Finishing outdoor project

I have a piece of deck furniture that I'm making out of well-dried douglas fir. I'll probably finish it with some sort of marine poly or SPAR varnish, but I was wondering if it would be OK to douse it in something like Thompson's Water Seal first. Would that help with longevity? Would the polyurethane or other varnish still stick OK?
One way to find out, of course, but I just wondered if anyone already knew the answer.
Thanks.
Jim Kirby
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James T. Kirby
Center for Applied Coastal Research
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James T. Kirby wrote:

Jim...
Just finished a quick look at your home page at http://chinacat.coastal.udel.edu/~kirby and confess amazement that you'd feel a need to ask that particular question here...
The options you listed are are designed to prevent water from penetrating the exposed surface. I think I'd be inclined to avail myself of the boat builders' experience and go with multiple coats of a good spar varnish (I like Minwax Helmsman's) - with the first coat(s) thinned to achieve maximum penetration of the wood; and the final coat(s) uncut.
My Iowa experience would lead me to conclude that fir treated with Thompson's might be more inclined to produce splinters where you'd enjoy them least...
I'd guess that, as with a boat, it'll be a good idea to check the finish at least anually; and to sand and re-varnish as made necessary by sunlight, environmental conditions, and youngsters.
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Morris Dovey
DeSoto, Iowa USA
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Fluid mechanics and furniture finishing have pretty much nothing in common..... since you suggest otherwise.
Dave
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David Radlin wrote:

Ok. I guess it was more of an expectations thing. I expected that CEs would have some grounding in hydology (in general) and interactions (if not in the chemistry) between wood and water (specifically); and that persons involved with marine studies at the PhD level would have some familiarity with watercraft and the hows/whys of their construction and maintenance.
Jim's credentials are /impressive/ and it struck me that he would be a good resource for many of us, rather than the other way around.
No offense intended; and as I non-CE about as far from salt water as anyone in the USA can get, I couldn't resist displaying my ever-expanding ignorance.
I do have some slight experience in acquiring slivers. (-:
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Morris Dovey
DeSoto, Iowa USA
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Tell that to the guys in Mechanical Engineering who get bucks from paint companies to tell them how "low Reynolds number flows" behave on inclined walls. Paint dripping is quite a science.
Getting finishes to do something like what I study (wave breaking, turbulence) only happens on really bad days :^)
Kirby
David Radlin wrote:

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James T. Kirby
Center for Applied Coastal Research
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I believe longevity was the stated concern, not drippings.
Dave
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Thanks - despite what my web page says, most of the water I deal with is in the form of electrons doing their thing in computer memory. (The wood in my wavetanks is marine grade plastic coated plywood with epoxy paint. My "boat" (canoe, actually), is Royalex.)
Thanks for the feedback.
Jim Kirby
Morris Dovey wrote:

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James T. Kirby
Center for Applied Coastal Research
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The general feeling here and in Consumer Reports is that Thompson's Water Seal (TWS) is not very good at all. As far as overcoating with varnish or polyurethane, it would not adhere to the TWS since TWS contains wax. Do not use it under varnish or polyurethane.
Good Luck.

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wrote:

I've read somewhere to put Spar on the ends of the wood that would sit on the ground and use the normal stuff, primer and exterior paint, as usual.
Thunder
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