How to Repair Wood With Epoxy
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Soft woods such as fir and
pine can absorb liquid epoxy adhesives, especially in butt or scarf joints
where end grain is exposed. Thickened (jelled or mineral filled paste) epoxy
adhesives glue only onto the surface, and the surface of wood consists
microscopically of broken cellulose fibers (which are hollow thin wall tubes).
Contact only on the surface does not produce as high-strength a joint as
contact by an adhesive that flows well and wets the microscopically rough
surface instead of bonding to the high points only.
Softer woods have very low shear strength and so an epoxy that soaks in and impregnates the wood offers a higher strength bond as it glues the wood surface down into the bulk of the wood. This allows a thick liquid or paste filler to develop a strong bond with the wood itself.
Our Clear Penetrating Epoxy Sealer was especially developed as a sealer for soft woods such as fir or pine. It also serves as an adhesion-enhancing primer on any wood before applying oil-base (alkyd) varnish, clear two-component polyurethane finishes, or enamel or even latex paints.
Harder woods such as oak, teak, maple, alder, apetong, araki, pau lope, osage orange, etc., may be glued directly with our Tropical Hardwood Epoxy or Oak and Teak Glue, as they are dense enough that adequate surface area is available for a high-strength bond. Any of our epoxy adhesives may be used to glue soft woods.
For best results any liquid epoxy adhesive should be applied to both surfaces to be glued and allowed to sit long enough for the wood to soak up as much as it wants, so that when the pieces are assembled the wood will not absorb the glue that would otherwise fill the gap between the pieces, leading to a glue starved joint. Scarf and butt joints are especially prone to soaking glue out of the joint, as it wicks into the end grain of the wood, which is the open end of the hollow cellulose tubes of which the wood is made. Edges of plywood are notorious for soaking up liquids.
Most adhesives, even epoxy adhesives, do not bond hardwoods because the saps and resins in the wood interfere with the bonding chemistry of the adhesive. Our Tropical Hardwood Epoxy or Oak and Teak Glue is specially formulated (by us - we're chemists) to overcome this difficulty. We designed a chemical system that would absorb and displace the saps and resins without becoming weakened by the absorbed oils.
Some woods (particularly
ebony) contain a wax rather than oils. Saw cutting or dry sanding can smear
this wax over the surface, making gluing difficult, especially on end grain or
45 degree bevels. Wet sanding or light abrasive blasting (such as glass bead or
200 mesh abrasive) can clean such material off the surface to be glued and has
been found effective in improving the bond strength of such joints.
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