ABL (STEVENS) Resin & Glass
Unit 4 Millbuck Way, Springvale
Ind Est, Sandbach, Cheshire CW11 3HT
Tel/Fax 01270 766685 E-Mail
PVA Release Agent.
Designed as a mould release/parting
agent for use when fabricating mouldings in polyester gelcoat and layup
resins in GRP construction.
PVA Release Agents are a liquid
solution of polyvinyl alcohol resin in a mixture of water and industrial
methylated spirits sometimes including small quantities of dye and/or
matting agent dependent upon the grade. Available in clear or blue and both
glossy and matt versions. They have been developed to give best results if
spray applied but glossy versions can also be applied by sponge or soft
brush. PVA Release Agents can be applied over waxed or polish but the wax
polish must be silicone free. Soluble in water therefore can be washed off
moulds and mouldings with water even when dried. Matt versions are
especially useful when producing low gloss finished mouldings.
To achieve the best results when
using PVA Release Agents it is recommended that they be spray applied.
However, the glossy versions can also be applied by sponge or soft brush.
The mould surface must first be thoroughly waxed and polished with a
silicone free wax ensuring no areas are left unwaxed as they will result in
sticking of the moulding during release. During PVA application care must be
taken not to flood the mould surface as this will cause variation to the
finish over the area coated leading to a similar finish variation in the
moulding. The best spray results are obtained by using as fine a spray as
possible and a high air pressure of between 80 and 90 psi. A low output of
PVA and a normal spraying distance of 30-40cm should be observed. One thin
coat of PVA should be applied via a continuous multiple pass technique to
give a wet film thickness of 50-150pm (microns). The spray gun can be washed
out after every use with water and flushed through with solvent to remove
residual water. The PVA must be allowed to dry completely before gelcoat or
resin application to the mould begins. Cold, damp conditions will retard the
drying rate. The drying rate should not be hastened by the simple expedient
of turning a warm air fan over the sprayed mould, this will cause the wet
PVA to skin over the exposed film surface whilst leaving moist solution
trapped underneath. Preferably the mould itself should be pre-warmed in
adverse conditions. Matt versions of PVA Release Agents should be stirred
well before and during use. A PVA film is strongly recommended on new
tooling for its insurance value in case waxing has been insufficient. Once
the moulding has been constructed on the mould and has cured the PVA film
may be dissolved to float the moulding free of the mould by working warm
water down into the interface between the moulding and mould. PVA may be
removed from both mouldings by washing them with water or methylated spirit
where moulds have become stained.