Epoxy on soundboards

[Richard Brekne]

Farrell wrote:

>Sure it would - wouldn't it? If you have a relatively dry soundboard with a
>coat of epoxy on the top surface, and then expose the board to a
>higher-humidity environment, what will happen. The epoxy will slow the rate
>of MC change, but the board will still attain the same equilibrium MC with
>the environment as a similar board without an epoxy coating. If you have
>that dry board and the wood tries to expand with increasing MC, won't the
>top surface of epoxy (or the top 1/10 of a millimeter of epoxy-saturated
>wood) be under tension because that presumably would not be able to expand
>as much as the wood just below it?
>
>Terry Farrell
>
>  
>
Thats the funny thing about all this.  I would think it all depends on 
the condition of the wood to begin with.

The panel is presumably old and has seen many seasons and no doubt has 
experienced its share of compression set.  So when you wedge it upwards, 
and at the same time dry it out you are certainly stretching that top 
surface... perhaps even beyond the point of what ithe panel can handle 
if you arent careful.  I am really not sure anyone can state with any 
degree of certainty just how stressed the panel is and in what direction 
after the epoxy is dried and cured and the wedges removed.

Initially, I would think the top surface wood would want to compress as 
the panel relaxes after the wedges are removed, That would be resisted 
by the epoxy, stressing ithe epoxy in a compresive sense and perhaps 
thats enough to hold the wood itself in the state of tension it was 
while wedged upwards. As it takes on moisture the wood would want to 
expand, and the top surface would be inhibited by the layers underneath 
being held by ribbing, and by the epoxy on top.  Double Jeopardy :)   
Whats actually happening to the wood cells visa vi whats happening to 
the epoxy is a mystery yet me thinks.

Cheers
RicB