Epoxy Wood Glass Wood Cold joint strength?

Epoxy Wood Glass Wood Cold joint strength?

Post by Ro » Mon, 03 Mar 2003 06:11:38


Is there a significant difference between attaching another piece of
wood to wood that has already been epoxy glassed and rough sanded?

I have bulkhead that will have more pieces attached to it, however I
would like to pre-glass it and rough sand it before I install it, and
I'm wondering if that will decrease the joint strengths down the road?

Thanks
Rob

 
 
 

Epoxy Wood Glass Wood Cold joint strength?

Post by Simon Brook » Mon, 03 Mar 2003 07:05:02

in message

Quote:

> Is there a significant difference between attaching another piece of
> wood to wood that has already been epoxy glassed and rough sanded?

> I have bulkhead that will have more pieces attached to it, however I
> would like to pre-glass it and rough sand it before I install it, and
> I'm wondering if that will decrease the joint strengths down the road?

In my experience you can make a good bond to a pre-epoxied surface if you
abrade it a bit.

--

                ;; when in the shit, the wise man plants courgettes

 
 
 

Epoxy Wood Glass Wood Cold joint strength?

Post by Frank Haga » Mon, 03 Mar 2003 11:21:06

I've heard that abrading the surface of a cured epoxy surface before
using epoxy to glue another piece on makes a better bond than not
abrading it. More "tooth" for the epoxy to stick to.  But you're
asking if such an abraded epoxy bond is stronger than a bond directly
between one wood member and another wood member, right?

If both surfaces are equally rough, to provide the same "bite" for the
epoxy, then I suspect the bond strength will be the same at the joint.
I saw a report once that claimed the "penetrating power of epoxy" in
wood was very slight, so that you are really dealing with the surface
bond with wood, just as you are with an epoxy-to-epoxy or epoxy-to
wood-joint.

If the designer is available, you might ask him.  It could be that
part of his design requires glassing the bulkhead in place, with
fiberglass tape and a fillet along the mating edges.  I think in that
type of construction, the bulkhead could be pre-coated without ill
effect.

Quote:

>Is there a significant difference between attaching another piece of
>wood to wood that has already been epoxy glassed and rough sanded?

>I have bulkhead that will have more pieces attached to it, however I
>would like to pre-glass it and rough sand it before I install it, and
>I'm wondering if that will decrease the joint strengths down the road?

>Thanks
>Rob

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Epoxy Wood Glass Wood Cold joint strength?

Post by Brian Nystro » Wed, 05 Mar 2003 21:47:59

Quote:

> Is there a significant difference between attaching another piece of
> wood to wood that has already been epoxy glassed and rough sanded?

> I have bulkhead that will have more pieces attached to it, however I
> would like to pre-glass it and rough sand it before I install it, and
> I'm wondering if that will decrease the joint strengths down the road?

Bonding the additional pieces to the bulkhead before the epoxy has fully
cured will produce the stongest bond. At that stage, the new epoxy can
still form a chemical bond with the old. Once the old epoxy is fully
cured, the new epoxy can only form a mechanical bond with it. Sanding is
necessary to provide some "tooth" to the surface. A purely mechanical bond
is not as strong as an epoxy-epoxy chemical bond, nor is it as strong as a
bond directly to the wood, but it may be strong enough for your purposes.

--
Regards

Brian