Making your own Silicone Mould

Darley · Feb 25, 2009

How To Make your own
Silicone mould

Material:

2 RTV cartridges silicone (300 grms each) "standard acetic acid cure silicone caulk." It smell like vinegar, the one you use in the Bathroom or wet area or you can use the 2 pour RTV, but more expensive. If you can't get any RTV cartridge near by just drop a line to Matt aka Gadget he migth help you with some 2 pour RTV.
Clamps
Strap clamp
Wood 'Master block 'this will define the size of your casting blank
Wood frame
Glad wrap / Saran food plastic film
Wood or corian board here I use an off cut of 3m/m MDF
1 Potatoes :biggrin:

Cut all your wood to size for the frame here I'm doing a 1" mould by 5 1/4"x 5 1/2" ( size of the master block ) I will have then 5 blanks 1" x 5 ¼" . The wood frame is 2 length 6 ¼" x ¾" thick x 1 ½"high and 2 length 8 ½" x ¾" thick x 1 ½"high , Wrap all your wood pieces including the 3 m/m MDF base with glad wrap ( saran ) then make your frame.

Secure the master block to the board with double side sticky tape

Darley · Feb 25, 2009

Cut the RTV nozzle cartridge to a wide opening and start the edges while holding the master block, make sure that the nozzle is in the silicone to prevent air bubbles, cover the top who will be the bottom of the mould and smooth the edge with the potato ( silicone doesn't stick to potato starch ) then cover with glad wrap to smooth the surface and let it cure 24 hours.

After 24 hours you can undo the frame and peel off each side of the mould, you have to go very easy as the silicone still fresh and can be tear easily

Base removed ( nice smooth edges )

Let cure the mould another 2 days before use, here are some of the moulds I made

Happy Moulding:biggrin:

dntrost · Feb 25, 2009

Man that was great now get this put in the library so we can find it when we need it...

Thanks

KenV · Feb 25, 2009

Nice -- The bottom (of the mould construction) becomes the top of the production mould.

Great tutorial - Have you considered clear packaging tape instead of saran wrap. The caulking does not appear to stick to it, and it stays smooth (*()*&& wrinkles in wrapping).

Now to get that string of posts into the library ---

Mather323 · Feb 25, 2009

I agree great job on the tutorial.

Jeff-in-Indiana · Feb 25, 2009

WOW! That is a truly EXCELLENT idea and posting .. I ended up buying two entire cases of silicone caulking for a project (don't ask) and still have all of it .. NOW I have a better project for it! Thank you Darley!

sbell111 · Feb 25, 2009

Great tutorial. It is kind of like how I did our molds, but different.

Instead of using wood for the box and master, I used a poly cutting board and some UHMW pieces. Since silicone won't stick to poly, the saran wrap wasn't needed.
I used a two-part pourable silicone rubber for my mold. It was more expensive, but worked well. Since it is pourable, it was self-leveling, which means I didn't need a potato. I'm going to try my next one with the RTV. The cost savings definitely are worth looking into. I might see about just laying another piece of UHMW on top to smooth it out, rather than to go the potato route.
I used Goop to seal the corners of my mold box and to attach the master to the box. It sets up quickly and holds everything tight without leaks, but doesn't really stick to the poly or the silicone, so it's easily removed when it's time to knock dowen the box and remove the new mold. I suppose that using RTV, you wouldn't need to seal the corners of the box, but you wouldn't need the double sided tape.
I don't hold the box together with the strap and clamps. I just tape it together using duct tape.
I only make individual blank molds out of silicone, not brick molds. Since silicone doesn't stick to poly, I make brick molds simply by throwing together a cutting board/UHMW box.

Darley · Feb 25, 2009

Thanks for the reply, hope this tutorial will help some of us.

Ken, I try the packaging tape and some some reason it stick to the RTV so I prefer to use the saron wrap,

Steve, side of the mould are not glued together the strap hold them up tight, the cuting board is a good option but I went the less costing material for this tutorial, the RTV cartridge cost AU$ 12.00 each at our Bunnings hardware store, the 2 part RTV is AU$ 399.00 for 20.4 liter

maxwell_smart007 · Feb 25, 2009

What is RTV caulking? Is it just the plain, standard silicone caulk I can get at the lumberyard, or is it something special?

Andrew

Darley · Feb 25, 2009

I use this one

LandfillLumber · Feb 25, 2009

How much caulk did it take to make the mold in tutorial?Very cool.Thanks for sharing,Victor

LandfillLumber · Feb 25, 2009

Oh 600 grams,DAH.I need to slow down sometimes and read a little more.I'm just not made that way,its go go go all the time.Victor

maxwell_smart007 · Feb 25, 2009

Went to every store in town - noone's ever heard of RTV caulking...we have Silicone, Silicone 1 and Silicone II...whatever that means!

wdcav1952 · Feb 25, 2009

For lazy people like me, Thank Goodness for Gadget and his moulds!! :biggrin:

Darley · Feb 25, 2009

RTV, caulk is the stuff you used to seal the bathroom with, it smells like
vinegar. It's cheap than the 2 pour, you can get it at any local hardware store, I use the clear, but any color will do, just so long that it is
the acetic cure (acid cure ) and not neutral cure. Neutral cure
silicone caulk is too flexible and your mold will fail, the weight of the resin will
cause the sides of the mold to bow.Acid cure silicone caulk, is what is called a moisture curing caulk.

Mudder · Feb 26, 2009

Added to Library.

dntrost said:
Man that was great now get this put in the library so we can find it when we need it...

Thanks

Ask and you shall receive!

(Disclaimer: If it's possible for me to make it happen

)

The tutorial has been extracted and posted here.

altaciii · Feb 26, 2009

Great tutorial, plain and simple and easy to follow.

sbell111 · Feb 26, 2009

Neutral cure caulk could still be used, but you would have to keep the mold in the box when you poured your blanks or create a 'mother mold'. Either way is pretty easy, but a mother mold would fit in the pot better.

Gadget · Feb 26, 2009

I believe that is the kind of silicone used in fish tanks, if so try the local aquarium supply. You can also try making the master compleatly out of corian glued together with ca. Thats what I use however it is hard to get the cured silicone out. Compressed air gets them out enough to pull the rest out. I use a pourable silicone mixed like epoxy. pourable silicone is great for molds but verry expensive. I can try to package this type of silicone for you guys. Being that I buy it in bulk maybe i can get the price reasonable enough to benefit everyone. It does have a short shelf life so it needs to be used within a month. I think that Darley did a good job for those of you that want a specific size mold and like doing it yourself.

tool-man · Feb 26, 2009

Go to www.amazon.com and search for "RTV silicone". I found one offering of a 10 oz tube for about $3, by Small Parts, Inc.

Also check eBay. Someone is selling 2 tubes of Dow Corning 732 RTV sealant for $6 plus shipping.(as of 26 Feb)

Read more about Dow Corning 732 here -
http://www.specialtyadhesives.com/dow_sealants/732_multi_purpose_sealant.pdf

maxwell_smart007 said:
Went to every store in town - noone's ever heard of RTV caulking...we have Silicone, Silicone 1 and Silicone II...whatever that means!

NewLondon88 · Feb 27, 2009

maxwell_smart007 said:
Went to every store in town - noone's ever heard of RTV caulking...we have Silicone, Silicone 1 and Silicone II...whatever that means!

That's the stuff.
Just make sure it says silicone and not 'siliconized'.
RTV just means room temperature vulcanized.. that means it doesn't need
a heat cure.

I picked up bunches of it at a department store for about $3 per tube. It
usually says 'kitchen & bath' on it. I think it was GE brand, but not positive.
Most often it is in a red and white tube.

Daniel · Feb 27, 2009

Silicone Caulk runs a wide range of prices so if the first tube you find seems expensive keep looking. Last time I bought some I got it for as low as $3.00 or so a tube. Just make sure it has the 100% silicone one it. Also be ready to have ventelation. the fumes will not harm you but they certainly will offend you.

NewLondon88 · Feb 27, 2009

Daniel said:
Just make sure it has the 100% silicone one it. Also be ready to have ventelation. the fumes will not harm you but they certainly will offend you.

You won't want another salad for 6 months :tongue:

pianomanpj · Feb 27, 2009

Yeah, that stuff certainly is offensive. I had to caulk a shower with that stuff, and there was no ventalation. The fumes were so bad, I had to take my contact lenses out as they were absorbing the fumes and seriously irritating my eyes!

maxwell_smart007 · Mar 2, 2009

First attempt didn't work out, unfortunately...the 'reverse mold' held the silicone in fine, and the stuff on top firmed up nicely, but when I tried to remove the mold, the bottom silicone was just as soft as when it came out of the tube; maybe it's too air-tight?

Andrew

maxwell_smart007 · Mar 2, 2009

Or, maybe it's too cold in my shop still...-30 outside today, and it's been consistenly -20 for a few weeks...maybe I had best just stick the next one on a shelf and let it sit for a month or two...

Andrew

NewLondon88 · Mar 2, 2009

Definitely get it up to room temp. Also, moisture helps the caulking set.
I made my first one by squirting the caulking into a bowl of warm water with
a little dish detergent in it. Then I reached into the bowl and kneaded and
rolled the caulking into a ball. Very easy to form after that. You can squish
it into shape, squish it into your form, pat it onto your positive, squeeze it
into the weave of some burlap or mesh for stability.. as long as you have a
good coating on your positive, it's all good.

Darley · Mar 3, 2009

Andrew did you use an " acide cure " silicone?

maxwell_smart007 said:
First attempt didn't work out, unfortunately...the 'reverse mold' held the silicone in fine, and the stuff on top firmed up nicely, but when I tried to remove the mold, the bottom silicone was just as soft as when it came out of the tube; maybe it's too air-tight?

Andrew

outfitter · Mar 16, 2009

Any other success stories? I tried the Silicone I from Lowes, let it sit for 10 days. The outside firmed up real nice, pulled the sides off and it was just like maxwell's- "just as soft as when it came out of the tube"

outfitter · Mar 17, 2009

Just a heads up, I checked Amazon and they are selling the RTV silicone for $1!

http://www.amazon.com/Bostik-Clear-Silicone-Sealant-Cartridge/dp/B001379WB2/ref=pd_ecc_rvi_cart_1

Draken · Mar 17, 2009

Currently out of stock, not known when it will be back in stock.

DurocShark · Mar 17, 2009

Currently unavailable.
We don't know when or if this item will be back in stock.

yup

outfitter · Mar 17, 2009

Sorry guys, I'm sure I ordered more than my share. I ordered 25 tubes- I needed to hit the free shipping! I'll keep everybody updated if I'm not able to use them all.

NewLondon88 · Mar 17, 2009

outfitter said:
Any other success stories? I tried the Silicone I from Lowes, let it sit for 10 days. The outside firmed up real nice, pulled the sides off and it was just like maxwell's- "just as soft as when it came out of the tube"

Did anyone try putting it in water first?

If the silicone DIDN'T react exactly as you describe (soft on the inside)
then each tube would be a single use caluking. Once the outside is set,
it protects the insides. You need to get it into water if you're not using it
for a skin coating ( >.25" or so) The (soapy) water will help you mold it and
it will help it cure.

W3DRM · Mar 18, 2009

I found the "GE Silicone I 100% Silicone Rubber Sealant" at Home Depot today and picked up three of the 10.1oz tubes. It was the only silicone rubber sealant I could find that contained the words "Acetic acid released during cure" in the warning section of the products. So, I am assuming this is the correct product that is being described in this thread. I did notice that the GE Silicone II did NOT have the words "Acetic acid" anywhere in the warning section of the label. It did mention some other kind of release but not acetic acid.

I have a couple questions before I attempt to make a mold.

What is the minimum width the outside portions (the walls) of the mold need to be so it is self-supporting and won't collapse during pouring of the PR? It appears the described mold is around 3/4" thick.
Do I really need to put it water and knead it before I place in the positive mold form? I confused on this point...

NewLondon88 · Mar 18, 2009

W3DRM said:
I did notice that the GE Silicone II did NOT have the words "Acetic acid" anywhere in the warning section of the label. It did mention some other kind of release but not acetic acid.

As long as it is 100% silicone, you're fine. Some of them say 'siliconized'
which isn't the same thing. The acetic acid smell is just a bonus. :tongue:

W3DRM said:
I have a couple questions before I attempt to make a mold.

What is the minimum width the outside portions (the walls) of the mold need to be so it is self-supporting and won't collapse during pouring of the PR? It appears the described mold is around 3/4" thick.

Do I really need to put it water and knead it before I place in the positive mold form? I confused on this point...

I would use 1/2" minimum for shorter molds (1" high) and move up to
3/4" thick for taller molds. This is based on 5 or 6" lengths, which I assume
we're talking about
The weight of the resin could push the side walls out, leaving you with a
deformed casting.

As for the water, yes. That's how it works best. If you just squirt it into
a mold box, only the surface area will cure. If you put it in soapy water
(few drops of dish soap in a bowl of warm water) it keeps the silicone from
sticking to your hands. And the water helps the silicone to cure*. The
kneading helps distribute the water throughout the caulking.
Someone described it as 'playing patty cake' with the caulking.. seems
about right.

*At least this is how I THINK it works.
I did what I described and it cured fine and worked well in the mold box.

W3DRM · Mar 18, 2009

Charlie,

Thanks for the tips. I'm in the process of laying out a mold box made out of 3/4"mdf. Should have it done later tonight or tomorrow. Will then try my luck with my first home-made silicone mold. If all goes well, I'll post some pictures of both my mold-maker box and the resulting mold after it cures...

This sounds and looks so simple I'm just amazed that someone hasn't come up with this layout before this.

W3DRM · Mar 19, 2009

My version of the Darley Silicone Mold...

I made mine just a little bit bigger to accomodate some things I wanted to incorporate in the mold. I made it so it could be used with different mold inserts such as,

a single brick mold that is 5" x 5" x 3/4" and,
four 3/4" x 3/4" x 5-1/2" pen molds.

The main board is 8-1/2" x 12". So, with all pieces being made from 3/4" mdf, that gave me an inside dimension of 7" x 7" x 1-1/2".

The entire mold maker was made from some 3/4" mdf I had lying around the shop.

Here are some photos of the unit:

The 1st shows all of the individual pieces.
The 2nd shows the base board with the outer section in place.
The 3rd shows mold with the brick mold in place.
The 4th shows the mold with the individual pen molds in place.
The 5th shows the assembly with the top in place.
The 6th shows the mold ready for the silicone to be added.
The 7th shows the mold with the silicone covering the brick mold.

I am now waiting for everything to cure so I can see how my first mold comes out. The smell isn't too bad (everything is in my garage) but I was lucky to have near 70 degree weather today so I could open up both garage doors.

One thing I see right off the bat that I need to work on and that is to make the mold forms out of some material that silicone won't stick to. Trying to put the poly wrap on things is just too much of a pain (IMHO). Does anyone know if there is a paint or coating that could be applied to the finished mold form that silicone won't stick too?

One other note. I added 1/4" wooden dowels to hold the various parts in place. Without them I can see where the loose parts would tend to move around during the pouring of the silicone.

Once everything cures, I'll post another set of pictures to show you how it came out. I did use a full three tubes of 10.1oz. "GE Silicone I". I also filled a bucket with water and added some liquid soap to it and then squeezed out all of the silicone into it and worked it into a ball and kneaded it for a while. Then, I just took it out of the water and placed it in the mold. I also used nitrile gloves and found that they worked very nicely and allowed me to smooth the silicone without it sticking to the gloves. I kept them wet during that process.

NOTE: I did not use the top cap that I had cut as I found I could get a pretty smooth base to the mold without it.

More in a day or two...

Darley · Mar 19, 2009

Look good to me from here very technical and good idea to use 1 size for block and pen blanks, I know that wrapping each wooden part with sarran is a PITB but much easy to un-mould, eager to see the final mould. Well done

NewLondon88 · Mar 19, 2009

W3DRM said:
One thing I see right off the bat that I need to work on and that is to make the mold forms out of some material that silicone won't stick to. Trying to put the poly wrap on things is just too much of a pain (IMHO). Does anyone know if there is a paint or coating that could be applied to the finished mold form that silicone won't stick too?

First off .. great job!
The dowels are a good idea. I thought about different ways to do that,
but at our last regional meeting jack barnes brought some double stick
tape that worked fantastic.. very sticky. I was able to put the tape on
the bottoms and then trim with an Exacto knife. Worked like a charm.

As for the sticking .. the silicone should be OK on most anything except
more silicone. But it wouldn't hurt to put a coating of wax on the MDF..
or even a coat of shellac. Any kind of release should also work, even
using something like Pam or walnut oil .. spray oil from the supermarket..
anything like that. But mold release meant for silicone is best, as the
silicone oil leeches from the mold with use. The release puts the
silicone oil back into the mold, extending mold life.
(don't know if this applies to caulking or not, though!)

It looks great .. can't wait to see the finished mold! :biggrin:

One other note: with a caulking mold, you don't get the same self-leveling
effect as from a silicone RTV, so you need to take care to level the mold
box as well as the caulking itself. Otherwise, you turn the mold over and
pour your resin into a mold that is tilted .. and you can't get square
corners! If your mold box is square and set on a platform, you can use
shims to make sure the box is level. Then you can 'eyeball' the caulking
and level it.

Making your own Silicone Mould

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