Everything You Need to Know About Mudding and Joint Compound
If you've been reading tips about painting or home remodeling you've probably come across the term “drywall mud” or “joint compound." You may have thought to yourself, “What is drywall mud and why would I use it in my home?" Quite simply, these terms are for the product that's used at the seams of your drywall (what your walls are probably made of if your house was built after 1940) to create a seamless smooth finish. Without joint compound, you'd have small lines and indentations everywhere the drywall meets. Since drywall usually comes in 12x4 foot sheets, that means there'd be a lot of lines throughout your ceilings and walls. These products are also what you use to patch and repair walls. Here's everything you need to know about mudding and joint compound.
The hardware store or lumberyard you go to is going to have a fairly large selection of joint compound products. There'll be different brands, but these are the basic types.
- Bags - Bags are a powder that you need to mix with water to make a useable product. If you try this method you'll see why it is called “mud." These usually come in 20, 45, and 90-minute setting times. The 20 is for pros who want it to dry very quickly, so they can do multiple coats in one day. We wouldn't recommend this for a beginner. It actually sets a lot faster than 20 minutes – more like 5 to 10. The 45 and 90 give you more time to work with the product, but for someone new to this, the powder bags can get messy and are a bit harder to work with. The good thing about the unmixed bags is that the powder will last a long time if stored somewhere dry, so you don’t have to worry about it drying up and setting. There's also less shrinkage when it dries than the premixed kind.
- Buckets - These products are premixed, so all you have to do is open the bucket and you're ready to get to work. They come in 4.5 gallon, 1 gallon, and 3.5 quart sizes. Unless you're doing a really big job, you probably will only need the 1 gallon size or smaller. The all-purpose type is going to work for any kind of patching, so we recommend using that. There are many advantages to the premixed mud. It's definitely easier for the beginner because it's a good consistency and less messy than mixing up the powder. It's also easier to sand once it's dry.
A note on safety: According to the Electronic Library of Construction Occupational Safety and Health, "A study by the National Institute for Occupational Safety and Health (NIOSH) has shown that "nuisance dust" from joint-compound mud used in drywall work can contain toxic materials. And, there can be dangerously high amounts of dust from sanding and other drywall work. Wear a high-quality dust mask while sanding or working in dusty environments.
You're going to need to buy a few specialized tools to apply drywall mud.
- Trowel or Mudding Pan - This holds the mud while you're working with it. You don’t want to have to constantly go back to your bucket, so this gives you a small supply to work with for a while.
- Taping Knives and Joint Putty Knives - These are what you're going to use to apply the mud to the wall. They come in various sizes – from 1 inch up to 14 inches. For a beginner, we recommend using a 6-inch size. This is a standard size that allows you to apply enough mud to the wall (but not too big), so that you're applying way, too much. There are corner trowels as well, but unless you are doing a lot of corners you probably won’t need this.
There are few other items you will need for this project.
- Tape - There are a few kinds of mudding tape, but we recommend you get the fiberglass mesh self-adhesive option. This sticks to the wall on it’s own, so it's very easy to work with.
- Utility Knife - You'll use this to cut the tape. Be careful – they're really sharp!
- Sandpaper - There are many different varieties of sandpaper, but we recommend using a foam sanding block. They're comfortable to hold and very easy to use. Regular sheets of sandpaper will work just fine as well, but the sanding blocks are more convenient. Get multiple grades – from coarse to fine.
- Dust Mask - Dust from sanding mud is very fine and you'll find that it gets everywhere. You definitely need to wear a mask! You don’t need a respirator, just the two rubber band strap mask will be fine. We don’t recommend that you buy the cheapest ones – there's a definite difference in quality from the lowest to just the mid grade.
- Shop Vac - You don’t have to have one of these to do a small wall repair, but they do make cleanup a lot easier.
HOW TO APPLY -
Imagine you have a hole in your wall about the size of a tennis ball. How do you patch it?
- Cut the mesh tape long enough to cover the hole, plus about 3 inches over it on both sides. You should have a piece of tape about 8 inches long. Put this tape on the underside of the hole not trying to entirely cover the hole.
- Now, cut another piece the same size and cover the top part of the hole. Don’t overlap the 2 pieces of tape. Put them side by side. Now the hole should be completely covered with tape with plenty of tape surface sticking to the undamaged wall. You've just created a backing for the mud so that it has something to stick to.
- Next, put some mud in the mud pan or trowel. Practice using your 6 inch knife scooping out mud from the bucket and placing it on your trowel. Put enough mud on your 6 inch knife so that it is about ⅓ covered on one side. The correct way to use these knives is to keep one side totally clean while the other is holding the mud.
- Now, wipe the mud onto the tape using firm pressure going lengthwise across the tape. Cover all the tape with mud, plus a couple inches out onto the wall. Using firm pressure, go over the area with your knife until there is only a very thin smooth layer of mud over the entire area. You want to see very few ridges or bumps in the mud, and the tape should be visible through the mud.
- Now you need to let it dry. A fan can help. When it's dry, the mud will appear white and will be hard when you touch it.
- Scrape the edge of your knife over the area lightly to take down any ridges. Now, apply another layer of mud going out a few inches further than the first coat. This is called feathering and it will help hide the patch. Now that your first layer is dry, you can apply the mud in any direction. This second layer should be just as thin as the first one and as smooth as possible.
- Let that dry, then do one more layer of mud with that one larger than the second. You should have a mudded area approximately 12 inches around.
- When this is dry, you take your sandpaper and lightly sand the whole area. If this is easy to do, then you did a good job mudding. Congratulations! The more ridges and bumps there are, the longer it will take to sand. Make sure you don’t sand all the way down to your tape. If you can feel tape with your hand, you'll be able to see it when you paint. Wipe your hand across the mudded area. It should be perfectly smooth.
- Wipe the dust off the wall with a sponge and you're ready to paint! You'll need to prime the repaired area first because the mud will absorb a lot of paint.
Here's a video showing how to apply the mud. He's only repairing a small dent in the wall, so he only coats it once, but you'll get a better idea of the motions by watching:
When it's all painted, you should barely be able to tell there was ever a hole there. Good for you! Hopefully this process doesn’t sound too difficult because it’s really not. The most important thing is to take your time and do it right. Some beginners will try to apply too much to speed up the process, but all that'll do is give you a noticeably bumpy wall where there used to be a hole. Applying multiple thin layers is going to leave your walls looking as good as new.
Still have questions? Leave them in the comments below. We'd be happy to help!