DIY An Instant 1/2 Rd RTV Silicone Mold For Under A Buck.

[Husky]

FYI.

Apparently all things labeled 100% Silicone are not the same. A friend tried GE 100% Silicone, and it didn't harden up.

In the past I've used DAP Silicone with good results but it pays to do a small test mix before committing, if you're using a brand other than the Mainstay product from WalMart.

[Sonny.Barile]

Thanks for the headsup on brands. My local Walmart doesnt carry it and I was going to get try the GE.....Guess I will have to find an on-line source.

[Husky]

Thanks for the headsup on brands. My local Walmart doesnt carry it and I was going to get try the GE.....Guess I will have to find an on-line source.

Try DAP white 100% silicone. I've used it in the past.. Ace Hardware carried it!

[Piscivorous Pike]

Husky,

Thank you so very much! I learned something of great value here from your post.

TU is a great place to learn and find like minded friends. Although I have used silicone since the 1960s, DAP (formerly DOW/Corning) from its beginning, it was only a few months ago from TU that I learned about water speeding up the vulcanizing. I carry several tubes of DAP Silicone with me on fishing trips.

Keeps my boat from sinking, literally. (look at the picture of the holes: Three things to preserve your trip from a trailer accident )

I just made my first rtv mold with your silicone sauce.

This project used 4 tubes of silicone and made a two piece mold of Castaics Platinum 8" swim bait trout. I will use these like Banjo minnows not a swim bait, nose hooked in the pursuit of Lake Trout and Northern Pike.

For such a large mold I did two things that were not mentioned above that worked out well. I used a coating of silicone on the models and made indexing points with the silicone.

Do not coat plastisol models with release agent because the silicone will not spread out correctly onto the model.

I used the silicone out of the tube to put a layer on the plywood bottom of the mold and on the down side of the model. A very thin coat and as it began to set I filled the mold box up half way with the water accelerated silicone. I set the model in it and then raised the level of the silicone where the model would sit in the bottom half by again adding a thin layer of pure silicone sealer on the exposed side up to a point that would bury it 3/4 way. Only the center portion of its up side protruded out of what would become the bottom half of the mold.

Now a layer of water/silicone was added up to the new line on the model. The caulking gun then made 4 indexing points by making a tapered blob, like an ice cream serving, in the four corners area. After the silicone began to set I trimmed the tops of these index points with a razor blade.

After setting enough that it would not compress and shift from putting pressure on it I used hot vaseline and a small glue brush to paint the areas (except the model body) that the top half of the mold would rest on. I was very careful around the margins of thin silicone and the model body. That took a steady hand.

I made a sprue from modeling clay and laid it in and put on the next layer of accelerated silicone and pressed on the top. A couple hours later it was done and the box was take off it.

I have been working on a DWP version for several weeks, trying to rescue detail from air bubbles and imperfections. This silicone mold cavity is perfect! The mating surfaces are rough and likely would index without the little mounds. Two bar clamps should hold it together and soon I am going to use my $5 injector on it. Link: ($5 plastic injector! )

Oops, forgot to make a vent hole for injecting. Well, I can drill a hole at the tip of the tail at an angle an out the bottom of the mold.

Anyone know the formula for how much water to add? I am thinking a mister bottle would help when mixing a large batch.

Soon I am going to remake all my first molds this way, these molds: TU taught me this, its long, pics too.

PP

[Husky]

Hey

Piscivorous Pike

It's good to hear you were pleased with the process. It is very simple, yet effective. I hope others here have found it to their liking. You have to admit, the price is right!

[Vodkaman]

Anyone know the formula for how much water to add?

I remember Husky writing, "just a few drops", but I wanted a more specific formula, so did a few tests:

In the first test, I measured out 10g of RTV and 5g of water. When I tried mixing them together, I found that the water was not being absorbed. After about 2 - 3 minutes of mixing. I poured off and weighed the unmixed water (3g) and left the RTV to set.

The texture of the watered RTV was very stringy and difficult to control, also the working time was only about 3 minutes and fully cured in 25 minutes. When I cut the cured sample in half, a lot of air bubbles were evident, due to the mixing process and the stringy texture.

In the second test, I measured out 10g of RTV with 3 drops of water, in the hope that the setting time would be extended, as 3 minutes working (rough guess) time does make the mold making process a bit rushed.

The sample was cured in an hour. It did have good elastic qualities, but could be marked permanently with a finger nail indentation. The working time was also longer and the mix was much easier to work with, but you still have to get a move on.

When I cut the cured sample in half, fewer air bubbles were evident, due to the mixing process. Air bubbles/voids are unavoidable as the liquid RTV is way too viscous to allow the bubbles to escape. PP

[Piscivorous Pike]

I used plastic putty knives and the lids off buckets of detergent to mix the stuff on top of. I laid it out like Husky and sprinkled a lot of water on it through my fingers from an open palm.

Then I poured off the water and gave the pallet a shake. I mixed very carefully to keep the bubbles down as I have seen this stuff frost up like making taffy candy. I pressed and folded the mass. One time I re-wetted it. That is also the reason I took the precaution to "skin" the model with virgin RTV.

I think I can cut down on folding the water in if I use a mister and get a fine coat of water over most of the surface. Another experiment I need to try is to dip the pallet with the virgin RTV laid out in lines into water and submerge it. Then remove it and shake it out. An even coat of water will cut down on the need to fold it in much. I also wonder if adding just enough detergent to break the surface tension so as to get an even coat will work without damaging the integrity of the RTV.

I do not need it to harden up faster than a couple hours.

If I were to make the mold without having it attached to a ply wood bottom I would use the plastic from these detergent buckets as a base. The RTV does not adhere to this type of plastic.

Having found that I could seperate two halves of a two piece mold I believe that a piece of ply wood given a thin skin coat of virgin silicone RTV and let harden then coated with release agent, I like warm vaseline, would easily not stick to the next layer of RTV.

This is a very useful thread and maybe we can keep experimenting and posting our results here.

[Husky]

Thank you, Grasshoppers! You've done well.

Questions:

Which Brand Silicone Sealants did you use?

Which color Silicones did you use?

I ask because one fellow used GE 100% Silicone, and it did not set!!

IOW's, all Silicones are not the same. As strange as it may sound, Some people live where there are no WalMarts:roll:. Caveat Emptor.

[ROWINGADUBAY]

I wonder if the air bubbles could be avoided by placing the silicone and water in a plastic bag getting all the air out [maybe using a vacuum sealer] and kneading the mix together instead of mixing

I also wonder if this could be done with the high temp silicone gasket maker for cars

I think then you could use if for pouring lead if all the water is evaporated

Just a thought

George

[Husky]

I wonder if the air bubbles could be avoided by placing the silicone and water in a plastic bag getting all the air out [maybe using a vacuum sealer] and kneading the mix together instead of mixing

I also wonder if this could be done with the high temp silicone gasket maker for cars

I think then you could use if for pouring lead if all the water is evaporated

Just a thought

George

George,

I've yet to experience any problems with air bubbles in the numerous molds I've made. Again, this was with White Silicone Sealant sold at WalMart, under the Mainstay brand.

You've opened a new door by mentioning the High Temp RTV Gasket Silicone! That is something worth looking into, for soft metal molds. TIA

[Vodkaman]

The tube I bought was Dextone RTV 100% pure sealant. Grey in color, $2.43US for 300ml tube (Indonesia).

Husky, I know you have experimented molding baits from this stuff. What kind of colorants work? I haven't tried anything yet.

Dave

[Husky]

The tube I bought was Dextone RTV 100% pure sealant. Grey in color, $2.43US for 300ml tube (Indonesia).

Husky, I know you have experimented molding baits from this stuff. What kind of colorants work? I haven't tried anything yet.

Dave

Dave, the only colorants I used were Artist Sand in Blk, Orange, Blue and Colored glitter. I used those in the Clear RTV. Coloring Gray could be problematic

Surely, a water based paint would color it but I don't know if it would be a vivid color. If you go to a paint store, the might give you a sample of straight colorant to try.

Remember, you can only use it in a rigid mold because it will turn a silicone mold into a silicone block!

The Baits will be quite stiff compared to Plastisol, BTW.

Mike P

[Vodkaman]

I will keep an eye out for the clear. I was thinking of water based dyes, but the amount of water required is so small, I doubt that it would be enough. Some experimenting will have to be done.

I am planning on trying a two piece paddle tail, from a 2 piece PoP mold, for my first attempt. The design of the master will have to take the reduced flexibility of the RTV into account. Also, I was planning to experiment with silicon microspheres, as RTV is a little heavy, BUT, a float test revealed that the cured RTV floated like a cork. I haven't calculated the density, but I would guess around 0.7gm/cm3 or 43Lb/cuft, I was not expecting that!

Also, the accelerated curing caused by the addition of water, causes the mix to give off some pungent odour and it does not smell healthy. The smell stung the inside of my nose. I could not determine what the smell was, a bit like vinegar. But confirmation of the chemical is required, just incase precautions need to be taken.

Dave

Edited July 16, 2009 by Vodkaman

[Husky]

I will keep an eye out for the clear. I was thinking of water based dyes, but the amount of water required is so small, I doubt that it would be enough. Some experimenting will have to be done.

I am planning on trying a two piece paddle tail, from a 2 piece PoP mold, for my first attempt. The design of the master will have to take the reduced flexibility of the RTV into account. Also, I was planning to experiment with silicon microspheres, as RTV is a little heavy, BUT, a float test revealed that the cured RTV floated like a cork. I haven't calculated the density, but I would guess around 0.7gm/cm3 or 43Lb/cuft, I was not expecting that!

Also, the accelerated curing caused by the addition of water, causes the mix to give off some pungent odour and it does not smell healthy. The smell stung the inside of my nose. I could not determine what the smell was, a bit like vinegar. But confirmation of the chemical is required, just incase precautions need to be taken.

Dave

That "Vinegar" odor is acetic acid. It's also found in Vinegar!

[Vodkaman]

LOL, well that is a relief.

I just tried adding half a teaspoon of olive oil (looking for a carrier for color pigment). The mix did actually cure, but much reduced elasticity. I was aiming towards glycerine.

Can someone try adding acetic acid to determine its effect. This could carry color and/or reduce the viscosity. I have no vinegar in my batchelor kitchen.

Dave

[mangeboy79]

vodkaman do a search on youtube on "homemade dildo" this guy reduces the viscosity with some sort off thinner before he brushes the rtv on his dildo , maybe you could brush on layer on just to get ridd off the air bubbles .

or thinn it like he does and add H2O to get the mix to cure fast

[Piscivorous Pike]

I used the Walmart Mainstay Clear. DAP clear I have used in the past, maybe I used too much water with it as it set up too fast, was stringy and had too much air in it. It appears to be less viscous to start than the Mainstay, however.

I think kneading in water in a vacuumed bag is excellent!

I will try to make another mold this coming weekend. I have a vacume machine, it makes bags to custom sizes. I see where a small amount of water, especially if we figure our the ratio amounts could be placed in a corner of the bag. Then the glue injected and laid oud on a side of the bag. Seal it next would give you quite of bit of time, I doubt any vulcanization would begin until you kneaded it.

Yep, I am going to have to try this one, its gotta work good.

PP

Edited July 16, 2009 by Piscivorous Pike

[Husky]

LOL, well that is a relief.

I just tried adding half a teaspoon of olive oil (looking for a carrier for color pigment). The mix did actually cure, but much reduced elasticity. I was aiming towards glycerine.

Can someone try adding acetic acid to determine its effect. This could carry color and/or reduce the viscosity. I have no vinegar in my batchelor kitchen.

Dave

I mixed some paint thinner into it before adding water and that made a thinner softer mold. More like a Shore 8 than the Appx Shore 25 hardness straight water yields.

Again, try some latex paint for color.

[Piscivorous Pike]

I found a better method to make a two piece mold than putting one side down with the RTV on any gender. Also I am not certain I can glue down a model onto an RTV base like you do when using POP or DWP. I probably will release. This clay method will hold it.

I prefer when possible to encase the model more than 50% in one side.

In the mold box for the first pour make a base out of a layer of modeling clay. Imbed the model to your desired depth for half the mold. 50% is good for symetric pieces. For robust pieces you can get a big creature out of a small hole so you can either imbedded it less than 50% or more than 50% to achieve that in the end product. Lay vent tubes by using copper house electrical wire, say, 12, 14, or 16 guage. A groove or channel or hole in the clay will be an index point. A channel around the model is good.

Coat it all except the model with release agent, I use warm vaseline. With the water accelerated RTV you should put a skin coat on the exposed model of virgin RTV. Cotton swab, glue brushed, finger tips all work OK for that.

Now at anytime add the the RTV. After setting invert the box and dremove the clay without removing the model. This works best if you exposed more than 50% on the first half. After cleaning up the clay again coat everything except the model with release agent, coat the model with a skin coat and then add the final amount of RTV to finish off the second half.

I like to permamently attach a ply wood base to each side so I put the ply wood ontop of the RTV for each half. Also if you use a thin slower setting RTV that does not have air bubbles you probably can skip the skin coat if you are careful not to put a bubble on your model.

I am experimenting with the cheap RTV sealer in a vacuum bag. My next experiment will put the amount I am going to use in the bag, manually close it and then open it so as to have coated all the bag. I will fill it with water then shake it out, maybe I will add just enough detergent to break the surface tension to get it to coat the RTV evenly. Next I will seal it with the vacuum sealer and knead it. Clip the corner and it should be appliabel by squeezin it out. I will report back on this part of it.

[Piscivorous Pike]

Inexpensive Silicone Molds w/ RTV? - Sculpture Community - Sculpture.net

and

Taxidermy.net and other taxidermy sites are referenced.

Lots of good info on accerators, xylene, acrylic paint, glycerine....

and more

Found a reference to casting lead in red high temp RTV:

HobbyMolding.com • View topic - Cheap RTV Silicon?

Well, here is a start to start looking for others who have been there.

Sculpture and Taxidermy are seach areas and sites, I hope someone besides me works on this to as it has greatere promise than I ever suspected.

[Piscivorous Pike]

I wonder if the air bubbles could be avoided by placing the silicone and water in a plastic bag getting all the air out [maybe using a vacuum sealer] and kneading the mix together instead of mixing

I also wonder if this could be done with the high temp silicone gasket maker for cars

I think then you could use if for pouring lead if all the water is evaporated

Just a thought

George

George you are a genius! IT WORKS VERY WELL

I laid out a flat spread in the bag, filled it with quite a bit of water then shook the water out and the put it in the vacuum sealer. I just worked with the manual vacuum button some to make sure the air is all out then sealed it, kneaded it then used a straight egde to pull the bag under on a flat surface to get the glue all to one side. I clipped a corner and squeezed it out like a cake decorating bag!

I got very little air in it. The more careful I was to vacuum the bag out the better the product.

[Sonny.Barile]

3 suggestions for swim baits.....

If the stuff is to stiff to get a flapping tail, try putting two dowel pins in the mold as to create a groove on each side of the bait. You would esentially be making a "live hinge" in the area you want it to flex. (similar to plastic hinged lid boxes) "OR" you may be able to use a blade to manually add it to the cured bait. However, fatigue could be an issue if the remaining section is to thin...........

Maybe make the bait hollow to get it to be more flexible. Try putting a solid protrusion down the center of the mold attached to the floor. This way the bait will still release. It would then have a pocket accessable from the bottom like some of those fancy ones you can buy at the store. It would be great for hiding the keel weight of a hook and also give more deflection to the material.

and finally......make it a two section bait (jointed). Put the hook in the tail section with the eylette being one side of the hinge. Use a twisted wire for the head section...........

I was going to try these myself but I just do not have the time or the work area to attempt another endeavour........

[Husky]

I made a 2 part mold using Silicone Cauld. I laid the Ist part out you normally do and placed it in a Foam cutout box. I mixed the caulK with some paint thinner (about 5 - 10% by wt) and mixed in some water. Then I filled the mold box to the top, pressing the Siicone in with a Spackling applicator. I then squished the Silicone done with a flat piece of wood. When it set up, I turned the box over and placed some shims under the box, which were slightly thinner than the box. (The Box was 1/2" and the shims 3/8") I pushed the mold half down into so the model side was still in the remaining 1/8th inch. Using WD 40 as a release agent, I sprayed the model and all surfaces.

Then I added another batch of Silicone Mixture as I had done previously.

When that cured I Made a silicone hinge, cut pour and vent holes and poured a Resin MB mixture. A little sanding was all that was needed to get the casting ready for finishing.

I'm sure you could do the same for soft castings.

And that's what I learned at Hammer Mechanic School, yesterday!

[Sonny.Barile]

Very nice!!!!!!!!!

Husky...I have looked in Walmart, Home Depot, and Lowes........Cant find Mainstays product. I see DAP brand but there are 20 diferent types. Most say they have phenol or some other crap in them. Is that the same stuff? or is it 100 percent silicone? Do you think brands sold for use in fishtank sealing are equivelent?

[Piscivorous Pike]

Very nice!!!!!!!!!

Husky...I have looked in Walmart, Home Depot, and Lowes........Cant find Mainstays product. I see DAP brand but there are 20 diferent types. Most say they have phenol or some other crap in them. Is that the same stuff? or is it 100 percent silicone? Do you think brands sold for use in fishtank sealing are equivelent?

This is the DAP 100% 50 year stuff the mainstay has replaced for me,

Here is a description:

http://www.dap.com/product_details.aspx?product_id=25

You can get it Harbor Freight stores, ACE and only sometimes from Home Depot, Ace has it consistantly. I pay $3.50-$5.00 a tube. Mainstay is $2.97

DAP will set up with water like the Mainstay,

I commented slightly on my experience with silicone rtvs in #29. I started using them in the 1960s, to build fish tanks. GE would kill the fish DOW now DAP does not. I have applied it under water in leaking tanks. I used to raise fish in 2000 gallon circular tanks in my back yard. All held together with this DAP 50 year. DAP purchased DOW/Corning after they pealed off their silicones after loosing a implant class action suit.

So, in general the fish tank silicone RTV will work. It is more expensive as it has all chemilcals that kill fish removed. GE did not hold glass well then and killed fish. Food grade likely will work too. Fish tank and food grade are very expensive because of the intended application.

Edited July 18, 2009 by Piscivorous Pike