Replies

1. 
   Wayne_from_White_Salmon | Oct 12, 2000 04:32pm | #1

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   Spar Varnish- what is it?

   I just started using some Spar varnish instead of my usual poly finish. What is the stuff made from? How is it different from regular poly? Can the two be mixed? Can I make my regular potion of varnish/oil/thinner?

   I'm hoping its more durable and will work better with stuff that may end up outside or in wet environments.

   Thanks all

1. 
   Robert_Schrank | Oct 12, 2000 05:41pm | #2

   *Jeff Jewittbook "Wood Finishes" Chap. 7 classifying finishes never mentions polyurethanes. Are they considered "varnish" ? Being an old timer I thought varnish was in a seperate category. AmI wrong ? Then what id any is the difference ?Robert Schrank E mail [email protected] Thanks

1. 
   Howard_Acheson | Oct 13, 2000 01:54am | #3

   *Varnish consists of a heated blend of oil and resins.The resins origially were natural substances, most recently phenolic but since the 1920's have been synthetics such as alkyd. The oils are either tung oil or linseed oil--most frequently linseed although some marine vanishes are still made with tung.Most varnishes are alkyd now days but recently polyurethane has been added to some varnishes to make them more scratch resistant. So, "poly" is a varnish with an addition of polyurethane and all modern varnish contain "plastic" as phenolic and alkyd are plastics.There are two basic types of varnish--short oil and long oil. This has to do with the percentage of oil used in the mixture. "Short oil" means that relatively a lesser amount of oil is used. This makes the cured vanish harder due to the higher percentage of resins. Most "interior" varnishes are short oil and they can be polished to very high gloss because of their hardness. However, they are also more brittle and can craze when dented. "Long oil" varnishes contain a higher percentage of oil and are therefore, more flexible and will "give" instead of crazing. However, they can not be sanded and polished to a high gloss because of their softness. "Spar" varnishes were developed for marine applications where the coating was exposed to high sunlight and subjected to the movement of the wood as the wood heated and cooled. Therefore, a spar varnish is a long oil varnish that has had UV protectors added to it to help it last in an outdoor environment. It takes about 6-8 coats for full UV protection but you will still have to maintain it annually.So, all modern varnishes are "plastic"; interior, short oil varnishes cure harder; long oil exterior varnishes are flexible; UV inhibitors are added to spar varnishes and polyurethane is only an additive to standard alkyd varnish.Finally, for indoor use, use interior if you want to "finish the finish" to a high gloss or use exterior or spar if you want maximum durability for a tabletop that will take a beating. Use poly if you want.All varnishes require learning and practise to apply sucessfully.