USING TROPICAL HARDWOOD EPOXY GLUE |
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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. 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. 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. 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 |
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