Molding and Casting Simple Parts : The Simple Way

Things you will need:

Liquid Latex Rubber (usually found in art stores)

Brush (disposable oil brush is good)

Glass Surface (so the latex wont stick)

Gauze Bandage

Hot Glue Gun and Stick

A lot of Patience (yes I mean lot’s of it!)

Step 1 - Prep

Set your cast master piece on the glass surface. It would help to make it more stable by applying a little white glue underneath so it won’t move during the initial application of latex over it. In this project I used a simple shaped M4 Sherman’s front transmission bolt rack, which has a flat back. Most liquid latex rubber can be purchased from art stores; the common brands you may find are Mold Builder by Castin’Craft or Mold Craft by Burma Rubber Company. Both brands usually sell the latex in 1-liter plastic containers and that will be enough to make a lot of simple molds.

Step 2 – Latex Layering

When the piece is stable on the glass, apply the initial coat of latex over it with the brush, making sure you fill any small spots and crevices with latex. Then thoroughly cover the piece extending at least an inch away on all sides.
Make sure you apply enough yet a thin coat all over, the biggest mistake you could make here is apply it too thick. What will happen is the top surface of the latex will dry quickly but the inner coating wont!
After the application, leave it alone for at least 24 hours to dry - IMPORTANT!

Make sure you wash your brush thoroughly with water after each use; this is done simply by running hot water from the tap until the latex is all gone from the bristles.

After drying, the top surface may feel a little bit tacky, but it should look more yellowish-clear in color. The good thing about using a glass surface for a base is that you will be able to look and check the status of your piece underneath. Image four shows both top view and bottom view (through the glass base). Now you can go ahead and apply another thin coat using the same motion and amount, but this time try to extend another half an inch at the edges, do this once every day for at least the next 4 days!

Step 3 – Gauze Layer

After a few coats (after a few days!) you can optionally add a piece of gauze on top of the mold then add another layer of latex to mix it in. This gauze will make the mold stronger and tear resistant. Image 5 shows gauze in a layer.

Step 4 – De Molding

After a few more coats (and a few more days) you may now remove the mold from the glass surface by using a flat blade or even a plastic spatula and carefully pull it away, image 6. Inspect the bottom part of the mold making sure the first coat from a few days ago has actually dried over your master piece. Remove it carefully from the mold and inspect it for any miss-matches or bubble holes, image 7. Trim the edges too so its not too flimsy, image 8.

Step 5 – Casting

Now you’re ready to cast!
Heat up the glue gun with stick, then with one hand open up the mold a little wider as you apply the melted plastic glue inside the mold. This will ensure that it will flow evenly to all the crevices in the mold and will also prevent making bubbles, image 9. I usually apply more plastic glue than the mold can handle therefore making sure I have completely filled it up, image 10. The melted plastic glue is also clear in color so it’s hard to see if your have put enough or not.

Step 6 – Removal and Cleanup

The glue normally takes a few minutes to dry and become solid. I usually leave it in the mold for at least an hour just to make sure it takes its shape. Then after removing your new cast from the mold, remember that plastic glue is softer and flimsier than polystyrene model plastic (almost like toy soldier plastic). So it takes a little time to trim off the excess flash properly, but then there you go!

After a few days I’ve got myself an extra Sherman transmission bolt rack. The biggest thing on this project is patience as I have mentioned above. This particular molding project started on the 17th and ending on the 26th of the month- almost ten days! And again remember this is LATEX, not RTV Rubber so you can't pour out a whole lot of it over your piece at one time cause it wont dry at all if applied thick, In the case of RTV which is more expensive, it dries faster no matter how thick it’s poured over because of the catalyst or hardener added to it. The bottom line is with latex you get to have your simple shapes duplicated cheaply!