Rubbie

I was sealing the edges of my parting board to plug with a polyester type sanding puddy (no name bondo) on the weekend and when I took the plug out in the morning all the PVA peeled off too (I just went around the edges of the plug with the bondo to seal the edges before I layed up my mold). The PVA just peeled off, some stuck to the sanding puddy, some stayed on the plug but most pealed off the plug in huge chunks like a plastic bag, or a huge snake. Is this normal?? I have 3 coats of "partall" wax all buffed out and 3 coats of PVA sprayed on with my old airbrush on the plug. it's not a big deal cause I can spray it again but is this normal?

davidfee

Yes, it's normal. The PVA dries to form a thin, water-soluble plastic film. The film doesn't stick particularly well to wax or the resin material, so it peels off. No worries...

-David

Mike James

Yep.

SCHMITY

In my opinion I would say this is far from normal, and there seems to be an incompatability between the brand of wax used and the release agent. Has this problem occurred before combining these products and if so I suggest you try another brand of wax, just make sure the mold release wax doesn't contain silicone. Otherwise omit the pva release and go with the wax - providing you have applied several coats and polished off the plug and parting board effectively. Final suggetion would be to repeat your procedure and then keep a vigil on the job to see what happens, in relation to ambient temp effects.

davidfee

???

newtech

??? I don't understand this answer? I don't mean to be disrespectful, but, this is what you would expect to happen. The PVA film, when dried, is very fragile and can be easily torn and/or scratched off with your finger nail. Just sand and finish your parting board. Wash off the PVA from your plug and wax some more (can't have too much wax), put your parting board back into place and thoroughly wax it all and spray with PVA. Then on to making your mold.

Steve Eberhart

goony

YES this is very normal as has been said the pva is a barrier between the resin and the mold, thats the whole point of it, BUT the way to use it is to wax the mold as many times as you can be bothered at least 3 VERY min then add pva, then after each PULL you wash off the pva add another coat of wax and then PVA again and keep doing this until you have pulled at least 3 parts maybe more depending on how easliy its releasing until you are confident that it will release without the PVA, the whole point of using PVA is that if you are struggling to release the part then you can open the sides on the returns and pour hot water down between the part and the mold,this will dissolve the PVA and release the part, by the way you only need 1 coat of PVA adding several makes NO difference to the releasing properties what so ever.
As there are a lot of guys in the states doing your own molding then perhaps you should look at buying some more modern release agents such as frekote its a bit expensive but if you where to split the contents and the cost it would save a lot of work
just a thought guys?

goony

davidfee

After having read this several times, I get the impression SCHMITY was thinking that the PVA was somehow peeling up when wet... like an orange peel on incompatible paints. That wasn't the case, however, as Rubbie said it was the next moring when he was removing the plug... so the PVA would have been dry.

-David

SCHMITY

Didn,t mean that the Pva wouldn,t peel away, but for it to merely fall off in huge chunks? I misinterpreted the question in thinking that the next morning when inspected, the pva had somehow shrivelled up and separated from the plug all on its own! However overlooked the fact that the plug had been disturbed. Sorry my mistake. ...................Schmity

boater

My Feedback: (2)

In haste, I've used as little as one coat of wax and one coat of PVA, and got acceptable seperation, ie didn't pop easily, but no transfer from mold to layup of any mold material. Too many coats of PVA may lose detail and fill sharp corners. One even, medium coat without orangepeal or streaks is the target to shoot for. Amazingly PVA always seems to work. I don't do production, most of my molds have less than three pulls, so I always use PVA. Just takes one scare to make you a believer.

Seppo K

You guys seems to use really thick layers of PVA in your molds. Why?

One day, when I was also in trouble with mold loosing details of my plug, I got a hint from one of my colleagues how to use the PVA effectively and easily. It goes like this: After really good waxing, take 2 pieces of cloth - one for wetting the plug with PVA and one for sweeping the excess PVA off. The sweeping cloth may be larger in relation 3:1 or so. (Size actually does not matter, but this helps both to explain the method, and also get the sweeper correctly damped.)

Wet the smaller cloth really well with PVA and sweep over the plug so that it will be very wet overall. Be sure that it is REALLY wet. At this time the smaller cloth gets also rather wet, so now cover it with the larger one and press it to dry. The idea is not to get the smaller cloth dry, but to make the larger just a bit damp for further step. The size actually here represents the wetness you need for the larger one - not wet, but JUST A BIT damp, not fully dry. Now check once again, that the plug is still wet overall, and if yes, you may proceed. If not, add some PVA still with the smaller cloth.

When the plug is wet, take the larger cloth and sweep smoothly over every square centimeter of the plug once - and I mean ONLY ONCE. Do not try to touch on areas you have already sweeped, or you will have trouble and need to wet the plug fully again and then re-start sweeping off. You may use zik-zak-path or sweep narrow paths - it is just important that every area of the plug is handled and all the excess PVA is sweeped off - but just once. When this is done, you can hardly see any PVA - there might be some minor visible stripes in the PVA coat, but they do not cause anymore any harm. Don't say that all the PVA is seeped off - yes alsmost all is and you can't see any, but there is still thin layer of PVA molecules and this is really enough to release the mold.

I agree, this is hard to believe - it was the same for me, but after trying it I have now used it many-many times and never had any problems with either excess PVA loosing details from my mold or loosing the mold in the process.

There is just one problem into which I am not very satisfied: this dam method will copy all the dam-diny un-wanted scraches from my plug into the mold I didn't even notice when using earlier methods, but that is another story that. And yes, the same "PVA-sweeping"-method works for building mold on top of plug, and then building the actual part using the mold you have done.

Seppo