roller painting. To prepare for spray painting, do not sand into the paper-stay on the joint compound. Any paper fuzz will catch the paint and hold it away from the wall. The result would be that at different angles, dark places would be visible underneath.

If you fuzz up the paper by mistake, it can be fixed only by sponging the walls down with water, which can be time consuming. Sometimes, you will be asked to sponge the joints rather than sand them.

To prepare for roller painting, you won’t have to worry about fuzz because the roller will press it down. Roller painting hides much more than spray. It can hide even better if you put a little joint compound into the paint and mix it up about half and half or whatever thickness you want. This is called a roller texture.

Smooth Walls, Spray Method, Enamel Paint
This is the most difficult method because this procedure shows everything. Walls done this way need three neat coats. Any imperfections will show, so never sand.

If joints are sanded, they will be smoother than the paper surface on the drywall. This difference will show. Preparation for this method starts after the second coat. Sand very well, skim the third coat on tight, and don’t sand it again. Some finishers skim the entire wall, depending on what the builder wants.

Smooth Walls, Spray Method, Semi Gloss Paint
All smooth walls need three coats. For this method, sand very carefully, taking care not to sand into the paper. It’s important to avoid getting fuzz on the surface. For any spray paint and smooth walls, use 100 grit sandpaper; 80 grit will leave scratches that may show.

Smooth Walls, Roller Method, Enamel Paint
This situation requires three coats and is best without sanding. The roller will help, but it will still be hard to hide the differences in the surface between the joint compound and the paper.

Smooth Walls, Roller Method, Semi Gloss and Flat Paint
Use 100 grit sandpaper. Sand well and don’t worry about fuzz. This surface needs three coats or two neat coats.

Nap Texture, Roller Method, Enamel Paint
This situation requires three coats or two neat ones. Sand with 80 grit or 100 grit sandpaper because this texture is very light.

Nap Texture, Roller Method, Semi Gloss and Flat Paint
For this situation, use two neat coats. Sand with 80 grit or 100 grit sandpaper.

Light Spray Texture, Spray Method, Enamel Paint
This situation requires two very neat coats. Sand lightly with 80 grit or 100 grit sandpaper. This texture will hide small imperfections, but it will show bad joints.

Light Spray Texture, Spray Method, Semi Gloss or Flat Paint
This situation requires two neat coats. Sand lightly with 80 grit or 100 grit

Medium to Heavy Spray Texture, Spray Method, Any Paint
For any kind of paint, use two coats and no sanding. This texture will hide most bad joints, shallow metal, scratches, and so on.

No comments: