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Has anyone mixed 3/8" loose fiberglass strands into drywall mud. I restore boats for a living and we commonly mix these fiberglass strands into the resin to produce a workable paste. This can then be worked with a putty knife. These fiberglass strands are commonly called "chop" and are the same fiberglass which is being put into concrete. I see no reason why they would not reinforce drywall mud also. I am doing some test pieces with 1/2" drywall to determine if this is a good idea or if I am out is left field. Please comment.

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    Might well be a finishing nightmare when it comes to sanding smooth. Also, if you need "strength" from drywall mud (joint compound) you're doing it wrong. – Ecnerwal Jun 24 '17 at 23:25
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    This is typically done for fire stopping, filling gaps where drywall is used for fire blocking. Foam rated as fire stopping is used nowadays for the most part – Jack Jun 24 '17 at 23:28
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    In some parts of the world they use a fiberglass mesh (and I mean big areas, not just a tape) embedded in the mud. If you do this, make sure to apply a mud layer fist, don't put the mesh on bricks/concrete as it will not adhere properly. – Fizz Jun 25 '17 at 17:41
  • It would be extremely difficult to finish, and prevent voids, as would a fraying piece of mesh tape. – tahwos Jun 27 '17 at 0:48
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In a marine fiberglass-in-resin situation, the resin's surface tension pulls the fibers into the mass, with few protruding fibers. Plus, since the resin is of similar strength to the glass, sanding will remove both fiber and resin at the same rate, leaving a relatively smooth finish.

With strands in drywall mud, however, the mud is likely to leave strands protruding. Plus, if you try and sand it smooth, you'll find that the mud is much weaker than the glass fibers, and you'll inevitably remove more mud than fiber, leaving a "hairy" finish.

People use fiberglass tape or mesh to reinforce the mud, but that only works if, when you're finishing, you only remove some of the mud but never get down to the fiberglass.

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Fiber reinforcement is not a new idea. People built houses with straw reinforced mud brick and straw reinforced mud plaster thousands of years ago. Before drywall became popular in the 1950’s, wooden lath and plaster was the dominated way of building and finishing interior walls. The plaster was reinforced by animal hairs like horsehair, cow hair and goat hair. It took decades for people to accept drywall after it was introduced in to North America. After 1950, wooden lath and plaster was abandoned. Building interior walls entered into an era of drywall plus tape and mud finishing. Animal hair reinforced plaster was forgotten. Hardly any body use fiber to reinforce drywall joint compound in North America nowadays.

Is “ tape and mud” the best way to finish drywall? I doubted it about 10 years ago. I’m a professional drywall taper for 20 years. In 2009 I started mixing polypropylene fiber and cellulose wood fiber into setting compound for the taping coat without either paper tape or fiberglass tape. It worked great. And then I tried mixing fiber in premixed taping compound. It worked really good as well. I finished my garage with fiber reinforced taping compound in 2010 without any tape. For 9 years now it has no problems. The joints were a little hairy after final sanding. But slightly sand it after priming can take all the protruding fibers off the walls and after two coats of paint it’s flawless.

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Fiberglass won't bond well with water-based mud. The mesh works because of all the holes. If you want to add some fibers, experiment with dryer lint.

Work it in well to get it thoroughly mixed and uniform, you don't want pockets of a wad of uncoated fibers. The fibers are extremely thin, so you need to blend in a fair amount to provide significant reinforcement.

At the extreme, if you mix in enough fibers, you create more of a mud-reinforced fabric that can be used almost like a moldable "structural" material (it doesn't have the strength of a real structural material, but enough strength to be useful).

A significant amount of fibers will make the mud a bit more putty-like, or even clay-like in a clumpy way, so it won't be easy to work for a finish coat. Also, it will add color to the mud, so you will need primer to hide it.

All that said, I've never compared lint-reinforced mud to using conventional methods for handling routine needs. The preparation is work because it takes a lot of mixing to get it uniform. It's more of a "specialty material" that's an option for getting creative with unusual problems.

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