[Public-List] Spar urethane over epoxy glaze

[Gordon Laco]

Hello Stephen - 

The only way polyurethanes are better than varnish, no matter who makes a
particular brand, is in hardness.  Polyurethane can be fortified to boost UV
resistance, but it still won't be as good as varnish.

The things against varnish are the fact that the first year it's a lot of
work getting that six coat minimum...but once you do, you'll have a flexible
and durable finish.  It's still the best for wood.

The company I distribute for in Canada makes polyurethane finishes too;  so
I'm not slagging that chemistry out of hand.  But it has it's place and on
wood, exposed to sunlight, polyurethane is not as UV resistant as varnish.

A varnish job worked up to eight coats in the first year (yes, it's more
work) and maintained with a light coat every spring, will last 10-12 years
before one will have to consider stripping and starting again.

The #1 way varnish jobs go wrong is the fact that they start looking really
good after 3 or so coats, and people stop applying it there.  The next most
common way they go wrong is failure to do the maintenance coat every year or
two.  The third way is water intrusion through chips, moving joints or even
through the wood from an uncoated surface (this happens with trim a lot).

There are ways to minimize the labour in that first year - but I'm sailing
close to the wind now with regard to 'selling' and I don't think I should do
that on line when describing a particular product I've obviously got an
interest in.  We should take this off line so I won't feel inhibited!

Gord #426 Surprise


On 12/05/14 3:39 PM, "Stephen Gwyn" <stephen.gwyn at nrc-cnrc.gc.ca> wrote:

> About clear polyurethane finishes being not so good at UV
> resistance:
> 
> System Three suggests their Clear Coat epoxy followed by
> their WR LPU cross-linked polyurethane. Are they out to
> lunch?
> 
> SG
>