The Technique of FURNITURE MAKING

GLUING DIFFICULT MATERIALS

Brass, metals, etc. Araldite epoxy resin glue in accordance with maker's instructions; hide glue with the addition of a teaspoonful of Venice turpentine per pint of glue, or plaster of Paris (alternatively rub metal with garlic).

Ivory. Coat with celluloid dissolved in ether, or glue with hide or Araldite.

Tortoiseshell. Araldite or UF resin glue, Salis­bury glue or freshly made hide glue. Add flake - white or rouge to colour, or lay on gold-foil. Leather, baize, etc. Casein, Cascamite One Shot resin glue, dextrine, thin hide glue, shoe­maker's glue, etc., allowing surfaces to tack off slightly before laying, especially with baize. Laminated plastics. Casein, Cascamite One Shot, Aerolite 306 with GUS glycerine-based hardener where pressure is available, otherwise proprietary impact glues. For maximum heat and water resistance use Aerodux Resorcinal glue (CIBA[ARL] Ltd).

Rubber to wood. Bostik glue; or treat rubber with concentrated sulphuric acid, wash, dry and glue with Aerodux Resorcinal glue.

Wood to glass. Araldite where strains are im­posed, or Durofix tube cement if only for orna­mentation (sham glazing bars, etc.).

Many difficult materials (metal, ivory, etc.)

can be glued with simple adhesives provided both surfaces are immaculately clean. A test of the molecular attraction between surfaces can be made by scratch brushing two pieces of soft aluminium, placing together immediately and hitting with a large punch. Both surfaces will then adhere and cannot be separated, but if one surface is lightly touched with the finger it will not bond. The method usually adopted by old craftsmen for inlaying ivory, silver, etc. was to hide glue the ground or substrate, dry grind the inlay without touching the critical surfaces with the fingers and immediately place in position. Alternatively, the metal inlays were rubbed with fresh garlic, and while it was never exactly known why the garlic acted in this manner, it is possible that the garlic oil cleaned the surface and was itself so finely dispersed that it created no fresh obstacle; but no doubt the scientist could give a more valid reason.

Definitions

Cold-setting glues. Glues which set at normal room temperatures either by chilling or evaporation, etc.

Thermosetting glues. Glues which set with, and cannot be softened by, heat.

Assembly glues. Glues capable of supporting thick glue-lines without crazing—gap-filling glues.

Close-contact glues. Glues which will not

tolerate thick glue-lines, but require intimate contact throughout.

Shelf life. Storage life in original containers.

Pot life. Effective working life of mixed glue. Initial gel. First stage in curing of mixed glue. Gel has no strength.

Hardener. Accelerator or catalyst, usually an acid salt dispersed in water or spirit, or formic acid in solution. Function of the solvent is to ensure complete dispersal of acid throughout the glue, and can be coloured for identification. Crazing. Hair-cracks in solidified glue set up by excessive shrinkage, trapped solvent or inherent weakness in glue structure.

Extenders. Filling material used to extend volume of glue, or to prevent excessive penetration.

Pressing or cramping time. Minimum time glued surfaces should remain under pressure.

Basic setting time. Minimum hot-press time, to which must be added time allowances according to thickness of veneer, etc.

Note: All adhesives take several days to develop their maximum strength.