How seal Perspex on wood frame?

pugwash

pugwash

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To revarnish the teak frame of my forehatch I removed the pane of Perspex and found beneath it a thin layer of what looks like pale grey raincoat material. I would appreciate advice on the best way to put it all back together. Will ordinary clear Sikaflex smeared thinly along the top of the newly varnished timber do the job? The Perspex is secured by lots of screws. Any thoughts welcome. Thanks.
 
pugwash said:
To revarnish the teak frame of my forehatch I removed the pane of Perspex and found beneath it a thin layer of what looks like pale grey raincoat material. I would appreciate advice on the best way to put it all back together. Will ordinary clear Sikaflex smeared thinly along the top of the newly varnished timber do the job? The Perspex is secured by lots of screws. Any thoughts welcome. Thanks.
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Use a foam rubber gasket.Wood moves too much for an adhesive sealant like Sikaflex.At the first change in humidity everything changes shape and the seal is broken.
 
What sort?

Thanks to you both for that. I think a mastic would be easier under the circs. Vyv, could you suggest a brand I could look for in B&Q or do I need to go to a chandler?
 
After having experimented with a number of methods of sealing perspex I have given up on Sikaflex UV as all the joints failed. I tried neoprene and that was just as bad. I am now using neutral-cure silicone and it seems to be doing the business.

The vital thing is not to use a 'thin smear'. It is essential to have a good thick bed of whatever mastic you use so that a little expansion or contraction doesn't put strain on the bond. A minimum of 3-4mm thickness is recommended. Use spacers to stop the goo being squeezed out before it sets.
 
ARBOSIL GZ Mastic Strip

Hadlow Marine supplied my refurbished aluminium frames windows with Arbosil's GZ Mastic Strip (which is a butyle rubber).

I fitted the frame into the window and tightened the screws until the strip just started to extrude. The seal is excellent, looks neat and the application was easy peasy.

The advantage of the strip is that it can be stuck to your hatch, trimmed to size, and then the Perspex fitted. No need to clean up any excess residue.

I found Hadlow Marine to be friendly and free with their advice.
 
Be very careful with mastics and Perspex acrylics. Acrylics are notorious for "stress cracking" due to incompatible solvents. I would stick with known brands and not gutter sealant or similar because you have no idea what is in them. Sikaflex is a damn good sealant and does not affect Acrylics. Butyl rubber compounds similar
 
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