Questions about two-part silicone molding

[sswift]

I bought some Amaco brand air-dry clay because I could find it locally and cheap, but the only information I can find online regarding it's sulfur cointent is Amaco stating that it's clays are all low sulfur. Will 'low sulfur' clay interfere with my Mold Max 30 silicone setting up? If so, can anyone reccomend an inexpensive clay I could get online that would be okay to use?

Also, are there any downsides to making a block mold and cutting it apart rather than going to all the trouble of making a two part mold?

And if I can lay one portion of my model flat, is there any reason why I should not simply do that, pour the silicone over it, and leave that as one big pour/air hole about 1" x 4" and then after cutting the mold down the sides so I can extract the models, pour into that hole until my resin is flush with the surface? (Think molding a shoe box witht he top open, and the bottom sitting on the base of your mold box, then flipping that mold over to pour the resin into the bottom. Except my box has a handle sticking out of the side, so I have to cut the mold in half so I can extract that.)

 

[Grant Da Modeler]

I would strongly recommend a sulphur-free clay ... I've been extremely
happy with Chavant's line of sulphur-free product, such as the NSP line :

http://www.chavant.com/new_site/index.htm

You can order clay from Chavant directly, but I think you have to
order a whole case (they do also sell a sample kit !!) from their hotline :
1 800 CHAVANT


This store sells Chavant clay in the Boston area, and as 2lb bricks :

http://www.artistcraftsman.com/

although they only seem to carry the "LeBeau Tusche" clay .. which is
still sulphur-free, but I'm not sure how it differs from the NSP.


I use the Chavant NSP with Smooth-On Mold Max 30 and it works
perfectly. No issues.

Also, are there any downsides to making a block mold and cutting it apart rather than going to all the trouble of making a two part mold?

The only real downside would be damaging your original sculpt while
cutting the mold slit. Some sculptors seem to prefer the slit down one
side, versus the two-part molds .... I assume time saved is an issue.

My only concern would be area slit has to be thick and strong enough
to not move around when resin is poured into your mold and a really
noticable seam line created.

 

[swgeek]

Klean Klay http://www.kleanklay.com/ and Chavant http://www.chavant.com/new_site/index.htmhave non sulpher clays.

As far as an open face box mold, there's no problem, I've made hundreds without any real problems. I've found a few downsides to making a one piece mold that would normaly be a two piece mold. First, it's sometimes hard to get the mold to register correctly after you've cut it open. Second, a true two part mold will last longer. And third, Depending on the complexity of your part, it's sometimes hard to get the part out of a cut mold. But if it's a simple shape and you're not trying to get hundreds of parts out of the mold, it should work fine.

 

[Bondo Fett]

You should switch to sulfur-free clay. But if you've already finished your sculpt with the other stuff I'd recommend spraying the finished sculpt with some kind of sealer, like shellac or clear lacquer. Make sure you get total coverage, like inside ears or nostrils, sulfured clay with definitely inhibit silicone cure. Shellac can be brushed so you can be sure of getting it into every detail, but it is alcohol-based so go easy over the clay surface. Hope this helps.

 

[sswift]

You should switch to sulfur-free clay. But if you've already finished your sculpt with the other stuff I'd recommend spraying the finished sculpt with some kind of sealer, like shellac or clear lacquer. Make sure you get total coverage, like inside ears or nostrils, sulfured clay with definitely inhibit silicone cure. Shellac can be brushed so you can be sure of getting it into every detail, but it is alcohol-based so go easy over the clay surface. Hope this helps.

My 'sculpt' is actually a model made from basswood, which looks like this other one I built previously:

Well, that minus the antenna, knobs, screws, switches, and other doodads.

I've divided the above into three parts. The bottom half of the shell (with handle), the top half of the shell, and the cowl around the screen. The cowl, btw, is 1/16" thick, and I decided to seperate it because I'm worried I'm going to have problems getting the resin to flow into the cracks, and I was worried about whether I'd be able to slip the mold off with the huge undercut that would create. (Plus there's a lip around the top of the shell which it sits on that's a bit wider than the cowl which stuff would also get caught up on.)

The clay I planned to use to embed the model to make a two part mold as shown in this video:
http://www.youtube.com/watch?v=dcRv__zNxYE

Though now that I know my clay isn't going to work, I'm consideirng whether I should just try to pour a block mold with one side flat on the base for a pour hole and cut the things out. It doesn't matter if the original gets destroyed removing it. And since they're big flat surfaces I should be able to sand down any imperfections without too much difficulty.

 

[sswift]

Well, I guess I'll be returning that Amaco clay and ordering some Klean Klay. I looked at both the Klean Klay and Chavant's NSP, and the Klean Klay is like half the price, and offered at many more places. Just need to decide on what density to get now. Probably go with the regular firmness. I'm not planning to sculpt it, just embed my wood model in it. (After sealing the model with krylon clear acrylic spray.) Couple pounds should do I think for a model of this size. Probably only need one pound actually, but I'll get some extra just in case.

Not sure what I'll make my mold box out of. Could use foamcore, but I'm making a two part mold, and I may want a mold box that I can reuse to keep the silicone from leaking out. Perhaps silicone leaking out of the sides of the mold isn't really a major problem though.

 

[swgeek]

Not sure what I'll make my mold box out of. Could use foamcore, but I'm making a two part mold, and I may want a mold box that I can reuse to keep the silicone from leaking out. Perhaps silicone leaking out of the sides of the mold isn't really a major problem though.

I use sintra for my molds. you can seal the joints with hot glue and then use denatured alcohol to break the glue free after your silicone has set. And YES silicone leaking out of the mold is a big problem. The great thing about silicone is that it flows into every little nook and cranny, the bad thing about silicone is that it flows into every little nook and cranny.

 

[exoray]

For a cheap clay to embed the master in just for molding get Amaco X-15 Pottery clay, it's dirt cheap at Hobby Lobby and if you print off the 40% off one item coupon they have almost every week on their website it's even cheaper...

It's a WED clay meaning water based so it will dry out but it works fine for this application, as long as you cover it will silicone it won't dry out, and just re-bag it when you are done or toss it...

It's not advertised as sulfur free but I have used it with both tin cure and platinum cure silicones without any issues, and I know for a FACT that the platinum cure silicone I use plain hates sulfur so I'm sure I would have noticed... But every silicone is different so it's always bet to double check with your specific products, even if the label says sulfur free!

A nicer more expensive oil/wax based sculpting clay will last forever and is overall nicer but I find it overkill for simply embedding for molding in most cases...

 

[sswift]

For a cheap clay to embed the master in just for molding get Amaco X-15 Pottery clay, it's dirt cheap at Hobby Lobby and if you print off the 40% off one item coupon they have almost every week on their website it's even cheaper...

Unfortunately, there are no Hobby Lobbies around here, the closest one is a three and a half hour drive to NY.

But as for the X-15, I looked that up and found this page:
http://www.amaco.com/amaco-safety/talc-free-clays/

It appears the X-15 is the same as the X-11 and X-12, those are just 5 pounds and 50 pounds respectively. Also I found out that the X-11 is the one carried by Walmart:
http://www.walmart.com/ip/Amaco-Moi...0000003260370&ci_src=14110944&ci_sku=12347700

Unfortunately they don't carry it in the store, but I guess you can get it shipped there for free.

As for the clay I bought, the model # is 46310F, and the box looks different than the other Amaco air dry clays I've seen, so I think the box may be old. That would explain the 1/25/10 date stamped on the bottom.

It appears to be this clay though. The UPC is the same anyway:
http://www.amazon.com/dp/B0038NYJP8...e=380333&creativeASIN=B0038NYJP8&linkCode=asn

And that clay's part number is 46310F. Sadly, that partt number appears to have been on Amaco's price list at one time, but has since been removed:
http://www.amaco.com/amaco-retail-price-list/

So... I don't know what sort of clay it is that I have. But I guess it's going back. No sense in taking chances with expensive silicone.

If I see the pottery clay when I'm out though, maybe I'll pick that up.

I kinda like the polymer clay though. Not having to buy new clay each time I make a mold would be nice. Dunno how many times you can use it, but I don't suppose it'll get too contaminated too quickly. And it's really cheap online. Like $2 for a 1lb brick. I'll get killed on the shipping, but I don't need much so it won't be too bad.

It's a WED clay meaning water based so it will dry out but it works fine for this application, as long as you cover it will silicone it won't dry out, and just re-bag it when you are done or toss it...

It's not advertised as sulfur free but I have used it with both tin cure and platinum cure silicones without any issues, and I know for a FACT that the platinum cure silicone I use plain hates sulfur so I'm sure I would have noticed... But every silicone is different so it's always bet to double check with your specific products, even if the label says sulfur free!

Well, like I mentioned, the Amaco data sheets I found state their clays are low sulfur:
http://www.amaco.com/pdfs/C5.pdf

"For your protection, AMACO® clay bodies are formulated with ingredients
that have the least amount of contaminants: All AMACO® clays have
a low sulfur content to give added protection from release of sulfur dioxide."

A nicer more expensive oil/wax based sculpting clay will last forever and is overall nicer but I find it overkill for simply embedding for molding in most cases...

Yeah, I was trying to avoid those because of the cost. I have some Scupley. I think it was like $20 a pound. Not using that cause I don't want to waste expensive sculpey by mushing al lthe colors together and besides I've read it has sulfur and will inhibit the cure.

But that Klean Klay is pretty cheap. I just wish I could find it locally instead of online. Sucks paying $10 shipping for $5 worth of clay.

 

[sswift]

I use sintra for my molds. you can seal the joints with hot glue and then use denatured alcohol to break the glue free after your silicone has set. And YES silicone leaking out of the mold is a big problem. The great thing about silicone is that it flows into every little nook and cranny, the bad thing about silicone is that it flows into every little nook and cranny.

Did I say silicone? I meant the resin. I don't know if the silicone will make a tight seal.

I do hope the resin will get everywhere though. That cowl concerns me because it's so thin. (1/16") But the Smooth Cast 305 i bought supposedly has the same consistency as olive oil so maybe I'll get lucky. If not I may be cutting those out of plastic sheet.

As for Sintra, I have no idea where I'd get that locally. Suppose I could get some online, but probably not worth the trouble and expense just to make three or four molds. Also, how do you cu that? It looks pretty thick. Score and snap? I don't have a lot of luck doing that with plexi.

 

[JtotheP]

WOW! Thanks for this thread. I'm learning alot from it. If I used a sulfur clay, I would just spray Krylon crystal clear over the sculpt to keep the sulfur from reacting with the silicone. Looks like you got alot of other options.

 

[swgeek]

As for Sintra, I have no idea where I'd get that locally. Suppose I could get some online, but probably not worth the trouble and expense just to make three or four molds. Also, how do you cu that? It looks pretty thick. Score and snap? I don't have a lot of luck doing that with plexi.

You should be able to get sintra at a local plastic supply store. As for cutting it, you can cut it with a utility knife it's pretty soft. If your molds are small enough, foam core (as you previously mentioned) should work fine for you. Or even better, gator board.
When you get your mold made and are ready to cast parts, dust the inside of the mold with talcum powder, it will help to eliminate any surface bubbles.

 

[sswift]

You should be able to get sintra at a local plastic supply store. As for cutting it, you can cut it with a utility knife it's pretty soft. If your molds are small enough, foam core (as you previously mentioned) should work fine for you. Or even better, gator board.
When you get your mold made and are ready to cast parts, dust the inside of the mold with talcum powder, it will help to eliminate any surface bubbles.

I don't think we have any plastic supply stores locally. I looked around when I needed some acrylic in various colors. There were plastic suppliers, but they didn't seem to carry anything, they had to special order it. Might as well order it online myself and save the money in that case.

Will spray on mold release work in place of talcum powder? Cause I bought some of that. And I saw some videos where the resin makers reccomended spraying some on top of resin poured into open block molds to break the surface tension to prevent bubbles there.

As for gator board, never seen it. Looking online, it says it's hard to cut by hand. Is that something I would find at a retailer, or another thing I'd have to order special?

Also, I suppose there's different types of foamcore out there, because I'm not sure the carboard covered stuff walmart sells would be very good for making a mold. I think I've seen some with a shiny coating though. I'm not even sure that stuff is what people talk about when they mention foam core though.

But yeah, my molds will be small. Hm... I guess I could just get some cheap poplar hobby wood from Lowes and use that after sealing it. I'm gonna have to get some krylon acrylic to seal my wood models anyway.

Oh, and I was planning on using some plastic straws to make my vent holes. You don't suppose those might inhibit curing, do you?

 

[sswift]

Hey guys,

When I brought the Amaco clay back to Michael's Crafts today I found a synthetic clay called 'Plastalina' by Van Aken. It comes in 1lb bricks for $3.79, which is a bit more than the Klean Klay is online, but not having to pay shipping it probably worked out to be cheaper.

You can find the clay here:
http://vanaken.com/plastalina.html

It doesn't say online, but on the package it says it's a non-toxic oil based clay that never hardens. More importantly it states that it's sulfur freee and is compatible with silicone mold compounds. It also has a similar level of firmness to sculpey.

 

[JtotheP]

Hey guys,

When I brought the Amaco clay back to Michael's Crafts today I found a synthetic clay called 'Plastalina' by Van Aken. It comes in 1lb bricks for $3.79, which is a bit more than the Klean Klay is online, but not having to pay shipping it probably worked out to be cheaper.

You can find the clay here:
http://vanaken.com/plastalina.html

It doesn't say online, but on the package it says it's a non-toxic oil based clay that never hardens. More importantly it states that it's sulfur freee and is compatible with silicone mold compounds. It also has a similar level of firmness to sculpey.

That is the same brand of clay I used for my Viper helmet sculpt:
http://www.therpf.com/showthread.php?t=47784

Worked well, but I remember it sucking all the oil from my fingers and drying them out.

 

[sswift]

That is the same brand of clay I used for my Viper helmet sculpt:
http://www.therpf.com/showthread.php?t=47784

Worked well, but I remember it sucking all the oil from my fingers and drying them out.

Cool helmet!

 

[swgeek]

Will spray on mold release work in place of talcum powder? Cause I bought some of that. And I saw some videos where the resin makers reccomended spraying some on top of resin poured into open block molds to break the surface tension to prevent bubbles there.

I'd go with talc. One of the great things about silicone is you don't really need release unless you're going silicone to silicone.

Oh, and I was planning on using some plastic straws to make my vent holes. You don't suppose those might inhibit curing, do you?

They shouldn't. You might want to use solid plastic rod instead, it would be easier to glue down. Are you molding this part horizontaly or verticaly?

 

[sswift]

They shouldn't. You might want to use solid plastic rod instead, it would be easier to glue down. Are you molding this part horizontaly or verticaly?

I'll be molding the cowl and the top and bottom halves of the PKE horizontally, with the air and pour vents sticking out one side.

The handle I will be molding vertically. By making it one solid piece I'll have a large surface area with which to glue it onto the body, and I'll have a large hole making it easy to fill the mold.

I have been toying with the idea of laying some parts on their end or side so I'll have a large hole in which to pour resin for those as well, but I'm concerned about how the surface of the exposed area would end up, and whether I'll be able to pour everytime right to the edge so the wall thickness is consistent. Also, I don't want to have to do a ton of sanding to remove raised edges caused by surface tension. So with that in mind, I'll probably stick wit the horizontal molding for everything but the handle.

 

[wolff]

Hey guys,

When I brought the Amaco clay back to Michael's Crafts today I found a synthetic clay called 'Plastalina' by Van Aken. It comes in 1lb bricks for $3.79, which is a bit more than the Klean Klay is online, but not having to pay shipping it probably worked out to be cheaper.

You can find the clay here:
http://vanaken.com/plastalina.html

It doesn't say online, but on the package it says it's a non-toxic oil based clay that never hardens. More importantly it states that it's sulfur freee and is compatible with silicone mold compounds. It also has a similar level of firmness to sculpey.

I bought Plastalina for the same reasons, and used it a few times to build up and seal around a model in prep for casting. I liked the consistency, but it stuck to the box, my fingers, tools and especially, the model :angry everything had been sealed and sprayed with Smooth-On mold release too! Unfortunately, the damn stuff was not just sticky, the brown clay got sort of slick - like ... :confused ... uh, mud.

my .02

wolff