Adhesives

[wvernie]

Does anyone know what kind of adhesives Trojan used to put around the metal frame on the engine hatches?

[Mac32]

Cant confirm trojan, but I have talked to a few boat builders about re bedding my window frames and hatches to find out what they use and get this, They use DOW 795 industrial exterior sealant, it comes in colors and has a 20 year warranty and best of all it is 1/4 the price of 5200. I figured the manufacturers dont just go to west marine to buy supplies

[chumwithabottleofrum]

The Dow 795 is a silicone sealant. 3m 5200 is a urethane sealant. They really arent' interchangable. Silicone sare good sealants and are effective to use when wanting to form a casket. Urethane sealants are more adhesive than sealant. A good urethane sealant is SikaFlex 1A-you can purchase it at most commercial "hardgoods" distriburtors-concrete and masonry accessories. (those same distributors usually stock Dow 795 also).

[Mac32]

That makes sense, because the boat builder I talked to said use the 795 on the hatches if I just wanted to seal the water out (gasket) and if I felt that I wanted to permantly glue the hatches in place and make it difficult for possible removal down the road use the 5200.

I have read a few articles on using the 795 for teak caulk joints also whaddya think.

Here is one of them.
http://epole.tripod.com/sailinfool/id7.html

[chumwithabottleofrum]

Mac-I think I'd agree with most of what the author said in that article, but 5200 is a single component polyurethane sealant, not a polysulfide. The key to using a silicone to rebed windows-make sure both the substrate and the hardware are very clean. When you gun the sealant in place do not tighten the screws down all of the way. Give the screws a couple of turns, wait 15 minutes or so, give them another turn. Wait 15 minutes give them another turn. Tighten the screws down to about 80-90% then come back the next day and tighten them down all the way. Doing so will help form a better gasket.

[randyp]

I spent 25 years with GE Silicones, the major competitor to Dow Corning (DC 795), and now run a small silcone manufacturing company, so this stuff I know all about. NEVER use silicone under the waterline. it has a tendency to lose bond if submerged on fiberglass or wood. Interestingly it makes a great aquarium sealant and sticks like hell to glass under water. That's because the silicon molecules in the glass and the silicone have an "affinity" for each other and not just bond but become "interwoven" Don't use silicone around oily woods (like teak) it won't bond well to the oils. Urethanes are a much better adhesive, can be used below the waterline and can be painted, unlike silicone.

SILICONE - GASKETS and SEALS ABOVE THE WATERLINE
URETHANES - SEALANT AND ADHESIVE BELOW AND ABOVE THE WATERLINE.

Silicones remain flexible. Urethanes not as flexible over time. Prep for both is just about the same....clean mating surfaces well. Acetone or ethyl alcohol work well....and you can drink the leftover ethyl alcohol!!

[rossjo]

Good rules on Silicone and Urethanes Randy!