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3M 5200 for Canopy

Hello All, I have read a lot about using Sikaflex for the canopy. I have also read some reports of cracking with that method due to chemicals in the primer. Has anyone had cracks or other issues using 3M 5200? 5200 has less than 1% of the offending chemicals from the MSDS info. Thanks.
 
295uv is specifically designed for acrylic bonding and is the gold standard for securing acrylic windows in the marine industry. I struggle to believe it contains chemicals that are damaging to acrylics, as sika is a premiere adhesive manufacturer. Sika also has way more flex to it and that is important to avoid cracking due to the very different expansion rate of acrylic compared to steel or fiberglass.

The chemicals in the primer are purel for adhesion promotion and necessary to get things to stick to acrylic. Many adhesives don’t bond well with acrylic and I would not use an adhesive on my canopy that was not designed to bond to acrylic.
 
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5200

5200 has a much lower viscosity than Sika Flex , it would not stay where you put it ... and takes days to cure . It’s a great product but not for installing canopies
 
295uv is specifically designed for acrylic bonding and is the gold standard for securing acrylic windows in the marine industry. I struggle to believe it contains chemicals that are damaging to acrylics, as sika is a premiere adhesive manufacturer.

As the OP pointed out the problem is not with the Sikaflex 295 Sealant but with the Sikaflex 209 Primer.

The Sikaflex 295 Sealant will not adhere to the acrylic without the prior application of the Sika 209 Primer. But the 209 primer is 20% Ethyl Acetate, 25% MEK, and 0.5% Isocyanate Monomer. All of these solvents are "N" class which means that on acrylic sheet "immediate damage may occur such as severe crazing, cracking, or permeation losses". In particular, without very fastidious preparation of cut edges the primer can exacerbate microscopic cracking in that location....plenty of examples reported on VansAirforce.

As you have pointed out Sikaflex was developed for use in the marine industry...not in the aviation industry. And the manufacturers recommend it only for use by professionals....not one time amateurs.
 
I used 3M AC137 adhesion promoter and AC251 adhesive. Both are aerospace materials formulated for use with acrylics. The AC251 will not sag or run.
 
Thank you

Thank you to everyone who responded to this post. I am going to follow Martin's lead and use the 3M AC-251. Like he said, it has been specifically developed for aircraft acrylic. I had never heard of it before.
 
... only a SEALANT!?

I used 3M AC137 adhesion promoter and AC251 adhesive. Both are aerospace materials formulated for use with acrylics. The AC251 will not sag or run.

On the manufacturer datasheet, this material is rated as a SEALANT, not a glue!

Done my RV-7 with Sikaflex 295UV, 5 years ago, all fine.
 
I think that the Captain's advice to ensure that the canopy's edges are very smooth should not be overlooked, no matter how you affix it to the frame.

If you use any type of glue, a good gap between the frame and the canopy will help allow for the different coefficients of thermal expansion between the plexi and the steel frame.
 
If you use any type of glue, a good gap between the frame and the canopy will help allow for the different coefficients of thermal expansion between the plexi and the steel frame.

This only applies if the glue has some flex to it. One of reasons that Sika is so popular for acrylic bonding is that it has 300% expansion/contraction and lets the acrylic move around due to the different expansion/contraction rates. I would not use an adhesive with limited flexion in this application and definately would not trust my canopy to stay in place with a "sealant."

I hope this all works out for the OP.

Larry
 
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On the manufacturer datasheet, this material is rated as a SEALANT, not a glue!

Perhaps it would be useful to look at the reported values. 3M AC251 is a polysulfide, same family as tank sealant, with pretty much the same physical properties.

AC251 Tensile and Elongation
Required: 200 psi/200%
Typical 350 psi/370%

Sikaflex 295UV
Required
Typical 290 psi/500%

CS3204 (common Flamemaster tank sealant)
Required 200 psi/200%
Typical (from a private test report) 270 psi /460%

They could call it hemorrhoid cream, but I'll bet it would still stick your cheeks together.
 
SikaFlex RV7 TU

I used the Sika 295 with the mentioned primer system.

I observed cracks in the paint/filler fairing on both sides where the riveted canopy rail meets the forward canopy structure as if the joint between the two were not stiff enough.

Later in very cold weather I got a canopy crack in the same place as the paint crack.

So I got a crack but I don't believe the solvents were at fault because there was a mechanical hinging going on well before the acrylic had a problem.

I wonder if the sika is flexible enough to allow a stress concentration at that joint. If I were to do it over again with Sika I would probably make that joint stiffer with rectangular tube rather than the small plate called for in the plans.
 
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