Acrylic/Perspex hatch question

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cindersailor

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I am currently building a perspex companionway hatch which will be framed with wood (iroko). I had intended to attach the wood (routed with a slot to accept the perspex edge) with epoxy, but having looked at the thermal expansion coefficients they are rather different, and the wood will also expand/contract with humidity of course. I am therefore rather concerned that the bond will not last. The perspex sheet is approx. 700mm square and 12mm thick. Has anyone any experience of how well this would last in the long term, or should I be looking at an alternative more flexible adhesive (Sikaflex)?
 
I would use Sikaflex - I cant see any down side, and it will eliminate the risk of the wood splitting. I dont see that epoxy would offer much greater strength anyway.
 
Acrylic (and, even more, polycarbonate) can react badly to adhesives and solvents. Any stresses, chemical or mechanical (as you fear) are best avoided. I am, though, pretty sure that Sika (and no doubt others) make an adhesive suitable for use on acrylic. In use it's barely distinguishable from their caulking, and I imagine is intended to allow some movement to allow for expansion. No doubt the Sika site can add more.

I did come across a very comprehensive data/best practice sheet for acrylic a couple of years ago, but sadly the link died with my last laptop. It may be worth your Googling around.
 
PCUK said:
Use silicone as it will allow expansion and contraction which Sikaflex won't. I am sure you can get suitable types for acrylic.
Click to expand...

No-one mentioned Sikaflex...partly because it's pretty meaningless. There are many types with different properties and purposes (and I'm not pumping any of them up...I prefer another brand). But, like West with epoxy, they're usually the easiest to get hold of.

Silicone. Mmmm. The silicone gasket in my coffee machine is brilliant. It's also the only bit of silicone I'd allow anywhere near the boat. Awful stuff. It should be confined to domestic bathrooms by law.

Different types of silicone sealants also release chemicals (commonly acetic acid or alcohol) during cure. Unless one knows the effects these might have on the materials being bonded, best stay clear.

As to use on acrylic: "...nor is silicone used for the manufacture of acrylic aquariums as silicones do not have long-term adhesion to plastics".

Which is also one reason I don't use the stuff on boats. The other is that nothing will ever stick to that spot again without some fairly violent cleaning.
 
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Can you not use screws or bolts? Acrylic can be drilled with special drill bits. For security reasons, perhaps you could use the screws with special head tha only allows you to tighten the screw?
 
Thanks for comments. Research suggests that Sikaflex 295 UV is the one to use, but I have now decided to use CT1, partly because the Sikaflex seems to need a variety of cleaners and primers to ensure a good bond which makes the total cost rediculous. CT1 seems to be the dogs danglies if all I have read is true!
 
cindersailor said:
I am currently building a perspex companionway hatch which will be framed with wood (iroko). I had intended to attach the wood (routed with a slot to accept the perspex edge) with epoxy, but having looked at the thermal expansion coefficients they are rather different, and the wood will also expand/contract with humidity of course. I am therefore rather concerned that the bond will not last. The perspex sheet is approx. 700mm square and 12mm thick. Has anyone any experience of how well this would last in the long term, or should I be looking at an alternative more flexible adhesive (Sikaflex)?
Click to expand...

Sikaflex do sell an etching primer for acrylics. Think how Lewmar bond their hatches!

Donald
 
cindersailor said:
I am currently building a perspex companionway hatch which will be framed with wood (iroko). I had intended to attach the wood (routed with a slot to accept the perspex edge) with epoxy, but having looked at the thermal expansion coefficients they are rather different, and the wood will also expand/contract with humidity of course. I am therefore rather concerned that the bond will not last. The perspex sheet is approx. 700mm square and 12mm thick. Has anyone any experience of how well this would last in the long term, or should I be looking at an alternative more flexible adhesive (Sikaflex)?
Click to expand...

With good thick 12 mm perspex why are you framing it? On a previous Fulmar the washboards were just acrylic with no framing and even had a lock cut in. They came to no harm. If you need to thicken them so as not to rattle in the slides two thin battens could be easily fitted down the edges. The joint between the two boards was cut at a bevel to prevent water running in.
 
+1.
12 mm acrylic is strong stuff, use it without anything else, problem solved.
It will last forever - since you asked. Surely will outlast any wood or other framing...
 
Aja said:
Sikaflex do sell an etching primer for acrylics. Think how Lewmar bond their hatches!

Donald
Click to expand...
Hanse had serious trouble fitting windows with sikaflex
Some boats reported windows blowing out whilst under way & one owner returned to the boat to find the window just laying on the deck
It seems that uv on the primer was at fault
They solved the issue in some cases by bolting the windows in place
There is a lot of info on the Hanse owners forum
 
Hi, Philip.

On Mojo I have a spare top washboard in Acrylic for occasional use - it doesn't work with the locks. The companionway hatch is also smoked acrylic and thankfully to date hasn't started crazing (famous last words). I think the whole issue of framing and sealing depends on the design of the frame. On the T24 I used to sail on, the forehatch had a curved glazed panel (GOK what it was made of) bedded into a rebate in a wooden frame. Struck me as the worst possible scenario and it had to be rebedded every couple of years. I think that sealing the edge into a groove will help maintain a seal - just a gut feeling, brain not necessarily in gear - why not check with the Engineering Dept?

From memory my hatch is probably also 12mm acrylic with strips glued along edges to fit to the track. The aft edge has a nicely shaped lipping glued on, which adds a tremendous amount of rigidity. Of course, it makes it easier as she was built this way with a flat hatch. I just checked a photo of your hatch and realise it is flat - whew, that makes it a much simpler enterprise, fitting curves is a bitch. I do find that the extra light through the hatch is very welcome, it never seems dark and gloomy in the cabin. Mine was designed from scratch to suit the materials, so the acrylic slides in an aluminium extrusion. I think the iroko frame will suit the method of fitting on SB and blend into the whole design. Look forward to a picture of the completed hatch!

Rob.
 
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