This guy who is casting Legos (maybe I should post in the plastic caster forum) looks to just use slurry on the first dip, no silica. https://www.instagram.com/p/B4ibqVdAJbu/?igshid=1wj63dyrf0rji Anyone else doing this?
I tried it that way and wound up with some alligatoring of the surface finish. I though that that not sanding the first coat was the culprit, but on a recent cast where I did sand the first coat I had the same resulting alligator skin look in a few spots. Im now thinking that this may be caused by a viscosity issue........or perhaps this is what happens when the slurry has gone past its life span.... R&R does say to sand the first coat. I suspect this helps pop any air bubbles in the first layer of slurry.....
I'm with David. It's not necessary. If you are having bubble issues, the best I can suggest is dip in the slurry and take compressed air and very gently blow the wet surface before hitting it with the fine silica. This will get rid of the bubbles. When mixing your slurry, try not to be too violent and introduce a ton of air into the bucket. The alligatoring you got David was probably due to shrinkage as the stuff dried. It really needs that silica to hold it together.
Imagine if you are sanding the first layer.... You still don't know what's happening to the layer in contact with the wax...?? Then how does it behave on burnout? I know I read somewhere on R&R that slurry only first coat is not advisable.
