Does anyone know why my latex is cracking when drying inside the mold?

Hi, I've been learning how to make latex masks and I'm always running into new problems. This time my latex is cracking and ripping apart when drying in the mold. I assume it's because the latex is thicker in some spots so the difference in drying time is pulling it away from itself, but i don't know how to avoid that. I fill-dwelled the mold and let it drain for at least 10-20 minutes. What more can i do to make sure its evenly coated?

"This time my latex is cracking and ripping apart when drying in the mold."
Do you mean it cracks/rips by itself or when you try to demold?
How long are you allowing it to dwell in the mold before emptying it?.
Are you using a plaster mold?, what kind/brand?
If plaster, is it bone dry?

In any case, unless I´m misunderstanding something it sounds like your latex is either in bad state or it´s bad quality. Where did you get it from?
For example, if latex freezes it will turn into an unusable material. Could it be that it froze at some moment?
I´ve also known of suppliers that might try to add water to gain bulk...which gives a poor latex.
One of latex best properties is stretchiness. Cracking is not one of them, besides old casted latex, but should not happen with freshly casted latex.

As for the thickness, if you are getting uneven thickness there could be some problem with the porosity of the mold that could affect the moisture draw in certain areas. For instance, that some kind of grease (your hands grease could do) had got in the surface of the mold it could cause that some areas are nor drawing as much as others.
Also, very fresh plaster molds could give some problems, but all I´ve seen is pin hole bubbles in this case.
A good thing is that molds are bone dry, and prior to pouring latex you wet them before doing so. Helps to get good castings and correct moisture draw.

As I said before, not sure I understood correctly, but my two cents. Could be something else.

It's cracking as it's drying. I used ultra-cal 30 for the mold, I let it sit on my desk for over two weeks before I poured anything in it. I added water before pouring the latex too and I'm using two new gallons of Monster Makers brand. :confused

Wow. I’ve got to say, in the decade I’ve been making masks, this is something I have NEVER seen happen. That is super interesting.
Given time to dry and demolded, does the rubber in that area feel any different to the rest of the cast? Is it hard?

Is it only doing this in one specific spot? Is it possible there is sealer or release stuck in your mold that is preventing the stone from drawing moisture in that spot? If that is possible, a quick scrub down with solvent wouldn’t hurt.

The last few buckets I’ve used of Monster Makers has been of really dodgy quality. Engineer Guy and even Reynolds latex has been giving me better results.

Hi there. Looking at the pic you posted, I'm going to guess the crack didn't go all the way through the pull, correct? If it didn't, I have seen this before and I believe I can explain what's happening... From the pic, it appears that the crack appeared in an area where the latex pooled. What's happening here is the outer layer of latex that is exposed to the air is curing faster than the rest of that pool. As latex cures, it shrinks slightly, so while it's still soft, it splits, not unlike the top of a loaf of bread as it bakes. this will happen on occasion in areas where the latex pools up thicker than the rest of the piece. It's should be only superficial, and since it's on the inside, won't affect the appearance or structural stability of the piece at all.

the more uniform the thickness of your piece is, the less often you will encounter this.

Mr Mold Maker said:

Wow. I’ve got to say, in the decade I’ve been making masks, this is something I have NEVER seen happen. That is super interesting.
Given time to dry and demolded, does the rubber in that area feel any different to the rest of the cast? Is it hard?

Is it only doing this in one specific spot? Is it possible there is sealer or release stuck in your mold that is preventing the stone from drawing moisture in that spot? If that is possible, a quick scrub down with solvent wouldn’t hurt.

The last few buckets I’ve used of Monster Makers has been of really dodgy quality. Engineer Guy and even Reynolds latex has been giving me better results.

Click to expand...

No it feels the same but you can see in the light where it was really thin in some areas especially around where the cracks were. What kind of solvent do you use to clean the mold? I can see some splotchy-ness in the same ares where it came out thin, it's got to be why it's not coating evenly.



The mold for comparison a couple days after I cleaned it.

Buliwif said:

Hi there. Looking at the pic you posted, I'm going to guess the crack didn't go all the way through the pull, correct? If it didn't, I have seen this before and I believe I can explain what's happening... From the pic, it appears that the crack appeared in an area where the latex pooled. What's happening here is the outer layer of latex that is exposed to the air is curing faster than the rest of that pool. As latex cures, it shrinks slightly, so while it's still soft, it splits, not unlike the top of a loaf of bread as it bakes. this will happen on occasion in areas where the latex pools up thicker than the rest of the piece. It's should be only superficial, and since it's on the inside, won't affect the appearance or structural stability of the piece at all.

the more uniform the thickness of your piece is, the less often you will encounter this.

Click to expand...

No it went all the way through, it didn't really pool like i thought it just didn't thicken enough in some areas because of the mold probably isn't evenly dry yet.

wow, ok. I totally misread that pic then.... I'm with these other guys, then. I've never seen this particular issue. The best I can guess is what you suspect, that the mold wasn't completely dry. apart from that, I'd go over the materials you are using... What type of plaster are you using, are you using a mold release, and if so, what type, are you mixing up the latex before pouring or just pouring it straight, are you noticing separation in the latex inside it's container, what's the weather like.... man, the list of variables are large, but if you continue having this problem, it'll pay to start checking off that list...