Plexiglass crack

FORANE

FORANE

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Whats the best way to address a small crack in plexiglass wingtip light cover?IMG20250419125437.jpg
 
I am interested to hear what the correct method is.

I can tell you my non-aviation version (neither certified nor experimental): drill a small hole at the end of that crack to prevent growth, then cover it with a dab of clear silicone (like a caulk), with a “smear” along the crack itself, using masking tape to have a clean line. I would also try to find a type of glue or epoxy on the inboard end of that crack to prevent it from expanding at speed and compromising your fix.
 
I'm tempted to try the windshield crack fill liquid that is cured with UV light. That works pretty well hiding blemishes on my windshield.

Edit: Google search says the windshield crack resin will not work. It suggested an acrylic product like Weldon #4.
 
Last edited:
FORANE said:
E/AB
Permanent
Click to expand...
Since the cover is not a "structural" panel like a windshield, stop-drill the end of the crack, and apply an acrylic glue like Weldon or PS-30 to the crack line on both sides with a toothpick or similar device. If aesthetics are not an issue use a small paint brush to apply the glue. And in a pinch, super glue will work as well but not as good as the others.
 
For stop drilling plexi, I'd use a very dull bit that won't grab and "pull" itself into the hole, creating a bigger problem.
 
FORANE said:
I'm tempted to try the windshield crack fill liquid that is cured with UV light. That works pretty well hiding blemishes on my windshield.

Edit: Google search says the windshield crack resin will not work. It suggested an acrylic product like Weldon #4.
Click to expand...

We had a 4” long crack thru and thru on our windscreen last fall. It was up near the wing root and we talked with some CAF guys that repaired a ball turret by “glueing” it all back together.

I’ll find out the product we used and let you know. Essentially we stop drilled the crack, used a syringe to fill the crack, then let it cure and sand it out to finish.

There’s probably something I’m missing, but that was the basic process.
 
You might combine suggestions and sacrifice a drillbit by heating it and gently using to drill a stop hole. This will create the proper size hole and prevent the plastic from cracking.
 
Do you have to drill both ends of the crack?
 
mandm said:
Do you have to drill both ends of the crack?
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Looks like this particular crack progressed all the way through to the edge on one side, so no, you only drill one end on this one. But if it was a crack that hadn't progressed to the edge of the plexi, you'd drill both ends. Another way of doing it is with a small unibit. Those don't have the habit of grabbing plexiglas and creating more cracks.
 
TCABM said:
There’s probably something I’m missing, but that was the basic process.
Click to expand...
FYI: for a permanent repair on windshields the recommendation is to install a doubler over the cracked area and is even acceptable on TC aircraft as well.
 
Don't put any goo like silicone or RTV on it to seal it temporarily. That will greatly impede a better repair later.

You can get 1/8" diameter acrylic rods from Amazon. Stop drill the hole with a 1/8 bit, put some acrylic cement in the hole, work the pieces to draw cement into the crack, then fill the hole with a short segment of rod. After it dries, cut and file the rod down to just proud of the surface. If you are really fussy, use successfully finer sheets of sandpaper to get the rod flush with the surface and remove scratches, then compound and polish to near invisibility.

Be careful and sparing with cement. It works by chemically melting the acrylic. Any that you get on your surface will permanently mar it.
 
The solvent stuff works great. Keep in mind it can be water thin. In theory people use a syringe, but I never had much luck with that. I used to use a cheap natural bristle artist paintbrush, it'll wick in.

For drilling the stop hole, mcmaster carries plastic bits that really are less likely to crack the plastic more. With skill you probably don't need that, but when I look at acrylic sideways it cracks on me.

www.mcmaster.com

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.
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