Mike,

The real problem is in the language:  coatings.  As long as the industry keeps developing easy to use, quick clean-up, drinkable for under six year olds,  coatings that only adhere to freshly applied primers we are going to have coatings, and just like your and my coats they come off about as easy as they go on, and just like masonry the coating is the easy part, the substrate and the systems behind it are the tricky part.  For clear coats I like products that require a flood coat to dry (7%) wood to get deep penetration.  I used to be a big believer in thinning the first applications, but I guess we are not allowed to do that with most products, nor stir in lead or mercury.  Oh well.  We have been using Cedar Naturaltone and Penofin, depending on wood type for decks and outdoor furniture.  But we keep getting notices that they have changed the product for us, so I have no idea how long it will last, but the Naturaltone is “Guaranteed for 3 years”!  Wha whooo.

Best,

Leland

 

 

Though wood is one of my least favorite materials for exterior exposures (inherently UV-unstable), I am interested in the group's knowledge base on this one, as a manufacturer of waterborne aliphatic polyurethanes.

So my understanding of it is that wood fibers quickly (within a few weeks) UV-degrade in direct sunlight, and it is the failure of the wood surface fibers that leads to paint delamination/peeling. The problem with clear coats, almost regardless of their composition, is that they can't block the UV from getting at the wood. So when we get calls from people wanting to clear coat exterior decks, we have always said that you need pigments to block UV.

This is just the opposite of masonry applications, where the challenge is to produce coatings that will be durable enough to remain effective over what is otherwise an inherently UV-stable substrate. So what good does it do to use a 30-year polyurethane on a wood surface that was born to decompose in 6 weeks? Has anyone ever managed to produce a clear coating that stays clear and protects wood for longer than a year?

Mike E
---------- Original Message -----------
From: Rudy R Christian <[log in to unmask]>
To: [log in to unmask]
Sent: Tue, 1 Jul 2008 09:32:05 -0400
Subject: Re: [BP] Treatment / Varnish for exterior mahogany


> Maybe they didn't squeeze enough Brazilians? We've had really good
> luck with water based urethanes. Most of the varnish you can buy today
> is poly anyhow. I would check with: www.jamestowndistributors.com.
> They carry a lot of marine stuff. I buy all of my high grade fasteners
> from them. They have good dust masks and respirators too.
>
> Rudy
>
> --
> To terminate puerile preservation prattling among pals and the
> uncoffee-ed, or to change your settings, go to:
> <http://listserv.icors.org/archives/bullamanka-pinheads.html>
------- End of Original Message -------

-- To terminate puerile preservation prattling among pals and the uncoffee-ed, or to change your settings, go to: http://listserv.icors.org/archives/bullamanka-pinheads.html