Civil Engineering Reference
In-Depth Information
Bone glue and hide glue have been used a great deal for gluing veneer. Right up to the
Second World War, animal glue was dominant in furniture making, and there are still
craftsmen who say that the quality then was much higher than that achieved today with
adhesives such as urea formaldehyde (Brenna, 1989).
Animal glue can be used on all woods. The disadvantage with the animal glues is their
lack of resistance to damp, which restricts their use to dry interiors.
Blood albumin glue
Blood albumin is soluble in water. It is prepared from fresh blood or from blood serum
which is allowed to swell in water. The glue is made by adding ammonia and calcium
hydrate solution in certain proportions. Ammonia is corrosive and can cause eczema. The
objects must be warmed up during the actual gluing. At certain temperatures the protein
coagulates, and the glue joint becomes totally watertight. The joint should be kept dry, if
the glue has no added fungicides.
Casein glue
Casein glue was used by craftsmen in ancient China. It is made from skimmed milk. The
milk is warmed up and rennet is added to separate out the casein. The casein is then dried
and mixed with 2.5 g of lime per 100 g casein. The powder is mixed with three times as
much water so that the lime is slaked. A glue is then produced which, after setting, toler-
ates damp better than sinew glue. In permanently damp surroundings and with timber at
18 per cent moisture content, the glue can be attacked by micro-organisms. This raises
the question of the addition of fungicides such as sodium fluoride.
Casein glue can be used for internal load-bearing structures, stairs, plywood, laminat-
ed timber, etc., without fungicide. However, it is seldom used nowadays. Producers of
laminated timber prefer adhesives that can be used in all situations, and therefore choose
resorcinol formaldehyde, which has a high resistance to moisture. Strengthwise, casein
glue is as good, and there is proof of its long lasting qualities in structures that are 50 to
60 years old which have kept their strength (Raknes, 1987). A very impressive example
of its use can be seen in Stockholm Central Station, where enormous laminated timber
arches have been put together with casein glue. During the Second World War, casein
glue was used in the manufacture of fighter planes.
There is a need for a renaissance for environmentally-friendly casein glue. This does not
necessarily conflict with economic considerations: it has been shown that casein glue can
be produced for less than 25 per cent of the cost of resorcinol formaldehyde.
Casein glue is often classified as poisonous, due to the addition of lime which can burn
bare skin. By adding fungicide the whole situation is altered and the glue loses many of
its environmental advantages.
Plant glues
Glues from plants include soya glue, natural resin glue and cellulose glues as
well as glues based on rye flour and potato flour.
Soya glue is a water-based protein glue taken from the waste products of cook-
ing oil production. Natural resin glues are based on the sticking properties of
resinous substances, such as lignin from coniferous trees, and have to be dis-
solved in organic solvents. Cellulose glue is available in both water- and solvent-
based variations. The water-based cellulose glue is usually called paste, and is
