Fiberglass drywall tape is popular for drywall work and plaster repair. But there are big problems with it. A professional’s opinion.

fiberglass tape, drywall tape, drywall seams

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The truth is, it has its place, but – please! not on your drywal
Yes, my view of this is controversial. And I have my (good) reasons.

Actually, people who use fiberglass tape instead of paper tape for drywall taping are helping me make a living.

As a drywall finisher and a plaster repair specialist, I have made thousands of dollars over the years repairing drywall seams taped with fiberglass. Thanks, folks.

What happens? Drywall seams need a RIGID tape to stay closed. Especially over butt joints, the fiberglass taped seam will wiggle ever so slightly some time down the road after finishing, and presto! a hairline crack develops right down the middle of the joint.

The tape isn’t broken. It’s just that the drywall mud overcoat is not rigid enough – tough enough – to add the strength necessary to permanently secure the joint.

How do I know this? Well, for one thing, I have noticed that the long, recessed drywall seams tend to stay taped better. With those seams, the mud overcoat is thicker because it is filling the valley where the tapered edges of the drywall come together. You get some extra toughness.

I understand the allure of fiberglass tape. Slap it down on that crack and mud ‘er up. No blisters, etc. So easy and comfortable, especially for the novice taper. And every do-it-yourself website and magazine article promotes it.

Yes, it is harder to learn to use paper tape properly. For the newcomer to drywall taping, there are issues of laying the mud on evenly, wiping the tape down properly, avoiding humps on the butt joints, and so on.

These are learnable skills, and they pay big dividends after the job is finished and painted. Nothing is more irritating to the customer or homeowner living in his new home/addition than to see cracks developing in his new walls or ceilings.

As I said in the beginning, there IS a place for fiberglass tape. First of all, it the tape of choice for plasterboard seams under veneer plaster. This is what it was developed for in the first place. It works very well in this setting, because veneer plaster is far harder and tougher than drywall compound.

But, there is a place where fiberglass tape can help in the drywall trade, and that is in the repair end of the business. Around doors and windows, cracks in the drywall are common. A little extra movement in the framing there and you get these unsightly defects.

When I repair such cracks, I want some extra insurance. What I will do is use short pieces of fiberglass tape – maybe three inches long or so – and place them in a bed of mud ACROSS the crack and parallel to each other. I wipe out the excess mud, just as I would with paper tape.

When this first layer of tape is hard, then I lay down a line of paper tape right across the fiberglass and centered on the underlying crack. Now I have double insurance: the glass for lateral strength and the paper to keep it tight to the surface. This usually takes care of such cracks, or any cracks you are particularly concerned about. (Don’t forget two or more topping coats.)

I do the same operation or a variant of it on bad plaster cracks.

One last point. I’ve emphasized toughness of the compound you use. For that reason, I like “hot mud”, a setting type joint compound more like plaster for strength. If you are unsure of yourself and your speed, it would be good to use hot mud with a longer setting time, like an hour or 90 minutes. Mix small batches and don’t forget to wash your tools and pans well between batches.