# Spar Urethan over Polyurethane Resin??



## cyclefrog (Jan 5, 2016)

I'm seeking advice on the possible effects and or compatibility of putting Minwax Helmsman Spar Urethane over Emmet's Good Stuff polyurethane gel. I called Minwax and the maker of Emmet's to no avail. Does anyone know if the two products are compatible. They application is red oak in the bed a of a 1955 Chevy pickup truck. Thanks for the help. Sincerely cyclefrog.


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## Steve Neul (Sep 2, 2011)

The finishes are compatible but you can't do that, not unless you are going to keep the truck indoors in a museum. The polyurethane will have to come off to use for outdoor use. Another issue you will have is red oak isn't suited for exterior use. Any place the finish gets damaged and allows water to get in will turn black. White oak is suited for exterior use. 

The Helmsman spar isn't one of the better spar varnishes for one thing. A spar varnish is similar to polyurethane with the exception is it's formulated to be more flexible to deal with the temperature extremes of being outdoors. You would be better off with a marine grade spar. Epifanes is the best but expensive. Cabot makes a good marine grade spar that is cheaper. It's also available at Lowe's. 

A spar varnish was originally designed to use on tall ships. They had trouble with varnish cracking on the mast of a ship because varnish was too hard and the constant bending of the mast had the varnish coming off. They needed a finish that was softer and more elastic so they came up with the spar varnish for that application. In the process they discovered it just worked best for outdoor wood like benches and front doors do to the expansion and contraction of wood. Now the modern finish is polyurethane. It's harder than the old varnishes used to be. For this reason polyurethane isn't suited for outdoor wood. It will just crack and peal off used outdoors.


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## HowardAcheson (Nov 25, 2011)

In general, finishing products containing polyurethane or urethane (same stuff) do not perform well in exterior environments.The UV in sunlight will rather quickly cause the finish to turn yellow, then crack and peel. This is particularly true of "big box" consumer spar varnishes. At the very least you should be using a true marine varnish. Go to a marine supply store and look for products true marine exterior varnishes.

Is this finish going to be used on a vehicle that will be an actually "working" vehicle? Is so, there will be no finish that will last long with that type of abuse. You will be constantly repairing and refinishing. A longer lasting solution would be a "deck" finish.

As has been already mentioned, red oak is a poor choice for a truck bed. When it gets wet for long periods, it begin to rot. White oak is a much better choice for your application.


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## cyclefrog (Jan 5, 2016)

Steve and Howard,
Thanks so much for the detailed information and directing me toward the correct finish for my truck bed boards. The truck will live in doors and covered when I'm not driving it. I will definitely change the boards to white oak on the next reconfiguration. No the truck is not going to see heavy duty "work" use.  Groceries and the odd cardboard box once in a while. It has a very expensive paint job and I don't plan to do anything that will hurt the paint. Best Regards, Matt


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