Drywall Tape: What Kind To Use For Plaster Repair

Drywall tape is essential for bridging seams between drywall panels. It's also very useful for plaster repair, especially over cracks.

But there is some controversy as to which kind of drywall tape is best. A lot of home improvement centers promote the use of fiberglass mesh tape by do-it-yourself folks, both for drywall and for plaster cracks. But I have my reservations regarding fiberglass tape.

First, let's make it clear what we are talking about. Self-adhesive fiberglass mesh tape was developed to bridge the seams in plasterboard before veneer (thin coat) gypsum plaster is applied. This is where fiberglass tape shines. Veneer plaster is tough stuff, much tougher than most joint compounds.

A thin layer of veneer plaster over glass mesh tape bonds through the tape to the board underneath, and supplies a rigid overcoat to reinforce the seam even further.

Joint compound, on the other hand, is less rigid than plaster. It will bond just fine to the board under the tape, but the thin topping coats do not have adequate toughness to add much more reinforcement power.

Often in my business, here is what I see. Someone tapes plaster cracks or drywall joints with fiberglass mesh tape. It's quick and easy - faster than using paper drywall tape which has to be laid in a bed of drywall mud. So, they top the fiberglass tape with two coats of mud and think they have it done.

Actually, I like fiberglass tape when used like this. Only because I have earned thousands over the years repairing this kind of stuff!

Here's what often happens. There is some subtle movement in the underlying structure - maybe nothing more than the drying out of wood studs/joists, or the slamming of a door - and now we suddenly have a hairline crack showing up right in the middle of a glass taped seam or crack. Especially common around door or window openings, or with drywall butt joints.

The glass tape is not torn. It's just not rigid enough. The solution is to pull out the glass tape, clean things up a bit, and retape with paper drywall tape. Paper tape is not mesh. I believe it bonds better to the flat surface, when mudded in right, and is tougher and more rigid when coated than is glass tape.

Some people recommend using hot mud (setting type joint compound) over glass tape because they reason that this is tougher than regular mud. Well, that may be true, depending on the brand of hot mud. But even then, I have seen the glass taped seams develop hairline cracks without breaking. So my preference is not to use glass tape for regular taping work. However, having said that

There IS a place for glass mesh tape when plaster repair in on the agenda.

If you or your plaster contractor decide to coat old plaster with veneer plaster, self-adhesive fiberglass mesh tape makes an excellent choice for laying over the prepared cracks first. The two thin coats, which end up about an eighth inch thick layer of plaster, are strong enough and rigid enough to hold the tape in place and secure the crack.

I have my own unique use for glass tape. When I have a particulary bad plaster crack to work with, I will clean and fill as usual. But I want some extra lateral reinforcement to lock in the crack for extra security.

In that case, I cut glass tape into three inch sections, and lay them across the crack, rather than down the crack (first bedding each piece in joint compound and laying them parallel but not overlapping). For extra security in cases like this, I like hot mud. Check out Hot Mud

When they are dry, I come back and glue paper drywall tape down the length of the crack with joint compound, just as I were taping an ordinary plaster crack for the first time. Then I coat the seam with two or more coats of mud to hide the tape, per normal.

Note: a double taped joint will be a bit thicker than the ordinary single-taped one, so you will have to work a little harder to hide the "hump". You will probably have to go wider when you put on the finishing coats.

Drywall tape: works best when you use the right stuff!

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