What happens if the wrong proportion of catalyst is used in the primer or varnish mixture

There are several types of A+B products that are used in woodworking to obtain different objects: varnishes, adhesives, glues. They are two-component products that react when mixed to form a third product, different in properties from the first two. In the case of finishing products, the reaction between components A and B leads to the formation of a film on the wood. The two components must be mixed in a certain proportion, indicated by the manufacturer, for the resulting film to reach the desired parameters. What happens if the amount of hardener added is accidentally higher?

How components A and B react

Being a chemical reaction, the proportion between the two parts is well studied and determined to achieve a well-dried and resistant film. The proportion must be chosen so that the two components react with each other and practically consume each other. When mixed, the molecules react by bonding together to form a new product, a polymer, with very good surface properties. This new product is the film formed.

What happens if the ratio between the two components is not respected? A quantity of one of the parts will not react, it will remain freewhich will influence the properties of the resulting film. If the differences are small - e.g. 52-55% instead of 50% - the consequences are virtually insurmountable. The manufacturers provide a margin of safety because the products are used under factory conditions, not in laboratories with high-precision measuring systems. Problems arise, however, when the differences increase.

What happens when you get the proportions wrong

If there is too much hardener (catalyst) in the mixture, the film can become brittle. What is the explanation? The catalyst, in contact with water, hardens instantly, forming a brittle solid. As it is not neutralized the reaction with the other component, the excess remains free in the film and comes into contact with the moisture in the atmosphere, becoming brittle. The unreacted amount is spread randomly, so that brittle spots appear in different places, compromising the whole film.

If, on the contrary, the lake is in excess, the unresponsive party remains soft and will transfer this property to the film in which it is embedded. The film becomes spongy, soft, without mechanical and chemical resistance, i.e. without precisely those properties for which a catalyst varnish, such as polyurethane, is chosen.

What happens if no catalyst (component B) is added at all? Remains soft and sticky. If the catalyst is applied on top, the whole film will crack. The applied layer must be removed completely and the process restarted with the correctly made mixture. Removal is done with thinner or a suitable paint stripper.

There are also products that, even if no catalyst is added, still harden. They usually have a low catalyst percentage of 10-20%. In this case the catalyst is added to increase certain properties of the film (mechanical strength, chemical resistance) and/or reduce its drying time. Drying will take place even if no hardener is added, but it will take longer until the film is dry enough for the object to be used.

To avoid such problems, the recommendation is to carefully read the instructions on the data sheets (in the case of industrial products) or on the label before starting to work with them. The mixing ratio is always listed on the packaging of the main product (primer, varnish, insulator).

I hope you find the above information useful. As usual, additions are welcome. And if you have any questions or queries, please leave them in the space below. I'm sure I'll reply.