[Alberg30] (no subject)

[chrishardy]

Polyurethane varnish is great if it never is allowed to degrade but if 
it does it must be removed before getting a good job on recoating. It 
also gets very hard not "moving" a little with changes in the moisture/ 
tempurature of the wood under it. thus cracking more easily than regular 
varnish. The bonding is as Eddie Diver states. I would never use it on a 
boat over wood.

EddieDiver at aol.com wrote:

>Succeeding (second, third, etc.) coats of regular varnish bond to each other 
>both chemically and mechanically. Minimal sanding between coats is required 
>to get them to bond. If one applies another coat within a few hours, sanding 
>is only required to knock off the "defects" in the preceeding coat. It is 
>easy to touch-up nicks and scratches.
>
>With polyurethane varnish, there is no chemical bond. The bond requires a 
>mechanical "tooth" on the preceeding coat by abrasive sanding. If 
>insufficient "tooth", the next coat can delaminate. It is difficult to 
>touch-up nicks and scratches.
>
>Both types can be purchased in a "hand-rubbed dull" finish.
>
>I would not recommend any polyurethane on a boat. Ed. Schroeder, #303, 
>Emotional Rescue
>
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