HOW TO WORK WITH HYDROCAL
AND OTHER MODELING TIPS -
I shouldn't tell you this. Casting Hydrocal, that is production casting,
is sort of like washing dishes. Actually, it is a lot like it. Boring as hell
and they just keep coming. Any idiot can do it.
The main trick is to keep the bubbles out. To do this we need to reduce
the surface tension. Sort of like static friction air bubbles like to cling
to the rubber molds. Just like a wetting solution used for scenic ground
covering we can simply use a few drops of liquid detergent in a jug of
Let me explain the process.
PREPARING THE MOLDS
Okay, we've just pulled some castings out of our molds. They are somewhat
self-cleaning however there will probably be a few chips and flash left over.
I wash my molds of in a sink that has a trap so I do not have to worry about
the plaster clogging my drains. You want to be very careful about this unless
you happen to know a cheap plumber. I do not.
Once they are clean I prepare the molds for casting by wetting them down
with a 50/50 mix of Spray-n-Wash laundry detergent. I only apply a little,
about a toothbrush full. I gently (quickly) scrub the brush around touching
all surfaces and especially every corner that likes to trap air bubbles.
At this point the detergent is still a little too strong. It will create its
own froth so we want to dilute it down. I use a spray mist of straight tap
water. We don't want to wash all of the detergent away but just enough
so the mold is evenly "wetted". The excess water is shook off and we are ready
I usually pour two or three boards at a time. The boards are 9" x 24", more
or less, half-inch thick plastic cutting boards. You don't want to use wood
as over time it will warp on you. This is a very wet process. There is
plaster, wet plaster, everywhere. And water. Plastic boards don't care.
I lay out the molds I am doing on the boards in an orderly manner.
MIXING THE HYDROCAL
With them prepared we next turn our attention to mixing the Hydrocal. The
book says you should add the plaster to the water, at a ratio of 100 pounds
to 45 water. I always do it the other way around. Not ratio-wise, but I add
the water to the plaster. (I should explain that I am using the generic term
"plaster" to mean White Hydrocal.) I've just always done this. And I don't
bother with weights. Experience has taught me to estimate the correct amounts.
I mix my plaster in cheap plastic pails, actually, the bottom of Wesson oil
containers. I usually do about three or four pounds of plaster depending upon
the size and number of molds I am doing. I use fresh Hydrocal. If you have some
with lumps in it you're better off throwing it out. Over time it absorbs moisture
out of the air and begins to set- it would be strong or consistent. It's only
twenty-two bucks for 100 pounds- so throw it out and start over.
Next we add the water. The trick is to add all the water we need before
we begin stirring. If you start too soon you'll get some hard lumps that are
very difficult to loosen up. You don't want that. Instead wait, then start
stirring. I use, on, about a 1/2" square wooden stick. I keep it clean of old
plaster as it may chip off and contaminate the mix. The same is true with the
mixing pail, we want to clean it out each time. At any rate, rapidly stir
the mixture. Work it until you have a smooth consistent mix. We are after a
nice thick soupy mix. Not too thick and not too thin. After a while you'll
determine the mixture you desire. As a rule of thumb, my mixture level is
slightly above the dry powder level, by maybe 10%.
Since I am in production, I cheat a little and use a Braun electric hand
blender. It gives a nice consistent mix.
Let's fight those bubbles a little bit more before we pour. I vigorously
tap the bottom of the pail with my stirring stick which helps bring the
bubbles to the top where they can be skimmed off.
POURING THE HYDROCAL
Okay, now we are ready to pour! I use my stirring stick to guide the
pouring plaster into the molds. Otherwise it would tend to splash everywhere.
We are in a bit of a hurry as you only have a certain amount of working
time. You can use cold water to delay its setting or hot water to speed
it up. If you want a really long working time add a little vinegar.
With the plaster all poured now we want to shake the bubbles out and
level off our castings. I try and pour in just the right amount so the
molds are just slightly over filled. I use a small but weighty metal bar
to vigorously tap the bottom of the boards and vibrate the bubbles up. I've
thought about building a vibrating table however this method serves its
purpose. Besides, it leaves everyone in the house know I'm pouring- and
not napping like I think they might suspect.
I know, you think we are done, just wait a while and we can pull out
our new castings. There's one last thing. I like to have nice smooth backs
on all my castings. So just as the plaster begins to set up I quickly
scrape the excess plaster off with a metal straight-edge, actually, an
aluminum triangle. And that does it. In about 15-20 minutes they are
set enough to remove and start the process over.
I am always thrilled to pull the first castings out of a new mold. After
all, it represents what may have took several days to create. Now I can
recreate them in just moments.
The thrill wears off though when I have to
stand there and cast one dozen, two dozen, three... Darn dishes!
You'll probably want to check out my postings on the Durango Roundhouse model.
I've loaded a bunch of pictures showing many of these processes.
For more illustrations see:
DURANGO RH CONSTRUCTION
Hey Clint, where can I find some Hydrocal?
Maybe at your local hobby shop, but note that he is probably as
tired of answering this question as I am. The price will likely reflect his
tax on dumb questions. Just go down the street, turn left, go four blocks and
there's a huge bag of it for what he's selling 5 lbs. for. I do not sell it
because of the shipping expense. Let's leave that up to the professional truck
drivers. I purchase mine in 100 pound bags (actually I now get them in 50 lb. bags
too late to save my back) at Glacier Northwest
a large concrete distributor in South Seattle.
Another local source is Seattle Pottery Supply
Now I know more than likely you do not live in Seattle or Washington State, so go
to your phone book or on-line and look up a similar place that's close by. If
you are really way out there Builders In Scale can ship about 16 pounds in a flat
rate box for $25 plus shipping. See part #118-B. You'll find it listed under
modeling supplies, scenery. See: BULK HYDROCAL