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--- Kevin Guthrie – NtheBasement ---
…............---
Rock Formation Techniques ( Terraforming ) ---
=========================================
Intro:
I
majored in Geology for two years before switching majors a long time
ago. I can say from my studies then that I feel NtheBasement who
posts on nscale.net ( HERE
), my go-to N Scale Forum, has some of the best looking/most
authentic rock formations I've seen in model railroading. He posted a
tutorial there on how he does rock work, ballasting and other
woodland/trackside scenery. You can find that tutorial ( HERE
). The following is more or less a reproduction of the tutorial minus
a lot of other comments that went on in the thread there. I think it
is an exceptional useful tutorial in a number of ways. I'll turn it
over to him now.
NOTE:
All the pictures in the tutorial are NtheBasement's along with all
the text.
------------------------------------------------------------------------------------------------------
I've
used Great Stuff canned foam on my layout to build terrain, then
covered it with Sculptamold and Durabond plaster.
Advantages
of spray foam over foam sheets are
1)
The stuff is Gorilla Glue with bubbles. It strengthens your benchwork
as it binds to it.
2) You don't need
a flat surface to put it on. I cut up cardboard, staple it under the
wood roadbed and on top of any plywood bench top at any angle I want,
and apply the foam so it glues the cardboard to the wood. The result
is surprisingly stiff, like foam core products.
3)
You can add more any time you want and carve away after it cures.
4)
It's not pink.
Disadvantages:
1)
The stuff is Gorilla Glue with bubbles. Don't get it on your hands or
any valuable part of the layout, like track work. Don't let it drip
on anything.
2) You can't create a
flat surface with it, though you can carve a flat surface into it.
3)
You don't have much control over the expansion.
4)
It looks like snot.
This is one
of the last "protomolecule" areas of the layout. Over the
years I've done sections, and when there is leftover foam in the can
I add it to the next sections. 20 year old foam is dark orange on the
surface (UV exposure I think). The first layer was added to cardboard
stapled under the benchwork. I always add in layers. Add too big a
blob and huge hollows form on the blob's interior.
I
use a serrated steak knife to carve the foam. 1st carving step is
make sure there will be enough clearance next to the tracks to add
Sculptamold or Durabond rockwork.
One
way to make a layout look realistic is to have consistent slope
angles on all the man-made fills. I use a drafting angle and point
the knife parallel to it when starting the cuts.
Sculptamold
and plaster won't stick to the slick cured surface of the foam.
Cutting into it exposes the underlying open cells. Then when I start
applying Sculptamold or Durabond I smear it into the foam and hear
bubbles pop. That creates a good mechanical bond using the open cells
as keyways.
One
advantage of using Great Stuff is you can always add to your terrain
later. There are two issues here. One is there is no reason for that
curve to be where it is on that mid-level track. I need a rock
outcropping to justify it. The other is the changing slope between
mid and lower level tracks on the left. There needs to be a retaining
wall or a cut into solid rock.
After
marking the areas that need building up, I added about half a can of
foam. This will expand over the next hour or so. Great Stuff's
nozzle-end valve helps, but once its used the shelf life of the rest
of the foam in the can is limited.
In
an hour the foam has expanded some. I misted it with water to speed
curing. That also limits the expansion somewhat. Wet foam sticks to
everything but once it skins over it won't stick to what it touches
up to as it expands.
It'll
take a day or so to cure, at which point I can carve some more.
---------------------------------------------------------------------------------------------------------
Day
2. I carved the new foam, which makes a static charged mess. Now the
curve in the track gets around a rock outcrop. I still have half a
can of foam but no place to put it. The new foam is much more
flexible than the old stuff, and so whitey bright!
Durabond
time.
I don't use untinted plaster or
Sculptamold because its white, which means any little nick in the
rock shows up like a beacon. I've used Tempera, inks, and dyes to
tint it but concrete tint is by far the cheapest option. There are
not a lot of color choices but they are all sort of a rock color. One
bottle colors a whole bag of cement so a little goes a long way.
!
I
added a dab of Buff cement color and two dabs of Charcoal to a
Durabond mix of about a cup of water and cup and a half of Durabond.
Then I added some yellow food color.ncrete tint is by far the
cheapest option. There are not a lot of color choices but they are
all sort of a rock color. One bottle colors a whole bag of cement so
a little goes a long way.
Whoa,
not the color I was looking for. It looks green! I know it will
lighten up when it dries but this was not what I had in mind. I'm
thinking this will be a layer of shale. Regarding the mix
consistency, you want "whipped cream tips" to hold up. A
vertical slope should slump a little but not a lot. And let the mix
slake for a few minutes before applying to avoid lumps.
I
use a putty knife to apply the plaster to the foam. My layers run at
a slant, and I try to do a whole layer in one batch so that the color
and texture will match. I smear some plaster on, then smoosh it into
the foam with my finger to get adherence. Then I add a thick layer,
maybe a quarter to half and inch, depending on how deep I want to
carve, with the putty knife held vertically. I leave some big divots
that will will be carved out as joint lines later, trying to line
them up across layers. Joint lines are weak fracture planes in the
rock. For sedimentary though the layers are the key.
Durabond
45 is supposed to give you 45 minutes of working time but in my cool
basement it takes twice that long to start to set. Next time I'm
getting Durabond 20. Once it sets up enough to not stick to a tool I
start working it. My favorite tool is a screwdriver but for shale I'm
mostly going with the putty knife. You can see on the left how it
looks working when the mix is still a bit mushy. As it hardens you
can get sharper and sharper detail, but it starts to crumble if you
abuse it. An eroded face would not have the sharp features that a
dynamited cut would have. I try to get continuous layers into it with
the knife and add vertical joints by pushing in with the blade. I cut
the tops flat to mimic the tops of layers.
I
don't worry about the bottoms of vertical faces or the more
horizontal slopes as they will be covered with debris, soil and
vegetation. Speaking of debris, save the carved up scraps. And rather
than washing out your mixing bowl before the stuff sets up, let it
harden and then break it up to create more talus and debris.
Also
you can see the thin stuff is drying to a color that comes closer to
the foam's snot yellow.
I'll add more layers with Durabond over the
next few days and then get into limestone layers with Sculptamold.
------------------------------------------------------------------------------------------------------------------
Took
a couple of days to get back to this. Saturday was actually nice,
which around here means the sun is out (a rarity in SE Michigan in
the winter) and it got up into the mid 30s, so I put 20 miles on the
kayak. And yesterday, well, Bell's Hopslam arrived and my COVID beer
drinking buddy (my daughter) helped me taste this year's batch.
Tonight I've got an NMRA meeting which, ironically, got rescheduled
to Monday nights from Saturday afternoons because so many of the
members watch college football. It starts an hour before the
championship game...
The previous
layer dried to a light yellow, a problem easily addressed with ink
washes. I couldn't find Durabond and bought an 18 lb sack of Proform
Quickset Lite 20. It seems very similar to the Durabond. I used a dab
each of terra cotta, brown, and black concrete color and it somehow
ended up pinkish. Stay tuned for the dry color, I'm guessing a very
light pink.
The
Quickset 20 took maybe 45 minutes to start setting. I got a bit
nervous about the "20" because it was setting up so fast
when I started carving but it turned out just fine. I used mostly the
putty knife, cutting along the bedding plane and adding vertical
joints that crossed the beds.
As
the plaster hardens it gets more crumbly and you can get finer
details. I usually save the man-made cuts for this stage. Lots of
small light raps with the putty knife, across but mostly along the
bedding plane. When things are dry I'll brush off the crumbs.
Brushing now would make the rock look more water-worn.
I'll
probably add another layer today before the game. Er, meeting.
-------------------------------------------------------------------------------------------------------------------
For
variety the next stratum is Sculptamold. Although initial application
is similar to plaster, its has very different characteristics. It
sets like plaster but also contains fiber and a glue, probably PVA
powder. When it starts to set it has the consistency of clay but you
can't carve it because the fibers tear out and you get fur instead of
rocks. When the glue finally dries it is very hard and strong, not
brittle like plaster, due to the fiber reinforcement. Another huge
difference (and detriment) is you can't really apply washes because
they don't soak in. I think the PVA migrates to the surface during
drying and creates a skin that makes washes bead up. So I color it
with a lot more color than the plaster. I'm hoping this black will
dry to a medium gray.
Also I like it
lumpy so I don't let it slake before applying.
I
apply same as plaster, smearing some into the foam and then applying
a quarter inch or so layer. This mix is actually too wet - it took a
couple of hours to set.
Sculptamold
isn't as cheap as plaster. I bought a 50 lb box, probably enough for
my whole layout, from a Dick Blick store an hour away for well under
$2/pound. This is way less than the little craft store bags.
Instead
of carving Sculptamold, after it sets you shape it by pushing it in
and around. In this case I mostly use the end of the putty knife to
make the layers. Like plaster, as it continues to set you get sharper
and sharper edges. But they are never as sharp as carved plaster.
With
Sculptamold the fineness of the detail is liimited only by your
patience. If you keep going with plaster as it sets up harder, you
start to crumble it. Sculptamold always has that weathered look to it
due to the rounded edges.
This
mountain is also Sculptamold over foam. As it set up I emphasized the
dents and wrinkles by pushing them in with a screwdriver blade to get
the glaciated granite effect. Dramatic glancing light angles are a
plus for any rock work.
Snowing
out so I got 3 layers done.
Start
of a Sculptamold strata. This brown color is Charcoal and Buff.
The
two layers of Sculptamold are supposed to model dolomite. At the top
is a layer of Quickset. A lot of it will be obscured by
vegetation.
Once a layer is
completely dry I can clean off the "crumbs" with a wire
brush. Brushing hard along the grain also add grooves that mimic
shale.
The
track now looks like it has a reason to be routed around that bend.
Before
going further I checked to make sure the rock work didn't impinge. My
NMRA gauge scraped on the promontory and sure enough, my Concor hi
cube rubbed the wall on the inside of the curve. I scraped and shoved
the perp into the foam with a small screwedriver. The gauge still
hits it but I know from past experience that the hi cube test is
sufficient.
My
usual batch size is a pint of water. After adding rock face any
leftovers go to cover the flatter areas of foam that will be covered
with soil and vegetation, or get smeared on to crumpled tin foil for
later use as talus. After saving most of the loose chips I vacuumed,
Did some finer carving on the remaining foam and went thru two and a
half batches of Sculptamold to cover the remaining foam. I use dark
colors to that any bits won't glare thru the upcoming soil layer.
I
cleaned up the sloppy edges between the layers somewhat. The upper
layers are still not completely dry so I've got a fan on.
Next
steps are finishing up with the wire brush once the top layers dry,
gluing down loose rock, talus and soil, then washes.
----------------------------------------------------------------------------------------------------------------
Week
two continues with talus and washes.
I've
saved chips and tinfoil sheets from each layer and vacuumed the
layout. You don't want rocks to appear above the layer they came
from, so a clean collection from the top layer is important.
Rock
from the joint compound has nice sharp edges when you break it. I
separate large and small and remove large pieces that look like gobs
instead of broken rock.
The
dark talus on the lower level is Sculptamold. Edges are rounded and
sometimes even furry, a far cry from the sharp-edged joint compound
talus.
I
start from the top, paint glue on the ledges on and below each layer,
add big pieces and then the smaller ones. It's important not to get
glue on exposed rock as glue keeps washes from soaking in. I'll douse
everything later with water/glue/iso mix. Lower ledges get mostly
rock from the stratum immediately above, but also a mix from anything
higher up.
I'm not sure adding the
talus at this step was a good idea. I did it to color match but I
probably should have stained the talus separately and added them
after, because knocked off talus revealed unstained spots.
Next
is a mist with dilute ink wash to mute the different colors and
visually tie the layers together. I went too dark here and although I
tried to spray from all kinds of angles I ended up with some
"negative shadows". A good wash is an eyedropper full of
ink to an ounce or two of 50/50 water alcohol.
Monochrome
rocks don't look real. I painted various layers with different color
washes. The effect is subtle but it really makes a difference. I use
Bombay sepia, brown, and yellow.
I
use an eyedropper to add wash to emphasize the joints and cracks.
It's best to use a light wash and add it several times. Washes won't
soak in as well to already-wet plaster so I make sure everything is
dry before each application.
Next
up: dirt.
…..................................................................................................................................
I
was wondering if I would have to toss the rest of that Great Stuff
until I realized I forgot a section.
Its going to be a hard
reach to do the strip between the Atlas stone arch bridge and the
wall. A 1x4 fit just fine so it became the "benchwork" for
a lift out that I can terraform and forest off-layout. I papered and
masked it off and used the rest of the can of Great Stuff on it.
Once
the foam set, about 12 hours with help from misting, I made cuts in
the foam at ground level between the arches to mark the profile. Then
I cut the ends at a bevel and lifted it out. I'll have to carve it
and add Sculptamold in another room to catch it up to where the rest
of the layout is at.
Great,
now I get to clean up in another room...
…......................................................................................................................................................................
Next
step is to add "ground" over the rock ledges and the flat
areas that are covered with Sculptamold and joint compound. The four
piles are are from my garage: sifted 40-lb bag topsoil, sifted dirt
that that has been drying out in a 5 gallon pail, something called
paver sand, and cheapo kitty litter (the non-stinky kind) for sopping
up oil drips.
About
the paver sand, this stuff is crushed limestone. I recently tried to
buy some more and the same brand was sand. I stay away from sand
because the quartz granules don't scale and it wrecked my drill bit
when I planted trees.
I
used kitty litter then sifted dirt to fill in all the potholes and
level the ground. First I brush 50/50 glue/water on the areas to be
covered, using both a cheap trim brush and a small Testors brush.
This makes sure the ground stays attached to the substrate, and it
helps the kitty litter to not bounce all the way down hill. Then I
mist small areas with isopropyl and add 33/33/33 glue/water/iso mix
with a child's medicine dropper. These medicine droppers hold way
more than the standard ones. I flood it. You especially want the
areas near the track glued well to avoid hand damage during
operations.
This
is the first time I've used kitty litter and I'm impressed. Its clay
so I was sort of expecting it to mush out, but it makes good talus.
I
started from the back and the top and worked my way forward and down.
The stuff on the cliff sides settles just like the prototype.
I
added rockwork and fill to the adjacent area years ago and never
finished it so now is the time. The fill is all sifted Sculptamold
pieces.
At
this point I'm maybe halfway done with the ground. The room smells
like isopropyl and the fan is always running. I might have to buy
another gallon of Elmers, but fortunately I have a couple of quarts
of pre-COVID isopropyl stashed away.
…....................................................................................................................................................................
Took
several sessions and a quart each of isopropyl and Elmers to finish
the ground. I stuck with sifted dirt and kitty litter.
.
I
still have to break out the insert behind the arch bridge (again) and
add cover to the areas under the arches. Sifted crushed limestone
paver sand should work.
Next step
though is ballasting and I really don't like ballasting. Still need
some buildings for the yard so that will still be plywood. I will
probably add a track off the turntable with a diesel refuel station
but not sure what else to put there.
Next
up is ballasting.......
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