Jul
31
2008
1

How to Mud and Tape Drywall

If you’re patient, you can make a professional quality drywall repair.

Taping and Finishing Techniques:

You only need to learn two very simple techniques in order to learn how to mud and tape drywall. For either technique the knife blade is held to the drywall at an angle, and the knife is moved in the direction that the handle is leaning as though you were trying to force the mud into the drywall (which you actually are). The steeper the angle, and the harder you press, the thinner the coat of drywall will be. Leaving the desired amount takes a little bit of practice, but it’s pretty easy to learn. I recommend that you do practice (on a scrap of plywood or drywall) before you start the actual repair.

Step One – Taping

Bedded drywall butt joint

A flat joint that has been taped with mesh tape and the initial skim coat of joint compound. Notice that the skim coat is so thin that you can clearly see the tape through it.

Step Two – Bedding

2) Bedding – The point of a bed coat is to actually leave an even layer of mud on the entire area, and not just in the low areas. Do it just like you would a skim coat, but instead of removing most of the mud use a shallower knife angle and lighter pressure to leave a reasonably smooth, opaque layer.

Note that you can do a thin (skim) coat that is smooth, but a thick (bed) coat will never be really smooth, so don’t worry about “craters” in your bed coat, and don’t worry much about them in the skim coat either.

Bedded drywall butt joint

Bedded flat joint. The bed coat has to be thick enough to embed the tape and fully cover it. That is why the bed coat is always a little bit rough. You can’t spread mud thick and smooth at the same time.

Bedded drywall butt joint

Closup of the bedded joint. This amount of roughness really is fine during the bedding stage so don’t worry too much, all of those low sposts will fill in during the final skim coat. It is far worse to wipe off too much mud in an attempt to make it smooth. However, you don’t want big protruding humps of mud, because those would have to be sanded down – lot’s of work, and mess.

Step Three – Skimming

1) Skimming – To do a skim coat, first with a clean knife, load your knife with a moderate amount of joint compound and apply it to the drywall in a layer that is thick enough to be opaque. That is, you shouldn’t be able to see any texture of the drywall, and the mud will be 1/16″ to 1/8″ thick. Then use the knife to remove almost all of the mud. This will leave a smooth layer of mud that is so thin that you can see the drywall through it, but it will fill in any low places and bring them up flush with the surface.

Bedded drywall butt joint

Profesional drywall finisher applying mud to a flat with a paint roller in preparation for the final skim using a 12″ knife. For smaller jobs you will usually just apply the mud using the same knife that you are wiping down with. For your information – premixed joint compound will wash completely out of your clothes, but setting types like durabond might not.

Bedded drywall butt joint

Here, he’s wiping it off. Note that he is using a shallow angle and considerable pressure. This is the last application of joint compound prior to sanding. This coat is just as thin as the first skim coat, and smooths out most of the roughness of the bed coat. It’s relatively easy to make a very thin coat like this smooth. However, a do it yourselfer will probably have to do more than one “final” skim coat to achieve really good results. By the way, he is working from left to right in this picture.

The Process:

Allow each coat to completely dry, until it no longer has any give at all when you push on the mud lightly with your finger tips.
1) Fill up all cracks and voids with mud and Skim the excess off of the surface.
Allow to dry.
2) Lightly sand to remove any high spots or crumbs.
Light sanding is almost like “wiping” you really shouldn’t have to work very long or hard at it. Be careful not to sand the paper and make it fuzzy, but if you do it won’t ruin anything at this point.
3) Apply self stick mesh tape,
Apply tape over all of the cracks or voids that don’t have continuous drywall under them. Rub it down so that it lays nice and flat everywhere. Try not to overlap the tape, and certainly don’t allow more than 2 pieces of tape to overlap at any one place.
4) Apply a Skim coat of joint compound over the entire repair.
Use either a 4″ or 6″ knife. Allow to dry.

Bedded drywall butt joint

Flat taped area around a fiberglass tub. Areas like this get a very thick layer of mud to fill in large gaps before they are taped. However once the hole is filled with joint compound it is then taped and skim coated for the initial finishing coat. This is identical to how you do a repair. Lightly sand again as in step 2

5) Apply a Bed Coat centered over the tape

Use either an 8″ or 10″ knife. If you have tape joints that cross each other or otherwise form an angle with one another, such as the corners of a square patch, then you will notice that you can produce a nice reasonably smooth bed coat in one direction, but when you bed the joint that crosses the first one, then the first bed joint gets kind of messed up. Don’t worry too much about it at this time; just do the best you can. Try to finish each joint with a single smooth stroke of your knife. Again, don’t sweat the details too much at this point. Allow to dry. Lightly sand again as in step 2

6) Apply a Skim coat of joint compound over the entire repair

Use a 12″ knife. You want to use that big knife to feather the repair out in all directions starting from the high point that you made with the bed coat in step 7. That is when you strike off (remove) most of the mud one end of your knife will be riding on the slightly thicker bed coat right over the tape joint, and the other end will be on the drywall. Don’t use too much pressure so that the 12″ knife will bridge the gap and leave a layer of mud that is just thick enough to fill in the low place between these two points. Allow to dry. Lightly sand again as in step 2

7)Take a good look at your work
If the patch was just a single straight tape joint, then it probably looks pretty good at this point. If you see low spots and/or craters, then you probably need to do another thin skim coat using a 6″ or 8″ knife.

It may take several cycles of skim coats and sanding to achieve the desired result, but you can do it, even with no previous experience.

The final step is to sand thoroughly, until the repair is as smooth and flat as possible.

You should be aware that a drywall repair is always a multi part process, and is usually going to stretch over more than one day, and you will need a few specialized tools.
Drywall tools

Tools:

1) Mud Pan or Hawk – This is what you use to hold the drywall joint compound while you work with it, and to clean your knife while you are working. Instead of buying a pan or hawk you can also use a scrap of wood or drywall that has at least one good straight edge to wipe your knife on.

2) Drywall knives – You might think of these as “putty knives” If the repair you are doing is very small (smaller than a quarter) you can get by with one 4″ knife, but if it is any bigger then you will need 3 knives:

  • a) Either a 3″ or 4″ or 6″ knife for taping
  • b) Either a 8″ or 10″ knife for bedding
  • c) A 12″ knife for the skim coat
  • 3) Sandpaper or a sanding sponge

    4) You might also need a utility knife, and/or a drywall saw.

    Professional quality tools will help you to more easily get high quality results, and I would always recommend that any time you make a tool purchase that you buy the best quality that you can afford. Good tools are an investment that will last a lifetime if properly cared for. However, if you are on the cheap, you can actually get very good results with plastic drywall knives.

    Materials:

    1) Drywall tape – Either paper tape, or mesh tape will work, but mesh tape is easier to work with.

    2) Drywall Joint compound – “Premixed” lightweight joint compound will work just fine, but I recommend that you use “setting type” joint compound which comes as a powder that you mix with water, because it dries faster, doesn’t shrink, and it will last almost indefinitely on the shelf if you keep it dry. Be SURE that you get the “easy sand” type if you use setting type joint compound, because the kind that does not say “easy sand” should be labeled “so danged hard that you can’t sand it at all”. Setting type joint compound is also rated by how long it takes to harden. There are 20, 45, and 90 minute varieties. I do not recommend the 20 minute variety for the do it yourselfer, because it hardens too fast, and if you mix more than a very small amount you can’t use it up before it becomes unusable.

    3) If you are repairing an actual hole that is no larger than 6″ square you can use a self adhesive drywall patch, if the repair is larger, you will probably need to put in a piece of drywall using drywall repair clips. If you are only repairing a crack or dent, then you don’t have to worry about it. However, joint compound is only intended to be used in thin layers (usually a total of about ΒΌ” for the entire repair), so don’t try to reconstruct a gapping hole with only join compound.

    Drywall and Mudding tips:

    1) Keep your knife clean throughout the process.

    2) Always do a good job of cleaning and drying your tools between steps.

    3) Mix a drop or two of dish washing liquid with the mud. It will allow you to get smoother results.

    4) If you use pre mixed joint compound, to avoid contaminating your material with bits of dried mud, use a knife to scrape all of the mud that you can off of the sides of the bucket, smooth out the top of the leftover mud, then cover the surface with saran wrap before tightly replacing the lid. A tiny bit of dried mud mixed with what you are trying to use will make it almost impossible to get good results.

    5) Usually “pre mixed” joint compound is too thick and you will need to add a little bit of water to thin it.

    6) Always allow the previous work to dry thoroughly before you continue.

    7) Sanding drywall creates a lot of fine dust, and you should take appropriate measures to protect yourself from breathing it.

    8) An expert drywall finisher will accomplish good results in fewer steps, and probably won’t need to sand much, if at all, between coats, but this isn’t intended for the expert.

    9) If the effort it takes to learn how to mud and tape drywall seems like a lot of trouble, then keep this in mind; a pro will probably charge you at least $200-$300 for a repair like this, because of the multiple steps and return trips.

    Bedded drywall butt joint

    Bedded butt joint showing a little (acceptable) roughness.

    Bedded drywall butt joint

    Profesional drywall finisher skim coating a flat using a 12″ knife.

    Bedded drywall butt joint

    An inside corner that has been taped with mesh tape and the initial skim coat of joint compound.

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