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spar varnish questions


Brendan

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Hi All,

 

I am just finishing the sewing on my very long and slow vardo Build. Whew, it has been a long journey and I am happy to see the light at the end of the tunnel.

 

I finished the laminated coaming with Interlux Origional spar varnish I picked up at the local marine store. I love the way it looks but I think I jumped the gun on my 3rd coat because I find that the cure even after ~40 hours is not "sticky" but rubbery soft and far from hard enough to survive a sanding. I think it would gumb up and roll. I am trying to keep it in a low humidity place with the dehumidifier going and I am curious if people, based on experience,

 

Thoughts on if it should pull through with time? Somwhere I read it can take forever for spar varnish to cure.

 

 

This has me partly concerned because my plan for the skin is to seal the polyester with the spar varnish. My test coat on a scrap of material came through nicely but I am concerned about whatever went wrong with the coaming scrapping my skin.

 

I dont think it *needs* to be thinned as the spar varnish fully pentrated the test piece however should I do that to improve the drying time? I had read that may help however I do not have any experience thinning anything not waterbased.

 

I would greatly appreciate any thoughts on 

-thinning

-how many coats

-guidance on time between coats, I mostly followed the can (only cheated a few hours), I think the can may lie.

-how soon I can safely take it to the water? (assuming it feels dry). This will help with some self discipline since I am itching to get it in there.

 

Thanks in advance.

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Real varnish, like what you used never gets nearly as hard as polyurethane.  That being said, it should not be sticky or gooey either.  It takes several days to cure well.  If you put the coats on too thick, or too quickly, it can take longer. I can do a coat one day, sand and do a 2nd coat the next day and so on.  Or, I can do 2 coats in one day, the second one is a hot recoat, meaning it is done after the first dries, but does not cure yet.  If I do this, I take the next day off completely as it is need for cure. Many people put varnish on too thick, it should be well feathered out with slow strokes to avoid the small  bubbles.

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Hi Dave,

 

Yes, I see what you mean. Its not hard (like Polyurethane) but does seem to be becoming less soft.

 

I think I saw in an earlier post from you on this subject that the overcoats and trap the earlier coat and slow down the curing process. I suspect that is what happened.

 

How many coats do you imagine I need for the fabric? I am thinking two maybe three but I don't want to over or underdo it. Logic says "until it floats" but I want to make sure I want to get enough on there before it fully cures so that it burns in nicely.

 

I will be more careful when I apply it to the fabric to ensure things are well cured (although due to surface area I imagine that the fabric dries fairly nicely).

 

Thanks!

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8 hours ago, Brendan said:

How many coats do you imagine I need for the fabric? I am thinking two maybe three but I don't want to over or underdo it. Logic says "until it floats" but I want to make sure I want to get enough on there before it fully cures so that it burns in nicely.

 

Painting the fabric is a whole different process than your combing.  I always used paint on the cloth.  But as varnish is an oil based product, and similar viscosity to oil based paint, it probably takes the same 2 or 3 coats to seal the hull.  I have always used 3 coats.

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As Dave said.  just no way to say but an easy to way to check if  you have enough is turn the boat upside down/ Put a lightbulb inside. Darken the room and see if you have pin holes in the skin. They will show as bright spots in the frabric and a sure sign you need to add another coat.

 

I do this with all the boats I paint and it works really well with paint. Varnish is going to be a bit harder to see the pinholes I expect but it should work. Probably need a not to bright light.

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Thank you both for the help.

 

A little status update and comments for anyone else considering doing the same at some point ( I will try to update again when its fully done).

 

Despite some uncertaintly I have rolled ahead with the varnish but I did have a chat with a guy at the marine store as well (who used to live on a wooden boat and "has a bit of experience" with the product).

 

Guidance was to a certain degree that my controlled indoor finishing environment was part of the problem. Summarizing:

 

*Do it outside (preferably in the shade) on a low humidity day (40% ideal, 60% max) then move it into the sun to help it dry as fast as possible. People otherwise use heaters and fans. This is likely where I went wrong, it was a humid day when I did my coaming, indoors with AC, the AC probably helped with the humidity and I could have later let it sit somewhere warm but I did not.

*Basically after a certain point if its not dried it might not because the hardeners that are involved in the curing will be less effective (not sure about the chemical reason for this either used up or whatever).

*The third coat can trap the second between it and the first if it is not completely dry and cause problems. People will use thinners to help this along especially when the end of the season is nearing and they really need to launch their wooden boat. [I am using the 216 thinner for the second and and probably third coats for help this along]

*If something is gummy after a couple days (as per #2 above) it might not harden. if this happens rather than stripping it down sometime there is nothing to lose trying another coat of the varnish as the hardeners can help finish the job. I did this with the coaming and it seems to have helped. It is at the very least no worse than before.

 

I also used a roller to help ensure an even coat. I feel that with the finish, because its very picky about overcoating, above and behond aethetics having an even coat is super important. Patience is also key, rushing a new coat onto one not yet dried will be trouble.

 

So far I am on my first coat for the deck and second coat for the haul. It is raining today here and humid so no finishing to be done.

 

In terms of the fabric, the areas where I strunk with the iron seemed to stay closed and I like the look so far, after coat #3 it will be an amber. The areas where the fabric has dimpled at my my sloppy sewing or areas I did not go over with the iron. 

 

One thing I should add: when I painted the haul I did it in the shade, when I did the deck I did it in the sun. I saw that the fabric was getting seemed somewhat loser or at least seemed stretchy even before I applied the first coat. I think this could be a factor in peoples finishing troubles. Had I really carelessly pressed into the fabric with the roller I would have caused sagging.

 

Would I do it again? Well, to be honest I am still not clear what else to buy since almost everything people recommend is not available here in Canada, known to cause loosening or discontinued. That said I can get oil based Kilz and I saw someone had a good result with that, I would try that.

 

Again I will try to update this when complete and floating for anyone considering the same thing. so far this is all academic but at the very least it could make some great wall art/light diffuser...

 

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It floats well and paddled nicely.

 

Varnish has cured fully but fabric stays flexible. Result produces a very waterproof material.

 

One minor issue at the bow seam I found after taking it out of the water, there was water in the boat still (from my paddle) and a slow drip from some spot along the bow seam. I will need to find the spot I somehow missed and hit it with some aquaseal.

 

Which also made me wonder when I install the bow keel protection, Jeff just skews those on IIRC. Do people just use aquaseal on those to prevent leaking around the skrews?

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