How to Repair Damaged Drywall with a Skim Coat

Before we could move on to tiling in the kitchen, we had some serious drywall repair to do: that meant doing a skim coat.

What kind of drywall damage needs skim coating? For starters, any place you’ve got ripped drywall paper. A great example of this in our case is where I ripped off our terrible multi-layered tile backsplash:

See all that ripped paper? It’s all furry and rough… You certainly don’t want to paint directly over it. Water-based paint would soak through the paper and potentially cause mold/structural issues. No good. But in this case, I was just planning to tile over it. I still wanted to have a smooth, undamaged surface to apply the tile to!

The entire wall didn’t need skim coating, but there was still plenty to be done. I skim coated in places where there was a transition between painted and unpainted areas behind the old cabinets (there was a noticeable “step” between zones), any place with damaged drywall, and any other area that looked uneven.

What is a Skim Coat?

So glad you asked!

A skim coat is just thinned out joint compound applied in a light, smooth coat over the wall. In the photo above, you can see all the tools required:

• a putty knife (for mixing/application)
• a wide taping knife (for smoothing)
• a mud pan (for holding your mud!)
• …that’s it!

Or, is it?

I was tipped off to the importance of sealing the damaged drywall paper by various bloggers (and a commenter here on this blog!) and decided on this product to help me out. It’s Roman RX-35, and it worked great for me:

After sanding until as smooth as possible, I did a couple coats of the RX-35 (this stuff dries FAST) everywhere I noticed damage, then waited till it was completely dry to proceed.

Why is the sealer necessary? Without it, the drywall paper sucks up moisture from the skim coat and then warps, creating a bubbly texture when dry. No amount of re-skimming fixes this, since it just gets the base layer wet all over again. If this happens to you, sand down to the drywall paper again, re-seal, and then proceed.

So, how to skim coat: It’s pretty simple, really. Grab a generous glob of joint compound, plop it into your mud pan, then thin it out with a bit of water. Too little water? Add some more. Mix, mix, mix. Too much water? Add more joint compound! Here’s (approximately) the consistency you’re going for:

If anything, it’s a little on the thick side here. You could certainly get away with thinner, but not too much thicker. Your practical bounds are on the one hand so-thin-it-runs-down-the-wall and, on the other, so-thick-it-doesn’t-smooth-out-well.

Applying it to the wall is a bit of an art form. When dry, it sands easily, so it’s not like you’re going for absolute perfection, but you do want to be applying the stuff evenly! What worked for me was applying it in gobs on the wall with the putty knife, then doing gentle smoothing passes with the taping knife.

Is it weird to admit I kind of enjoyed this part? I only did two coats, since I planned just to tile over everywhere I was skim coating. But if I’d planned to paint over the walls, I’d have considered doing a couple more.

What comes next?

After the skim coating, wait for it to dry completely and then sand until smooth. I got a little carried away in places and had to come back in again with more mud, but it doesn’t take much time and isn’t too unpleasant to clean up. It’s fun to play with mud, especially when it’s making your walls look not-so-terrible!

Next up: tiling…