plexiglass repair?
September 2, 2006 3:09 AM   Subscribe

What adhesive is best to repair cracked plexiglass?

The 3' dia plexiglass (aka perspex) dome on a yurt has a crack moving in from the edge. The crack is six inches long and a replacement dome will cost hundreds. What's the best glue to hold the crack, and how best can it be stopped from extending? Maybe laminate (how?) over the crack?

Yurts are nice spaces. The crickets are so loud through fabric walls.
posted by anadem to Home & Garden (8 answers total)
Acrylic solvent or epoxy are the usual methods of gluing bits of acrylic together I believe.
posted by public at 5:06 AM on September 2, 2006

Epoxy's always what I've seen used for this.
posted by limeonaire at 6:51 AM on September 2, 2006

Three methods come to mind:
  • Acrylic Solvent: Done properly, an acrylic solvent can be used to bond two pieces of acrylic such that the resulting piece is essentially a single seamless piece of acrylic. However, it is difficult to properly apply solvent to repair a crack as opposed to joining separate pieces of acrylic. In addition, acrylic solvent is really nasty stuff. An easy to find brand of appropriate acrylic solvent is IPS Weld-on #3 or #4.
  • Epoxy: There are many kinds of epoxy and many do not adhere well to acrylic, but epoxy that bonds acrylic is available in most hardware stores. For best results apply the epoxy to both sides of the crack. Unfortunately epoxies that form the strongest bonds with acrylic are not transparent, they're generally amber or off-white in color. Easy to find brands are Devcon Plastic Welder or Loctite Plastic Epoxy.
  • Cyanoacrylate: Colloquially called "super glue" or "instant adhesive", an appropriate cyanoacrylate will form a decent acrylic bond and most cyanoacrylate adhesives are transparent. I'd probably apply it from above, allowing capillary action to draw it down into the crack. For acrylic, I'd recommend Loctite 401 Prism Instant Adhesive.

posted by RichardP at 7:51 AM on September 2, 2006

Oh, I should mention that uncured cyanoacrylate can induce stress fractures in acrylics. If you choose to repair your acrylic dome with a cyanoacrylate adhesive, make sure you immediately remove any excess adhesive from the surface of the repair.
posted by RichardP at 9:18 AM on September 2, 2006

Ridout Plastics recommends the following procedure for repairing a crack in a piece of acrylic:
...cracks can be stopped with a simple procedure. Using a very small drill bit, 1/16" or so, drill a hole through the material at the end of the crack. That's it. If it is a long crack, you might be able to inject some IPS WeldOn #3 (methylene chloride) into the crack to partially seal it. If the plastic is on a sign, and therefore most likely opaque, you should glue a 1" strip of 3/16" Plexiglas to the back side to reinforce the cracked area.
Since your dome isn't transparent, I'd think epoxy would make a suitable substitute for the strip of acrylic they suggest for reinforcement. If you choose to inject an acrylic solvent in an effort to seal the crack, wait at least 24 hours before applying epoxy as reinforcement.
posted by RichardP at 9:33 AM on September 2, 2006

Methylene chloride is the solvent for Plexiglas. It is toxic; find the MSDS and use proper precautions.
posted by Kirth Gerson at 9:39 AM on September 2, 2006

Also, be sure that it's Plexiglas (acrylic or PMMA), not one of the other transparent hard plastics (Lexan is polycarbonate, for example).
posted by hattifattener at 12:18 PM on September 2, 2006

You don't want to handle methylene chloride/dicholoromethane without proper PPE. DCM goes through most rubber gloves or masks almost instantly and it's very hard on your skin. It's not especially toxic (when compared with other drycleaning solvents) but it's really unpleasant to work with and hurts like hell if you get splashed.
posted by bonehead at 6:48 AM on September 3, 2006

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