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Old 08-09-2004, 10:52 AM
  #1  
daven
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Default PVA

I touched on this briefly in the "Mold Wax" thread, but thought it derserved its own.

I attempted to apply PVA (diluted with 1 part water, and 1 part alcohol) to a set of molds that I have been waxing for the past few days.

I used a small detail (4oz) HVLP gun hooked to my aircompressor at roughly 25 psi.

1st attempt I tried applied like I was using Paint and ended up with a bubbly, runny mess.

2nd attempt I put down a very light mist coat and waited 15 minutes, and then tried to apply a heavier coat which ended up similar to the 1st attempt.

3rd attempt I put down 3 very light mist coats with a 5-10 wait between coats. This turned out the best, although not perfect. Still some very small bubbles and a slightly rough (almost orange peal) finish. My only concern, is that there doesn't appear to be very much PVA on the molds??

Heres my questions.

Any good PVA out there (thats easier to use)?
Am I over or under dilluting it?
Wrong type of gun? I borrowed a non-HVLP gun that I could try. too much pressure?
Method of application? Gun, Brush, rag, whatever?
How many layers are necessary?

Thanks for your help.
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Old 08-09-2004, 12:06 PM
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Ed Smith
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Default RE: PVA

Hi Dave,

I think that just changing the thread will not get you different answers.

I have never been able to get PVA to lay on the mold surface smoothly. It always fisheyes and/or separates. That is why I do not use it. In any case, even if you can get it on smoothly the finish you see when it dries will be dull and streaky. This is the finish you will get on the laid up part. If you intend to paint in the mold then you definitely cannot use PVA.

What is the matter, arm getting sore???

Ed S
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Old 08-09-2004, 01:17 PM
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daven
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Default RE: PVA

Arm is sore.

I don't want to use PVA, but am scared to death the wing will get stuck inside.

It is an epoxy mold, and I am concerned the heat generated by the epoxy when making the first part will weaken the wax and possibly kick off any remaining cure left in the mold (are they ever completely dry)?

I'm not looking for a perfect wing off the get go, but would like to at least put some clear paint on the bottom and a little color on the tips on the top (painted freehand).

I suppose I could put a thick coat of clear over the PVA and plan on polishing / buffing it smooth.

Yes my arm is sore
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Old 08-09-2004, 02:11 PM
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Default RE: PVA

Dave,

To overcome your fear of not using PVA may I suggest you try this. Lay in a small patch of a couple of layers of cloth say on the bottom wing mold at the centre section. See what happens.

Ed S
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Old 08-09-2004, 04:36 PM
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Default RE: PVA

Has anyone tried Frekote Aerosol from Aerospace Composites?
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Old 08-09-2004, 07:13 PM
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Default RE: PVA

Daven

We have always used PVA along with our partall wax. You can use it straight from the bottle applied with a foam sponge type brush.

It doesn't need to be thick at all. A thin coat will still provide the barrier it is designed to provide. It is not considered a mold release on its own. It is mearly an additional protection for your mold.

Even the thinnest coat will serve its purpose.

All our "parts" are made to be painted. So our composite models get washed, maybe a light sandind (molded details inwarbirds) and a vinigar wash before primer and paint.

Now if your need to paint in the mold. Then you may want to wax and buff your part after its out or don't PVA. Like Ed said, experiment.

Steve
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Old 08-09-2004, 07:16 PM
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Default RE: PVA

Thanks,

I will try 3 light coats of PVA and see how it turns out. This first wing is an experiment, but its tough to not try and get it perfect right out of the get-go when you have a lot of money tied up in the materials that you use. The Rohacell alone is close to $60 per wing, not to discount the Carbon Fabric which isn't cheap either.
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Old 08-09-2004, 08:17 PM
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Default RE: PVA

Don't use your good stuff until you get your release down. Just
layup a couple of layers of cloth only. I have had a new gallon
of pva on the shelf for 6 years never need it. I use collinite
wax, best stuff I have ever used.

Chuck
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Old 08-09-2004, 09:11 PM
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Default RE: PVA

Well, I heard a lot of good things about Dolphin wax, so that is what I used (7 coats). After that, I finally got a good coat of PVA down by lightly spraying 3 mist coats with about 10 minutes to dry between each coat. After this dried, I put down my paint. Some black stripes, the green tips, and then the White in the middle (which covers the black stripes). For the bottom I used Clear epoxy KlassKote.

I can't see why I shouldn't try to make the first wing useable? If I use other materials, how will I ever figure out how to use the proper stuff corectly?

Maybe I'm off base, but I intend the first wing to fly.

Heres a picture of the painted mold halves.
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Old 08-10-2004, 10:55 AM
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Default RE: PVA

Dave,
I'm sorry to hear that you have been having a bit of trouble with the PVA, you are far more patient than I am with it. I did not like it at all for paint-in-the-mold preps, this is why I switched to Dolphin wax. For all of my paint in the mold projects I use ONLY Dolphin wax...I have NEVER had any sticking or problems removing a part....even for parts with lots of sharp corners. And it maintains a high gloss and smooth finish after I pull the parts....PVA was dissappointing in this respect.

Now, with that said, if I'm not going to paint in the mold, but rather just pull fiberglass or carbon parts I have used, with great success, SafeLease 30 (a water based PTFE release). I really love this stuff...it applies very easily and goes on extremely thin. I just wipe it in the waxed mold with a piece off an old soft cotton T-shirt. I have used this with all sorts of Epoxies and Ploy resins and all parts come out beautifully with little effort.

I have not heard others mentioning this and am just curious why more people don't use this over PVA??? Anybody?? As someone who has used PVA for a LONG time in the past, after using SafeLease, I will never go back to PVA.

Anyway, I hope things work out well....please post some more pix of your results!!

Erik
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Old 08-10-2004, 11:00 AM
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Default RE: PVA

I am opened minded. Where do we get Safelease 30 from?

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Old 08-10-2004, 12:37 PM
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Default RE: PVA

Hi Ed,
I got my Safelease 30 through Composite Structures Technology (now called the Composites Store) in Tehachapi, CA.

Here's the link:

https://www.cstsales.com/Epoxy_&_Mol...g_supplies.htm

You will see that it is definitely NOT cheap (@$40 / quart and over $100 / gallon). HOWEVER, you don't use much of it. I still have over a half a quart left in some that I purchased several years ago. It takes very little to cover the surface area of a mold.
If you Google "Safelease 30" you will also find other suppliers and more info.

Like I say, I really like the stuff, it is clean, essentially oderless, and very easy to apply......No more "green flakes" and "green mess"

Erik
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Old 08-10-2004, 01:49 PM
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Ed Smith
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Default RE: PVA

Erik,

Thanks for the information.

When it comes to my hobby and glass work in particular, no expense is too much!

Ed S
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Old 08-10-2004, 04:35 PM
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Default RE: PVA

Dave,

"I can't see why I shouldn't try to make the first wing useable? If I use other materials, how will I ever figure out how to use the proper stuff corectly?"

Sure do what you want but on one hand your crying about the cost of the materials and not wasting them? If it where me I would
get the release down first, then progress as you might end up with more problems and will have no idea what caused it. Buy doing
it in steps you wouldn't be guessing.

Just my opinion[&o]
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