Discussion
cold thursday said:
Definitely do not do this it will end in tears.
PVA release agent and PVA glue are not the same thing
Release wax does the job, seems expensive because you can only get it in large cans. Otherwise I read that a decent carnuba-based wax polish will be as good.
Plenty of wax in lots of coats.
We wax and then polish 6 layers and then sometimes we use PVA as well. Once you've made a mould and taken a pull or two then you can drop to 3 coats of wax and polishing. It's hard work and boring as hell but beats the 'excitement' of struggling with no end of plastic wedges and more trying to prise mould and components apart. You need to look at the sections of mould carefully regards it's shape and make sure you've not got lock around or what I call re-entrant.(think of a jigsaw puzzle you don't want pieces locked together due to their shape)
We wax and then polish 6 layers and then sometimes we use PVA as well. Once you've made a mould and taken a pull or two then you can drop to 3 coats of wax and polishing. It's hard work and boring as hell but beats the 'excitement' of struggling with no end of plastic wedges and more trying to prise mould and components apart. You need to look at the sections of mould carefully regards it's shape and make sure you've not got lock around or what I call re-entrant.(think of a jigsaw puzzle you don't want pieces locked together due to their shape)
gtmdriver said:
You can use any wax polish as long as it does not contain silicones.
PVA is better on less than perfect surfaces but on a good mould wax will leave a better final finish.
^^^^^^^PVA is better on less than perfect surfaces but on a good mould wax will leave a better final finish.
This is the truth
Silicones are almost universally used in household furniture polishes because they give an instant shine. However Silicone and polyester resin will cause a stick. This is why Mould release waxes contain no silicone.
If however you were using Epoxy resin then silicone is good , it will release like a very slick thing.
I rarely use any of the "Old school" stuff any more.
Semi permanent's are very very good.
I've just finished a run of 40 mouldings (polyester mould, polyester resin /glass/kevlar/diolen.lay up vacuum bagged.) No re treatment in between and the last release was the same as the first.
The mould acts as if it were teflon coated.
Fastpedeller said:
Agreed - I've tried the blue PVA with disastrous results - will only use wax now.
The PVA works really well if you use it properly, it's actually a physical barrier which can be clearly seen whereas the coverage of a wax is not easily judged.The GRP industry use it on 80ft yacht hulls etc , do you really think they would take any chances on getting a "stick up" with that amount of time and money at risk?
PVA must to be applied to non porous surfaces only, either sprayed or wiped on, if not spraying then one coat only should be EVENLY applied, if spraying then multiple coats, although not manufacturer recommended ,can be used.
The PVA must be allowed to dry thoroughly before gelling /laminating onto it.Safe release is guaranteed if you have no re-entrants on the mould.
BTW the first GRP moulding I did was a copy of a Cortina Lotus air box which was the same as a S 4 Lotus 7 T/C for which I made a lovely split 2 piece plaster of Paris mould which I then PVA'd several times and then allowed to dry thoroughly. I gelled and laminated the new airbox up no problem, that was until I tried to release it from the p.o.P mould tool!!
I ended up chipping the p.o.P mould off very carefully, took f***g hours, still I did get one off despite my ignorance/stupidity.( Lotus/Caterham couldn't supply at the time )
Auntieroll said:
The PVA works really well if you use it properly, it's actually a physical barrier which can be clearly seen whereas the coverage of a wax is not easily judged.
The GRP industry use it on 80ft yacht hulls etc , do you really think they would take any chances on getting a "stick up" with that amount of time and money at risk?
PVA must to be applied to non porous surfaces only, either sprayed or wiped on, if not spraying then one coat only should be EVENLY applied, if spraying then multiple coats, although not manufacturer recommended ,can be used.
The PVA must be allowed to dry thoroughly before gelling /laminating onto it.Safe release is guaranteed if you have no re-entrants on the mould.
BTW the first GRP moulding I did was a copy of a Cortina Lotus air box which was the same as a S 4 Lotus 7 T/C for which I made a lovely split 2 piece plaster of Paris mould which I then PVA'd several times and then allowed to dry thoroughly. I gelled and laminated the new airbox up no problem, that was until I tried to release it from the p.o.P mould tool!!
I ended up chipping the p.o.P mould off very carefully, took f***g hours, still I did get one off despite my ignorance/stupidity.( Lotus/Caterham couldn't supply at the time )
I take the point that I may not have used it correctly - but I don't know where i went wrong. Should wax be put on the mould prior to the PVA? or what. Mine was a similar tale to the above, and the PVA seemed to be glued solid to both the part and the mould.The GRP industry use it on 80ft yacht hulls etc , do you really think they would take any chances on getting a "stick up" with that amount of time and money at risk?
PVA must to be applied to non porous surfaces only, either sprayed or wiped on, if not spraying then one coat only should be EVENLY applied, if spraying then multiple coats, although not manufacturer recommended ,can be used.
The PVA must be allowed to dry thoroughly before gelling /laminating onto it.Safe release is guaranteed if you have no re-entrants on the mould.
BTW the first GRP moulding I did was a copy of a Cortina Lotus air box which was the same as a S 4 Lotus 7 T/C for which I made a lovely split 2 piece plaster of Paris mould which I then PVA'd several times and then allowed to dry thoroughly. I gelled and laminated the new airbox up no problem, that was until I tried to release it from the p.o.P mould tool!!
I ended up chipping the p.o.P mould off very carefully, took f***g hours, still I did get one off despite my ignorance/stupidity.( Lotus/Caterham couldn't supply at the time )
You can put a couple of coats of wax and then PVA as insurance if you are only wanting a "one off", saves lots of time and elbow grease.
The industry uses wax as a first choice for production mouldings, there are several types, as Cold Thursday posted previously, most of them are too expensive to consider for "one-offs".
PVA is very useful when wanting a quick moulding from a new mould say before the mould is finish polished or if variants of the moulding are needed or ,as is sometimes the case, a deadline is looming or it's a "one off", the resultant mouldings will need to be flatted down and polished themselves, or possibly painted as a prototype before much effort is put into finish polishing the production mould tooling (if it needs to be polished that is.)
PVA can be thinned for spraying by mixing equal parts of meths and water together then adding the resultant mix to the neat PVA in the ratio of 1 part mix to 3 parts neat PVA. Tack off the mould then spray at 70-80 psi using a THIN coat to avoid puddling or runs.
Warmish conditions make the job so much easier as a quick evaporation rate helps avoid the runs/puddling problems.
I always allow the first coat to dry off completely, then repeat.
The reason for the meths/water mix is that when I tried to dilute with straight H2O the PVA "curdled" and wouldn't mix properly, a chap who makes propellers for aircraft suggested the process to me , it works beautifully.
As mentioned wax is generally the first choice for industry, it is quick ,reliable and relatively cheap to use and very well proven.
The industry uses wax as a first choice for production mouldings, there are several types, as Cold Thursday posted previously, most of them are too expensive to consider for "one-offs".
PVA is very useful when wanting a quick moulding from a new mould say before the mould is finish polished or if variants of the moulding are needed or ,as is sometimes the case, a deadline is looming or it's a "one off", the resultant mouldings will need to be flatted down and polished themselves, or possibly painted as a prototype before much effort is put into finish polishing the production mould tooling (if it needs to be polished that is.)
PVA can be thinned for spraying by mixing equal parts of meths and water together then adding the resultant mix to the neat PVA in the ratio of 1 part mix to 3 parts neat PVA. Tack off the mould then spray at 70-80 psi using a THIN coat to avoid puddling or runs.
Warmish conditions make the job so much easier as a quick evaporation rate helps avoid the runs/puddling problems.
I always allow the first coat to dry off completely, then repeat.
The reason for the meths/water mix is that when I tried to dilute with straight H2O the PVA "curdled" and wouldn't mix properly, a chap who makes propellers for aircraft suggested the process to me , it works beautifully.
As mentioned wax is generally the first choice for industry, it is quick ,reliable and relatively cheap to use and very well proven.
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