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Posted by pipedown on August 5, 2006, 12:29 am
>
>> pipedown wrote:
>>> Marine spar varnish is a type of high quality polyurethane.
>>
>> I suppose that spar varnish made with polyurethane exists but it isn't
>> normal.
>>
>> Spar varnish is made with more oil than normal so it dries softer and
>> more flexible because it is meant for spars. And spars bend.
>>
>> The merit of polyurethane lies in its hardness. Hardness and
>> flexibility are mutually exclusive.
>
> Not all varnish is polyurethane, but all urethane is varnish. Minwax
> Helmsman is an example of a polyurethane spar varnish.
>
I stand corrected, the traditional spar varnish is tung and linseed oil
modified by Phenolic resins. Didn't look deep enough to say the difference
between phenolic and urethane but when cured, both have similar appearance
and properties.
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