USING TROPICAL HARDWOOD EPOXY GLUE

Harder woods such as oak, teak, maple, alder, apetong, araki, pau lope, osage orange, etc., may be glued directly with our epoxy adhesives.

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 ends of the hollow cellulose tubes of which the wood is made. Edges of plywood are notorious for soaking up liquids.

Improper clamping of wood may be the largest source of glue-joint failure.

Poorly-fitting wood elements, clamped to bend them into contact, will have tremendous spring-back forces pulling them apart, as much as a metal C-clamp can develop. Yet, the shear strength of wood is only 200-300 pounds per square inch, and the wood fibers at the glue joint will pull away from their parallel neighbors, often within hours to days after the clamps are removed.

Curved beams are best made by steam-bending the individual laminations, letting them dry in a fixture that sets the new shape, and then gluing them. If steam bending is not an option, cross-grain fasteners or splines (tenon, biscuits) should be screwed or glued at each end, because the curved structure will want to straighten, and the glue joint will fail by cleavage.
Straight, smooth, well-fitting wood elements can yet be made to fail by using excessive clamping force.

Squeezing a glue joint down to zero glue-line thickness forces out almost all the glue from between the pieces, and the natural porosity of wood wicks away the remaining microscopic residue of glue. The result is a glue-starved joint, and they will fail when the clamps are removed, or sometimes days or weeks later. If the failed joint shows no divots of wood pulled out of the opposite side, the cause of the failure is almost certainly excessive clamping pressure and not enough time allowed before clamping. The wood element should be clamped gently: Just enough to squeeze out the excess glue and bring the wood pieces into contact at the microscopic high points of the joint. Thick pads of soft rubber under the clamp faces ensure gentle, even clamping forces.

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 glues are 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.
Side grain bond strength, even with ebony, was found adequate with saw cut or dry sanded surfaces.
It is important to remember that wood is a natural product and varies.

It is also important to remember that surface preparation is at least 50% of adhesive bonding technology.

Our products have fairly long thin-film set times, and so the user has plenty of time to wipe up drips or shape into the desired form before the epoxy gels.

Do not use solvents to “clean” hardwoods before gluing. The solvents are absorbed by the wood and will cause the epoxy bond to the wood to fail. Even solvent cleaning hardwoods after gluing (while the glue is still wet) has in some cases, caused glue-line failures. Wiping up drips with paper towels is safe. These comments apply not only to our glues, but to any glue on any wood.

In mixing two-component products, it is important that the product be thoroughly mixed or it will be physically weak when cured. One of the most dependable methods of ensuring complete mixing of liquids is to mix well in one container, transfer to a second container and mix again.

With all modern products there are certain safety procedures that must be observed if the user is to avoid developing a rash or allergy. Do not get epoxy or other resins on your bare skin. If you do, stop what you’re doing and go wash with soap and water. While casual exposure at infrequent intervals may not be harmful to most people, it is impossible to predict who will become allergic after some exposure. So, be neat and work clean.

MIXING TWO-COMPONENT PRODUCTS

In mixing two-component products, it is important that the product be thoroughly mixed or it will be physically weak when cured. The most important part of the mixing process is to mix it well in one container, transfer to a second container and mix again.

Sophisticated adhesives, sealants and coatings are two-component systems. One part has to be mixed with another part before they are applied. After a while, a chemical reaction takes place, and what is created is a filler, paint or glue with exceptional properties. It is not possible to obtain those properties by taking some simple thing out of a can.
Each of these two parts, whether they are liquids or pastes, consists of very small components called molecules. The manufacturer designed the system so that the individual molecules of each component would react with each other in certain proportions. That is why the instructions say to mix the materials in those proportions.
If the materials are mixed in different proportions, then some molecules of one or another component are left over, scattered among the molecules of both components that did react together. In that case, the material will be softer or weaker than it should be, or will soften in water when it should not. It might be a gooey mess. It is therefore important to mix the components thoroughly, so that everywhere in the mixture the ingredients are in the correct proportions, even down to the individual molecules. Visual appearance of uniformity is not always an adequate guide, as there are millions of molecules in a single inch. A few ounces of material, for example, should be mixed for at least a minute or more, until visually uniform, then transferred to a second container and the mixing procedure repeated, scraping off the mixing tool frequently. This ensures that the small amount of A or B in the bottom corners of the first mixing container has the opportunity to be thoroughly mixed with everything else.
Glues should be mixed by hand, as power mixers can whip in many small bubbles which will give a weak glue joint.
If there are any soft or gooey spots in the final cured product, that is proof that the material was not thoroughly mixed.

HYGIENE

With all modern products there are certain safety procedures that must be observed if the user is to avoid a rash or allergy developing. Do not get the resins on your bare skin. If you do, stop what you're doing and go wash with soap and water. While casual exposure at infrequent intervals may not be harmful to most people, it is impossible to predict who will become allergic after some exposure. So, be neat and work clean.

© copyright 1972 - 2009, The Brain Trust, a California irrevocable trust, reprinted with permission