TrainTalk

Home

Subscribe to our free "TrainTalk" E-letter>

Modeling Asphalt by Joe Crea

November 13, 2006

I have been working on a gas station diorama for a client,
and I decided to pave the driving area in old broken
asphalt. Surprisingly, asphalt has been in common use as a
paving material since the turn of the last century. Its
first recorded use for this purpose was actually in the 7th
century. Asphalt is a naturally-occurring material, and it
was this natural asphalt that was used until manufactured
asphalt came into use about 1910.

For my diorama, I wanted the asphalt to look old, weathered
and cracked. So, I hopped in the old Jeep and went looking
for some old asphalt. The first thing I noticed was color.
We all think of asphalt as black (hence the term
’blacktop’), but in reality, even fresh asphalt is a dark
gray color. The older asphalt I was looking for is actually
a fairly light gray with some earthtone mixed in. I found
an old parking lot beside a small, defunct business, and
proceeded to take reference photos, being sure that I was
photographing areas that were in the sunlight. A couple of
pictures have been reproduced here. Notice the varying
shades of the material, the patterns of the cracks, and the
way that the ‘potholes’ appear. In some cases, asphalt has
been applied over other paving materials, such as
concrete/brick and this also affects the pattern of
cracking, as these subsurface materials move and
deteriorate.

Armed with these photos, I stopped at the local Hobby Lobby
and searched their craft paint section for colors that
would be close to the asphalt I’d seen. I use these craft
paints in virtually all of my model work, with the
exception of metal surfaces (which first have to be
primed). The paint is inexpensive, readily available,
non-toxic and between a half-dozen manufacturers, is
available in a myriad of colors. It is fairly thick when
applied straight from the bottle, but can be thinned with
water until it goes on as a wash if desired or to any
consistency in between. I purchased dark gray, medium gray
and light tan or sand colors.

I applied my paving directly on a piece of ¾” plywood,
using Durham’s Water Putty. This is another product I have
used for years. It is available from most hardware or
building supply stores, and comes as a powder which you mix
with water. Mix to the consistency of sour cream and
apply. I usually wait until my wife goes shopping, then
borrow one of her large rubber kitchen spatulas. This is
good for rough application. I spread it fairly thin, about
1/16” to 1/8”. It will begin to set quickly. If you are
doing a large area, do it in smaller sections, about 8”x
8”. As the material sets and becomes firm, I use a heavy
metal straightedge as a screed, drawing the edge of the
straightedge over the surface to smooth it. It’s not
necessary to be perfect, but try not to have any tooling
marks remaining.

After the water putty has set thoroughly, it will have a
light tan color. I used a blade screwdriver to dig into
the surface and create potholes. Be careful that they are
not all the same size or that you are not creating a
regular pattern in their placement. Be random! Again, try
to conceal all tooling marks.

Using the photographs as a guide, I began to mix the paint
color. I mixed enough paint to be able to apply two coats
to the entire paved area. I started with a medium gray that
was fairly close to the right shade then added some light
tan to lighten and warm the color. This paint is easy to
mix, and you should soon arrive at a color that looks like
the photograph. Paint a sample area then wait for it to
dry. If required, you can adjust the color then test again.
Apply the final color to the paved area, let it dry
completely then apply a second coat. I used the paint
straight from the bottle, without thinning.

Let the paint dry overnight, then mix a black wash, using
black craft paint and just enough water to make a rather
thick consistency for a wash. Paint this over the paved
area, not attempting to cover more that about a 6”x 6”
area. Immediately, wipe lightly and blot with an old damp
washcloth. Do not scrub. This should remove most of the
black wash, leaving some to accent the potholes and other
irregular indentations. Continue the process, working
fairly quickly, until the entire paved surface has been
completed.

After the paint has dried, look at the photographs again,
paying special attention to the cracks. Notice how the
cracks are usually a series of cracks, interconnected. Use
a fine point felt tip pen to draw some cracks on your
asphalt paving, trying to duplicate what you’ve seen in the
photos. You can also use the pen to accent darker areas
around the edges of potholes. I kept the major cracks
running mostly at right angles to each other, rationalizing
that this asphalt had been applied over old brick paving.
The results seem to look good. Be sure not to overdo it,
and also try to draw the cracks in kind of an ‘indefinite’
way, with the lines fading out and then reappearing again.
If you also vary the pressure on the pen, the thickness of
the line should change slightly. This is a good thing.
If you wish to replicate an asphalt surface that has been
maintained, use a dark gray paint and simply paint on
patches or repaired cracks.

That’s about it. It takes more time to write about it than
to do it. You can also glue on bits of ground foam or other
natural material to represent weeds in the cracks. I
haven’t reached that stage yet in my diorama, but plan to
do it in areas near the edge of the paving, where vehicular
traffic is minimal. See other modeling ideas in the DVDs
featuring Joe Crea on our website.