Replies

1. 
   frenchy | Apr 05, 2005 06:37pm | #1

   if you seal the wood there should be no problem, another words paint/varnish shellac etc. prior to assembly. do all the sides and take an extra moment or two to do the end grain at least twice.. (since that will absorb so much compared to the other surfaces..

2. 
   joinerswork | Apr 06, 2005 08:18pm | #2

   Sope,

   I'm given to understand that epoxy is a very good vapor barrier, to the extent that objects should be completely encased in the stuff, to prevent warpage from moisture migration from uncoated areas.

   If the object is exposed to u-v light, then the epoxy should be coated with a u-v barrier of some kind, as it degrades with exposure to u-v rays.

   Regards,

   Ray

1. 
   frenchy | Apr 07, 2005 08:28am | #3

   Joinerswork,

     if something is completely covered  (all four side and both ends) it doesn't matter what the material is, it will seal the wood, what happens ios when the covering fails due to cracks, peeling etc, moisyure is allowed in and the sealing effect is gone..

1. 
   joinerswork | Apr 07, 2005 03:32pm | #4

   Frenchy,

   Most wood finishes (varnish, lacquer,shellac, oils), to the best of my knowledge, do not prevent, but only slow the movement of water vapor, some moreso than others.  Epoxy, I'm told, is impermeable to water vapor.

   Regards,

   Ray

3. 
   KeithNewton | Apr 07, 2005 05:30pm | #5

   You are not describing a balanced panel, which could lead to problems.
   Epoxy is one of the least permeable coatings out there. That is why it is used for boat-building. The plastic laminate on the other-hand is not as stable as you might think.

   If you choose a brand of epoxy, you can get the numbers for all of their properties from the manufacture.

   If you use it on oak, I recommend that you use a filler first. Because of the slow cure time of epoxy, it will flow down into the open grain while rapidly building on the dense latewood, leaving a very unappealing finish.
   It is best to it apply to warm wood which is cooling down. If it goes the other way, you will get bubbles from the expanding air in the wood cells.

   If you apply your veneer with a water-born adhesive to one side, you will already have an unbalanced panel under whatever finish you choose due to the expansion caused by that moisture being absorbed into the veneer face while it is being applied. When that moisture evaporates, the veneer face will contract across the grain causing the cupping. For this reason I like to use epoxy for glue to lay the veneer face. There is no water in epoxy, so if the substrate and veneer are already at a MC which matches the final expected atmosphere, no shrinkage should be expected.

1. 
   user-6870461 | Apr 07, 2005 08:03pm | #6

   Thanks for the insights, everybody.

    

   Here's what I have decided to do:  I have laminated a test structure using 12" x 12" x 3/8" MDF core, a Formica top, and an oak veneer bottom.  I have used West System epoxy 105 resin / 205 hardener.  I brushed the epoxy onto both the MDF and the laminates and put the sandwich into a vacuum press to cure.  When this is done, typically the epoxy is drawn into the veneer, sometimes penetrating to the other side.  Presumeably what I am left with is a very good, perhaps not perfect vapor barrier between the layers.  This imperfect barrier should reduce any cupping from unequal moisture expansion in the MDF.  Probably I should do the edges too, huh Frenchy? What is left as an unknown are the relative moisure expansion properties of the plastic laminate as compared to the partially saturated oak veneer.

   I agree about using epoxy to finish wood.  It looks like cheap encapsulation.  And I have seen the bubble problem. Once they form there is a foggy appearance that never can be removed.  Probably I should finish the outside of the veneer with a couple of coats of varnish to make a proper test.

   Anyway I am leaving the panel exposed to varying humidity conditions to see if it warps or cups.

    

   P.S.  Here's what Brian Knight from Gougeon Brothers (West System) says:

   Three coats of WEST SYSTEM Epoxy on the flat grain surfaces should beenough to balance the plastic laminate moisture infiltration.   Isuggest you apply one coat of 105/207 to the veneered surface.  Allow itcure overnight and then after a light sanding, apply two more coatsabout 4 hours apart.  Allow the first of these two coats to become verytacky before overcoating.   Also make sure any exposed end grain of theveneer is sealed. Three coats may not have the exact moisture permeability but it will beclose and any warping will be minimal. Sincerely,West System Inc. Brian Knight 

   Edited 4/7/2005 1:12 pm ET by Sope