Why would you want to remove and reposition your deck after you've built the boat? I don't get that one. In any case, 5200 can be cut through with a razor blade utility knife, which is the standard way of seperating caulked/adhered together things. If you've gotten the impression that 5200 does some sort of instant weld, it does not. You've got quite a few hours after application to move things around before it sets up.

The advantage of using an adhesive type caulk like 5200 is that it holds the materials firmly, spreading the load out, and is inherently more watertight as a result. That's why cloth built skin on boats use so many nails or staples and often rub rails. To prevent localized stresses on the skin. Simply using screws or nails to hold the skin in place in a few areas will result in fractures and tears in the skin, and leaves long areas unsupported for water to work on and create leaks. Bonding the skin to the frame relieves these localized stresses, makes the boat stronger, and does a far better job of repelling water.

I'm also not sure what you're reading that has lead you to believe silicone is best for plastic. There are several types of silicones, and many many types of plastic. A blanket statement like that really doesn't make sense. It's about as misleading as saying nails are best in wood. Keep in mind, silicones are not recommended for water immersion by the manufacturers, for good reason.

The choice of what to do and what to use is certainly yours Alice, but remember the problems you were having and the reason for posting your original question.

> Nick - RNS and the manufacturer are correct. I've just returned from a
> marine supply place - After checking out the 3M 5200 caulking *adhesive*
> and talking to the staff, it was clearly inappropriate for my use - it is
> not removable and could tear apart the plastic should I want to remove it
> or reposition the deck at any time. I do not want to glue the pieces
> together, just to seal them after they have been fastened in place. The
> best item seemed to be a marine silicone-polyurethane combination by Boat
> Life called Life Seal which is a sealant/adhesive but not quite as strong
> a glue. The caulking manufacturer's recommendations state that silicone is
> best for plastic and that it is for above or below waterline. Let you know
> how this turns out. Alice