Posted by Jeff Van Etten (Member # 1961) on 07-22-2000, 08:31 AM:

Has anyone ever varnished over 3M 5200 or 3M 101. If so how well has it held up? Thanks, Jeff

Posted by Ian McColgin (Member # 32) on 07-22-2000, 09:49 AM:

It didn't for me.
Except where the 5200 exposed was just an ultrathin glue line.

Posted by thechemist (Member # 1468) on 07-22-2000, 03:19 PM:

There is a high probability of mechanical failure when putting a relatively hard and less flexible coating with less elongation capability on top of a relatively soft and more flexible substrate with high elongation capability. EVEN IF IT STICKS. Expect eventually (as the varnish ages and sfiffens) to see cracks in the varnish.

Posted by Jorma Salomaa (Member # 793) on 07-22-2000, 06:58 PM:

Depends on where and why one would do it. In principle, you cańt expect any paint or varnish to stick to any polysulfide or polyurethane sealant for very long. But it may stick long enough for your purpose. For instance, a coach roof teak planked and with polysulfide seams was kept varnished with Deks Olje No.2 for ten years. The owner simply wanted it to look nice. Of course the seams always received the same varnishing as the planks. In a few years the varnish on the seams had crumbled but none the less received a couple of new coats each year. The seams did́nt look that nice, but the general picture was neat. Being varnished, the planks did́nt move a lot, there was less stress on the seam compound and if it let go in some place the void was filled with varnish. The roof never leaked. Comes a new owner who thinks teak should be left bare. The next year the seams start leaking.
Another example: The cockpit seats form hatches for stowage room below, and are made of plywood covered with teak planks, seams are polysulfide. Since everything is 40 years old, water gets into the plywood through minute checks in the planks. Everything is thoroughly dried, then sanded and varnished with two part polyurethane with a plasticiser added. After three years everything is still fine. There are no leaks anymore, and the varnish is sticking to the seam compound even if hair line cracks can be seen. It will hold on for a couple of more years.

So, in principle the 3M or any other elastic sealants should not be expected to hold varnish but it all depends on what you are after.

Posted by Jeff Van Etten (Member # 1961) on 07-22-2000, 08:26 PM:

Jorma, thanks for the reply and to everyone else too.
I am building a mahogany speed boat like a 1939 chris craft 21'. Only mine is only 7' long and it will be used as a cargo trailer behind my Honda Gold Wing. The deck will hinge open just forward of the windshield and open to about 1' forward of the stern. It will sit on a scaled down boat trailer and have all the deck hardward to make it look good.

The boat is made with 1/2" plywood ribs covered with 1/8" ply then 1/8" mahoganystripes from 5/4 lumber. The deck has 1/8" spaces for the calking just for looks this is were the 5200 will be varnished over. The boat will not be in the sun a lot but it may be in the sun for 2-3 weeks at a time a few times a year when we travel.

Jeff Van Etten
Pensacola, Fl
Vintage Motorcycle restorer

Posted by thechemist (Member # 1468) on 07-22-2000, 09:40 PM:

I'd go with a high-elongation 2-part polyurethane, because it will stand up to the road dust and dirt and gravel hitting it at high speed and still hold its gloss, etc. Any oil or alkyd varnish will lose appearance due to sandblasting pretty quickly. That is the reason why only the 2-part high-elongation poly is used on airplanes.
Now you've got me thinking....I have a 1956 BSA 650.....had not considered a trailer, but now that you mention it.......something traditional might work.....

Posted by Jeff Van Etten (Member # 1961) on 07-22-2000, 09:48 PM:

Any recomendations on a good 2 part varnish? I understand they are very clear, but I will be putting it over west system epoxy to get that nice honey color in the wood and to help seal the wood from movment.

Posted by thechemist (Member # 1468) on 07-23-2000, 04:01 PM:

Take a look at

Posted by Steven Gould (Member # 1912) on 07-27-2000, 07:04 PM:

WEST makes their own 2 part urethane that is expensive but bullet proof.

Posted by TomRobb (Member # 1216) on 07-28-2000, 09:00 AM:

TheChemist, what's the softish resilient clear stuff they spray paint on the leading edges of cars where road grit chips the paint? Maybe that stuff, in strategic places, would save the finish on the "ChrisCraft" trailer.

Posted by thechemist (Member # 1468) on 07-28-2000, 11:30 AM:

That IS the two-part polyurethane, the same sort of thing that goes on the leading edges of airplanes. If it was not for that the airborn dust would sandblast away the aluminum skins on the leading edges of the wings and engine inlets. That is the sort of property you want over wood. Tough, highly tear-resistant, high-elongation, etc. A flying bit of grit just bounces off it.

Posted by Ironmule (Member # 1065) on 07-30-2000, 05:52 PM:

Jeff, what sort of components are you using for the trailer? That sort of lite weight trailer might be just the thing for those of us with traditional skiffs that are a little too heavy for cartopping. Most "boat" trailers are sprung for 500lb and heavier boats. A 100lb to 200lb skiff gets shaken and stirred by them. This might be a good subject for it's own thread JWSmith