Wooden Boat People

By McKenzieDriftBoat.com

Epoxy and Glassing Question

Just sealed the ribs and plywood with epoxy that will mate did this for waterproofing . My question is do I need to scuff the surface before I 5200 and screw the sides and bottom on ? Next question do I need to scuff the dried epoxy between coats when glassing or will it bond well to itself without sanding ? Thanks for the input.

First time boat builder fron Montana

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Permalink Reply by Guy Fredrickson on March 16, 2012 at 5:07pm

The West System website has some good technical information on epoxies.

http://www.westsystem.com/ss/use-guides/

I have been lightly scuffing the wood surfaces with 80 grit paper before bonding with epoxy.

Sanding between coatings is sometimes necessary when the epoxy fully cures between coatings. But there are exceptions, like the 105/207 West System combination. But all of that is there in the technical literature.

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Permalink Reply by Guy Fredrickson on March 16, 2012 at 5:12pm

Here is some information from 3M on the 5200 sealant. (That's a big link.)

http://solutions.3m.com/wps/portal/3M/en_US/Marine/Home/Products/Ma...#

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Permalink Reply by Phillip Westendorf on March 16, 2012 at 7:32pm

Loren,

RE, your quote: "Next question do I need to scuff the dried epoxy between coats when glassing or will it bond well to itself without sanding ? "

simle answer YES!!!!!

Long version,; When glassing the sides or bottom there is an advantage in applying multiple coats of epoxy (3-4 coats) all in the same session. According to West System User Manual, Page 6, Primary Bonding produces a chemical linkup of of adhesive layers. All of the layers of the eooxy cure as a single fused layer. Epoxy applied over a partially cured epoxy will chemically link with it and is considered a primary bond. With 105-207 you have about 1 1/2 hrs. between coats to achieve this.

Secondary bonding requires a mechanical rather than chemical linking to the cured epoxy surface. The second coat must "key" into pores or scratches in the surface. Proper surface preparation provides a texture that will link the cured epoxy to the surface. West System recommends 80 Grit paper.

When laying f'glass cloth on the sides or bottom I'd reccomend you use the primary bonding method. The first coat of epoxy is required to wet the glass and surface of the wood. About 1 1/2 hrs approx. as the epoxy is partially set up you need to apply the second coat to "fill" the weave of the cloth . The third and fourth coats will then bury the cloth. This results in a durable water barrier for the wood.

There are different methods to apply the different coats of epoxy. When I used this technique the first time I used a brush to apply the wetting coat (West's 105-207) and then after about 20 min's as it began to setup my son using a plastic bondo spreader began to scrape off the excess epoxy to force it down to the wood. As we were doing a 16 ft. canoe I was still wetting the cloth while my son started the scraping. It took about 1 hr. to brush on the first coat. The second coat was applied with a brush also. The third and fourth coats were applied with a roller and tipped with a clean/dry brush. I started at 11:00 AM and finished the fourth coat and clean up at 1:00 AM the next morning. Sounds like a real pain, but in reality it was just busy work requiring attention. There were rest periods between coats so it wsn't unbearable.

If you have already coated the sides and/or bottom prior to applying the cloth it needs to be cured and you REALLY need to scuff the first coat prior to wetting the glass to get a good mechanical bonding of the cloth. West's 207 Hardner is different from the others in that it will not blush, has an UV Inhibitor and provides a clear finish. It still requires a scuffed surface to bond to.

When I added a second layer of cloth (partial, football shapped piece) to the canoe I did use 80 Grit paper and scuffed the cured epoxy. I used the same procedure as above for the second layer with a good result.

It's been about 5 years and still holding up and looks like new. I'd recommend, if you have any doubts call West System Tech Support and discuss it with them I talked with them for 45 min's the morning I did it to gain the confidence to do it. Was glad I did. They provide great tech support, just the price of a phone call.

Sorry to drag this out but, after all the hard work building your boat you don't want to screw it up glassing it.. I have seen a canoe like mine that was not done correctly and it had milkey look to it, not pretty.