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It seems some folk never use PVA as a backup release agent when doing fibreglass work, prefering wax only. Others, after inittially waxing up a new mould and going through the breaking in process, will then delete the waxing from the equation and just use PVA.Then there are those folk who use wax and PVA combo as part release agents.PVA can be wiped, brushed and sprayed on. I must confess I have had no success with wiping the PVA on and brushing left less than satisfactory results. Spraying also has its drawbacks until such time as one acquires the right skill set to apply correctly. I am sure the same is true for wiping it on with a cloth. Since I have got the spraying thing happening pretty good now, I'd like to explain some processess that may help others.Most stuff I read suggests the proper course is three coats of PVA on a previously waxed mould.A DVD sent to me by Dave B goes like this. (This guy uses the PVA only and doesn't worry about waxing at all). The first two are mist coats. Turning up the flow rate slightly for the second coat. Again for the third coat the flow rate is increased and a slight orange peel effect is required. Sounds crazy but wait. As it dries (mist coats 15 mins wet coat give an hour to be sure) the PVA skin stretches tight covering any blemishes. I tried this process and one of the problems that can occurr is that the PVA may pick up dust or pick up on itself and congeal, throwing little flecks against your mould. This usually will happen on the third coat and is a real pain in the neck as one then needs to wash this off and start all over.FRP Pools and Spa's in Tassie wax their moulds, then turn out up to 70 or 80 parts before having to wax again. They deleted the PVA from the process due to the same problem I discussed above. This a large industrial application and they needed to purchase a $20,000 filter system to eliminate or reduce said problem. They chose not to. All their product is 'mechanically' worked after release from the mould.I was advised by friends in the US that after waxing one mist coat only is reqired and the client will wash the PVA off the product.I was further told if I was peeling off the PVA like glad wrap or a snake skin, then I was using to much PVA. Yet, many sites (composite product suppliers) recommend this wet coat process and advocate that the PVA should depart the mould and end up on the part.So, many experts and lots of advice.My experience is this.Spraying PVA can result in most excellent finishes that require no further 'mechanical' working and provide a gloss or satin finish.PVA (Poly Vinyl Alcohol) should be sprayed at 60 plus psi some suggest between 80 and 100psi. I like 70-80psi. You are looking for high pressure low volume.This means low volume. So when you first start shut your gun right down so that the fine mist that is sprayed is almost invisible. Now give one quick coat staying a good 400mm - 500mm from the product. This will give you an overspray type effect, barely visible.Second coat 1/4 turn on the volume. Repeat. 15 mins is usually all that is required between mist coats.Third coat another 1/4 to 1/2 turn on the volume knob and this time looking for a slight orange peel effect. Stay well back as suggested from the part, starting your gun before your pass and off again once passed.I found if you leave the gun running or you are to close to the part the third coat can 'fleck' on you and fisheye and a poor wet out can result.So dont be tempted to turn up the volume flow rate to dramatically and the results can be excellent. This results in a gloss finish. (see Pod mould)A satin finish can be obtained by one to three mist coats depending on the texture of the satin finish required. (Face plate mould had three mist coats).There is little danger of 'flecking' the mould during a mist coating and an article requires no further mechanical working. The same is true for a gloss finish once the spray technique is in hand.Ensure two moisture traps are installed and clear them before and after each coat, to reduce the likelyhood of moisture droplets causing the flecking. Please note that these are moulds and as such will require processess to season and break them in. The photos are only intended to give you an idea as to the possible finishes for the final articles. Further note that neither mould has been mechanically worked. The only treatment was a quick wash with a warm soapy flannel to wipe the PVA from them. That's It!I have found this process the most fool proof for me.The last three months has been a rather interesting learning curve. I would like to thank everyone who helped me with this process. Larry Neal and his glassman Bernie (in the USA), Dave B (ex Victoria) for sending the DVD and to Peter Barsden who, as always, is willing to help with advice or hands on help.Mitch.Image Insert:
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], Well done Mitch and thanks for shareing your experiances with us. I envy you with having the patience to do such a good job.What you focus on grows. Des Gravin
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