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Mixing the Ultra-Cal

- Always sift your detail coat

- Always start with water and add the Ultra-Cal

- The warm the water, the faster the Ultra-Cal sets up

- It's probably a good idea to wear a resperator when sifting or pouring Ultra-Cal, it contain some nasty silica particals and other things that lungs don't really get along with

 

 

Mold Making Process - Pt. 2

Next, we’ll build the front and back halves of the mold. I prefer to do each with 3 coats of Ultra-Cal. The amount of Ultra-Cal needed to make a mold is relative to the size of the sculpture. I strongly recommend having more Ultra-Cal on hand than needed for the job. For most masks, 50lbs will do. It’s OK to finish with left over, you’ll use it on your next mold. But, it’s a horrible feeling to run out in the middle of making a mold. It’s really important to begin and finish the whole process in one time block. If we stop in the middle of adding coats we risk making a weak or uneven mold.

Step 3 - Detail Coat

The detail coat is the first coat of Ultra-Cal. For this type of a mask, I add 1-1 ½ “ of room temperature water to the bottom of my bucket

Next, using a sifter I add my Ultra-Cal. I always sift my detail coat as I want to make sure I eliminate any chucks of gypsum cement. The Ultra-Cal is added until it rises slightly above the water and forms a cracking “dry mud” look.

The mixture should have the consistency of thick milk or cream. Not too thick or thin. If it’s too thin, it’ll run right off. Adding more Ultra-Cal will help. Too thick, and we risk trapping air and not capturing all the detail.

I will apply the mixture with a chip brush. I use the brush to drizzle the mixture on the sculpture and periodically use my airbrush to spray air on the mixture to force it into cracks and details, 30-40Psi will do, anything higher will shoot the mixture right off the sculpture.

The detail coat takes the longest to apply as your building up a thin layer of Ultra-Cal. Slowly but surely my goal is to make sure that the entire backside of the sculpture and dam wall is covered. You shouldn’t be able to see any of the back half of the sculpture.

Step 4 - Second Coat

The second coat is where we will build up mass and strength. I will clean out my bucket and add 2-3” of water. Again, I will add Ultra-Cal, this time I am not concerned about sifting. When I see the cracked mud form I will add a bit more Ultra-Cal with the intent of making this mixture a bit thicker.

I begin coat #2 by with a quick covering of Ultra-Cal. Next I begin dipping my burlap strips into the mixture and laying them on. I cover the whole backside with burlap and then again a second time placing the strips in the opposite direction. Be sure to build up burlap and Ultra-Cal against the dam wall also. Any remaining Ultra-Cal is added and smoothed on.



Step 5 - Finishing Coat

My final coat is mixed up in 1” of water in my bucket and I tend to add even more Ultra-Cal for this final round. I lay the mixture on quick and thick (½”-1") and smooth it with my hands. I'm aiminf for an overall mold wall thickness of 2 ½”-3”. minutes.

After letting it sit for 10 minutes I will rub down the surface with clean dry burlap to smooth down any rough edges. The Ultra-Cal will get very hot as it sets. You’ll probably see steam pouring out of the mold for a good several minutes.

Once the back half has sat and set for about a half hour I will tip the entire piece onto the back with the face of the sculpture facing upwards.

Step 6 - Removing the dam

Now it’s time to remove the clay dam wall. Carefully peel back the clay dam. Be careful not to distrub the sculpture when doing this. I ofter remove the bulk of the dam with my fingers, and then remove smaller pieces with a clean-up sculpture tool. When the clay has been removed, I will brush down the exposed plaster edge with a thin layer of petroleum jelly with a small paint brush. This will prevent our two halves from sticking together. Keeping the layer as thin as possible, as I want the mold to be good and tight I work around the whole outside edge. Be sure to remove any keys, and to brush down the key areas also.

Finally I add 4-5 small wedges of clay to the wall. These will be the points were I will wedge my pry bars into to separate the two halves.

 

Step 7 - One More Time!

The front half is created in three coats, just like the back half. The detail coat on the front half should be easier to apply, as the face is pointing up and you can drizzle the Ultra-Cal into most of the details. Don’t forget the airbrush! Repeat all three coats on the front half, making sure to also cover the surrounding edge.