Casting With Alginate and Resin

[Joe Campbell]

Any problems I should be aware of that occur with alginate as opposed to silcone?

This is for a 1/4 scale head cast.....

Thanks for your expert advice!

 

[Eopie Herder]

Any problems I should be aware of that occur with alginate as opposed to silcone?

This is for a 1/4 scale head cast.....

Thanks for your expert advice!

Alginate shrinks pretty rapidly, other than that it may work just fine. I think one of the guys who used to work with Sideshow used that as a quick mold to do fine details, but he may have been pouring wax into the mold. The wax would likely be hotter than the resin gets, so I would think it would work. Though, if you try it and it doesn't work, you're not out that much cash.

What head are you casting?

 

[JtotheP]

Consider your casting material and how much it will hate moisture since alginate uses water. A urethane casting resin will end up with many pinholes because of the moisture.

 

[punisher]

although for plaster casts its great.

 

[LeMarchand]

Although i haven't tried it, a megafast curing resin (like smoothcast Q) seems to work well as the resin has too little time to react with the moisture. I tried smoothcast 305 once in alginate and was treated to a real bubblefest.

shrinkage is indeed also a factor, the longer you leave alginate, the more it dries and shrinks.

 

[GunsAndGloryFX]

Word. Crystal Clear by Smooth on hates water too. Though, I believe most epoxies aren't effected much by it. Recommend running a small test first.

Also, I've got about 100 gallons of slow-set alginate sitting in my apartment. To anyone near LA, I'll donate some to your project.

 

[Joe Campbell]

Pinholes would be bad....

I'm casting an Indy head in translucent resin, and am going to attempt to paint it in a style similar to the one used by Mindbook....

Phenomenally realistic.

 

[Eopie Herder]

Pinholes would be bad....

I'm casting an Indy head in translucent resin, and am going to attempt to paint it in a style similar to the one used by Mindbook....

Phenomenally realistic.

Yeah, translucent resins are usually are slow set, so it's not likely to work well. I'd get a small batch of silicone.

I do want to see pics when you get it done though, sounds interesting!

 

[protokev DMD]

Alginate also absorbs any water around it, and if left out will dry out as well giving a distortion to the mold

 

[spcglider@aol.com]

I've been casting urethane for about 19 years. Here's an encapsulation of what I know:

In general: Using urethane in a high-moisture situation is BAD. Urethane resins are corrupted by ambient atmospheric moisture which is why they have a certain shelf-life unmixed. They sell a heavier-than-air chemical blanket in a spray can to help keep moisture out of your resin and extend the shelf life. Alginate is a water-based material... your urethane will NOT like it. No matter how fast-setting it is. If you get good results, you should go buy a lottery ticket because your luck is infallible.

Something else to know about CLEAR urethanes is that they are particularly susceptible to moisture. They also aren't overly fond of standard "blue" silicone molds. Its a reaction with the catalyst (which is tin based). The best results are gotten using a silicone that has a platinum based activator. It tends to be more rigid, but your urethane will like it much better.

The next thing to know about urethanes is how freaking toxic they are. I have posted many times about the toxic nature of urethanes here and on other boards.

Products that will cast well in alginate: plaster (hydrocal, ultracal, casting plaster, plaster of paris), cast-able acrylics (fiberglass, bondo, clear acrylic), water extended polyester (W.E.P.).

 

[voice in the crowd]

I used alginate with resin before and the alginate sweated out water leaving a slightly rippled effect on some of the lenses I tried to make.

The results were rubbish :lol

I used smooth on rebound 25 and the results were fantastic.

I would leave alginate for plaster life casts etc.

Chris

 

[Weapioneer]

Well, i recently cast some polyester resin into alginate, results weren't 'that' bad. Surface of the resin in contact with the alginate got pin holed like hell, and i found out the hard way that my stirring cup was susceptible to acetone solvents, similar to the stuff that is used in resin. Results- 1 pair of ruined pants.
I digress, I bought a pound of alginate, and a liter of polyester resin, and I want to know how to seal the alginate so i can cast without any bubbles or pinholes. I don't have shellac, so please don't suggest that.
Just in case anyone wants to know what i am casting,

the insignia of the assassin's on ezio's belt.

TIP- To make a decent mold, you can use plasticine to make the model, then pour alginate over it. both are pretty cheap and easy to get, for people like me who can't get super sculpy and silicon rubber. The plastecine also REALLY easily comes out of the alginate, no release agent needed. Just find a method of sealing the alginate if using resins.

 

[OldSkoolEffects]

I've cast Smoothon 300 (305) into alginate for a headcast, and while it worked, the resin foamed inside, and bonded to the alginate in spots, so I had to scrape it off. If you're using urethane resin, don't use it on anything that is moist. Either do alginate and then a wax or clay, or use a skin-safe silicone instead of alginate.

 

[adamnetium]

I have cast a few different materials in to alginate. The two thinks you have to remember are:

1) alginate is water based so what every you put in there biter like water. ( this has been mentioned already)
2) being water based when you put a casting material in to it, and that material needs an endothermic reaction to cure. The water and to some extent the alginate (because it is a form of gel) will draw out that heat pretty fast. So the irate time I did resin in it it took forever to cure because I mixed it for air temp, and the alginate's temp is much lower. In my experience this is what causes the pin holes on the surface.


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[Weapioneer]

I've cast Smoothon 300 (305) into alginate for a headcast, and while it worked, the resin foamed inside, and bonded to the alginate in spots, so I had to scrape it off. If you're using urethane resin, don't use it on anything that is moist. Either do alginate and then a wax or clay, or use a skin-safe silicone instead of alginate.

Well, I mentioned that i was using polyester resin. However, I am going to try doing the insignia using hot glue, with steel rods as a skeleton.

I have cast a few different materials in to alginate. The two thinks you have to remember are:

1) alginate is water based so what every you put in there biter like water. ( this has been mentioned already)
2) being water based when you put a casting material in to it, and that material needs an endothermic reaction to cure. The water and to some extent the alginate (because it is a form of gel) will draw out that heat pretty fast. So the irate time I did resin in it it took forever to cure because I mixed it for air temp, and the alginate's temp is much lower. In my experience this is what causes the pin holes on the surface.


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This does make a good deal of sense, I never understood why resin didn't like water that much. Will it work if you keep it in a hot environment? or will that deform the alginate? Also, the cooling factor of the alginate may help in casting hot glue into the mold, I shall experiment with that.


by the way, has anyone ever tried using rondo(bondo + resin) in an alginate mold? or just bondo? How well does it work out?

 

[pitchforknumb]

by the way, has anyone ever tried using rondo(bondo + resin) in an alginate mold? or just bondo? How well does it work out?

I've done the rondo in an alginate mold before, for a life cast. I think I sprayed one or two layers of crystal clear in it, but it came out with no problems.

 

[adamnetium]

If you keep the alginate in a "hot" environment I don't think it will work. See the air temp will be a minor issue if the alginate is cold. And if you "heat" up the alginate the water will start to evaporate and you start to loos the mould. Everything you are talking about is possible but it just takes some experience to make it work. Good luck I am sure you will make it work.


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[JD Douglas]

Any problems I should be aware of that occur with alginate as opposed to silcone?

I've been casting urethane for about 19 years. Here's an encapsulation of what I know...

Many years ago I was tasked with creating a game controller prototype from the foam concept model we had. I loved alginate (for pulling lifecasts, etc.) and I loved TAP Plastics Quik-Cast polyurethane resin, and I had plenty of both on hand. However, I had never used them together before. I needed to preserve the foam model, so the alginate was perfect. The controller needed to be strong and have internals mounted, so the Quik Cast was perfect.

Two great tastes that go great together, right? Right?!?!

Well, I didn't want to ruin our solitary foam model, so I did a test pull from an older foam model and quik-cast a test model. Unfortunately for me, it turned out perfectly. An absolutely beautiful model.

I showed my proof-of-concept model to the boss and got the green light for the real deal. That's when I nearly went mad because no matter what I did, I couldn't reproduce my initial success. Every cast was a disaster. I changed everything, everything I could think of...except the alginate/polyurethane combo. :sick

So, 24 hate-filled, sleepless hours later, I ended up hand grinding the shape out of bondo-covered abomination.

Bottom line: I wish I had been as smart as you and asked someone before I tried it. Unfortunately, the RPF didn't exist yet...

- JD

Edit: Whoa, I didn't realize the original post was years old. Oh well, maybe these new replies will help someone avoid this particular problem!

 

[Weapioneer]

Right, I have got some advice for people which i think could help.
making models- Plasticine is a cheap, reusable clay often played with by children. It is soft and can be easily sculpted.

Cheap Casting- For molds, one can use Alginate. It is used for making dental impressions and is quite cheap, at around $4-5 for a 1lb bag. 1 pound goes a good way with alginate. It tends to dry up and become stiff, but is useable and is non toxic. You can smear alginate all over a plasticine model and then easily peel it off afterwards with little/no damage to the plasticine and alginate. I did not use any release agents.

materials to cast with-
Polyester resin- used with fiberglass mats and cloth, it is resonabally durable, but touchy about curing. It does not work well with alginate due to the water in alginate, so sealing is required at the least.
hot glue- this stuff comes in sticks which are loaded into 'guns' which extrude hot glue out. It is Essential for every household, even those who don't do modeling due to its versatility and ease of use. Sticks can be melted directly in a small metal cup, then poured into molds. It pours easily enough when hot, and also cools quickly compared to resin, but cannot be sanded easily due to its rubbery constituency and liquid hot glue is very hot. 2nd and 3rd degree burns are very easy with this. CAUTION!- The fumes hot glue produces when melting is no joke. My throat still slightly burns due to it, and i was working in a well ventilated area. Try to get a large fan beside you to blow the fumes when melting.
I cast ezio's belt buckle with it, and i am quite happy with the result. Lots of flash(excess material on the back of the cast product)but a pair of scissors solved that quickly.
Hot glue works with alginate, allowing for flexible parts to be cast with ease. parts can be modeled with plasticine and then molds made using alginate and hot glue poured into the mold. You may want to use iron wire as rebar inside the hot glue for strength or stiffness.

I hope this helps everyone!

 

[JD Douglas]

hot glue- this stuff comes in sticks which are loaded into 'guns' which extrude hot glue out. It is Essential for every household, even those who don't do modeling due to its versatility and ease of use.

I'm embarrassed to admit it, but in all the years I've been doing this stuff it never crossed my mind to use hot glue in a mold, and I've tried casting with some pretty weird compounds... :devil

But now you're the second person I've heard this idea from in as many days!

It's brilliant and I can't wait to try it.

- JD