Deck Prism

aruggiero · #1 (**permalink**) 07-11-2006

We recently bought an old boat that we are currently restoring. In the cockpit there was a big hole that had a piece of plywood screwed on over it. We decided to put a deck prism there to fill the hole and also give more light at the nav station. We didn't receive any instructions with it. I was wondering if anyone knows what is the best type of sealant to use to attach the prism to the trim ring?

sailingdog · #2 (**permalink**) 07-11-2006

5200 is a good choice if it is a glass deck prism and metal or wood trim ring. 5200 will attack some plastics...

camaraderie · #3 (**permalink**) 07-11-2006

No...use silicon. Water WILL eventually find its' way back in and you will appreciate being able to get the dang thing back out and re-bed it in 20 minutes rather than hours. I have 6 on my boat and the last guy used 5200...every one has silicone now.

sailingdog · #4 (**permalink**) 07-11-2006

BTW, is the deck on your boat cored? If so, does the hole that is drilled through the deck have the core removed around the edges and replaced with thickened epoxy??

Silicone can be a good sealant, but it has to be installed properly. How does the trim ring attach to the deck? What you might want to do is use 5200 to attach the prism to the trim ring, but use silicone to bed the prism.

Silicone is not really a good sealant. It really works best under compression, more as a gasket than a sealant. None of the silicones on the market have very strong adhesion properties...and as such, aren't usually all that suitable, unless allowed to form a fairly thick gasket and then held under compression.

Omatako · #5 (**permalink**) 07-12-2006

One major issue with silicon is that you should only use it in areas that you NEVER want to paint again. Once you've had silicon on a surface, even the wiped areas after you have cleaned may look clean but will shed paint like ducks shed water.
I would use a mastik type of non-hardening sealant and make sure that the fasteners are really good.

aruggiero · #6 (**permalink**) 07-12-2006

It is a cored deck. We haven't filled it with epoxy yet but we plan to - the plywoood that is there is screwed in and it doesn't appear to be sealed. The trim ring screws on with #6 screws. The prism is glass and very, very heavy.
Thanks for your responses!

sailingdog · #7 (**permalink**) 07-12-2006

Don't forget to drill the holes for the screws oversized and fill them with thickened epoxy too. Also, best to throughbolt the deck ring, rather than relying on screws to hold it in place.