breading

Breading technique for lostfoam patterns

As I have, you may have already tried the drywall texture dip technique on www.buildyouridea.com and found it to be less than ideal, but still pretty good. Kudos to Dave Kush for documenting his process.

The breading technique:
Similar to breading a chicken wing for deep-fry. Fill a spray bottle with water and a good squirt of dish soap. I used "seventh generation" soap. This makes the water stick to the foam and wax better instead of beading up. Hold your pattern by the sprue, spray it all over and into nooks and crannies, and shake it off gently so there are no drops clinging to it. Now, take some _dry_ drywall texture compound and sprinkle it all over your wet pattern. Shake most of it off, and flick the sprue with your finger to get most of the rest of it off. Spray it again lightly with water or soapy water for a more durable coating. Sometimes this last step is a bad idea because the coating will form a gas barrier during casting instead of letting gas through into the sand. This has happened to me; one face of the pattern lifted off entirely during casting, pushing up the surface of the sand and leaving me with a perfectly formed pattern that was 1/4" too thick. The pattern had some wax fillets and had no vents.

comparison to drywall texture dip technique

• you aren't limited by bucket size
• dries much much quicker
• can be gas permeable
• no air bubbles or drying cracks
• consistent coating thickness regardless of part shape
• buoyancy can sometimes cause a glued together foam piece to break when immersed in a liquid

• dust can fall off if handled roughly - add wood glue or elmers glue to spray mixture, or use 3m spray adhesive instead of soap and water mixture (untested use at own risk)
• dust gets all over the place if you aren't careful

fenn