I'm a little confused. The upshot from what I can tell is that the surface prep is extremely important so that the primer can soak into the wood to be able to 'grab' hold for the top coats. Is that right?
Jim Hicks
On May 2, 2013, at 7:53 AM, John Leeke wrote:

> Jim,
> 
> See the Pre-Treatment discussion here:
> 
> http://historichomeworks.com/forum/viewtopic.php?p=6257#6257
> 
> I started developing these pre-treatment methods back in the 1980s, based on studies at the Forest Products Laboratory and my own experience.
> 
> If the paint is lifting off down to bare wood the main cause is excessive moisture in the wood. The source of the moisture may be from inside the house, or  from rain water seeping in through joints in the woodwork, or through cracks in the paint film.
> 
> Extreme Prep:
> If the existing paint film is thicker than .015" (a dime is .023" thick), then it is thick enough that the water vapor cannot easily escape from the wood directly through the paint film, so it simply pushes the paint film off the wood on its way out. When we want to get the maximum durability of the new paint coating we remove all the existing paint down to bare wood. We also clean the wood with a Wet Abrasive Scrub:
> 
> http://historichomeworks.com/forum/viewtopic.php?t=1751
> 
> Durability:
> With the combination of 1. Removal of heavy paint buildup, 2. Wet Abrasive Scrub, and 3. Pre-Treatment, plus experienced and skilled workers we have been able to get 20 to 30 years of life out of a paint job. With an extreme salt water micro-climate that drops down to 15 to 20 years.
> 
> Sealing the Wood:
> >>It seems to me that sealing the wood would reduce the opportunity for the primer to soak into he wood for more "bite."<<
> 
> An effective pre-treatment should not seal the wood. It should leave most of the wood cells at the surface open so the primer can still make a mechanical bond by soaking into the cells. About 40% of the bonding is mechanical and 60% of the bonding is chemical. The pre-treatment improved chemical bonding by making the highly variable surface conditions of old wood more consistent and suitable for better performance of the primer.
> 
> John
> by brush and hand it looks right grand
> 
> --
> **Please remember to trim posts, as requested in the Terms of Service**
> 
> 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>

--
**Please remember to trim posts, as requested in the Terms of Service**

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>