RE: A few newbie type questions

RE: A few newbie type questions
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RE: A few newbie type questions - 1/9/2008 3:18:13 AM

JKEpps

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Joined: 12/10/2004
From: Greenbelt, MD, USA
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quote:

ORIGINAL: jantrit

Looks very nice,just a quick question, what purpose does the pva serve and is this applied before or after wax?

Well, I'll give you my understanding of it. Those with more experience can correct me. The wax serves to provide a very slick surface so that the resin doesn't stick to it. It takes quite a few coats of wax in most cases. I think 6 - 10 is the most common number of coats. In some cases, the wax used isn't enough to ensure that you get a clean release without damaging the plug. The PVA serves as an additional barrier to aid in clean releases. It dries to form a film that peels away from the plug and mold and layups. Some folks don't like to use the PVA because it leaves a residue on the plug and mold and layups that requires cleanup, and may even permanently stain the pieces. The PVA goes on after the waxing has been completed.

Hope that helps.

-Jorden

< Message edited by JKEpps -- 1/9/2008 3:19:33 AM >

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Post #: 51

RE: A few newbie type questions - 1/9/2008 3:23:18 AM

JKEpps

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From: Greenbelt, MD, USA
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Hey, look what I found at my local Harbor Freight store. It's regularly $14, but on sale this week for $7. Looks like it'll be great for spraying on PVA. At $7, hey, it's worth a shot. I'll let you know how it goes.

-Jorden

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Post #: 52

RE: A few newbie type questions - 1/9/2008 7:12:31 AM

bigben2k

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Joined: 10/18/2007
From: Tomball, TX, USA
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quote:

ORIGINAL: JKEpps

...I'll let you know how it goes.

-Jorden

Please do; I'm tooling up for an all-composite construction too. thanks for sharing your experiences!

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Post #: 53

RE: A few newbie type questions - 1/9/2008 3:10:40 PM

TeamSeacats

Posts: 161
Joined: 3/9/2007
From: Greenville, SC, USA
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quote:

ORIGINAL: jantrit

Looks very nice,just a quick question, what purpose does the pva serve and is this applied before or after wax?

The PVA (poly-vinyl-alcohol) is a product that dries quickly and leaves a thin water-soluble film. It is applied after the wax and it makes the release of parts from a mold very easy and further reduces the chances of a part sticking resulting in damaged parts or a damaged mold. However, the PVA is difficult to use and obtain a glossy finish. If spraying, it is tricky to get it to set without tiny bubbles (you have to adjust the amount of water in it to the ambient humidity for proper drying time) and it is very sensitive to dust or other contaminates - spraying a glossy layer is more of an artform than doing so with paint. If brushing, it will leave some (very minor) brush marks on the part or the mold.

I've never had any trouble with staining the part using either epoxy or polyester resins. When using with epoxy, you need to understand that the epoxy will bond to the PVA (since it is water based and water is soluable). The result is that you will not be able to "peel" the PVA off but just rub it down with some water and the film will go away.

< Message edited by TeamSeacats -- 1/9/2008 3:13:49 PM >

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Post #: 54

RE: A few newbie type questions - 1/9/2008 3:40:11 PM

Ed Smith

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Joined: 12/29/2001
From: Brantford, ON, CANADA
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My experience with PVA is the same as TeamSeacats.

I never use PVA on a plug prior to laying up the mold. The streaky or little bubble finish with PVA is what the mold inside finish will be. I make sure the plug has many coats of wax applied over a couple of weeks to allow the wax to harden.

I will use PVA for the first couple of parts to come out of the mold. I can always fix those.

Ed S

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Post #: 55

RE: A few newbie type questions - 1/9/2008 7:42:49 PM

jantrit

Posts: 31
Joined: 10/4/2007
From: london, UNITED KINGDOM
Status: online

ok thanks a lot, im 16 and just getting into composites, hoping to make some simple servo covers for my first little project. Looks like for all the work you put in you get a nice reward

.

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Post #: 56

RE: A few newbie type questions - 1/9/2008 8:10:53 PM

daven

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From: Andover, MN, USA
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PVA can be tricky, but once you know what works for you and your gun its pretty easy to apply and you can get a mirror finish using it. I won't risk my molds to just wax, and always use PVA after waxing and prior to paint.

The biggest trick in applying PVA with a gun, is patience. I apply an absolute mist coat that barely covers the surface and let dry till smooth (about 10-15 minutes) before applying my 2nd coat. When a mold is new, I'll go to three coats until it gets to what I would call "seasoned".

I've had one wing stick in the molds, and won't go through that hastle of cleaning and repairing, and repolishing my mold back to a state I can pull good parts. So now I use PVA.

One of the things about PVA I never liked was removing it from the molds (the flanges) after the part came out. I've found a pretty good solution, I just take some 2" box sealing tape and stick it to the mold, rub it down, and pull it off. Removes the PVA residue / paint overspray very well.

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Post #: 57

RE: A few newbie type questions - 1/9/2008 11:12:02 PM

RabC

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From: BANBRIDGEN/A, IRELAND
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Cheers Ed for the advice with the parting board,i had actually looked at the post you refered me to although for some reason the penny failed to drop,it has now,i can catch up with the rest of this very productive thread again,head is going wild now cant sleep thinking of moldings

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Post #: 58

RE: A few newbie type questions - 1/10/2008 11:44:53 PM

RabC

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From: BANBRIDGEN/A, IRELAND
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JKEpps i am impatient also,cant wait to see the finished goods.

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Post #: 59

RE: A few newbie type questions - 1/11/2008 11:48:00 AM

JKEpps

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From: Greenbelt, MD, USA
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quote:

ORIGINAL: bigben2k

quote:

ORIGINAL: JKEpps

...I'll let you know how it goes.

-Jorden

Please do; I'm tooling up for an all-composite construction too. thanks for sharing your experiences!

Well, I finally tried the sprayer last night by using it to spray PVA on the other half of my plug/mold combo. I used 20 PSI of pressure, and it sprayed on a nice mist of PVA. The spray pattern leaves a lot to be desired. This set definitely is not to be used for any kind of detail painting, except maybe with using a lot of masking, and that's a big maybe. In any case, it's definitely worth the $7 I payed for it. Plus it comes with the adapter needed to convert from the standard compressor size hose (3/8th I think) to 1/4 inch. I missed that little detail when I bought it, and ended up buying an adapter that I didn't need.

Hope that helps.

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Post #: 60

RE: A few newbie type questions - 1/14/2008 3:09:44 AM

JKEpps

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From: Greenbelt, MD, USA
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OK, I've finally laid up the other side of the mold, and let it cure for nearly 24 hours. I seperated the halves, after a little coaxing, and voila! The first half looks beautiful, with a mirror finish to it. After a few anxious moments trying to get the plug to release from other half, it finally popped out. The other half was just as beautiful as the first. I am soooo pleased with the results. I'm totally hooked on mold making now. Even the details of the nickles I used came out great, even though the photos don't do it justice. The PVA did leave a pinkish hue to my plug. I wonder if it'll come out, or if it is permanently stained. I'll try and clean it up and see what happens.

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Post #: 61

RE: A few newbie type questions - 1/14/2008 4:53:18 PM

jantrit

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Joined: 10/4/2007
From: london, UNITED KINGDOM
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Wow looks really good, this is inspiring stuff. It just clicked for me why you use the nickles, never would have thought of that until it would be too late .

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Post #: 62

RE: A few newbie type questions - 1/14/2008 7:12:26 PM

JKEpps

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From: Greenbelt, MD, USA
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Man those picture came out HUGE!!!! That sometimes happens to me when I post pictures, and I don't know why. Am I doing something wrong ( iused a different application to "resize" the pics this time) or is it a RCU anomaly?

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Post #: 63

RE: A few newbie type questions - 1/15/2008 4:03:59 PM

TeamSeacats

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From: Greenville, SC, USA
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rinse the molds with water and rub with your hand - the PVA will wash away. It's there because the epoxy started to dissolve and bond with it since water is soluble in epoxy. Fear not though, the PVA is still cleanly on the outside of the mold, just needs to be dissolved away.

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Post #: 64

RE: A few newbie type questions - 1/16/2008 1:54:07 AM

N1EDM

Posts: 1902
Joined: 7/19/2002
From: Brockton, MA, USA
Status: online

JKepps, That happened to me on another post. I've been posting photos for years and that was the first time that it happened to me. I think it might be something to do with this board, just a glitch or a fluke. Normally it doesn't happen.

Several years ago, I worked for a company that did polyurethane molding for electrical connectors. We ran out of PVA mold release and when I called the company to order a rush shipment, he told me on the side that I could get by using something like PAM, that we use to keep our cookware from sticking. Hey, it worked!! Granted, it wasn't epoxy. And, we were pouring the poly into the mold, not brushing it on (which could disturb the finish of the PAM if used for one of our molds). Has anyone used something like this? And, if so, what were the results?

Bob

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