On Fri, 14 Oct 2005 01:28:20 -0700, ahoy wrote:

ahoy, I epoxied some one inch strips of wood in slats to make up a
little decorative rope bin which was intended to sit on deck but it
warped and popped apart in about 3 days in a damp shop. Does
everything have to be notched or biscuited or doweled and pinned or
screwed? I thought epoxy was an invincible adhesive. I used left over
strips of purple hart and mahogany and west system 105/205 in a dry
room if that makes any difference. thanks as always.
There is epoxy and then there is epoxy. In other words there are various
formulations of various quality for various purposes. Oak in particular has
problems (the tanin in it). Unless the wood was epoxy coated the force of the
wood warping exceeded the strength of the joint.

Epoxy is an adhesive, it is not a miracle substance of unlimited strength.

Squeeze too much out and the joint is weak. Have too thick of a layer and
again the joint is weak. Some formulation are known to suffer from excessive
creep, but those are intended for finishing not wooden joints. All epoxies
soften at warm temperatures, the point depending on the formulation. But a dark
hull on a sunny day can easily exceed that point. It is also waterpermiable.
It doesn't let in much but it is not like a metal barrier, some moisture will go
through epoxy, the amount and speed depending on the formula and the thickness.

For very highly stressed wood to wood joints I would either use resorcinol or
epoxy with the joint REINFORCED by fiberglass cloth. De lamination with epoxy
is not uncommon when the wood is not completely and properly epoxy coated to
control moisture.

Epoxy resin is much stronger and less permeable than polyester resin, but again
it is not a miracle substance. It has limitations just like any other material.

JJ




James Johnson
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