How do I stop glue showing through the veneer?
A common problem experienced when veneering is veneer adhesive and glue bleeding through the veneer. Unfortunately, this sometimes only shows up once the final coating is applied to the wood and then the whole piece of work is wasted and has to be discarded. A lot of wasted time and cost.
Why does adhesive soak through the veneer?
This problem occurs for a number of reasons.
- The veneer is very open meaning the adhesive can come through the veneer very easily
- Too much pressure is applied in the press making the adhesive
- The adhesive is very low viscosity (runny) which means it soaks through the wood easier.
How can I stop bleed through happening?
There are a number of solutions to this problem, either by changing the product you use, using colour additives, or through some application techniques. Read on for further information.
What adhesive should I use to stop bleed through happening?
A variety of adhesives can be successfully used for veneering, including PVA adhesives and One Shot (e.g. Cascamite) adhesives, but they don’t give you the flexibility of being able to thicken up the liquid and stop the bleed through happening.
The best adhesive system to use is one which is high viscosity enough (thick) to stop soaking through the veneer. A UF (urea formaldehyde) resin with a powder hardener is ideal for this application. There are two types of UF systems available;
- A three component UF system which includes the resin, a powder hardener and a filler extender. This system and be used in a hot or cold press, and has the benefit that you can adjust the amount of filler you put into the mix. Examples of these systems are Woodstikk UF Fast and Woodstikk UF Slow systems, and then adding the Woodstikk UF Filler Extender.
- A two component UF system which includes the resin and a filled powder hardener. This system already has the filler mixed in with the hardener, but they can only be used in a hot press. Another benefit of this system is that it has an all day pot life, meaning you can mix at the beginning of the day and it won’t cure off in the pot all day. An example of this system is the Woodstikk UF Hot Press system
Can I colour the adhesive?
Another simple way of reducing the visibility of the glue line is to colour the adhesive. Many inert colours and dyes could be used, but you have to be careful that they are compatible with the adhesive. The dyes are added to the UF resin mix as per your requirements.
Woodstikk Colour Additive has been formulated for this purpose and has been tested for full compatibility.
In this video, you can see how to use Woodstikk Colour Additive in your glue mix.