THE BEST GLUES TO USE
A CONVERSATION OVERHEARD
proceeded to strip off stringers and borders, took the board that was cut to size and drew lines from corner to corner then placed the picture lining up the corners with the pencil marks. Next he applied his contact Adhesive (Thix-o-fix) and laid the picture. Next he proceeded to glue each stringer and applied them to the picture, and then the borders, and to finish off, cut the mitres. HO-HUM !!!!!!!!!!!
We all marveled at this finished piece, but thought, no this is not for us, too smelly, too sticky and too complicated. All my working life as a Veneer Preparer I have spent in the cabinets — joinery trade and in my time I have come across many different types of adhesives but I do stress that I am not an out and out expert, although I do have a good working knowledge of most of them. When the Chelmsford Marquetry Group started to produce our initial work we laid the pictures using one of the ‘urea formaldehyde’ glues. This Glue requires constant pressure so we needed a screw press, similar to the one described by David Walker in a past Marquetarian. This ‘urea formaldehyde’ glue comes as a resin and is basically thermal setting glue which uses various types of powder hardeners in its mix.
Some of the professional level users will set the resin hard in as short a time as 30 seconds by using a heated press. However, it is worth noting here that when mixed, the “pot life” of this resin glue can easily be up to eight hours. We however, pressed our pictures without heat, complete (stringers and borders attached) and left them all week in the press until the next meeting. The main really big advantage that this glue has is with its gap filling qualities, plus the fact that it sets like concrete.
Unfortunately this particular glue resin has not been available to the public in small quantities, but the nearest available resin I know of that comes closest in formulation to this professional grade of glue is Cascamite (now known as Powermite) or any such of the similar products which we now use. This glue is supplied in the form of a powder that is just mixed with water to a thick creamy consistency and it will set hard in a warm room in about three hours. Urea and the powder glue can be used to lay the edges of pictures using a hot Iron. Another of the popular and widely used glues is PVA (Polyvinyl Acetate) a one part emulsion all purpose Woodworkers glue. This now comes in many types including waterproof and quick drying (five minutes). Unfortunately most never set really hard and tend to remain rubbery and sink or shrink as they dry out over time (they are therefore non-gapfilling). This PVA has to be used in a press of some kind but must not be left in over a long period as a mould will develop in the form of a small blue-black spots, which are impossible to remove with sandpaper. It is also advisable once removed from press, to leave and allow it to “settle” and dry completely before starting work. Be very careful if using water to soak off gum tape as most are not waterproof and could loosen veneer.
(BEWARE: NEITHER UREA NOR PVA PERFORM WELL UNDER lO°C AND ARE BEST USED IN A WARM AREA).
I am not stipulating that any of these glues have good points. Any marquetarian who is just starting will probably not have the facility of a press and will instead try a contact glue/adhesive as being the easiest option. They will, of course, get very respectable results with those ‘easy to use techniques’ and I am sure many experienced marquetarians still use such methods with great success. However, for the experienced marquetarian, there are many advantages to be gained from adopting the aforementioned urea glue method.
When visiting the Woodworker Show, many years ago, an old experienced marquetarian used to demonstrate marquetry techniques on the Art Veneer Stand (long gone). He used to explain to his audience how important it was to leave some gaps in cutting to allow for movement (I think I must be doing it all wrong!!!!!!!!). I however, would advocate against using contact glue and leaving gaps as this can cause problems when polishing with cellulose sealer, the sealer could easily seep into the gaps which can cause a chemical reaction resulting in the loosening of the veneer.
The Urea glues have a great advantage over both PVA and contact glue, especially when forming Curved parts, as when set they stay in shape, whereas PVA tends to move and straighten slightly. This type of ‘forming’ work is undertaken using male and female shapes or moulds and is set in a vacuum Press. Be very careful with UREA and PVA. If spread on too thick, when pressure is applied in the press, on certain veneer types, especially those with interlocking grain i.e. mahogany, sapele, and African Walnut, you will get some percolation through the grain, which is difficult to sand out.
This conversation originally took place between Alan Townsend and Arthur Gunton at an Executive Meeting.
Thanks are due to Alan Townsend for his excellent help in making the dialogue of this conversation available to your "Web Master" - Editor. Thanks Alan it is a superbly educational article - got any more?