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Poly vs Alkyd Varnish (Read 536 times)
 
Bruce Kamp
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Poly vs Alkyd Varnish
Jun 9th, 2016 at 9:18pm
 
I have been reading a lot about this and it seems the consensus is that the poly will cure very hard vs the varnish. This seems to mean that eventually the poly may crack where the varnish will not cure quite so hard and therefore will better withstand movement over time.
My current project is a segmented bowl. I have applied Danish oil, let it cure and want to apply the best topcoat. I know I could use the Danish oil but do not want to, I want a protective, smooth final finish.
Pros and cons?
Thank you for any insight into this.
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william trench
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Re: Poly vs Alkyd Varnish
Reply #1 - Jun 10th, 2016 at 4:59am
 
If you are talking about WB poly, I would think it would not stick to the Danish oil.
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Ed Weber
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Re: Poly vs Alkyd Varnish
Reply #2 - Jun 10th, 2016 at 8:08am
 
Bruce Kamp wrote on Jun 9th, 2016 at 9:18pm:
This seems to mean that eventually the poly may crack where the varnish will not cure quite so hard and therefore will better withstand movement over time.


All top coats will fail in some way over time.
Most polyurethanes these days (oil-based) remain flexible enough that cracking is no longer an issue.
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Ron Sardo
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Re: Poly vs Alkyd Varnish
Reply #3 - Jun 10th, 2016 at 9:21am
 
There are long varnishes and short varnishes, and they are both used for different reasons.

Long varnish (spar varnish) has more oil than short varnish. Because of the higher oil content it is softer, more flexible and is better suited for outdoor use. Why, because under normal conditions will move along with the wood.

Short varnish has less oil and more resins. Its harder and more resistant to scratches, but its not very flexible. Its better suited for indoor use such as floors, counters and furniture.

Oil based poly, oil based polyurethane, urethane, alkyd varnish, phenolic varnish and varnish are really the same thing. The only real difference is the ratio of oil to resins and thinners. Most polys have other chemical compounds that will make them harder and in my experience more cloudy than varnish. A satin poly also has an added compound that helps refract light, creating a satin look and increases the cloudiness. Water-based polys are the most cloudy of all finishes.

IMO, we as turners love a beautiful looking bowl with a fabulous grain. Why would we apply a finish that clouds, or hides what we love? If you want the grain to pop, stick to oil.

The way a properly assembled segmented piece is glued up makes it very stable. So choosing a long or short varnish is really a personal preference. That said I prefer a long varnish.
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« Last Edit: Jun 10th, 2016 at 9:24am by Ron Sardo »  

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Bruce Kamp
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Re: Poly vs Alkyd Varnish
Reply #4 - Jun 24th, 2016 at 10:11pm
 
It appears that Pratt and Whitney's #38 is a popular choice for those that prefer varnish. My plan is to try it using gloss. Then use rottonstone to dull that finish just enough to get a hand rubbed look.
I know many prefer  more satin look but I like more gloss but not so much as to make it look plastic.
I understand that rottonstone is a little old fashion but I have tried it once so far and like it.
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Ron Sardo
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Re: Poly vs Alkyd Varnish
Reply #5 - Jun 25th, 2016 at 7:50am
 
Bruce Kamp wrote on Jun 24th, 2016 at 10:11pm:
I understand that rottonstone is a little old fashion but I have tried it once so far and like it.

Absolutely not. That's what's in the brown buffing compounds bars (aka tripoli) people buy to put on their buffing wheels. (what's old is new again)

Another alternative to knock down the gloss is #0000 steel wool with a little mineral spirits
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Don Stephan
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Re: Poly vs Alkyd Varnish
Reply #6 - Jun 25th, 2016 at 7:03pm
 
My finish is gloss P&L 38 mixed 50-50 with mineral spirits in a squeeze bottle.  A small squirt on a bit of clean rag and wipe thoroughly all surfaces of the bowl.  Using two pieces of clean paper towel, scrub dry as possible and let dry on nail board.  Be sure not to leave wipe marks on inside bottom of bowl.

First coat I let dry overnight, then additional coats 9AM 1PM and 6PM until sufficient look, for me I guess a semi-gloss.  Usually takes 507 coats depending how fine grained the wood is.  Always add some Bloxygen or similar to the can and the squeeze bottle, but the mix always starts curing in about 7 days.  I have used it after noticeably thicker but tends to leave wipe marks.

Recently I tried using some mix with satin P&L 38 over my usual finished bowl and didn't notice any difference in sheen.
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