Automotive clearcoat sprayed vs spar varnish brushed | SouthernPaddler.com

Automotive clearcoat sprayed vs spar varnish brushed

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canoecrafter

Member
Jan 24, 2011
5
0
I'm wondering if any of you southern builders have experimented with spraying 2-part automotive clearcoat—rather than spar varnish— on cedarstrip boats to protect the clear epoxy from sunshine.

I'm a canoebuilder in northern Wisconsin and I've been experimenting with a common PPG automotive clearcoat, applied with an HVLP sprayer, on my cedarstrip canoes. I've seen very encouraging results so far in the way the coating protects epoxy from UV degradation, but we don't have the intense sunshine up here that you southern builders experience. 8)

Anyone using sprayed automotive clearcoat in place of the traditional five wet-sanded coats of spar varnish?

If the finish holds up for several years to Florida sunshine, I'd consider that the acid test!

Gary

When people finally figure out what's important in Life, there's gonna be a big shortage of canoes.
 
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Oyster

Well-Known Member
Dec 5, 2008
254
0
OBX North Carolina
This is a wooden hull thats just been sprayed with the clearcoat over a wooden runabout in florida. There are guys doing this now even though I am a fan of varnish on boats that are actually used.
Malahini001.jpg


Malahini012.jpg
 
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oldsparkey

Well-Known Member
Aug 25, 2003
10,479
123
Central , Florida
www.southernpaddler.com
I haven't tried it , always use varnish but if the clear coat holds up on the cars down here then it should hold up on the boats. Most folks would keep a nice wood boat under cover when not being used while a lot of cars sit outside year round.

Then follow up with a good wax job , the same as you would do with your vehicle. Another benefit is the boat would not be in the water year round.

If there would be any worries , take a scrap piece of wood and do a test on it.

Chuck.
 
C

canoecrafter

Member
Jan 24, 2011
5
0
Jack,
The degree of UV protection is directly related to the thickness of the coat doing the protecting.

Five coats of spar varnish, wet-sanded between coats, builds to about 0.005" (5 mils)—or about 1 mil per coat. 2-part urethane clearcoat builds about 2-3 mils per coat, and you can easily spray on three coats within 30 minutes of each other. So three coats of sprayed clearcoat builds up to 6-9 mils.

The reason that the mil thickness of clearcoat is so much higher per coat than spar varnish is that there are no solvents to evaporate out as there are in spar varnish. The urethane clearcoat chemically "sets" rather than drying like spar varnish does.

I like the sensual pleasure of varnishing as well as any boatbuilder does, but I can't argue with the results above. Five coats of spar varnish take five days to apply and give 5 mils of protection. Three coats of urethane clearcoat can be spray applied in an hour and a half and give up to 9 mils protection. And the materials cost is about the same.
 
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Oyster

Well-Known Member
Dec 5, 2008
254
0
OBX North Carolina
I have never been a person that uses a boat that did not at some time need to fix a ding, scratch or upgrade a finish. If it was not me if you have any family or guests on board neithe are as particular as I will be knowing the differences in finishes if a problem arises. Not having the luxuary from year to year either to spray larger boats bigger than canoes, also creates a problem with trying to redo with clearcoats too. For sure patching is just not that easy when you use clearcoat over any finished or stained and finished hull.

For the sake of this topic and thread, I personally do not know what type of use your canoes get. So I find myself replying to the worse case scenerio for your job and for anyone else reading and attempting to do the same. My .02 worth,
 
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Kayak Jack

Well-Known Member
Aug 26, 2003
13,976
171
86
Okemos / East Lansing Michigan
canoecrafter said:
Jack, The degree of UV protection is directly related to the thickness of the coat doing the protecting.<SNIP>
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Thanks. I'm not so sure that it is directly proportional to only thickness. Doesn't the UV protectant that's added to the varnish also have something to do with it? It isn't varnish, in and of itself, that protects; it's an additive. Right?

Any information and training that can be provided will be appreciated.
 
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canoecrafter

Member
Jan 24, 2011
5
0
Jack's point is well taken, that the film thickness is not the only measure of UV protection in spar varnish or 2-part urethane clearcoat finishes. Most marine spar varnish manufacturers add UV protectant as a separate ingredient in varying amounts. So if the UV protectant concentration is the same in two spar varnish formulations, then the amount of sunlight protection will be equal to the mil thickness of each varnish.

But here's a monkey-wrench in the equation. Some marine spar varnishes have no UV protectant added. Instead, the makers depend on the natural reflectance of high-gloss varnish to deflect damaging sunlight. A call to the varnish maker's Technical Customer Service Desk is about the only way to find out how much, if any, UV protective ingredients are added to the marine spar varnish you use.

Automotive urethane clearcoat formulations always add UV protective additives to their products, and customarily in much larger amounts than in spar varnishes. Why? These clearcoat finishes on cars are not meant to be wet-sanded and renewed each 3-4 years as our spar-varnished wooden boats are. Auto makers have one shot at getting enough UV protection over their basecoat paint to stop that paint from fading in sunlight for the life of the car. So they add enough UV additive to their clearcoat formulations to ensure over-protection for life.

While it seems likely that several coats of sprayed urethane clearcoat will protect epoxy beneath the clearcoat for many, many years, fixing dings in clearcoat is a great deal more difficult than would be the case with a softer and simpler spar-varnish coating. So I don't use auto clearcoat on items like paddles or gunwales that are going to be subjected to abuse or excessive wear.

WEST System published a short article on protecting epoxy-encapsulated wood with spar varnish or urethane clearcoat a few years ago. You can read it at: http://www.epoxyworks.com/18/pdf/varnish.pdf
 
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uzzma123

New Member
Dec 19, 2011
1
0
oldsparkey said:
Kayak Jack said:
It's sad to see someone, under the guise of saying thanks, try to use a post to sell their stuff. No interest in boats or discussion, just selling their stuff - power tools.
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Yep .. I found him also and as with any spammer ... he is GONE. :D
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Hi there, I'm not a spammer, give me time to proved my self... :cry:
 
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