Will,

re: sawing the pattern in half.

This method is useful to make mold halves easier to part.  I remember doing it, but a long time ago.  Glue a facing of paper (grocery bag) to the material for the master mold on the parting line, both sides.   This gives a easily "peeled apart" surface and also serves as a reference line for carving the pattern.  This would save the sawing and accompanying loss of material.  You do have to be careful when carving to not put too much stress on the paper otherwise it comes apart.

First of all the stuff is lightweight joint compound which is sort of a plaster.  second, I usually fill my forms somewhat with with anything bulky like scrap balsa or crushed paper to reduce the amount of compound required.  I mix about a quart of compound at a time and smear it on with my bare hands, then wash my hands, mixer, bucket and all.  It washes quickly with just flowing water, takes about a minute and is ready to repeat the mixing.  the best part about this stuff is that it cuts beautifully with a Sanley Sureform shaper which is kind of a rasp with hundreds of openings for the shavings to pass through.  With the Sureform, the 20 minute compound cuts easier than balsa and sands well the next day with a power sander to remove carving marks.  I fill two Bearcat half fuselage mold forms with 6-8 mixings of compound for each side.  The operation is continuous.  I add compound to one form while the other is setting up.  As the form begins to fill, I begin to carve it down to shape.  Another nice thing about the compound is that there is no detectable seam where the layers meet.  It takes about two hours to mix, clean, apply and shape the two fuselage half forms.  The next day I sand for about five minutes and glass the molds.  Plaster molds have to be waterproofed for molding wet balsa.  I have simply painted them, which worked OK but glassing is nearly as quick and makes a longer lasting mold.

First of all the stuff is lightweight joint compound which is sort of a plaster.  second, I usually fill my forms somewhat with with anything bulky like scrap balsa or crushed paper to reduce the amount of compound required.  I mix about a quart of compound at a time and smear it on with my bare hands, then wash my hands, mixer, bucket and all.  It washes quickly with just flowing water, takes about a minute and is ready to repeat the mixing.  the best part about this stuff is that it cuts beautifully with a Stanley Sureform shaper which is kind of a rasp with hundreds of openings for the shavings to pass through.  With the Sureform, the 20 minute compound cuts easier than balsa and sands well the next day with a power sander to remove carving marks.  I fill two Bearcat half fuselage mold forms with 6-8 mixings of compound for each side.  The operation is continuous.  I add compound to one form while the other is setting up.  As the form begins to fill, I begin to carve it down to shape.  Another nice thing about the compound is that there is no detectable seam where the layers meet.  It takes about two hours to mix, clean, apply and shape the two fuselage half forms.  The next day I sand for about five minutes and glass the molds.  Plaster molds have to be waterproofed for molding wet balsa.  I have simply painted them, which worked OK but glassing is nearly as quick and makes a longer lasting mold.

Thanks, Al.  That pretty well answers what I needed to know.  I am intending to make a turtle deck mold that is fairly large, and I only have white beaded foam which isn't real good for the purpose.  Wood and joint compound I can get!

Cheese and bread are both pretty good mold-making materials.  If you leave them uncovered in the refrigerator, or just out on the countertop, you should have some pretty good mold after about a week.  Just make sure that the bread doesn't get dried-out too much.

Bill,

I have also used foam to fill the mold forms.  It works OK, but I prefer the finish I get from the joint compound, plus, the joint compound is very friendly to carve.

Al

Thanks, Al.

I *might* partially fill the *holes* with some of that dreaded beaded foam, and the rest with the joint compound.  How's that sound?

Merry Christmas!