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 Post subject: Varnish
PostPosted: October 18th, 2005, 3:18 pm 
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Joined: April 22nd, 2003, 8:26 pm
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Location: London, Ontario, Canada
I'm varnishing the outside of the hull this week.

Normally I wait 24 hours to sand and recoat.

Is there any advantage or disadvantage to re-coating before the varnish has dried for 24 hours?

Do you get a better chemical bond if the varnish is some what tacky?

I am itching to go for a paddle in it before it gets too cold.

Thanks,
Doug


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 Post subject:
PostPosted: October 19th, 2005, 12:39 pm 
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Joined: September 4th, 2003, 3:00 pm
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Location: Paris, On
Doug,

I used Epifanes, they say that you can do it either way. i re-coated prior to the full cure to avoid sanding. i was led to understand that this would provide a chemical bond which was more desireable. after sanding the bottom coat, you are left with only a physical bond. sanding takes time and exposes your lungs to undesireable/dangerouse chemicals.

edit - i found that the second coat would re-activate the bottom coat, and they would flow better leaving a smoother end reslut. this is in no way a scientific observation!!!!!!


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PostPosted: October 22nd, 2005, 6:05 pm 
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Location: Swartz Creek, Michigan, USA
As far as sanding between coats is concerned, the longer amount of time that you can wait the better unless the varnish is specifically formulated otherwise. I see that Epifanes was mentioned and the way it was described it must be their Wood Finish type. Epifanes Wood Finish is only one type of varnish that they offer and it is designed to leave open microscopic pores that slowly close over a 72 hour period, depending on conditions, which allows the following coat to adhere to the previous without sanding. With the regular Epifanes you have to wait.

There are a couple of reasons that I can think of off hand why it's best to wait as long as possible before applying the next coat. The first is that if you apply another coat over one that hasn't cured enough and do this numerous times the bottom coats will play heck trying to dry, which may cause problems but will surely increase the length of time that it will take for your varnish job to fully cure and give the wood the best protection possible.
The second reason is that if you are sanding between coats the harder {cured longer} surface won't clog up your sandpaper, which increases not only your effort but how much sandpaper you will need to finish the job. This "gumming" is usually a good way to tell if a coat has cured enough before moving on to the next one. If you hit it with sandpaper or a scotch brite pad and it doesn't gum it up you should be good to go.

In the past I only used the Epifanes Wood Finish Varnish but found myself sanding between coats anyway so I started using their regular spar varnish. I will use the Wood Finish {no sanding required} for my sealer coat and the next two but that's only because I will be aggressively sanding out any crud I picked up before moving on to my final build & finish coats, which is where I switch to the regular spar varnish. I find it's important to sand between coats at this stage because if you don't any crud that settles on your project only builds up as you add coats and by sanding you get the best possible bond.
Actually I only use sandpaper when knocking down my first few coats that I didn't sand in between as I find it too aggressive, especially if working on thwarts, seats, paddles & the like, pieces that have edges. When applied varnish will pull away from edges with this being more pronounced the sharper the edge so your coat will be thinner in these areas. I generally use Scotch Brite Pads which are far more forgiving and still do a good job of scuffing up the surface for the next coat. Just like sandpaper these pads come in "grits" only in this case it's really not grit but how course the pad is. If I did pick up a serious piece of crud while applying my last coat I may spot sand using sandpaper but usually the Scotch Brite can handle it.

Jack


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 Post subject:
PostPosted: October 24th, 2005, 8:53 am 
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Location: Paris, On
Jack is bang on.

I varnished my boat with about 4 hours of work total (if that, hull only, all else was oil rubbed) in about oh, 2-3 days lets say. i was on the water about 48 hours after my final coat. I definitally did not have a 100% perfect mirror finish musium type of finish.... and i am very glad i did not. the boat now looks like its been used for a half a season, as it should. i would have been crying in my beer if i had of taken an extra 20 hours for a flawless finish and then dragged her up on shore at the mass on her maiden voyage!!

its all about what you want out of your boat... and how much your willing to put into it!!


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 Post subject:
PostPosted: November 4th, 2005, 6:58 am 
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Joined: September 28th, 2004, 6:52 am
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After over forty ytears of boatbuilding the one thing I have learned is that things usually work bets when you follow the directions. Sometimes you can get away with not following them but most of the time the manufacturer of a product knows what they are talking about.

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John Winters


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 Post subject:
PostPosted: November 4th, 2005, 7:00 am 
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Joined: September 28th, 2004, 6:52 am
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Notice the Freudian slip " ytears" in the previous post :D :D :D :D :D

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John Winters


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