Bonding Acrylic Plexiglass to Powder Coat

[Boatwright]

Replacing crazed / cloudy acrylic glazing in powder coated aluminum hatch frames.

The hatch frames have approx 1/8" expansion clearance to the edge of the acrylic. So we need good gap filling with UV resistance for our sealant spec.. The sealant is backed up with mechanical fasteners so we need flexibility with decent bond strength. Color black.

Any opinions / experience please on adhesive sealants:

1) 3m 3000 UV and other 3m products?

2) Sikaflex 295 UV & how important is the very expensive ($90) recommended primer on clean new material?

3) Boatlife Polysulfide? - Jamestown recommends against polysulfide on acrylic but the 40 year old caulk sure looks like polysulfide deck caulk to my eye.

3) Any other recommendations or negatives?

[AKA-None]

I’ve used the sikaflex 295uv and did the preparation with denatured alcohol. Seems to have worked for the past 3 years.

[44'cruisingcat]

Dow Corning 791 silicone.

[john61ct]

Yep apparently the one and only use case where sillycone is not just acceptable but highly recommended.

Not sure why but my notes for acrylic say

Dow Corning 795, product id 28-DC795W

[thinwater]

Originally Posted by AKA-None

I’ve used the sikaflex 295uv and did the preparation with denatured alcohol. Seems to have worked for the past 3 years.

Beyond 3 years, the primer may become important.


The primer is NOT just a primer. It is an opaque UV blocker. The purpose is to block UV from attacking the bond area through the glazing. Although polyurethane is reasonably UV resistant, it is vulnerable if the UV strikes the bond. I have seen this effect in testing.



It is gradual and may not be noticeable for quite a few years.


This does not apply to DOW 795.

[Matt Johnson]

Another vote for DOW 795.

Matt

[Bycrick]

After trying numerous adhesives/caulks over the years on my five hatches (acrylic lenses with aluminum frames), with only marginal success, I finally ended up with Dow Corning 795. After 7 years, it’s still there even though the acrylic is showing its age. None of the hatches leaks. Lenses are held in the frame with nothing but adhesive; no mechanical fastenings. Four of the hatches are opening deck hatches exposed to tropical sun and heavy rains.

The only problem I’ve had with 795 is that you really have to pay attention to the expiration date. One tube that was 8 months out-of-date took many months before it finally hardened. I threw the other tube away.

[Breaking Waves]

surprised it has not yet been mentioned...but the industrial standard is double-sided tape.

is clean and uniform with very strong adhesives. Used in on both auto glass and glass curtain buildings.

Also for UV protection they have UV screening film/tape for the outside edge - again what is used on most automotive windshields.

see https://www.3m.com/3M/en_US/company-...94857497&rt=r3

Use a foam tape if the surface is not smooth/flat, otherwise just the straight double sided.

You can then used one of the structural silicones to fill in/level-up around the edges if the acrylic is 'countersunk/flush'. like https://consumer.dow.com/en-us/indus...l-glazing.html just as an example (just google for structural glazing or adhesives for other options)

[stormalong]

I used a product from GE named Ultraglaze in my anodized hatch frames. Done in 2000 and still good. It is a silicone product. May be hard to find - I think it was marketed to industry. I got mine from Florida rigging and hydraulics.

[CHRIS V CLEMENT]

Breaking Waves is only partially correct. I am a commercial glazing contractor so I have 40 years of experience with both double sided tape and sealants of many types, in both commercial and marine applications.

The double sided foam tapes are used to hold the plastic in place until the silicone cures. Curing should take 14 days, and maybe longer in low temperature or humidity climates.

Cleaning is the key. Denatured alcohol is recommended, but I prefer Xylene or Acetone. Make sure to wear gloves and goggles. Make sure to ventilate the area.

Dow 790, 791, 795, or GE Silpruf are all excellent sealant choices. They are all neutral cure one part silicones. They will all last 20 years or more.

Do not try to clean up any sealant "mistakes" until after the sealant is cured. it may look messy for a while, buy clean up is much easier.

[s/v Jedi]

3M VHB tape then Dow Corning 795 to seal the perimeter

[bstreep]

Yet another vote for Dow 795. And absolutely, ditto on the expiration dates. We had to pull 2 windows...

[Cheechako]

I'd use one of the Dow products used to hold skyscraper windows in. 795 I think.

[tanton37]

What would you recommend for safety laminated glass to aluminum?

[Breaking Waves]

Originally Posted by CHRIS V CLEMENT

The double sided foam tapes are used to hold the plastic in place until the silicone cures.

Cleaning is the key.

Let's agree that best solution is acrylic foam tape (like the 3M VHB) backfilled with a structural silicone glazing (like 795) with a UV Shield film/tape/paint. And that scrupulous prep and cleaning is critical.

as a practical note: This is 'proper', but it may well be considered a bit of overkill for bonding a relatively small acrylic into an aluminum powdered coated hatch. The peeling loads likely are going to be small.

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Originally Posted by CHRIS V CLEMENT

Breaking Waves is only partially correct.

I am not sure what you are disagreeing with. You may not use or approve of this practice, but there have been many commercial projects just using the tape with no backfilling. From 3M's Architectural Specifications "Structural tape glazing utilizes a high-performance acrylic foam structural glazing tape to attach glass panels to metal glazing frames in lieu of sealants or gaskets and mechanical fixing."

And from just one random independent technical assessment of 3 relatively demanding buildings build that way (eg no backfilling) Conclusion / Test Results:
1. 3M Brazil CTC (approximately 5 years old, constructed in 2005): testing was completed at two locations with no evident signs of failure.
2. Dallas Tower (approximately 10 years old, constructed in 2000): Testing was completed on 5 locations of various installed configurations with no evident signs of failure (see the recorded test data listed in this report).
3. Glass Tower (approximately 16 years old, constructed in 1994): Testing was completed on 12 locations of various installed configurations with no evident signs of failure (see the recorded test data listed in this report).

This may well be more common in Europe than in the USA. And you certainly would not want to use the tape only solution in any/every application. Because the tape and cured silicone each have properties which they are 'best on'. On the OP's acrylic to powder coat bonding application, in a marine application, the powder coat will probably fail before the 3m tape gives up.