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

> I still don't know why on earth the vendor/manufacturer would be saying
> silicone caulk. Silicone is *not* a suitable structural caulk. It's one of
> the weakest on the market. Suitable only for sealing up the gap between a
> counter top and edge at resturants and such. It barely does the job on
> aquariums. You can rub silicone caulk off with your thumb!

> I would use the 5200, though there is one other that's perhaps better. I
> can't remember what it is, and I don't have my catalogs here to look it
> up. Something like 100 I believe. In any case, reading the label will tell
> you how it works. If you've got a big boating store near you, they'll be
> even more helpfull at making sure 5200 is the best, or if it's second
> best.

> I would *not* do the multi-layers your engineering friend suggested.
> That's a road to disaster. You'd get cured layers of lumpy caulk to try
> bonding to instead of smooth plastic. Coat the joining surfaces with the
> 5200, clamp/tape/whatever them together, let it cure. If you can get to
> the inside seam, run a bead there as well. To give you an idea of just how
> strong 5200 is, it is the normal method of fastening splashwells onto the
> transom of power boats. You know, those splash wells people stand in all
> the time, and throw gas can in and such.