Duralac is an anti-corrosive jointing compound for use between joints of dissimilar metals.
Form Duralac Jointing Compound is a yellow paste prepared from an elastic varnish
medium of low
moisture permeability, a corrosion inhibiting material barium chromate and an inert filler. It
conforms to specification DTD 369B.
Barium chromate is only very slightly soluble in water
and hence is not leached out of the joint
even in the presence of a considerable flow of water
. It is however readily decomposed by
acids with the liberation of chromic acid so that it is brought into action only in the presence of
corrosive influences. It is tough and flexible, absorbs little water and is resilient to seawater.
Duralac is indispensable for the sealing of joints between dissimilar metals of all types
including magnesium and its alloys. It is also valuable for the protection of metals in contact
with wood, synthetic resin compositions, leather, rubber, fabrics etc. When the components
of a structure are of different materials, it is essential that the points or faces of contact should
be treated with corrosion inhibiting materials because in the presence of electrolytes
considerable differences of potential arise, not only where different metals are in contact, but
also where components of the same metal under different stresses are in contact: for
example as between the aluminium alloy plates or extrusions and rivets or bolts used in
building up the structure, in industrial areas where structures are exposed, in flue ducts and
acidic vapours. In close proximity to the sea where a salt
laden atmosphere will be met with,
structures will need the maximum attention to prevent corrosion due to the electrolytic cells
set up by the salt
laden moisture deposited upon the structure.
Duralac is supplied ready for use and must not be thinned. It is best applied by brush. When
Duralac is applied to metal or other surfaces the volatile solvent evaporates and the
compound sets to the touch, but remains tacky for a considerable period. It is important that
the joint should be closed while Duralac is still tacky – so that it is in such a condition that it
will flow sufficiently under pressure to close the gaps in the joint. It will harden somewhat if a
thin film is left exposed to the atmosphere for a long period and this will prevent the making of
a close joint.
Availability: Duralac is available in the following packaging:
Supplied in 250ml, 500 ml, 1 litre, and 5 litre tins. Also supplied in tubes.