Finishing and preserving

[flarud]

Hey all,, got a question and not sure which folder to ask it in... so I'll try here.  I have a big slab of Boxelder that I'm gonna use for a small table top.  The bottom of it has a lot of rot.  I've cleaned most of it out and was wondering what to do to keep it from decaying more.  The piece is a good 2" thick and at some spots it may have rotted close to all the way thru.  For the top I'm just gonna use some poly for the top coat.  But what can I use on the bottom?  I may have to attach a 1/2" piece of plywood to the bottom to be able to attach the boxelder securely to the legs of the table.  I'm hoping that by doing this I don't make the rot worse.  Should I use some kind of wood preservative on the bottom of the piece then spray some poly on top of that?  Any help would be appreciated.  I'm gonna try to attach a couple of pics.  I've never tried that on this site yet. 

Nope, can't figure out how to do the pic. 

Thanks,
Barry

[spirithorse]

Hi, Barry,
I'm definitely not an expert in this area but, I would use
a good polyurethane. Probably Helmsman Spar Polyurethane.
It is good enough for exterior use.
A friend of mine uses that when he makes signs that still have
the bark on the outside edges and the Helmsman definitely helps
keep the bark from falling off.
I have no affiliation with thier company but, just think it is a good product.
God Bless! Spirithorse
By the way, your idea about adding the plywood sounds like a good idea to me
and I would use the same polyurethane finish on that.

[scrappile]

There are products for stabilizing wood.   I just don't happen to know the names.  I think Home Depot or Lowes carries some.

[Norm Fengstad]

I am no expert but heard of using a diluted white glue painted on to help stabilize the wood. Some glues can be diluted with water or mixed in with a Spar or Poly varnish. even the varnish will help stabilize it

The rot should not get any worse if it is not exposed to moisture.

[flarud]

Thanks guys, I appreciate the input.  What about a 2 part resin/hardener type product that I can pour into the rot cavities?  It may not even be necessary really.  Might just spray in some poly and attach the piece of plywood to the underside and call it a day!