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

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