Civil Engineering Reference
In-Depth Information
EVA and PVAC adhesives
These have softeners added, most often dibutyl phthalate (DBP). Together with the
excess monomers of vinyl acetate, these can be released from ready glued surfaces and
result in irritation in the inhalation routes. Softeners, particularly DBP, are also suspected
of causing more serious damage, such as nerves damage, hormonal disturbances and
reproductive problems. PVAC adhesive can also contain sulphonamides which can dam-
age the immune system.
Animal glues
Animal glues are based on substances rich in protein such as milk, blood and tis-
sues, and are divided into three main types: animal glue, blood albumin glue and
casein glue. These are soluble in water. They are all good glues for wood, and can
be used on everything from veneers and furniture to large laminated timber
structures.
Animal glues are mostly based on waste from slaughterhouses and fisheries.
Casein glue comes from milk. In buildings, under dry conditions the products
cause no problem. In combination with damp cement they can emit ammonia
which irritates respiratory passages. In continuous damp there is a good chance
of mould or other bacteria developing and the rotting products can cause bad
odours, irritation and allergies. This can also lead to the deterioration of the
building structure. Waste from the glues can lead to the growth of algae in water,
but this risk is insignificant because the amount is usually small. Glues that have
strong fungicide additives must be deposited on special tips.
Materials glued with animal glue can normally be energy recycled in ordinary
incinerators, or can be dumped without any particular restrictions.
Animal glue
This glue is made from the tissues of animals containing collagen, a protein. Collagen is
not soluble in water, but boiling it at a low temperature in an evacuated vessel turns it into
glue. This is then dried into a granulated powder or into small bars. Gelatine is animal glue
which has been cleaned of colour, smell and taste. There are three different types of ani-
mal glue: bone glue, hide glue and fish glue. The first two are often called glutin glue. Bone
glue is made of bones and knuckles, hide glue is made from waste hides from places such
as tanneries. Fish glue is made of fish bones and other fish waste and has a characteris-
tic smell. All of these glues are strong, but hide glue is considered the best.
Animal glue bars or powder can be placed in cold water to soften up and then dissolved
in water at 50-60°C using about two to three times as much water as the weight of soft-
ened glue. The powder can also be released directly into warm water. Temperatures
above 60°C decrease the quality of the glue. Bone glue and hide glue have to be used
warm and the pieces to be glued must be put under pressure before it stiffens. The glue
cures quickly when cooling. Fish glue can be used cold, as can the other animal glues
when calcium chloride is added.
To make a good animal glue filler, sawdust or wood flour can be mixed in. Colour pig-
ments can also be added. The filler works well on timber surfaces and is not as visible on
untreated surfaces as on treated ones. Adding gypsum makes the filler white.
