Spar Urethane

good question Fred

not sure myself. Perhaps the incompatiblilty with spar varnish? Perhaps it is more difficult to strip the next time it needs refinishing? Or is it because it is considered non traditional?

I have heard that a few others have used spar urethane like helmsman by Minwax. I use epiphanes. Used Captian's Z spar once. I made a couple practise canoes that I cut up for bookcases and used poly urethane.

Maybe someone will chime in?
I used Helmsman Spar Urethane by Minwax on my 15" Huron.

The canoe was ready for the kindling pile before I got it and the inside had been painted brown and then scraped to and mostly into bare stripper was used by whomever did it. As it was my first w/c rebuild, not knowing any better and against learned council I decided to give it my best shot. I'm glad I did, it's a wonderful little boat...sorry, I digress.

So, a comment on the urethane. I varnished (urethaned) the inside after canvasing and filling the canvas. I had a real problem with the urethane that dripped into the spaces between the planks (there are lots of gaps and spaces between planks in a Huron) and soaking into the canvas reacting with my filler. This left spots where the filler became soft (peanutbutter soft) and left a "divot". It cured again in a few days (week) but then there was the chore of filling and leveling all those spots. The thinner in the urethane was obviously not compatable with my filler!!

Since that bit of trouble, I varnish before canvasing and have gone back to my familiar oil based varnish. I suspect that the urethane would be fine if allowed to cure before canvasing. BUT then there is the time when the interior needs touching up...more soft filler? I didn't/don't feel like experimenting further on my canoes.

Since the inside of the Huron is so rough it is hard to tell the real quality of the finish but it does seem to protect well. As I noted above, I'm not quite sure what I'm going to do when I have to touch up the interior. I'm using up the remaining cans of Minwax on some pine and bamboo furniture and it seems fine. It's not my favorite finish but does the job and is easy to work with.
Thought I would post this FYI. My daughter is the office manager for a big furniture stripping and finishing company in the Boston area...I asked her to find out what they used for a good outdoor marine quality varnish. They use a product called "Last-N-Last" I checked around and got the light blue can called "Door and Marine" clear can also get it in an amber semi-gloss...It flows on excellent, self levels, sets fast, and sets hard and is scratch resitant....NOW...the good part.....$49 a gallon now...price just went up due to delivery costs...As they say...."try it, you'll like it!";) I eventually went to a local lumber company in this area, got it delivered...4 to a case, and split it 2 each to another restorer buddy of mine

Just got back from a fantastic canoe trip up in Maine and was dinging around in the motel lobby and saw your post. Here's my take for what it's worth. I've experimented with a number of urethane so called spar varnishes. I think all they do to call it spar varnish is add a uv filter to the mix. The problem I've always encountered is that after a while the urethane stuff starts to delaminate from the wood and crack. On the other hand, I used some cheap spar varnish (hardware brand made by Sherwin Williams) on some exterior doors. After about six years the stuff still looks great. My theory is that the real stuff stays pliable and moves with the seasonal changes in the wood whereas the urethane stuff becomes rigid and inflexible and tends to leave light colored streaks and cracks that eventually start to chip and break off. Urethane is great for interior woods that don't get much sun exposure, but I've pretty much given up on the stuff for canoes or anything that gets much weather exposure. I also find resin spar varnish easier to repair and recoat.

So there it is for whatever it's worth.
That and if you get a chip in urethane it can be really tough to fix. With oil-based spar its just sand, tack, fill, and then repeat until you are level. Spar sticks to itself, spar urethane doesn't seem to do as well after it has once cured completely.
Thanks everyone for all the comments. I used "Helmsman Spar Urethane" on the first two canoes I restored. So far, they are both holding up very well.

The people at Minwax say they have not heard of any issues about removing their products with chemical strippers. They say it will start brakeing down after 8-9 months of exposure to the sun. That being said, these two canoes should be ok for the next 40 years. I will start using old fashion varnish. What are the pros using? Fred
That fellow/member that works/worked for Interlux wrote a couple of varnishing articles a while back (they were in the Wooden Canoe), and in them he related the following (IIRC);

"Traditional varnish fails/deterates at/from the outside layer, and when it needs refinishing, it just needs sanding and a new coat,

Urethane finish fails by cracking through the whole layer, and needa to be totally removed when it needs to be refinished."

Also, in my limited experience, the urethane is much harder, and sanding between coats takes much longer. I used it on my 1st stripper and traditional on the 2ed, I probably saved a month of time going to the traditional finish.

One more "gotcha"

I think that previous comments cover most of the pro's and con's about the urethane varnish. One thing that is worth adding, spar urethane should not be applied over spar varnish. At least that is my experience. It has a tendency to separate and crack when it is laid over traditional varnish. It appears to suffer from an adhesion failure when trapped moisture penetrates from the canvas side.
If you run across this, it's a real bugger to remove. I use it indoors and on furniture, never on canoes or boats.