newbiepilot

Hi,
I was just wondering if you can use a Plaster of Paris mold for making a fiberglass part. Would the finished product come out alrith, would the Mold be re-usable?
Thanks so much for the info.
I really appreciate it.

newbiepilot

woops I meant "alright" not alrith

FLYBOY

My Feedback: (11)

You can, I have, and the mold will only be useable for a couple pulls. I have one that has pulled many, but it is small. The larger ones tend to break unless you put stiffeners in, and they are heavy if large. They work well if you just need one or two of the parts.

T.S.Davis

great question.

What if you used Ulracal 30 or Hydro Stone. That stuff is like granite. Much better than Plaster of Paris.

davidfee

Ok, then they will be good for 3-4 pulls instead of 1-2. I've used plaster molds and I will never use them again. That's just me. If you don't care how good the surface of your part is and will be priming and painting after removing it from the mold, then plaster of some kind will work. But you need to seal it with a lot of wax/PVA and it will never give you the kind of finished product you can get with an epoxy surface coat/composite mold.

Good luck though,
-David

Ed Smith

Plaster molds seem at first, the ideal way to get a quick cheap mold for a small number of parts. To some extent this is the case. In actual fact though they are not that quick. Whereas the plaster seems to cure in a couple of hours it can take a couple of weeks for the water to fully evaporate, depending on the size of course. As David wrote the surface will have to be fully sealed before use. I prefer to apply a sealing coat before any waxing. I have used Shellac or clear polyurethane. In both cases the plaster sucked up the first coat like a sponge, so I apply a second coat. Then all of the waxing etc.

For strength the mold must have a fairly thick section around the cavity, because of this you will end up with a big heavy lump of concrete for even an average fuselage mold. Whatever you do, do not drop it, it will shatter for sure. If there are any sharp corners in the cavity they will break off very soon and from there the mold will deteriorate.

Apart from all that a plaster mold can be useful!

Ed S

TGoodwin

Plaster based products are OK for taking a quick !QUOT!splash!QUOT! and then using the splash to make a new male plug. Hydrocal b11 or a11 seems to work OK for this. It is similar to Hydrstone mentioned above. I would not use plaster of paris. The surface will need to be reworked but there is less chance of damage to the original. Paster molds are a fraction of the cost but they are no good for any kind of production work. As David stated above. Do not expect more than a few pulls from a plaster mold. As Ed said. do not try and seal it until all of the water is gone.

Just my $.02

Ted

hayman

In a week I will be releasing a new 2 hour video titled "Composite Molding Made Easy" showing you step by step from paper drawing to finished part.

check out
http://www.paonline.com/hayman/video.htm

Send me a message at [email protected] if you would like to be put on a list to be notified when released.

Bill

newbiepilot

Instead of sealing it all up, why not use duct tape or wax paper?
Thanks for the replies guys.

Soar Head

My Feedback: (5)

I have made a couple of plaster of paris molds. If you take the pieces everyone said, you have an accurate picture.
[ul][*] they make accurate molds[*] they are good for a small number of parts[*] you should probably seal them. I used laminating epoxy, then waxed them[*] sharp edges will break off of the mold[*] it is heavy, and a large volume is required.
[/ul]
All that said, PoP is readily available everywhere and is cheap. I say go for it, and have fun. You'll learn a lot in the process.

pt19 flyer

My Feedback: (1)

hi

[email protected]

thanks
joe

CoosBayLumber

My Feedback: (1)

I used plaster of Paris molds before also. Did it because the original part was of thin vac-u-form plastic. The plastic would not take the heat developed of Polyester nor epoxy fiberglass. It would distort before either of these set up.

The P-of-P molds were cool to begin with, and did not stick nor harm the plastic. The originals had rivet heads, and the soupy plaster picked up every single one when pulled off. I used common old parifin wax to seal up possible leaks too. The parifin melted at relatively low temperatures and could be trimmed quickly with just a razor blade.

As mentioned, the bad part was the curing time, and the sealing effort too.

Overall the molds cost about 1/4 of a $7.95 full sack of P-of-P which is a lot cheaper than fiberglass mixtures.


Wm.

djastram

I just got done making a plaster cast of an equipment pod for a plane I'm doing.

Check out the pics.

buttuh

If you're going to use plaster, I'd recommend Hydrocal FGR-95. You can get it for about $25-$30 for a 100lb bag. It's specifically made for building fiberlgass mold and it's a lot lighter than of the shell P-of-P. I would also recommend mixing some burlap or chopped fiberglass to make it stronger. It seemed ideal to me at first but sealing the surface and the short mold life killed the deal for me. I seal the mold with shellac spray and then lots of wax.

Evan