Make a silicone mold from common household materials in your kitchen in 1 hour

Picture of Make a silicone mold from common household materials in your kitchen in 1 hour

Taking off from this BRILLIANT 'ible http://www.instructables.com/id/How-To-Make-Your-Own-Sugru-Substitute/ I have started making silicone molds on the cheap and thought I would share. This is incredibly simple and fast and can be used for a ton of casting ideas...

Here is the podcast I did on it:

The basic instructions are below....

Step 1: Materials

Picture of Materials

You will need:
  • SIlicone Calking (the stuff that stinks like vinegar or acetic acid) I have a calking gun but you can get smaller tubes of it at the hardware store
  • Mineral Spirits (this is just paint thinner but somewhat less toxic than the rest. NOTE: you can use white gas or camp stove fuel but be CAREFUL if you do use that. The advantage of white gas is that it will cure the mold faster and the mold will not smell like mineral spirits after)
  • Corn Starch
  • Vaseline
  • Latex gloves (or what ever kind you like)
  • mixing sticks
  • Drill
  • Bent nail
  • Something to cast or mold
  • Small box
  • Mixing cups
  • Wax paper
  • Play dough

cashfl7 days ago

My two cents:

1) My proportions: By volume: 1 part caulk, 2 parts mineral spirits, 2 parts corn starch.

2) I strongly suggest that you steep the caulk in the mineral spirits for at least a couple of hours or overnight even. I've been casting large head and it was a nightmare trying to do it off the bat; not even one of the large mixing its you use for drills would work until I had let it dissolve some..

3) A drop or two of glycerin from the drug store will insure gelling.

4) As has been noted, the GE caulk is tricky. I've been using the DAP brand with success.

BananaaM1 month ago

the olny problem is that the thing I am trying to cast is made play dough :(

MechanicalMashup (author)  BananaaM1 month ago
In this case look up Gelatin Moulds

JohnLThornton5 months ago

Thanks for posting this Instruction. I made it! Not a Play-dough toy, but a mould of an essential - and
tiny - part of my wheelchair, which would have cost hundreds of pounds
to replace (because I would have had to replace the entire footrest
system, even though only one tiny bit snapped off).

I found that
the best place to get right silicone is at the cheapest stores (in the
UK that would be Pound shops or Wilko). The posher shops sell upmarket
stuff which doesn't have the vinegar smell.

When doing my initial
test, the only alcohol thinning liquid I had to hand was Nail Varnish
Remover (an essential part of my tool box because I'm constantly glueing
my fingers together whenever I use SuperGlue!).

I needed to use only a few drops of the Nail Varnish Remover, along with a teaspoonful of cornflour and a teaspoonful
of silicone caulk (the caulk I used for my initial test had been open and sitting on my shelf for
several years).

The mould dried fully within a few hours and it worked
beautifully. Now I've got the bug I'm going to try and make a mould of
my favourite Buddha statue.

MechanicalMashup (author)  JohnLThornton5 months ago
I never thought of nail varnish remover (here it is nail polish remover) Given you need less volume of it and it smells better in my opinion maybe that is what I should be using. Thanks!

How much mould shrinkage happened using this thinner?

Nail polish remover is actually just acetone if you need a larger qty

Given that the piece I was working on was no more than 12mm long, there was no perceptable shrinkage. But you've got me thinking. My Buddha statue is about 45mm high so I'll make a point of measuring the final product and record any notable difference. I think I've caught the bug! ;-)

Antwan10134 months ago

Will this mold work for plastic? I was thinking of recycling my milk jugs to make plastic parts for various things. I am new to this kind of thing so I am not sure if the hot plastic will either melt the mold or even just stick to it.

You should be able to do it with plastic. Many even talk about casting metal with this mixture.

You can always try using epoxy resin if you don't want get to the high temperatures required to melt plastic.
I've heard of people using a double boiler, the sort of thing you use for melting chocolate, but using oil instead of water for temperature regulation as you need a much higher temperature.

WeeRedBird5 months ago

Having a bit of trouble with mine. Even though I used Vaseline, both halves of the mould stick together.
Luckily I made a pouring hole at the bottom, so could dig my model out via it.

Any tips? Should I wait longer before lubing up and pouring the second half? Do I need a thicker layer of Vaseline?

SixFootBlue6 months ago

Are these molds oven-safe? I was planning on using them with polymer clay, and then baking the clay at around 120C while it's still in the mold. Since it's not food-grade, I'm not sure if it would release contaminants or toxins into our oven.

TwylaM7 months ago

Thank you so much for sharing, and the instructional video was exactly the type I learn with the best, creative, fun, and provides all the steps with hands on visual material! May you be blessed in Christ as this tutorial has blessed me, and beyond.


Good tutorial, thanks for sharing; Jesus Christ Bless you! :)

Thank you for blessing people according to faith, and not holding back! I am in agreement with you, I loved this tutorial, and it was also a blessing to me.

Very detailed information.


Ibadullah Safdar


ChrisO310 months ago

Thank you so much for this great instructable. I was looking for a cheap way to thin it out to create less bubbles and this is great! I made a colour test video using different mediums to colour resin for casting if anyone is interested. http://youtu.be/gqt8klshYAk

rlyndallwemm10 months ago

Forty dollars worth of failure. Probably because the State of California does not sell proper Mineral Spirits. The first batch was too thick to pour. The second was better. None of it stuck to the item properly and just fell off it, distorting the pour box and pushing out the sides. Horrible expensive mess.

C Diane1 year ago

I tried using 50/50 silicone and cornstarch since I wanted a more clay-like consistency to mold over an object. The stuff never dried and had to throw the whole thing away. I used GE premium waterproof silicone for kitchen/bath/plumbing (100% silicone and regular corn starch. What did I do wrong?

ge silicone is different and will not cure the same with corn starch. you need to use regular silicone that smells like acid.
Rossana671 year ago

I read that aquarium rtv is food save. If I use this silicone, can I make molds for cake decorations?

JestGold1 year ago
Will be trying this to cast some 5" square tiles in hydraulic cement. From what I've been reading in the comments in Mikey 77's great post, using naphtha thins the oogoo and does not give off odors once cured, as compared to using mineral spirits or paint thinner (evidently these continue to stink well after the oogoo is cured).

I think I will try thinning the silicone with the naphtha before adding the corn starch. If anyone has done this, I'd love to hear about your results. But I will try for myself.

Thanks for a great post, and video, which really helps to see what's in store for me.
I love it!!!!! Works great. Im using Naptha.
Thank you for sharing
MechanicalMashup (author) 2 years ago
I am thinking you need to add less cornstarch and add it last... This might sound odd but do you live in a humid environment? The more humid the less cornstarch as the cornstarch pulls water from the air to set off the silicone. If your in a humid area the there will be more water in the air thus set the silicone off early.

Experiment a little.
spider872 years ago
Not a single person has has the same experience? Lol
spider872 years ago
I don't understand what I'm doing wrong.. I tried 50/50 then a healthy portion of mineral spirits then I tried 4pts corn starch 8pts silicone. However, when I add the spirits, everything starts setting up right away instead of softening.. What's going on? I'm mixing with a knife not a power tool.. Could that be it?
thomas96662 years ago
Thank you so much, been looking for an easier and cheaper way to cast molds for a long time
jhante2 years ago
Very nice instructable! I work in the industry, my company makes prototypes by casting and other methods, so I was interested to see how it can be done in your kitchen!
owsamphoto2 years ago
Could I used the mold in fondant cake designs? Is it safe or food grdae
gemini17202 years ago

check out the link for food safe mold making for cake decorating mold making
dlrlt5302 years ago
Does anyone have a silicone recipe that IS safe for food and can be put in the oven, safe up to 500 degrees? Or is there such a product already out on the market? I need it in liquid form, so I can make my own mold.
binkibow3 years ago
Hi I'm in the UK & cant find 'Silicone calking' any idea what else it may be called here ?? I have been asking & retailers look at me blankly.

the silicone calking it´s the silicone in the tues using for bathrooms, fish tanks , seel window gaps, in portugal we can get it in drog stores, i think that in ingland is the same
Silcon sealant is the same, or bath seal. You can get it in any diy store
MechanicalMashup (author)  binkibow3 years ago
Did a little research and they should not be giving you blanks stares...

Maybe try asking for bathtub sealant. Sorry that's the best I can offer.
MrRetardo3 years ago
I've used Silicone Caulking to make molds before. For thicker molds, mix in some Glycerin. It helps the silicone cure in thicker layers, as silicone caulk cures by reacting with moisture in the air.. For a release agent (keeps silicone from sticking), try using a silicone-based spray such as Armor-All.
Hi, I am in need of molds for my project (it will be on instructable once I manage to finish it). I need a mold that has a minimal shrinkage. (IE 1% max). I am going to try the glycerine (I found a bottle at my local drugstore). I was wondering if I could add talc instead or starch? Anyway I think that 10:1 by weight for the silicone glycerine mix would work ok. I'll try and give you news.
MechanicalMashup (author)  svaillancourt3 years ago
Corn starch only it's hydrophilic. This is what sets the silicone off faster. Talc will not do that. Glycerin will also help set the silicone off and thin it but I have not experimented much with it. So make a couple batches and then after a week measure shrinkage.
I have failled miserably. Going to wait and buy the smooth-on kits ;)
halo994 years ago
Would this also be safe to use with food molds? (jello) would it be eatable?
MechanicalMashup (author)  halo994 years ago
NO!!! sorry this is far from safe for that.

I would imagine that if you got food grade silicone from a hardware store and only used cornstarch that it would be safe but I am not sure it would be pourable or as manageable as the video shows.

So I say again NO it is not safe for food as is but the above suggestion may make a mold that is usable. I am no expert in this though and you are on your own if you want to experiment with that...

Dont think I am being negative or being a jerk, far from that, we love our fans. I am just being concerned about your health an like our fans to be healthy and alive :) Otherwise they don't promote us nearly as well, last I checked there is no internet connection to the afterlife...
Food grade silicone, glycerine and corn starch.
oh ok thanks
See this link for food grade silicon: http://www.smooth-on.com/Silicone-Rubber-an/c2_1115_1131/index.html

I have used it many times with great results. If you look at my sugar glass 'ible http://www.instructables.com/id/Sugar-Glass/ you'll see my bottle mold in the pics. I have used it to make chocolate bottles, also.
neodymium3 years ago
Could I use a non-alcohol thinner like turpatinen or a low alhol content thinglike 70% rubbing alcohol? What would happen to the mix if I didn't add any at all, because it sounds like it would shring less without any thinner? Thanks.
Anyakin3 years ago
This is why I love Instructables :)
kommodore3 years ago
Dude!!!!!!! i just try this and it turned out excellent!!!!!! thanks for this great instructable!! i was wanting to make some silicone mold for a long time, and i didnt wanted to spend like 40 dollars on 1 kg of two part rubber silicone, so you save me a lot of money, i mixed silicone and corn starch on 1:1 ratio, and then add paint thinner, the mold turns out really well, alltough, next time i will use some more paint thinner so the mix gets more runny.

So thank you!!
mschell13 years ago
if you dont add the mineral spirits, does the mold still shrink?
MechanicalMashup (author)  mschell13 years ago
With no mineral spirits the mold will stink but very very little compared to a mix with mineral spirits. With glycerin it will stink but more than no additive and less than mineral spirits...
I bought odorless mineral spirits in the art section in Michaels. It's by the brushes, oils, canvases, etc. I don't think I added enough and my mold is lumpy but it got the job done. Ugly as all get out tho.
MechanicalMashup (author)  mschell13 years ago
Glycerine does not thin as well as mineral spirits but definately does not smell nearly as bad. Remember that when the silicone kicks it will smell very strongly if vinegar or acetic acid...
cathypeek3 years ago
I want to make triangle shape crayons from melting old wax crayons. Is it possible to pour hot crayon wax into this type of mold?
Also im going to be making a shed-load of molds for pouring casting-resin into (potting) and the resin cures by a chemical reaction causing the tepmerature to rise to about 60°c (140°F) and will be using a silicone caulk thats rated to be temperature resistant to upto 300°c (572°F !!!) !

The one i bought is called 'Heat Mate' in the UK (bought from my fav specialist shop, ebay, lol !)

Plus im going to be using this heat-resistant silicone to make some RC Buggy Parts that are located next to the engine so that it can better protect against a very high heat source !!!

Hope that helps !
Thanks offtherail2010! I appreciate the Heat Mate silicone caulk tip. I have made a mold--you should see it...pitiful but it's a triangle-shaped mold. I took leftover crayons home from school to melt and those crazy things would NOT melt! Oven at 300 degree F. They must have plastic in them rather than wax. Need to buy the old crayola brand and I bet they would melt. This is my goal over the summer. Have a great week!
Your most-welcome cathypeek !!

Always happy to help !

lol @ pitiful !

As long as your mold serves its purpose i always say it doesnt need to win any beauty-contests as long as it does what you need it to do lol x 2!

Also with repetition you will get much better at creating molds as after the 1st one its all a learning curve & the good ol' trial & error methods !

Just slightly curious thought, is there a specific purpose for having triangular crayons ?!?
MechanicalMashup (author)  cathypeek3 years ago
Yes it is... The temp of the crayons melted is fine with these molds
Thanks for your reply. Realized I needed a 3D triangle shape so I purchased sculptey clay to make it. I am going to try making a mold but need to watch the video again. I'll let you know how it goes. Thanks again!
*** !!! DUDE !!! ***

I'm back to finally test out your GREAT instructable !!!

i just have a question whilst i wait delivery of some Play dough !

Instead of using mineral spirits, would you think it'll be a good idea to use 99.9% Isopropanol as its the closest thing i have to any kind of spirits ??!!!??
grunt16123 years ago
hey guys if you guys need silicone RTV contact this guy its pritty cheep so1612@yahoo.com
Lonecoon4 years ago
You can also use Glycerine to produce a mold that won't shrink, as glycerin adds the necessary moisture content to the mold.
MechanicalMashup (author)  Lonecoon4 years ago
Ill have to give that a try. Where can you buy glycerin? I assume a pharmacy will have it?
have you given this a try? i am about to go out to the store to get the materials for this project and i need to know what i should be getting, the mineral spirits or the glycerin?
It will be in the laxative section, or in the beauty supplies. You can get the in droppers. You need about 3 drops per ounce of silicone.
cakeladyd3 years ago
Hi, I am very interested with this technique, is it food safe? Could I use Sugar Paste and it not be harmful to the cake? thanks
MechanicalMashup (author)  cakeladyd3 years ago
No its not safe for food. Using solvents in the silicone and the silicone itself will leach into the food and essentially poison it.
thanks for the update, very helpful, guess I am back at the drawing board or just spending the money to get the regular stuff. thanks have a great day
You can buy basic supplies from a lot of retailers cheaper than the "regular" stuff...it's a good "in-between" compromise.
To deal with the shrinkage problem, you might try just painting on a thin layer of this thin mix for a detail skin and back-filling with regular oogoo after it sets up. Since silicone sticks to itself quite nicely, it should work. The only thing I wonder is if the skin's higher shrinkage would tend to warp the mold. My guess is that if it's thin enough, it will be held stretched by the regular oogoo.
swankaliau3 years ago
Hi i need some help for making a big mold for faux stone .Could u pls tell me the ratio of silicone calking that you've used in the mix? And could the mold handle wet mortar on its surface?RTV is sooo expensive and this is a great idea for my students building project. studentsbuildingprojects.blogspot.com
Faux Stone Panels Stone Caster Studio_medium.jpeg
MechanicalMashup (author)  swankaliau3 years ago
Oh and wet mortar will not be a problem
MechanicalMashup (author)  swankaliau3 years ago
I really did not measure it was just a by eye and feel thing. One thing to keep in mind is that the more thinner you use the more shrinkage you will have in the mold.
think this could be used for making plastic injection molding stuff? Im trying to make some merchandise for a person I know. She has a pretty successful webcomic site and Ive been having trouble trying to make some molds.
MechanicalMashup (author)  EngineerJakit4 years ago
I think plastic injection is a bit much. This is more a press mold like seen with the playdough or a pour mold. Keep in mind to there is a decent amount of shrinkage in these molds...
Now that i think about it, plastic injection for a flat-sided mold probably isnt something i should go for when it works better for a two-sided mold. Any ideas for making homemade liquid plastic? I think it might have to be done with some bags of small pellets you can find at a walmart's craft section.
MechanicalMashup (author)  EngineerJakit4 years ago
Use MEK and the mini pudding containers. Liquefy the containers in MEK and then pour into the mold.... (this is really really stinky so maybe consider www.smooth-on.com
2 things.

1. whats MEK?

2. think i could also use a plastic making method found here on instructibles?


Saw what this guy did! made some biodegradable plastic out of potato starch!
MechanicalMashup (author)  EngineerJakit4 years ago
MEK is Methyl ethyl ketone a very powerful solvent. You can get it at HomeDepot or a paint shop.

That plastic looks cool. Let us know how it goes
im gonna have to make a list of the materials ill need for this thing. I definitely know ill need corn starch! and maybe some spray paint.
ilovegm4 years ago
What if I were to use lighter fluid to thin the silicone out?
can i use this type of mold for hot sugar? i would like to make sugar bottles for a cake...
bluebel954 years ago
Can I use it to make Gummy candies? :)
MechanicalMashup (author)  bluebel954 years ago
No the mold was made with solvents and non-food grade silicone so it would likely make you very sick
Javin0074 years ago
This is pretty awesome! Is it possible to make one that doesn't have the 10-15% shrinkage?
This is a brilliant 'ible, thanks so much for posting! i found that this stuff is MUCH easier to mix if you add the spirits (i've been using acetone) to the cornstarch first, then add in the silicone caulking; you can easily mix the mold mix with a spatula just like the one here . Would anyone happen to have any ideas as to how to make food-safe molds, such as different materials, curing processes, etc? And how well would this hold up in a 250-400*F oven?
mikesnyd4 years ago
Ok so silicone is silicone. I think. So what if i took some High temp RTV silicone and did kinda the same thing. Would it hold most of the same temp properties? Allowing for higher melting point. i am in need of a gasket for my water heat transferer and when i puke the stuff straight out of the gun i have a hard time molding it to keep its form. due to the lengthy cure time of 24 hours. Not to mention it makes a skin in about 20min and still is gooey on the inside. even after a day if i make it any bigger then 1/2 inch it will split open and spit red silicone on me. And the stuff is like bear poop. Once touched it will transfer everywhere.
MechanicalMashup (author)  mikesnyd4 years ago
Well the way it works is that silicone sets with water and corn starch absorbs water it draws water into the silicone to set it. So it should set faster. However how it changes the properties like the heat resistance I do not know...
well if it just adding water to set the silicone then i hope my theory is right. That your thinning agent might need to be avoided so as not to have the shrinkage and possibly altering the temp resistance. I am making a batch today and have to find a hotplate to test it on. When i have more info i will post my findings. Thanks for your quick response. Oh and i am using a silicone that does not release formaldehyde when heated. Found a couple of high temps that do. And i do believe it is food safe.
Did my test. Put my red cornstarch silicone onto a hotplate and i dont think it lost any or much of the properties. Mind you i didnt crank it to 400 deg F. Cause the wifey type needs her pancakes in the morning. And i like sleeping in the bed. I dont like the smell of the mineral spirits and the overall shrink factor with a 25% solution to thin.
As for the white gas. Naphtha or Kerosene fall into this category? And does the white gas have the same shrinkage? Maybe i will just use cornstarch and trim and sand for final sizing after all shrinkage has occurred.
Thanks again for this instructable. Never would have thought of adding a thickening agent to silicone.
MechanicalMashup (author)  mikesnyd4 years ago
Well I definitely would not be putting white gas on a hot plate! The silicone alone with no thinner does not shrink. FYI
well i was going to let the thinned silcone vent and degas for 1 week before testing it on a hot plate. Do you think it will still be flammable? I was wanting to pour my silicone into my mold for making my gasket instead of having to glob thick amounts in and hope for the best. but i just guess i will have to do what is safe. :(
MechanicalMashup (author)  mikesnyd4 years ago
I guess you can try but... I just dont know. If you do try it be safe and do it outside with a fire extinguisher and keep in mind that with the white gas the mold will shrink. You can find thin silicone that you do not have to thin apparently that you could try but i do not remember the name of it. You may have to google thin silicone or paintable silicone or pourable silicone....
I have a couple of buckets of sand on standby. I dont have an extinguisher. I try my best always to remain safe. Thanks. I am going to look for thinner silicone. but is going to have to be high temp RTV. and there are few high temps that dont release formaldehyde when heated. not to mention thin pourable silicone based ones.
Kaffe4 years ago
what about try using cooking spray instead of Vaseline?
MechanicalMashup (author)  Kaffe4 years ago
That should work fine too. I did not have any available to me
CementTruck4 years ago
My son has an old crayon maker (the kind that melts crayons with a 60 watt light bulb) and has gotten bored with it making the same old thing. If I use this idea to make a new mold for the crayons (or possibly themed candles) do you think this silicone will be able to handle the heat of the melted wax/crayons?
MechanicalMashup (author)  CementTruck4 years ago
Yes I am pretty sure it would handle the wax fine
paqrat4 years ago
Very good instructable. Informative and humorous. I am a bit curious though. Why not just use the caulking directly from the tube? I can see it could be a problem if your master was fragile but for something like a child's toy couldn't you eliminate the corn starch and mineral spirits?
MechanicalMashup (author)  paqrat4 years ago
Because you want things to flow easy so thinning out the silicone is necessary. Having to squish some thick stuff down on the model gives you a big chance of air bubbles and gaps.

The cornstarch helps set the silicone up fast so removing it can be done but be prepared to wait 8 hours instead of 5 minutes for it to set.

wocket4 years ago
Be sure to check the MDSS before you touch this stuff with your bare hands. One of the cheaper silicone's available at my local hardware is a neurotoxin.
MechanicalMashup (author)  wocket4 years ago
Really? Wow thanks for letting us know. I had no idea. I wonder how that can be used on bathroom tubs, sinks, and kitchen stuff?
You would be amazed at how much ick you can find in everyday household ingredients. Always look up the mdss!

apburner wocket4 years ago
You should probably check the MSDS also. (Material Safety Data Sheet)
wocket apburner4 years ago
lol, we know them as Material Data Saftey Sheet in Australia
apburner wocket4 years ago
LOL. Then I have to correct myself. And thank you I have learned something today and so the day has been a success. :-)
Typically once it cures it's okay.
could you post the brand name of that product here? It should be classed as a hazardous product and not be confused with a household item. thanks!
CB20014 years ago
For those who want to know, in the U.S., Wal-Mart sells both Mineral Spirits, or at least one Wal-Mart does. I found it earlier today, they sell it for $5.97. They have all purpose silicon caulk for $3. So, for almost $9 at least, or $12 at most (depending on which caulk you get), you can make the mold.
dsonley4 years ago
hey dude. that is brilliant!
wish my dad did that when i was small. heck i wish my dad played with play-dough with me.
might have to try using that resapy for other things. that silicon gloop looks really nice to work with if you didn't add quite as much thinner.
thanks for the tutorial mate
mikey774 years ago

Just wanted to mention that I have had good luck casting plastics that melt at low temperatures like shapelock and hot glue. They work well with Oogoo molds without a release.

You can also cast epoxy, polyester and urethane, Oogoo, and other kinds of silicone in Oogoo molds. But for them, I would recommend first spraying the Oogoo mold with a spray lacquer to act as a release. This kind of laquer dries in a few minutes and creates a thin film which keeps everything chemically separated but flakes right off when you peel it apart. This prevents them from sticking to the mold or having them polymerize incompletely which can leave some epoxies with a sticky surface where it touched the mold.

submark4 years ago
Great instructable.
Do be aware that your power drill motor may spark quite a bit as the drill starts and at low speeds. I've seen a drillmotor ignite flamable vapor when ventilation was not adequate to dispell the fumes. (Nitrocellulose laquer is spectacular when it goes off!)
If you use very flamable thinner or white gas you will need to ventilate with more than a kitchen fume hood. An additional fan to cross ventelate and exhaust the work area are necessary. Working outside or at least with the doors open and with the fan on is necessary.
The curing and outgassing should also be done with proper ventelation.
MechanicalMashup (author)  submark4 years ago
All VERY good points thank you for bringing it up.
DavidNZ4 years ago
Would it be possible to make and iPhone 4 case out of this???
MechanicalMashup (author)  DavidNZ4 years ago
Depends on a few things. first and formost make sure the iPhone is covered with a celophane wrap or something to keep the electronics exposed. Second are you making a mold of the phone or covering it? If you are covering it I would consider this 'ible first http://www.instructables.com/id/How-To-Make-Your-Own-Sugru-Substitute/
Very cool tutorial! Do you happen to know how well this type of mold stands up to heat? Say, for making wax forms?
I dont know what max temp it could take but I am sure hot wax or paraffin would be fine
Hi Behnt -

Thanks for sharing this. The video is really helpful.

I wanted to share some insight i have on this type of mold material. I learned to use household silicone for molding in an art class. Poor students need inexpensive materials.

Based on the process we used, it's not necessary to add anything to the silicone. Also, using the silicone without additives creates a mold that doesn't shrink. Here is revision:

Bucket of water filled about 3/4 full
A good squeeze of liquid dish detergent into the water. No particular brand needed - I've used various kinds and they work fine. This will keep the silicone from sticking to your hands. If when you go to pick up the silicone it sticks to your hands, add more detergent.

Follow Behnt's steps for setting up your item
Squeeze the dish detergent into the water and swish lightly with your hands. You don't want a lot of bubbles.
Squeeze the silicone into the water and then start picking up globs to fill your mold.
Pot / use time is about 5 minutes.

That's it. Thanks again.

Awesome! I will give this a try here in the future. Did you add cornstarch to the silicone or does the dunking in water activate the silicone?

I have never added cornstarch. I think that dunking the silicone in the water with the detergent makes it manageable for the mold making purpose.

I should have mentioned that the process does nothing to improve the smell. Stinky stuff.

If you decide you want to try a real mold making material, I'm a big fan of Knead a Mold, made by Townsend Atelier. I've tried many of the commercial two-part silicone products out there and really like theirs. It's really easy to use in either tiny or large quantities, the price is very fair, and the 1-1/2# kit lasts a long time...six -eight months for me. 'Worth looking in to for those who want to make candy molds...wouldn't use the household silicone for that.

Thanks again Behnt for taking the time to make the video and write the Instructable! Hail to Play-Doh King!
I am really starting to like this thread. I do believe that I am leaning more each minute on how to make molds and much cooler ways than this... Thanks for your advice!
372jpeg4 years ago
I made ice toys using this stuff, this stuff works great!
MechanicalMashup (author)  372jpeg4 years ago
Cool! do you have any pictures?
Cool? No, technically it's frozen.
Funnny! Still upload som pictures so we can see I am curious
dakois4 years ago
in the video you only put like one tbs of corn starch, but you say to use 50/50 blend of the silicone and starch. how many spoon fulls on the corn starch should i use?
MechanicalMashup (author)  dakois4 years ago
It's the magic of video editing. I don't think people want to see me put in 4 spoons of cornstarch. It is a 50/50 mixture by volume.
Helder4u4 years ago
What use is the corn starch for?
Brad I.4 years ago
What is the mineral spirits for? The cornstarch and silicone seems to work fine for sugru substitute. What does the paint thinner do?
MechanicalMashup (author)  Brad I.4 years ago
It makes the silicone pourable or flow so you do not have to squish the stuff down.
danny61144 years ago
It would seem that a non-stick cooking spray would work as a release agent as well, would it not?
MechanicalMashup (author)  danny61144 years ago
Yes that would work fine as well. I was using what I had in the kitchen and we do not have any spray
ste4 years ago
50/50 ratio it is by volume or by weight ?
MechanicalMashup (author)  ste4 years ago
By volume...
Funny and brilliant! I needed a system like this (i.e. making a mould but with no rigid plaster involved) to make an irreplaceable plastic part for my 1933 Austin 7. This, I think will do nicely. Thank you, Mr Behnt - I hope your exercise regime works out as well as your ingenious mould system! (And the magic bent nail…)
Given that this has considerable shrinkage, I don't expect this to be a good choice for casting replacement automotive parts, especially if the plan is to be as close to a replica as possible. I have seen other moulding supplies at one of our local plastics outlets (TAP Plastics) and they even have a worksheet to help determine which materials would be best for the project at hand.


They also have full guides on the subject, as well as videos:


(Not affiliated in any way with TAP Plastics....)
MechanicalMashup (author)  hairybaroque4 years ago
Nothing magical about the nail unless you consider I pulled it from Harry Potters wand... :)

Keep in mind the mold shrinks upwards of 10-15% over a week so if you use it for a part use it as soon as you can to keep the size of the original

I will be covering some other mold techniques soon with other kid play stuff. I was inspired by this and started playing with 'moon sand' and figured sand casting is in my future :)

Hope it all works for you and post pictures if you do make something
dakois4 years ago
what can i use instead of paint thiner?
MechanicalMashup (author)  dakois4 years ago
White gas. Better known as camp stove fuel or Naptha http://en.wikipedia.org/wiki/White_gas
Asrael4 years ago
Just a quick question. I once had a similar idea with paint thinner and silicone. Unfortunately it turned out that while curing the mould shrunk an awful lot. Does the starch get rid of that?
MechanicalMashup (author)  Asrael4 years ago
Nope the mold still shrinks. One thing you could do is measure the volumes of what you put into the mold for ingredients and then after the mold cures measure the difference in size. Once you know the % shrinkage you can make the plugs for the mold that % larger so that when the mold is fully cured it is the right size...

I wish I had a better answer for you but that is all I can come up with
Thank you none the less :o)
MechanicalMashup (author)  Asrael4 years ago
Depending on what you are doing if you can wait a couple of weeks I will be doing a sand casting episode for the blog. It does not shrink.

You could put it all together yourself by googling DIY sand casting and taking a look at the videos that come up. For non metal castings you can use 'moon sand' from play dough but you can easily make your own moon sand too again google home made moon sand....

Hope that helps...
Yes I can wait, but how cool ist this! Last year on a trade fair I came across moonsand and asked if you could cast with this stuff and they said "no". The reason they gave was that it would melt. That sounded strange but it was to expensive to get just to play around with it ;o)
So thak's again! =)
Hisart4 years ago
What a cool Dad!

The side bits in the video are hilarious!

Nice Instructable, well done!
MechanicalMashup (author)  Hisart4 years ago
Crocatiel4 years ago
This is great! do you know if you could use resin in this mold?
MechanicalMashup (author)  Crocatiel4 years ago
Absolutely. I would bet that neither epoxy or polyester will stick to it....
My favorite part out of a great 'ible is in the video where you mix the goo with the bent nail. I have never thought of doing that before.