Types of wood adhesives
Glue the bones are among the oldest adhesives used for wood. They are most often sold in solid form, in the form of beads or powder. They do not dissolve in water, they only swell. Only after heating is a sticky solution obtained. The viscosity of the solutions strongly influences the stickiness; further heating causes a decrease in the viscosity and strength of the glued joints. Normal bone glue dissolving temperature is 50-60 ° C. The glue should always be dissolved in a water bath; never directly above the burner or on the electric hob. Before heating, the glue should be soaked in water (in the form of beads for 1-2 hours).
After applying the adhesive to properly prepared surfaces, squeeze the joint or the object to be glued. On the assumption, that the wood is dry, the glue has the correct viscosity, and the temperature of the environment and the wood is at least 20 ° C, the so-called. curing takes over 2 hours. This period can be shortened by slightly heating the joint. The shear strength of the joint comes to 9 MPa. The joint is very flexible, however, it is not waterproof.
In recent years, bone glue has been replaced by synthetic glues, which have a number of advantages. Long and cumbersome preparation of the bone glue (swell, dissolving) prevents quick application, unlike new types of synthetic adhesives.
Casein glue it was also known for a long time. Its quality is confirmed by some products glued with it from ancient Egypt that have survived to this day, Greece, Rome and China.
The basic ingredient of casein glue is protein from cow's milk. Casein glue is sold under the trade name Arbus. It is a white powder, which is dissolved in water before use. Approx 30 min. The powder is poured into the water with constant stirring. Water must not be poured into the powder because it lumps and loses its value. A larger amount of glue can be mixed with a suitably bent piece of wire or with a special agitator inserted into the drill handle.
The joints glued with casein glue are partially waterproof, however, they do not withstand the effects of the weather. The hardening period is long and takes up 24 hours. The joint gap may be thicker. Tools dull faster when machining hardened joints.
It takes a certain amount of time to prepare the glue. One of the shortcomings of the glue is the need to use it on the day of preparation.
They are the most numerous group adhesives produced on the basis of synthetic resins. They are varied in many respects, but all of them are essentially waterproof and resistant to many chemicals.
The most common, a packaged synthetic glue is glue wikol. It is an aqueous emulsion of polyvinyl acetate with the addition of a filler and a small amount of toluene. It has the form of a white or creamy liquid with the consistency of a cream. Wikol is used for cold gluing wood with wood, wood with plastics, e.g.. "Unilam" albums, and wood with fabrics.
The glue should be thoroughly mixed before use. During gluing, it should have a temperature of 15-24 ° C. The surfaces to be glued must be carefully cleaned and degreased. The glue is evenly applied to one glued surface with a brush or a finely toothed spatula. After applying the glue, wait 2–4 minutes, and then assemble the parts to be glued and press them together. The weld reaches its full strength after 24 hours. Shear strength of the weld, when fully cured, it comes to 9 MPa.
The second of the adhesives produced on the basis of polyvinyl acetate is mosaic. It is in the form of a semi-liquid paste, consisting of a mixture of an aqueous emulsion of polyvinyl acetate with a solution of coumarone resin in toluene with the addition of a plasticizer and mineral fillers. This adhesive is used to stick mosaic parquet or other similar floor panels to the concrete substrate. However, it is not suitable for a sand-lime substrate. Before use, the adhesive should be thoroughly mixed and possibly heated to a temperature not lower than 15 ° C. Then it is applied to equal, cleaned of dust, dry and hard concrete substrate with a serrated trowel. At the latest after 15 min. wood panels are placed on the adhesive layer, avoiding shifting them. Each element of the panels should be pressed to the substrate with glue. The joint is fully hardened after 10 days, and only then can the further mechanical surface treatment be started (leveling, scraping, etc.).
They are commonly used for gluing wood and wood-based materials amine adhesives. The base substances are urea-formaldehyde resins and urea-melamine-formaldehyde resins. Amine adhesives are sold under the names of resins, because they are not ready-made adhesives, but they require the addition of hardeners and possibly other auxiliaries. The hardener is diluted acid or acid salt. Glued joints are characterized by high abrasion resistance. They are resistant to mold and moisture. However, they cannot withstand the action of acids and lyes.
Amine adhesives are non-flammable. However, they are toxic due to their free formaldehyde content. The hardener is also irritating to the skin, a containing ammonia, also for the eyes and mucous membranes. For these reasons, these adhesives are not found in retail trade.
The most common adhesives of this group are the adhesive resin 60, BZ-70 adhesive resin and M-1 adhesive resin. Adhesive resins can be used with or without filler. Fillers can be: rye flour, potato or wood. In addition to fillers for resins, hardeners with the symbols MZ and BZZ are added for cold gluing.
Epoxy adhesives they are traded as one- or two-component. The first are epoxy resins with an admixture of a hardener, the other is resins, to which you need to add the hardener yourself, e.g.. Z-1, or M. Epoxy adhesives either cold or hot glue metals, ceramics, glass, concrete, wood, rubber and some plastics. They provide welds with high mechanical strength (on shear even 30 MPa), are resistant to high temperatures, atmospheric influences, diluted acids and bases, oils, gasoline and a range of organic solvents. Once cured, these adhesives are completely non-toxic. Most epoxy adhesives have a commercial name epidianu, and depending on the composition and composition - numerical symbolism. Epidian is best suited for wood 57.
Adhesives produced on the basis of polychloroprene rubber are solutions of polychloroprene rubber modified with various synthetic resins. They are used for cold gluing many materials. Glued joints are, oil and grease resistant. However, they are not resistant to temperatures above 50 ° C.
It belongs to this group of adhesives Butapren L-40, M-40 i NT. These adhesives can be applied to both glued surfaces with a notched trowel or a brush with stiff hair.. After applying the adhesive layer, wait several minutes for the solvents to evaporate. Only then do you have to press the elements together, to remove air bubbles and leave until completely cured for several hours.
A selection of the most common wood adhesives are presented in the table below.