I must be missing something. You're probably goign to
get some burnt drywall plaster mixed in the sand. I
dont see how you couldnt. But actually less impurities
from that than the burnt foam puts in.
Here's what i do as well as what i should do.
I completely make the form including sprues etc. I use
clear tape to cover the foam and give it a smooth
surface. I then take drywall putty and thin it til its
about the consistency of pancake batter.. or probably
a hair thicker. I then paint it on the foam carefully
so i dont mess up the molds. What i SHOULD do is mix
up more at a time and dip it. In layers if necessary.
Ive stolen the ideas from you guys and i really like
to use straws as runners. I then sit it out and let it
dry a few hours in front of a fan. After that i go
over it again making sure i got any spots i missed and
got them well, especially the straws. Once that all
tries i cut the top of the sprues etc to let the al in
and out. Unlike regular lost foam youve got an
enclosed area here and the gas has to have somewhere
to escape. Putting extra straws in helps here too. I
like the kind that will bend. Once all thats done i
place it in the sand and gently fill with sand. Ya
know ya really dont notice how the sand will deform
yoru work til you go to machine it and see. I then
use something to burn down into the spru to guide the
al and put a can or whatever around it. I think a
better way to be honest would be to make up something
that looked like a crucible with a hole in the bottom
to place over the spru and keep the metal from ever
going near sand. Then i pour and pray i dont overpour
(took 3 days to machine down some big lathe castings
The drywall should be like 1/8" thick imho. After it
cools, and it needs longer i think(?) than normal lost
foam to cool you take it out and hit it with a hose.
The plaster will be pure gypsum now and appear to be a
paperthin coating. (Interesting note- if you
rehydrated it it would turn back into - drywall
plaster by recombining). As for getting in yoru sand
i dont think it matters. You should be using cheap
normal sand. ANY kind of sandworks even crappy
Hope this helps.
--- Daniel C Postellon <postello@...
> I must be doing something wrong. How long do you
> let it dry before casting?
> I let mine dry overnight, and just got burned chunks
> of plaster in my
> molding sand.
> > Yeah, I'm just starting to use the drywall stuff,
> and I already like it.
> > lance dulak wrote:
> >>What they said. Its almost impossible to get ALL
> >>sand out though. Which isnt important if you're
> >>casting but if yo're going to machine the al its
> >>important. Ive dulled at least three of my
> >>endmills that way. Its' suprising how quick one
> >>of sand will dull nad endmill (and turn into
> >>sand-microdust). There are special casting filters
> >>can get to remove junk.
> >>Best thing ive slowly learned is to remelt the
> >>with inclusions into ingots then remelt again.
> >>Skimming Heavily each time and using pool shock
> >>whatever. I dont cast lost foam anymore without
> >>coating it with drywall patch though. It makes a
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