I have had a lot of questions about the construction of rockwork. I must confess that I have little experience with making mountains out of anything except foam and concrete. My G scale layout is outdoors and so concrete is the material of choice. Many of the techniques that I have used can be employed equally as well with resin. This thread will start out with a straightforward presentation of what I did., then we’ll see where it goes.

DESIGN
It is hard to describe how something was created from a construction technique point of view without discussing the whole design process, so bear with me as I discuss the process that I went through and take from it what you will.

It is critically important to know what you want and what it should look like. This may sound contrived, but when it comes to rocks, most people do not have any grasp of scale, texture, color, placement and special considerations such as plantings and water features contained in the rocks etc. I knew from the beginning that this was going to be a major project and deserved adequate design time. I hope that you are sitting down and don’t laugh too hard, but I first built a model of the model railroad. This model was 1”=1’-0” scale and was a working design model. My backyard is roughly 30’ x 60’ so my model of the yard was 30” x 60”. The model sat on the dining room table for about a year and was the tool by which I worked out topography. sight lines for photography, track layout and major plantings. My wife was always supportive of the project, but wanted to be sure that her lawn did not disappear. This model helped her to see that she would still have a usable yard, and there was peace in the home. I was drawing the track plan in a CAD program along with the structures. I would print out the track plan at 1” scale and cut out just the track portion and lay it on the model. Structures were printed out at the small scale and little mock-ups made of each one in Sculpey. The rockwork was done in non-drying modeling clay. This way I could push peaks around and make sure tunnels would work etc. Mermaid Falls and Big Thunder Mountain were built off of this rough model and I could see that they were not detailed enough to guide the construction process. For Castle Peak and the Adventureland area, much more detailed models were made from Sculpey at a larger scale. These two projects went much smoother. At this time, I cannot find any pictures of this working model. It was done around 1997 and was pre-digital photography. The model was discarded, but I kept a few of the pieces. I shot these photos today for this thread.

Here is a picture of the model of Adventureland with the trellis shade structure. As we were cutting foam, we actually took measurements of rock pieces from the model and cut the foam accordingly.




Here are photos of the Castle, Big Thunder Station, skull rock, Jabba's Palace, Dwarf's cottage and Belle’s Village (yet to be produced.)




MATERIALS
1) The concrete mix that I used was; 1 part Portland cement (sold as plastic cement), 10 parts plastering sand, water as required to produce a very thick pancake syrup consistency
2) Latex or rubber “skins” that have rock texture. There are many patterns to choose from. Builders supply stores that cater to pool contractors will carry these. I purchased them at the “Big Tran Show” from a vender that gave a clinic on creating rocks using a 2 part resin.
3) Chicken wire as used for stucco work
4) #3 or #4 rebar
5) Powder release agent sold with the “skins”
6) Styrofoam.

BASIC TECHNIQUE
The Basic technique is really quite simple.
1) Cut the foam roughly to the desired shape
2) Wrap “chicken wire” around the foam and secure with bailing wire.
3) Apply scratch coat of concrete at least ¾” thick to cover the wire and let harden completely.
4) Apply finish coat of about an inch thick or as thick as in needed and sculpt major shapes in the concrete with a mason’s trowel.
5) As the finish coat is hardening there comes a time when it will take the texture of the “skin” rubber mold. Too soon and the concrete will stick to the mold and not take the detail, too long and it will be too hard to take the detail. The skin should be dusted with the release agent prior to pushing it onto the semi-set concrete.
6) Wash the hardened concrete (next day) to remove the white powder release agent. Paint the wet mountain with exterior latex paint that has been thinned. This is more of an art than a science. If the paint is too thin then there will not be enough “hold power” in the paint to withstand the weather and it will appear to fade with each rain. If you do not thin it enough, then it will just sit on the surface and look like house paint on your mountain. You should have about 4 or 5 colors that you like and mix them in small pail with water and “splash” it on with a paint brush, working it into the cracks. Start with the darker colors and apply them to the cracks and crevices. Work the medium colors in random overlapping patterns and lastly apply highlights to the edges.

This photo shows all 3 stages of the concrete application; Wire only on the right , scratch coat in the middle and final coat with texture on the left.

TIPS FOR WORKING WITH CONCRETE

1) When you first mix the concrete in a wheelbarrow or bucket, leave it a little soupy and then let it set for about a half hour. After a few tries you will get the feel of when it is ready to apply. You should be able to use it like frosting a cake.
2) Portland cement does nasty things to your skin. Try to avoid contact. Inevitable you will do some molding with your fingers. Be sure to rinse it off when you are done.
3) You may want to apply the scatch coat with heavy rubber gloves. With this technique, you basically pick up a handful of concrete with the gloved hand and smear it on the wire wrapped foam. This is faster and more controllable than with the trowel.
4) Completely cover every surface of foam with concrete including the inside of tunnels. Little creatures get into the tunnels and they scratch at the foam making little insulated burrows: very messy and frustrating.
5) Protect your hands! The wires will give you plenty of picks and pricks and the prolonged contact with cement will pull the moisture out of your skin and cause it to crack.

I’ve gone on for quite a bit here. I would enjoy you questions and/or experiences.

Rubber "skins"
Foam with chicken wire
Finish coat awaiting "skin" texture

"Skin" texture being applied
Final product after paint

Here are few other photo of construction around July 2001

This is a great thread. I have been looking for something like this for garden railroads for a long time.

How long have you had your rock work? Did it come out the way you wanted to? How has the weather treated it?

Did you have to use a sealant of some kind to keep the moisture out? How is the maintenance? Do you have to check for cracks etc?

I read where one guy did not do his cement work right and some metal inside rusted and he had to tear it down and do it all over again.

I am new to all of this so I hope I am asking the right questions.

I'm glad to hear that this is helpful. You have lots of good questions. The oldest rockwork that I have is 10 years old and it has not seen any detrimental aging other than paint. There are 4 major rock projects, each one attempting to be completely different that the others thus enhancing the difference between the various "lands". I was the most satisfied with the second two because I had modeled them at a smaller scale and knew exactly how I wanted them to look. The first two were more "eye-balled" on the site based on a rough clay massing model. I found that sculpting the little one made it possible to know how to sculpt the larger one. Concerning moisture resistance, foam and concrete are both weather proof as there are. Protecting the steel inside could be a problem if your steel is perform a structural function such as holding up a cantilevered chunk of rock. Most rockwork is however held in place by gravity and so this isn't an issue. If you have at least 1 1/2 inches of concrete over your steel above grade and 3 inches below grade (building code minimums) then you should be OK. One issue that could introduce cracking and subsequently water intrusion is differential settlement. This occurs when the ground beneath settles unevenly under the weight of the finished structure. The remedy is to be sure that the area where the rocks are to rest has been thoroughly compacted. This will probably only be an issue if you are bringing in fill dirt to raise an area up.

Excellent forum on rock work. You are answering a lot of my questions with just the first part. 2 questions with water features.

1) did you have to put any special liner or tubing down for the wateralls. IE there is always splash factor with a waterfall, so how do you protect the landscaping around it or are there special runoff and catch drainage?

2) how do you protect the paint from the sun on items that are not really out door extended use, such as the vintage Star Wars toys on display and the Dinosaurs.

Water features are a subject all to themselves. I'll address how they affect rocks here. Concrete, as we know, is a porous material. Water does not hurt it, but concrete will not stop water from passing through it. In the waterways and pool areas, I coated the concrete with a special cementitious material made for that purpose. I do not recall the name of it, but it is sold in a powder form similar to cement. You mix it with water to the consistency of heavy syrup. You then paint in onto the areas to be waterproofed. Several coats would be best as water will always find a way through if you let it. This material takes paint the same as the concrete. As far as splash is concerned, it has been a problem for me around track work. At this small scale, you get these stray drops that don't seem like much, but it is enough to get the track wet This is not the end of the world as the trains will travel over wet track, but after 10 or 12 times around the engines start to "sputter" around on the wet track. I am now in the process of making some kind of splash guard out of nylon window screen material to hopefully remedy this problem. I will post pictures as it is developed. Back to waterways, I have found that adding small rocks into the waterway help to create "foam" or white water which really adds to the effect. In the photos below, the small rocks in the waterway at the base of the falls are natural sharp rocks, not concrete, that were glued in place with polyurethane construction adhesive and painted to match the concrete rocks.

There is not any special paint on the Star Wars toys or dinosaurs. Star wars is mostly shaded and does not receive full sun. When the dinosaurs start to look shabby, I bring them in for repainting (about every 3 years.)

I am going to try to make a smaller version of one of the BTMRR mountain/rocks. I only hope it comes out as half as good as the ones you did.

All the talent on this board inspires people like us to try new things and to make our railroads better. Thanks for all the info.