Green Sand Formula - How to Make Molding Sand




Introduction: Green Sand Formula - How to Make Molding Sand

To makegreen sand or like it also called molding sand (foundry sand) we need 3 ingredients: sand, clay and water.

Step 1: Digging Clay

Buy or dig some clay. I couldn’t find any clay (except fire clay) in the nearby shop and even in the big supermarket. Clay is a thing, which is not use during building, and redecoration works now. Of course, I mean that it's not used in a pure condition though it's still important ingredient in many building materials.

I had to dig some clay in the cellar. This cellar was built half a century ago, so the floor made of clay. I should also mention that this is brown clay. I’ve heard that it’s recommended to use green (bentonite clay) but I didn’t have it, so used what I had.

If clay and sand are wet, you should dry them on the sun or any other accessible way.

Step 2: Find Some Sand

Buy or dig sand. I bought sand because it was far enough to the nearest reservoir and river where it’s possible to take sand.

Step 3: Make Clay Into Fine

Make clay into fine and clean the sand if it has any contaminant.

Step 4: Formula

My formula of green sand is 70% of sand and 30 % of clay. At first, I tried to use 15% of clay but it didn’t work well. I assume, that with green bentonite clay even 15% could be fine but not brown clay.

Step 5:

Finally mix sand with clay. During the process, spray some water. You will see that it’s enough when your mixture is able to maintain a form.

That’s all. This green sand formula is working. It is possible to use this molding sand again and again.



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    12 Discussions

    Do you mean to add cement to the recipe to make a mold permanent? Or to pour concrete inside to make concrete patterns?

    Another source for pure bentonite clay is a well drilling company. Ask is you can buy a bag of "driller's mud." It comes in a finely powdered form and is great for use in making green sand. A 30-pound bag will last a long time.

    1 reply

    Thanks for your good advice ChiGuy14. I can say that now I totally satisfied how my green sand works. I used it many times, so it's not bad. Also, I've got some bentonite clay from open-cast mine near my town. I will test it to find out if there is some difference. You can also see how this green sand formula works in my other casting instructables and youtube videos.

    I always wondered how green clay was made!

    Just so you know, pure clay kitty litter is bentonite (see step 1). I found that out while reading up on cobb ovens.

    5 replies

    Yes. I see that a lot of people use cat litter as bainder. The only problem that cat litter may consist of different ingredients. For example, I didn't see cat litter which is a good binder in my country. I usually buy for my cat, some cat litter which looks like wooden pillets! Before I bought cat litter which consisted of silica gel. I assume that I can find some other sorts of such things through the Internet or in big supermarkets but it's easier to dig some brown clay :)

    I'm with you, it's nearly impossible to find cat litter without added scents or "odor absorbing" crystals, unless you purchase online. In which case you might as well order powdered bentonite clay. However, I ended up grinding some that had the odor absorbing crystals and just filtering out the crystals through a screen. I used maybe 8-12 cups of cat litter and had more than enough clay for about 2-3 gallons of greensand that works perfectly.

    That's grate that you have found the solution. At first I thought that I could buy some clay in shops which sold building materials. I was suprised to find out that nobody sold pure clay. :) Does your green sand allows to use it many times. I mean there is nothing left which can just burn during casting?

    It's holding up so far. There doesn't appear to be any residue from stuff burning. I just crumble up the mold, mix it back into my supply, and add a bit more water if it's too dry.

    That's good. I do the same. Just throw away very thin layer of green sand which contacted with melted metal. This sand is black, so I think it becomes bad binder.

    Surprisingly little Bentonite clay gives very good results as far as cohesion goes, but if your home- brew formula works well enough for your needs, then it is a success too!

    1 reply

    Yes. It works good. As far as I know when we use bentonite clay, than 13-15% is enough. But with brown clay 15% doesn't work. So, I took twice more and it started to maintain a form. I also got some bentonite clay, so will try it in the future. I'd like to understand if I could notice some differences.