![]() Some will work well at levels as high as 10% to 12%. This also is the sweet spot for most PVA glues. For indoor projects, woodworkers typically build with lumber that has a moisture content of 6% to 8%. It won’t hold nearly as well on most smooth surfaces. The strength of a PVA bond depends on the glue’s ability to penetrate the wood surface, where it keys in to the wood’s tiny cell structures and forms molecular bonds. PVA glues only work on porous materials.Liquid glue can be wiped off with a damp rag, but many people prefer to wait for the glue to solidify and scrape it off while it is still plastic. The joint will need 24 hours to reach full strength. Minimum clamp times can vary, but typically run 30 minutes to an hour. As water volume is lost, and the glue shrinks, clamp pressure ensures that the glue surfaces are kept tightly together. Initially, the clamp force squeezes out excess glue, distributes the glue evenly and helps it penetrate. For loose or roughly constructed joints, consider epoxy, which excels at filling gaps, or add mechanical fasteners, such as nails or screws.Ĭlamping, with uniform pressure along the bond line, also is important for a strong joint. And beyond a two-sheet thickness, the weakness of the joint grows progressively with gap size. But below a half sheet thickness, the joint risks being glue-starved and weak. In a well crafted joint, the bond line may even be thinner. At the risk of oversimplifying, woodworkers aim for a finished glue line about as thick as a sheet of copy paper. It is a function of both how well the joint is prepared and how snugly and uniformly the joint is clamped. Glue-line thickness is critical to the strength of a joint. PVA glues require tight joinery and strong, even clamping pressure.Glues with higher initial tack are better at preventing parts from sliding out of position during clamping. Manufacturers tweak the recipe to enhance attributes that glue-it-yourselfers value, including water resistance working time, that is, the length of time the spread glue gives you to assemble, adjust and clamp your project and initial tack, or the stickiness of the glue while liquid. As the water diffuses into the wood or evaporates into the air, particles left behind link to form a flexible polymer film. They are ready to go from the bottle, inexpensive, safe, and clean up with water. When used properly, they create bonds stronger than the wood itself. This family of adhesives, the polyvinyl acetate glues, represent the most common, simple and useful general purpose woodworking glues. When people think wood glue, they typically think yellow glue. A small selection from these three groups will handle a broad range of wood-gluing tasks. PVA glues, polyurethane glues, and epoxies are all excellent adhesives for wood. Choose a two-part slow-setting epoxy for wood projects with loose or rough joints, where gaps must be filled, and for projects that will face extreme conditions: for example, when building in cold temperatures or with damp wood, or when the project will need to stand up to a wet environment.įor a more complete answer, read on.Polyurethane’s water resistance and strong bonds on end grain make it a good choice for exterior mitre joints. Choose a polyurethane glue for outdoor projects with tight fitting joints when using wood straight from the lumber yard that has not been dried further.“Dry” means the lumber is not just air or kiln dried but has spent at least several days indoors. If the project will be used outside or subjected to moisture, the glue label should include a term like water resistant, weatherproof or waterproof. Choose a PVA glue (the yellow stuff) for projects built with dry wood and tight fitting joints.If all you want is a quick answer to the question, “Which wood glue to choose?” follow this guidance: Choosing the right glue for your project is fundamental to a lasting assembly or a successful repair. No single wood glue is perfect for every job.
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