7 misconceptions about gluing wood with acrylic adhesives

Despite the fact that PVA adhesives - aracet adhesives or wood adhesives as they are also known - are the most commonly used adhesives in carpentry workshops and furniture factories, there is still the impression that they are only used when you don't have something better. Nothing could be further from the truth! PVA adhesives are very strong adhesives that can also be used in difficult, high-humidity places such as bathrooms or kitchens, or for gluing wood that has been subjected to pressure impregnation or high-temperature treatments. The important thing is to know which grade of aracite to choose. As lately I have come across all sorts of false claims about these adhesives, I think it would be useful to dismantle them. Here are just 7 of the most common claims.

1. "The aracite is not resistant to glue wood used outdoors."

Often, if someone dares to recommend the use of aracet outside, there is hysteria. Enough are found to advocate dismantling the object at the first rain, leaving a total disaster. I dare to contradict the ambassadors of the apocalypse by informing them that PVA adhesives with very good exterior resistance have been on the market for some time. The important thing is not to choose just any kind of aracite, but moisture resistance classes D3 or D4. D3 can be used if the object stands outside but is more protected from the elements (under a roof or a canopy, for example), while D4 adhesives can be used for objects that stand directly in the rain, such as beehives made from wood panels. About adhesives PVA TISZABOND, which have been used for years to make beehives that are mostly for export, we have already said here. And those used in the industrial production of solid wood panels, here.

For those who want to use aracet adhesives to glue objects used outdoors, I recommend to always use a adhesive D4. This will make sure that any risk is removed.

2. "The thicker the glue line, the stronger it is."

Rather than being too little, it's better to have too much, as a Romanian saying goes. It does not apply to gluing. A thick layer of hardened adhesive can lead to internal stresses and cracks in the layer that holds the two elements together. It is not very far from there to total destruction of the bond.

In the product data sheets or on the label it is recommended consumption/m². A slightly higher or lower quantity will not lead to problems with sticking, but if the quantity differs greatly from the recommended amount, problems will occur, either the layer is too thick or too thin.

3. "The higher the pressure, the stronger the bond."

In order to be bonded, the elements to which the adhesive is applied must remain in contact for a period of time. This is done using presses or cleme. They create that necessary closeness until the adhesive reacts to form the adhesive film that bonds the elements together. Some believe that the more pressure applied, the stronger the bond will be. It probably stems from the idea that the pressure "pushes" the glue into the wood, increasing the glue line, or from the idea that using more clamps gives a better bond.

Very high pressure does not help to increase the strength of the bond, quite the contrary. Too much pressure results in some of the required adhesive being pushed outwards, resulting in a weaker bond. A large number of clamps is useful to achieve as uniform a pressure as possible on the surface of the parts to be bonded so that a continuous and uniform adhesive film is produced. The number of clamps used does not influence the applied pressure. Methods must be found so that the pressure is evenly distributed (glue pieces placed between two panels which are clamped together).

4. "Even if the wooden elements are crooked, once pressed into the press they will stick together correctly."

The elements to be glued have had high humidity and, on drying, have warped. Or they have been stored incorrectly and twisted, bent or warped. It's nothing, some people say, just stick them in the press and that's that. Not so. The moment you try to straighten a crooked element, it will resist, internal stresses are created and the wood can crack. In addition, the warped piece has a 'memory' and will try to warp after gluing. This will put pressure on the glue film, lowering the overall strength of the glue. In other words, if that bond would have withstood a certain breaking force, it will drop and be damaged from the inside.

It can also happen that the deformation can lead to too much proximity between certain points of the two parts. At those points the amount of adhesive will be less or not at all. After bonding, that will be a weak spot and will fail at the first opportunity.

This is why warped elements must be straightened before being bonded.

5. "If the glue has thickened in the can and is different from the last use, dilute it and use it."

Adhesive thickening sometimes indicates that the polymerization reaction has already started. This means out of warranty and decreased bonding properties. What actually happens? As we said and herePVA adhesives are aqueous dispersions, i.e. they are molecules floating in water. As the water disappears, the molecules come closer together and the reaction begins to form the adhesive film. If the adhesive has still thickened in the can, it means that some of the molecules have reacted and there are fewer reactive molecules left to cause sticking. Adding water does not break the bonds formed but dilutes the remaining reactive adhesive even more. If we continue, we will obtain a weak adhesive film that will break at the first aggression.

If you know the adhesive is out of warranty, but it looks like it would work if you thin it, don't do it. You are risking much more than the price of another can of adhesive.

6. "If the aracite is frozen, it cannot be used."

Not always! Indeed, in the past, any water-based product used for gluing or finishing wood, if it froze, could no longer be used. Its properties were altered, even if its appearance was almost unchanged. In the meantime, however, the need has led manufacturers to come up with solutions to make adhesives less sensitive. We have already told you about the TISZABOND D3-D adhesive, obtained by Szolvegy especially for a customer from Miercurea CiucRomania's cold pole. As the existing conditions made it impossible to reach a temperature above 0°C in the factory's warehouse, they made an adhesive that could withstand repeated freeze-thaw cycles without losing its original properties.

Indeed, not all PVA adhesives can be used after freezing. But there are some that can be used, the important thing is to find and use the right ones.

7. "The arach can only glue wood to wood."

It was already known that aracite glues paper and textiles. But a good PVA adhesive can do more than that. It can bond wooden steps to concrete stairs or window or door frames to brick or concrete walls. In such cases it is very important that one of the glued parts is wood and the other part is a porous material so that the adhesive penetrates and the bond is strong.

Wood glue is an adhesive you can rely on when gluing wood. But it's very important to choose the right glue and put quality and durability of the final product first.