Need help with solicone mold and fiberglass with Clay

I made this out of fiberglass and resin to harden.. my goal is to surround it with silicone rubber for mold so when I take this product out I will have an empty space in my silicone mold to pour stuff in and make replica of it..


question is.. I need to put a layer onto the product(pic) so i can smooth it out and make it not stick when i pour silicone rubber on it to make the mold.

I gotta use a Sulfur free clay right? I could use that?

then buy rubber silicone mold liquid to make the mold.

Any suggestions?

im not certain exactly what your after. Are you asking how to make a silicone mold off a fiberglass master part? Or are you trying to make a silicone plug/back? After that, what material are you looking to use to make parts?

What about using a silicon release agent?

Well, silicone doesn't stick to much of anything, that's the beauty of it. Especially when you throw on a quick release-ease coat. What you should be more careful of is using substances that silicone won't CURE around. Those are: Latex (don't use latex gloves); sulfur (ditto on sulfur-based clays); and there have been some primers that I've heard inhibit cure. I personally haven't run into any cure inhibit with the Rustoleum brand primer (I use grey, white, and brown as standards).

So would you guys recommend sulfur free clay route to even the curves n lines on my fiberglass mold which then I can use as a non stick when I make my rubber mold?

Are you trying to avoid using Bondo and sandpaper? It might be the easiest route.

booksandcorsets said:

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Well, silicone doesn't stick to much of anything, that's the beauty of it.

Caution should be exercised on porous surfaces, it might not stick but it will soak into all the nook and crannies and for all intents lock together... I have had silicone bond to unsealed cut edges of MDF and trust me it might as well have been glue... Also use caution with glass, it can and will bond to glass...

What you should be more careful of is using substances that silicone won't CURE around. Those are: Latex (don't use latex gloves); sulfur (ditto on sulfur-based clays); and there have been some primers that I've heard inhibit cure. I personally haven't run into any cure inhibit with the Rustoleum brand primer (I use grey, white, and brown as standards).

This is always a good thing, best to get to know your product and stick with what you know... You will find many tin cure silicones are very tolerant of contamination and will set even with small contamination, while some brands might have more issues than others... When it comes to platinum cure silicones though they are very intolerant to several things and can cause nothing but trouble if you don't head caution... When using platinum cure it's best to really avoid any and all potential cure inhibiting things 100%... That also means don't share tools or mixing bowls unless you clean them 100% and remove any and all traces of the previous mix, best to just use different stuff in the end...

exoray said:

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Caution should be exercised on porous surfaces, it might not stick but it will soak into all the nook and crannies and for all intents lock together... I have had silicone bond to unsealed cut edges of MDF and trust me it might as well have been glue... Also use caution with glass, it can and will bond to glass...

I didn't know about it bonding to glass, that's a good thing to know. And yes, this is all assuming you SEAL your buck properly, whether via shellac or multiple layers of primer.

Would like to use bondo and sandpaper but will it react or stick to the silicone robber mold when I make it? Or is ti ok to use it? Its why I was trying to see if I should use a clay thats sulfur free and hardens which i can sand down.

Bondo is fine, just prime/paint it before you mold to get a better finish...

Could i get away with just bondo and sanding it down without painting it etc.. for my silicone block rubber mold.. like this in pic



also which rubber silicone to go with ?

dgcoupe said:

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Could i get away with just bondo and sanding it down without painting it etc.. for my silicone block rubber mold.. like this in pic

Yes, you might be able to but Bondo is porous and absorbs liquids you might have some issues as I stated with the silicone seeping into the surface and locking down even if it's not actually sticking to the Bondo... Your mileage will vary, it might and it might not, IMO not worth the risk... Why are you against hitting it with primer/paint? It only takes a few minutes to hit it with some flat grey primer from a rattle can, and have no worries... Even better in addition to primer/paint once it's inside the mold box hit it with a coat of spray mold release...

You are going to spend a tidy chunk of change on the silicone and you get ONE shot with it, don't be foolish and try to save $2 and 10 minutes of your time skipping the primer and the few bucks it cost for mold release... Trust me from experience this is a penny wise dollar stupid move...

also which rubber silicone to go with ?

That is a loaded question, I would just go with your average 10:1 tin cure, IMO brand is not all that important especially for a newbie that doesn't have any expectations...

Two things:
1: Make sure you read the directions for whatever rubber you use. Some you have to mix by weight and some you mix by volume.
2: This is minor but the the thing you are copying is not the mold, the rubber is. Or will be. The original is, well, the original, the master, your sculpt, etc.

Sent from my Apple Newton

I totally understand and thank you for the tip.. I will def use some bondo from the store smooth it out and hit it with primer..


just to verify before i do this, primer will not react/absorb/ or stick to the silicone rubber when I make it? Thanks again guys

Also any links to the rubber silicone? dont knwo where to start.

dgcoupe said:

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just to verify before i do this, primer will not react/absorb/ or stick to the silicone rubber when I make it?

Unless you use something really wierd then no, you should have no problems.

One question though, as exoray pointed out silicone isn't cheap and neither is resin if I'm gauging the size of the part you're trying to copy correctly. If you're just trying to make one copy you'd be better off just making a second from scratch. Making a mold and casting it is only really worth it if you're making a bunch of the same part and/or the piece is too complicated to make a second easily. Why do you need a mold of this part?

dgcoupe said:

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just to verify before i do this, primer will not react/absorb/ or stick to the silicone rubber when I make it?

Generally no, but I have had cases where flat paints and primers have soaked into and/or discolored the silicone, and flaked off when molding... This leaves a little blemished area of silicone in the mold, I have found that it's not a huge issue and doesn't cause any immediate or significant damage to the mold but I tend not to cast 'flat' finish molds all that often just to avoid this, or use a clear 'clear coat' instead of a clear paint... This applies to flat primers as well, I generally like a little more glossy top coat when casting the part... But consider that if you cast a satin finish master your copies will have a satin finish, and if you cast a high gloss part your copies will come out high gloss...

Another thing you can do if the master is just that a master and not something you are going to want to paint or finish later you can get some good old carnauba car wax, and wax the entire master, this will provide an excellent molding surface, with built in release properties...

i have to make a lot of these we use this for my work field so i made a custom one which i can make diff kinds.. ill be using a foam/sponge agent on the final silicone to fill it in.. this mold is just a copy of it and used fiberglass. Also this is the size of a big hand or bigger than a human hand.

I just dont know where to get the rubber silicone.. If you dont midn starting me off to the right irection of a site to order some. Thank you for your quick reply

dgcoupe said:

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I just dont know where to get the rubber silicone.. If you dont midn starting me off to the right irection of a site to order some. Thank you for your quick reply

Location?

You can't go wrong with Smooth On products, not the cheapest but they are solid performers...

I could bondo it and use clear coat.. will this method work better?

also do they sell clear coat spray paint in lowes or home depot for me to use?

location is jacksonville fl

dgcoupe said:

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I could bondo it and use clear coat.. will this method work better?

It will work, there is no better or best...

also do they sell clear coat spray paint in lowes or home depot for me to use?

Yeah, lots of options in the rattle can isle... Or even brush on options...

As for your silicone go to Smooth-On, Inc. - Mold Making & Casting Materials Rubber, Plastic, Lifecasting, and More and find a local distributor, or pay the shipping direct from them... They offer exception customer support so if you have issues you can always give them a call... This is a very nice option for the newbie...

wouldnt the brush on clear coat create streaks and line? Since the outer image is my final image and will be duplicated many times what is the best method to apply the our clear coat? Spray?

dgcoupe said:

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wouldnt the brush on clear coat create streaks and line?

Possibly, some self level quite well, others don't... Same with application, using a foam brush will reduce bush lines...

Since the outer image is my final image and will be duplicated many times what is the best method to apply the our clear coat? Spray?

Depends on the surface you want, do you want a high gloss surface on the final ones? If so paint the master with a high gloss paint and possibly wax it before casting... Same with flat or satin, what you do to the original will be replicated in the copies... Do you want a slightly textured surface? Is so experiment with misting the surface with your paint...

And yes I would suggest spraying the paint...