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First time casting with a question

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I'm attempting to make a couple of casts and have a question concerning two part molds. I have the first half of my molds made. Do I need a release agent between the molds before I pour the second part of my mold? I didn't use a release agent on the parts I'm casting for the first half of my mold and didn't have a problem. Any info/advise will be appreciated.

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Posted · Report post

yes you need to put release agent on the first part of the mold before you pour the second half. or you will get a nice solid rubber block with your part trapped inside.

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Mold release is readily available in many places. A common silicon spray lubricant works as sold in most hardware stores and of course a thin coating of Vaseline applied with a paintbrush works wonders, too.

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If you need a quick release using household items, good ol vaseline/petroleum jelly works well, just lightly graze a brush/your finger on the surface of the jelly to get its oils and rub the half of the mold.

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For years, I used petroleum jelly ("vaseline") dissolved in Model Master enamel thinner as a mold release--just used a fat brush to brush it on, let the thinner evaporate out, then made my second pour. It will also help if you do not remove the original part or master from the mold, but leave it exactly as the first half of the mold was poured, and you then cleaned out all the clay used for "packing" the original in place to start with.

Removing a master from the first half of any mold breaks the slight seal between master and rubber, and when the master is returned to that first mold half, chances are you will have a gap someplace in the system, which when making the second pour of rubber--most generally will alow liquid rubber to flow into the void or space that happened when you removed the part the first place and then tried to put it back in exactly as it was at the start.

Art

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Call Price Driscoll and get a free sample can of their Par 4 Parfilm paintable mold release. While using vaseline may work, using the spray is so quick, simple, and cleaner. And YES you most certainly can paint your parts w/out cleaning them (I've done it).

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I would highly suggest that you use the product mentioned above. Once a mold has been used a few times you should spray a light coat of mold release in it to make certain it continues to perform well.

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Call Price Driscoll and get a free sample can of their Par 4 Parfilm paintable mold release. While using vaseline may work, using the spray is so quick, simple, and cleaner. And YES you most certainly can paint your parts w/out cleaning them (I've done it).

Thanx Mike! That sounds like the answer I was looking for. Do you have a link to their website?

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Call Price Driscoll and get a free sample can of their Par 4 Parfilm paintable mold release. While using vaseline may work, using the spray is so quick, simple, and cleaner. And YES you most certainly can paint your parts w/out cleaning them (I've done it).

The main reason for using Price Driscoll Parfilms isn't that you need a mold release (parting agent) to allow the casting to come out of the mold, but more to protect the RTV rubber molds from the liquid resin! With each pour, without mold release, some of the chemical components will penetrate into the rubber (soak into it) and cause the surface of the rubber to degrade slightly, to the point that the surface quality of subsequent castings to be compromised. Eventually, even with mold release, there will be enough of those chemicals--principally the catalyst side of the 2-part resins to actually set up solid with a pour, at which time, the rubber will adhere in spots, pull out of the mold with the casting. Mold releases, such as P-D's Parfilm series, will delay that reaction; without using them you will experience this problem a lot sooner!

Art

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I'll second that Art. The catalysts in resin really do a number on molds after about the 15th or so casting. I've tried about 7 different silicone-based RTV's and it never fails. Of course I've finally found an RTV that will hold out to 30 castings until it starts to degrade. Alittle on the expensive side but well worth it. You guys are still using clay?

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Thanx for the link Greg!

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I'll second that Art. The catalysts in resin really do a number on molds after about the 15th or so casting. I've tried about 7 different silicone-based RTV's and it never fails. Of course I've finally found an RTV that will hold out to 30 castings until it starts to degrade. Alittle on the expensive side but well worth it. You guys are still using clay?

Yes, I use clay. I don't understand why the question. I use the synthetic clay that Alumilite sells. It is repackaged Klean Klay. It is the best deal I can find for their price. I am still using most of the clay I started with in 2007. I put it regularly in the microwave on a reheat setting to soften it to make it easy to work with.

Curing resin will reach a temperature of 140 degrees or more. Though the silicone can withstand a tremendous amount of heat the surface inside can still become damaged at delicate detail areas. The mold can get a dry feel to it and the mold release will help with this and aid the resin to get into all the nooks and crannies it needs to get into to make a part.

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Is the OP using talcum powder dusted inside the mold to ease surface tension? And thanks Art for the info, the PD release does indeed protect the mold and prolong the life of it.

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No, I'm not using any kind of release agent. I'm just making some parts for myself. Does the talcum powder have any effect on the finished surface of the part being produced? I'm not really worried about how long the molds will last. As long as I get at least ten or twelve parts from a mold.I'll be happy. I need to get a slower setting resin. This ninety second stuff just isn't cutting it for me. My biggest problem is air bubbles. I'm having better luck with my one piece molds for wheels.

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Yes, I use clay. I don't understand why the question. I use the synthetic clay that Alumilite sells. It is repackaged Klean Klay. It is the best deal I can find for their price. I am still using most of the clay I started with in 2007. I put it regularly in the microwave on a reheat setting to soften it to make it easy to work with.

Curing resin will reach a temperature of 140 degrees or more. Though the silicone can withstand a tremendous amount of heat the surface inside can still become damaged at delicate detail areas. The mold can get a dry feel to it and the mold release will help with this and aid the resin to get into all the nooks and crannies it needs to get into to make a part.

That's why I never used clay. I could never figure out how to get it soft enough. Now that's an excellent trick with the Microwave! Thanks-

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Here in AZ, I could just set it outside in the summer heat too.

Just don't let your spouse or significant other see you putting clay in the oven, they might throw a fit. I went to the good old Goodwill and bought a file box and converted it into a sort of warming oven for molds to do clear resin. If you had something like that it would be helpful. It will stay about 120 degrees with a 25 watt light bulb. I insulated the exterior of the box. Maybe you could pick up a kids bake oven, pretty much the same thing.

Another thing you could do is use a dryer rack in your clothes dryer!

Greg

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No talcum / baby powder does not have any effect on the part being produced. I lightly dust my molds for every resin pour. Does reduce bubbles.

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No talcum / baby powder does not have any effect on the part being produced. I lightly dust my molds for every resin pour. Does reduce bubbles.

Thanx Mike! I'll give that a try next time!

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