Hey guys, I have a mold question.

[Texan]

My wife bought some "Amazing Putty" ( http://www.amazingmoldputty.com/ )from hobby lobby last night, along with the resin from the same company. I had planned on trying out the oomoo stuff but she beat me to the punch.

On one of their videos they cast a seashell in a two piece mold, but never show how to do the two piece mold. I don't want the first part of the mold to stick to the second when I do it, so I assume I need mold release. What could I use for mold release? Would a thin piece of smooth tinfoil work?

[nightmareB4macross]

My wife bought some "Amazing Putty" ( http://www.amazingmoldputty.com/ )from hobby lobby last night, along with the resin from the same company. I had planned on trying out the oomoo stuff but she beat me to the punch.

On one of their videos they cast a seashell in a two piece mold, but never show how to do the two piece mold. I don't want the first part of the mold to stick to the second when I do it, so I assume I need mold release. What could I use for mold release? Would a thin piece of smooth tinfoil work?

No need to assume, you've already hit the nail on the head.

[Texan]

Awesome. So, what could I use? Olive oil, tinfoil, wd40? I'm at a loss since they didn't have anything like mold release there from what she told me.

[PetarB]

Don't use tinfoil. You really need a spray-on wax release. However, I've heard of some people melting down vaseline, and painting that on. where the first part of the mold will touch the second part.

[Texan]

Don't use tinfoil. You really need a spray-on wax release. However, I've heard of some people melting down vaseline, and painting that on. where the first part of the mold will touch the second part.

Oh. I wasn't sure as I've never actually done this before.

I'll try vaseline then, thanks!

[nightmareB4macross]

Oh. I wasn't sure as I've never actually done this before.

I'll try vaseline then, thanks!

Brush slightly warmed vaseline onto the mold. Just warm it up so you have a smooth and thin consistency. If it's lumpy the vaseline will leave unwanted brush strokes behind.

[theplasticwerks]

Tinfoil is a no-no, unless you want to cast the tinfoil itself

Whatever you put in the mold will be cast, including your mold release if it's thick enough (so make sure your Vaseline is baby smooth, or you'll have brush strokes on your cast part!).

I've used cooking spray to some success. WD-40 does the job as well. My shop supplies a sodium-based spray.

As to making the two-piece mold, here's how I do it.

Bury the part to be cast halfway in clay, uncured sculpey, something. Pour your mold material over it and scrape down the sides so you have a seam. Once it sets up, remove the clay and create register marks in the first half of the mold - as simple as drilling a shallow hole in every corner. This helps your mold line up. Spray some mold release on it.

Once your registers are in and your mold release is on, flip the mold over (with the piece still inside, facing up) and cover the other side in your mold material; scape the sides to maintain visibility of the seam (and you can do the entire process in a leakproof box to avoid scraping things down). Once it's set up, carefully pry your mold open and remove the part. Then, create a hole in the side of the mold that goes into the actual mold itself (the negative of the part) so you can pour your casting material in.

Another way to create a two-part mold is to build a leakproof box and stick your piece at the bottom of it with a piece of clay (do your best to minimize the amount of material you'll have to cut off the cast later!), spray with mold release, and pour your mold material over it until the piece is covered entirely. Once set, remove the mold from the box and carefully cut it in half wherever the seam needs to be (hopefully you planned this out before!). While harder to register, it does save a few steps. This method is best used with flexible molding material like rubber or alginate. Do not try this method with anything that sets hard.

Edited October 29, 2008 by theplasticwerks

[big F]

I use both Vasaline and the box method to great sucsess. I always use Plastacine which is a kids modling clay, its cheap and re workable.

There are a few guides arround the web on how to do it with some pictures,

This is a good one but a better one was submittedf by a MW member and I dont have the link as im at work.

www.aircraftresourcecenter.com

[Valkyrie]

My mold release of choice is vaseline thinned down with mineral spirits. It takes a lot of mixing to combine the two, but it works like a champ.

[Texan29]

Hey guys, I really appreciate the responses! I was surprised there isn't a pinned FAQ on mold/casting here.

I'm working with this mold putty stuff for the moment, I hope to get the liquid soon to try that out on multiple parts and a project I'm working on. I do remember the how-to fulcy did a long time ago but the medium I have is a putty, not a liquid. I couldn't find any instances of the mold putty or polymer clay on the forum through search, so I guess I'll be the first to try it as a two part molding process.

I did go out and get some vaseline, it's in a tube. I hope that works since it's already thinned a bit, I won't have much work rendering it down to thin liquid.

I'll try to post pictures when I'm done.

[Ignacio Ocamica]

Hope these pics help you!!!

(Courtesy of MW member Fulcy)

[big F]

You could alway try the sandwich method, fill both halves with molding material and squish them together. It will leave you with a bit of flash to clean off, but with practice you can minimise the ammount of flash you get. Ryjiu uses it to make his figures masters

[Texan29]

You could alway try the sandwich method, fill both halves with molding material and squish them together. It will leave you with a bit of flash to clean off, but with practice you can minimise the ammount of flash you get. Ryjiu uses it to make his figures masters

I was thinking of doing this except the instructions said not to press but to roll or it will distort the detail. Is there a certain method I should follow exactly or just do it already and stop worrying?

What I'm planning on casting is the right side flap on the old gakken mospeada bike (the larger one). The shape is not flat or I would just do a one-piece mold with this stuff and stop candy-@ssing around.

[MechTech]

I squash mold all the time. The secret is not to press too hard. Just like picking up a pencil for the first time; there's going to be mistakes and a learning curve.

If the part will be pretty thick in shape, it's best to go two part due to air bubbles. Squash molding is really only good for shallow stuff due to how easy air guts trapped in. Extra resin usually will flow the air out in a shallow mold.

For the record, Vaseline brushed on really thin is my choice. - MT

[Texan29]

I squash mold all the time. The secret is not to press too hard. Just like picking up a pencil for the first time; there's going to be mistakes and a learning curve.

If the part will be pretty thick in shape, it's best to go two part due to air bubbles. Squash molding is really only good for shallow stuff due to how easy air guts trapped in. Extra resin usually will flow the air out in a shallow mold.

For the record, Vaseline brushed on really thin is my choice. - MT

The part is about 1mm thick and not very deep. About how thick of a layer of thinned vaseline should I use and does it need to cool a bit before I brush it on?

Sorry for all the silly-ish questions. I'm not only a novice...I'm a poor one.

[theplasticwerks]

The part is about 1mm thick and not very deep. About how thick of a layer of thinned vaseline should I use and does it need to cool a bit before I brush it on?

Sorry for all the silly-ish questions. I'm not only a novice...I'm a poor one.

It should be thin enough that you can't see a layer of it if you look from the side. This may be a job for a misting of cooking spray or WD40. If you're heating it, I don't think it will need to cool, especially since you would be brushing it on so thin it'd cool to room temperature immediately anyway.

[Texan29]

Thanks for the help guys, I really appreciate it.

I'll post my results when I'm done.

[Texan29]

Okay, I did a two piece putty mold and it worked okay-ish. I'm having a hard time with the resin.

It comes out spongy and flimsy, i'm assuming that's because it IS full of air bubbles. I've casted 4 times trying different things and always the piece is a bubbly mess. I've tried pouring a thin line from a long distance, also tried pouring gently from the cup. I used a gram scale to measure A & B to perfect portions of each. I mixed it well and the resin ALWAYS pours crystal clear. After about 3-4 minutes the flash outside the mold begins to bubble up. I've tried using a colorant and without. Oddly the colorant seems to help a little bit.

So, I'm stumped and don't want to keep experimenting because I'm starting to wear out the mold a little bit already. What am I doing wrong?

Including pictures:

[MechTech]

If it's not curing right, you're mixture is off or if you're using 1 to 1 stuff, it's defective. High humidity can effect it too. You should not need any mold release agent either. Most resins have their own. If you're still using Vaseline, you can stop. It's only needed for mold manufacture. The fact that the color helps says it's a possible mixture or quality control issue.

Try mixing a small amount and sticking it in a bottle cap or something like it. See how it sets up. It should not bubble hard; in fact it should cure smooth on top with maybe a couple of TINY air bubbles. Just from what I can see it's not setting right, but that's just going by a photo. Hope that helps. - MT

[Texan29]

If it's not curing right, you're mixture is off or if you're using 1 to 1 stuff, it's defective. High humidity can effect it too. You should not need any mold release agent either. Most resins have their own. If you're still using Vaseline, you can stop. It's only needed for mold manufacture. The fact that the color helps says it's a possible mixture or quality control issue.

Try mixing a small amount and sticking it in a bottle cap or something like it. See how it sets up. It should not bubble hard; in fact it should cure smooth on top with maybe a couple of TINY air bubbles. Just from what I can see it's not setting right, but that's just going by a photo. Hope that helps. - MT

Well, last night I had the a/c on in my shop and it was about 65f out there. I did that so it would dehumidify the air, I do the same when I paint. Could it be because it was too cold? I'm mixing a miniscule amount each time I attempt this and I make very sure the amounts are the same or as close as possible. I'd use my postal scale but this stuff doesn't weigh enough. How often does this stuff become defective? Does it have a short shelf life?

When I pour it, it always seeps out and pools under the mold. That material ALWAYS bubbles up like crazy after a few minutes. I do use a mold release agent - I finally found some in a different location. I'll forego using that from here on out.

I have a small toaster I use to heat up things, would letting it set up in there help or make it worse?

Thanks for your help.

[MechTech]

Just try mixing a small amount and putting it in a cap - no enviromental changes from what you've been doing. That's the test. Lot's o bubbles and I bet it's the resin. Cool temperatures only delay or retard resin cure times. Your's sounds like the hardener is out of control. Some people store their resin in the fridge! Didn't work for me though.

Shelf life varies, but should average at least a month on the fresh side after being opened. After that it still works, but has various affects. If you check out those nice sheets attached earlier on in this post, you'll note how things look compared to your product.

You may have a bad batch, it happens! - MT

[Texan29]

Okay I did a control sample and...it came out perfect. Looks like a shiny, creamy white poker chip.

I believe it was the mold release I was using. I guess that stuff is mostly water? So I won't use that again, as you had said it was just for mold creation.

I poured resin one more time into the (now dry) mold and it still came out a little porous, like chalk. But this time it wasn't frothy. I'll try washing the mold this time with soap and water and let it dry before I try again.

I'll get it to work!

Edited November 3, 2008 by Texan29

[Ignacio Ocamica]

Glad to hear you're almost there!!!

[Texan29]

Well, I'm still having problems.

If I pour the resin into a container it comes out perfect, very few micro sized bubbles. But once I pour into these molds, it froths up (not as much as before) but it still does. The parts come out weak and spongy, like melted styrofoam or something. It's really frustrating, I've cast about 20 of these and all are failures. I feel like I've wasted a bunch of money, and like pitching it all in the trash...

What could I be doing wrong?

This is exactly the stuff I'm using, and I pour it the same way as described here:

[PetarB]

Here's a couple of thoughts. If you have any moisture at all involved anywhere, you will get issues with resin. It's possible that the moulds might still have moisture in them from your cleaning. Also, if your environment is too humid, you might get that bubbly problem with the resin. Here's a trick; prior to pouring resin, dust the moulds with talcum powder. This breaks the surface tension and ensures a better cast. You might still get bubbles throughout the resin, but you wont see them on the 'outside' skin of the resin, due to the talcum powder. Give it a go!

[TSP]

I would also say water or H2O. If the resin was cooking like boiled water while curing then it was water and or humid climate. But if the bubbles are greasy/oily then it could also be that the hardener is expired. This would also mean that the resin was raising like yeast dough during the chemical reaction.

[MechTech]

First off, DON'T GIVE UP! You do have a problem like TSP said. Moisture or expired hardener cause similar results.

1) If your hardener has been opened for a while, it could be expired. Later stages of hardener expiration are like expiring food. Color darkeners and solids begin to form in the bottom. Remember, it should be clear and only slightly tinted when new.

2) Excess humidity will cause the resin to bubble. If your resin cured fine outside of the mold in the same enviroment, it's your mold. You can let the mold sit in the oven on low for a while to chase out the moisture - if the mold is silicone.

3) You may simply have a bad batch, it does happen! Micromark (in my signature block) also sells molding supplies too. Out of all the stuff I've bought from them (A LOT), I have got one bad batch before, I just used it for filler and glue . They are responsive to customers too.

Be tenacious and don't give up, the shiny white part you'll hold in your hand is worth it! - MT

[Texan29]

First off, DON'T GIVE UP! You do have a problem like TSP said. Moisture or expired hardener cause similar results.

1) If your hardener has been opened for a while, it could be expired. Later stages of hardener expiration are like expiring food. Color darkeners and solids begin to form in the bottom. Remember, it should be clear and only slightly tinted when new.

2) Excess humidity will cause the resin to bubble. If your resin cured fine outside of the mold in the same enviroment, it's your mold. You can let the mold sit in the oven on low for a while to chase out the moisture - if the mold is silicone.

3) You may simply have a bad batch, it does happen! Micromark (in my signature block) also sells molding supplies too. Out of all the stuff I've bought from them (A LOT), I have got one bad batch before, I just used it for filler and glue . They are responsive to customers too.

Be tenacious and don't give up, the shiny white part you'll hold in your hand is worth it! - MT

Oh...I won't give up. But I will give up on the mold stuff I'm using right now as I believe that is my problem.

The resin: I've done a few control samples and they all come out shiny and pretty - color added to them or not. They do have a few very tiny bubbles but they are negligible.

I used baby powder as suggested and it worked somewhat but not how it was described. It drew out the moisture in the molds I made. I find this stuff has a tendency to sweat! It's not due to humidity, I always use the A/C unit to dehumidify my workshop and never leave the molds outside or anything of the sort.

After I used the baby powder (only once) the resin no longer froths, but subsequent castings never come out shiny or even remotely smooth. They are always matte, chaulky. The molds themselves are smooth. After so many tries, so many times I've remade the molds...it's painfully obvious this stuff won't do what I need.

I looked at micromark and it looks promising. What is your opinion on oomoo from smooth-on? I've seen several different manufacturers for this stuff but don't know which is best for the type of stuff I'm doing. I've been watching videos on youtube to reference two part molds, and found "tap plastics" videos.

They seem to be very informative and straightforward. Best part is the annoying catchy jingle at the beginning and end of each video. Makes me want to dance. But in all seriousness, have you ever used their products?

I just want to get what will actually work for what I'm doing.

Thank you, I really do appreciate all your help.

[MechTech]

I'm guessing the matt is from the talc. The resin should not sweat unless it's condensation you're talking about. Bad resin will leach out from cured parts. If that's the case, you have an old or bad batch!

I can't vouch for anyone other than Micro Mark. It's just easy to order my tools and resin from one source. Without talc your parts should be shiny as the master part. Minor bubbles are normal inside parts. I'm thinking your resin is bad if it is leaching liquid out after curing. - MT

[Texan29]

I'm guessing the matt is from the talc. The resin should not sweat unless it's condensation you're talking about. Bad resin will leach out from cured parts. If that's the case, you have an old or bad batch!

I can't vouch for anyone other than Micro Mark. It's just easy to order my tools and resin from one source. Without talc your parts should be shiny as the master part. Minor bubbles are normal inside parts. I'm thinking your resin is bad if it is leaching liquid out after curing. - MT

I don't think I explained properly. I only talc'd the molds once and the resin took it away with the first casting. Afterwards the molds were dry and shiny for the next usage. The molds sweat before I do this once. The molds are made out of polymer clay, two part mix you squish together and press onto the part.

Or could it still be the resin? I'm probably just confusing myself at this point.

My wife let her co-worker borrow the camera...if she gets it back today I will take pictures to illustrate what I'm trying to explain.

[PetarB]

The molds are made out of polymer clay

This could be your main problem. What is the product? Optimally, you want RTV rubber.

EDIT: oops just read the first post again. It's probably not the issue, but may still be...

Edited November 12, 2008 by PetarB

[MechTech]

Ah hah! Just get the micro mark (or other brand) set with proper silicone mold compound. Your resin not being shiny may mean it's bad and not generating enough heat during the cure process. - MT

[TSP]

I just toke another look at the pictures from 2nd Nov. Maybe the humidity comes from the talcum or baby powder.

Would say it's time to try something else.

Remember cooking and baking spray? You won't believe it but some people use these as mold release spray. I don't know which brands are usable but a fat free non-organic spray should be used. Spray a thin coat on your mold let it dry for a few minutes. Check again with a hair dryer on the lowest level of heat. Just make sure not to heat up the mold too much since this could cause immediate reaction/hardening while pouring resin into your molds.

Silicon spray would also do the job but these are quite greasy and require polishing just like mold release wax and industrial mold release sprays.

The other bubbles in the parts come from missing deaeration. Cutting some fine trenches into the molds should allow air trapped inside the mold to exhaust. If you can take some pictures of your mold then we'll be able to mark the trenches.

BTW what kind of Polyurethane are you using?

Edited November 14, 2008 by TSP