Repairing cracked plastic pieces
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LesGawlik
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Depends on the type of plastic. Most old plane plastic is ABS. You can make a slurry of old ABS scrap and MEK, but MEK is getting harder to find. Plumbing ABS cement will work, but it is usually black.
Otherwise, I would use 10P 2 Glue. It works very well on most substances.
Otherwise, I would use 10P 2 Glue. It works very well on most substances.
455 Bravo Uniform
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One method, for thin interior pieces:
-tape the back of the pieces with fiberglass drywall tape
-use cheap flowable superglue to fill in the tape voids
-supplement the strength and thickness with baking soda while the piece is wet
-layer more glue and soda (and tape) as needed
-sand to smooth things out
-fill in the front of the piece at the crack line with a finish filler like bondo that comes in a tube (auto parts store), sand, primer, paint
Don’t breathe the fumes of the super-glue and baking soda reaction.
-tape the back of the pieces with fiberglass drywall tape
-use cheap flowable superglue to fill in the tape voids
-supplement the strength and thickness with baking soda while the piece is wet
-layer more glue and soda (and tape) as needed
-sand to smooth things out
-fill in the front of the piece at the crack line with a finish filler like bondo that comes in a tube (auto parts store), sand, primer, paint
Don’t breathe the fumes of the super-glue and baking soda reaction.
Acetone works for abs glue. If you crumble up pieces of the plastic into the acetone you can even make a color matching putty.
Trouble is you go to the effort of repairing a 50 year old piece of plastic and it's likely to break again. This stuff is just so brittle. Replacement pieces are pretty cheap and available as aviation stuff goes.
Dan Thomas
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Use the yellow ABS solvent cement, the stuff used on black ABS drain piping. Cut patches from fiberglass cloth (not mat). Cut them with the weave at 45° to the crack so all the fibers work for you, and also at 45 across any compound curves so it will conform nicely. Tape the crack closed on the outside of the part, the interior side everyone sees. Apply the ABS cement to the backside of the part and set the cloth patch in it. Apply another patch to strengthen it and put more cement on. Let it set for a few hours, trim off excess, remove the tape, and reinstall it.
ABS solvent cement is just MEK and ABS plastic. You can make your own with abs shavings and MEK but it's a real pain and you don't need a color match if you patch the backside. The tape prevents bleed-through and keeps the edges aligned. Acetone is way too weak for this.
Superglue is expensive and doesn't work that well at all. No glue that simply tries to hold those thin little edges together will work in any worthwhile way. You need the reinforcement on the back. Polyester resin doesn't adhere. Epoxy doesn't adhere much either. The ABS solvent cement actually melts the ABS base so as to fuse right into it and never, ever comes off. If the backside is dirty or has grease or paint on it, get it off with some MEK, which will also prime it ready for the cement.
BTDT many times. Tried everything else, which doesn't work.
ABS solvent cement is just MEK and ABS plastic. You can make your own with abs shavings and MEK but it's a real pain and you don't need a color match if you patch the backside. The tape prevents bleed-through and keeps the edges aligned. Acetone is way too weak for this.
Superglue is expensive and doesn't work that well at all. No glue that simply tries to hold those thin little edges together will work in any worthwhile way. You need the reinforcement on the back. Polyester resin doesn't adhere. Epoxy doesn't adhere much either. The ABS solvent cement actually melts the ABS base so as to fuse right into it and never, ever comes off. If the backside is dirty or has grease or paint on it, get it off with some MEK, which will also prime it ready for the cement.
BTDT many times. Tried everything else, which doesn't work.
Clip4
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Devcon 22045 Plastic Welder - 25 ml Dev-Tube
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Rgbeard
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The ABS solutions and solvents cited above are all far better than superglue.
Practice first.
Practice first.
Superglue by itself, forget it. But thin (not gel) superglue dripped into thin fiberglass cloth on the back side works quite well. In a pinch any kind of non stretchy fabric will do. Sand the surface to roughen it first, and then clean it with solvent and don't touch it with your fingers before applying the glass.
I've also had good results fixing plastic with epoxy and a scrap of aluminum window screen when nothing else was available.
I've also had good results fixing plastic with epoxy and a scrap of aluminum window screen when nothing else was available.
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Google superglue and baking soda just for fun, too.
Dan Thomas
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25 ML for what? $17? Maybe it would work, maybe not, but if it's just trying to bond the edges of cracks together it will just break again as the part is flexed. There is nothing like the original molding continuity for strength. I've tried bonding the crack itself with stuff like this as well as the ABS cement. It doesn't work. It needs the reinforcement.
A 118 ML can of ABS solvent cement is maybe $5.
Clip4
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Devcon Plastic Welder is a toughened structural adhesive formulated for bonding dissimilar substrates as well as unprepared metals, ceramics, wood and standard thermoset plastics. The final adhesive bond is designed to be load bearing and resistant to weathering, humidity and wide variations in temperature.
Plastic Welder is highly resistant to hydrocarbon fuels (gasoline, jet fuel, motor oil, hydraulic oil). It bonds with PVC, fibreglass, ABS, steel, acrylics, polycarbonate, polyesters (PET; PBT) wood and ceramics.
I have used this stuff on the Royalite Plastic in Cessna aircraft. It bonds well, fills gaps, is sands easily and is paintable. A buddy used it on the panels in his M20J and it worked well on those too.
Plastic Welder is highly resistant to hydrocarbon fuels (gasoline, jet fuel, motor oil, hydraulic oil). It bonds with PVC, fibreglass, ABS, steel, acrylics, polycarbonate, polyesters (PET; PBT) wood and ceramics.
I have used this stuff on the Royalite Plastic in Cessna aircraft. It bonds well, fills gaps, is sands easily and is paintable. A buddy used it on the panels in his M20J and it worked well on those too.