HOW TO WORK WITH HYDROCAL
AND OTHER MODELING TIPS -
GENERAL TIPS and TRICKS
Hydrocal is great stuff. Not only can we cast all this great
stuff but I actually build most of my patterns with it, either using cast
stocks like my own brick, stone or concrete, or hand scribing and carving
all new originals in fresh Hydrocal.
So what's the trick? Hydrocal is supposed to be strong rock hard stuff!
Well, yeah, it is. But when it is freshly poured it is in a semi-hard state
that is idea for scribing and cutting. And when cured, it can be softened
with just a few drops of tap water and easily carved with repeated strokes
of your hobby knife.
PURE WHITE HYDROCAL
I use White Hydrocal from US Gypsum for my patterns and casting. Plain Grey
Hydrocal would be the same. Avoid Woodland Scenics Lightweight Hydrocal! That's
fine for scenery but the lightweight additive screws it up for what we are
doing. Ultracal, Plaster of Paris and the dozens of other plasters and gypsum
cements all have their advantages and disadvantages. Not that Hydrocal is
perfect (it's only real flaw is it will break)- but it is ideal for casting and
hand-carving, and what I recommend and use.
With that overview, let's look at the basics.
Like I said above, the trick is simple, you can soften the Hydrocal with
a few drops of tap water, applied locally. Then use repeated strokes with
your hobby knife (No.11 blade) to cut out an opening or a new edge.
To keep your cut straight cut along a metal straight-edge such as a
scale ruler or small machinist's square.
Use repeated strokes. The first should be held true, perpendicular to the
surface. Angle the next stroke, so as to widen to cut. Repeat back and forth
between true and angled cuts. Add more drops of water as needed.
You can use freehand strokes to remove excess plaster from the middle of
an opening. When cutting out an opening for a new window or door I will
leave a retaining lip along the edge at a certain depth. You might notice
these as hand-carved in my earlier work or as (wooden or plastic) inserts
in my later work. No matter the material used in the pattern it will become
cast Hydrocal after the molding and casting process.
You might wonder why I leave in those dumb sections behind the window
openings that you have to cut out. There are two reasons for this. One, if
I brought the cuts all the way through then in the casting process I like
to scrape the backs of my production castings flat and this would cause
some interference with that. Secondly, a little extra plaster strengthens
the castings during wrapping and shipment to you.
But back to cutting. If you are cutting the edge of castings in a straight
line you don't really have to cut all the way through. You can score it, sort
of like styrene, and snap it. When I do this I like to back score it as well
to keep the break just where I want it.
On thicker pieces or when I am in a hurry I'll use my band saw to cut through
the piece quickly. Before I had the band saw I even resorted to using my table
saw however I do not recommend this! Cutting Hydrocal is definitely tough on
your saw blades and it kicks up a lot of white dust! And I mean a lot. I bought
a small 9" Delta band saw to use exclusively for my Hydrocal cutting that I've
attached my shop-vac to.
I also use flat-faced router bits in my drill press to mill the castings
down to precise thicknesses. They can be as thick or as thin as a dime, as
DRESSING YOUR CUTS
After rough cutting I true up the edge with a large flat Bastard file. I
have nailed my file down onto the edge of my workbench with brads so both my
hands are free to hold the work. I employ blocks of wood to hold the work
square or to precise angles that the blocks are cut to. Holding the work to
the blocks as I draw them across the file transfers the angle precisely.
Filing is best done dry. Wet and especially fresh Hydrocal will attach and
almost instantly rust your good iron tools. Be sure to keep them clean. They
load up fast and a small wire brush is a necessity.
One of the really outstanding properties of Hydrocal modeling is it is
three-dimensional. Once we cut an edge we can take a little extra time to
scribe the brick or stone mortar lines around the corner. This is really
difficult to do in plastic or embossed brick but not so tough here. And we
will be rewarded with an outstanding model.
It is really quite simple. After cutting and truing, we soften it up with
a few more drops of water and scribe away. For window and door openings I
just use free-hand strokes. For wall edges it is a little more involved. You
need more control so I will use little squares to guide my work.
My scribing tool is actually two pin vises, one small one mounted in a
larger one, that are very comfortable to hold for long hours. The point is
just a steel needlepoint I picked up somewhere. It's about 3/32" round. If
you are doing just a little work you might be able to get away with using your
hobby knife or maybe a cheap scribing tool. Just take your time and be
determined to do a good job. Remember though, you cannot erase!
Hydrocal is really most like wood. It is a porous material so just about
anything that works well with wood will work well with Hydrocal. I'll go
ahead and repeat what I said in the fixing broken castings clinic.
First off, check to see that the castings will fit together properly. If
we start off with a good square joint we will end up with one. If we start
with a poor one that's not square, rounded because we sanded it, or didn't
bother to check we'll only end up frustrated with a poor joint. I've done
my part as best I can. I even dress many of my castings before they are
packed to assure you of the best results. It is up to you to be sure it all
Work on a firm flat surface. My workbench is 3/4" sanded plywood. If it
were less it might sage or bend and transfer that onto my work. We don't
want that. I've seen some good modeler's wonder why a casting broke when
they trued to cut them on a card table! Duh.
Okay, enough said, let's give it a try.
For gluing Hydrocal I recommend and always use
Elmer's Carpenter's Wood Glue, the yellow stuff.
It gives a good quick bond. We only need a little. The trick is to have a
good tight joint. Nice and square where two walls come together. A square
wooden block, a small machinist's square and other such tools will come in
Apply a small bead of glue along one side of the joint. Then quickly push
the two sides together. Apply firm pressure. Be sure they are square and aligned
just how you want them. In just a moment the glue will begin to firm up as the
moisture is absorbed into the plaster. For that reason we must work quickly.
You don't get a second chance.
Use good fresh glue. If it is contaminated with a speck of dried glue or
anything else you will not get a good clean join.
If you have used the correct amount of glue but a few tiny bubbles might
ooze out. We can pick them off in a moment. Be careful, we don't want to rub
excess glue into the raw plaster as it will tend to seal it. This is of little
consequences if we are going to seal the castings later on anyway however if
we plan to stain them it could be a major problem. Note that usually I am
assembling my models after I have painted them.
After holding the pieces together initially we can now relax and leave them
alone while the glue sets. Really, it only takes about fifteen minutes before
we are able to gently handle the piece again. In a few hours the you will have a
Sometimes I do not completely assemble my models with glue, that is, glue
them all together. Perhaps I'll glue certain assemblies or sections but then
just friction fit or pin them together. This allows for disassembly for storage
and possible shipment (I haul a lot of them around to train shows) or maybe
for the installation of interior details and/or lighting.
To pin a model together I'll use small pins cut for .020" or 1/32"
brass rod. To properly align the pins with the respective holes I first
drill and insert a short marker pin, that is on which is cut very near the
surface so the pieces can be held together and when aligned just right
wiggled together so the marker pin scratches in the proper location on
which to drill the other hole. Since these are very small drills I do it
by hand with a pin vise which does take a lot of time. You drill a little
and have to clean the drill groves- but you do get a good fit. Replace the
marker pin with a longer one and mate the pieces together. Sometimes it
helps to bend the wires just a bit to spring them for a better grip.
Each model is different. Obviously, the smaller models don't need pins
but they work well on the roundhouse and engine house. I use pins to hold
the walls upright too. A couple for each wall. I'll use pins and small
brass clips to hold them together and attach other elements such as trusses
Below is a link to the next clinic or you can jump back to the list.