Our First Casting

Why Casting?

The title should really be “Puppy Proofing”. They can certainly inflict some serious damage! One of the main themes of the Barkyard Railroad is sharing the space with the “pups”, so everything must be built much stronger than normal in order to withstand a direct impact from a hundred pound German Shepherd at full gait.

Another consideration is the longevity of any structure outdoors, under constant bombardment from the elements. Most plastics quickly becomes brittle after baking in the sun. Even treated lumber quickly rots in this environment.

Along those lines, I found an interesting approach to outdoor structures online, in the form of cast concrete. More accurately, cast concrete patch. I will include some links to this inspiration, as well as my source of pattern sheets for casting.

Lay out
Test fitting

A brief introduction to the technique is warranted. Using extruded foam insulation as a sort of “backer board” for the pattern sheet(s), inserts for openings like doors and windows are also fashioned from the rigid foam, then “T” pinned in position over the pattern.

Pinning Together
Pinning it all together

There are many different types of pattern sheets available. Brick, concrete block, lap siding, and corrugated roofing are but a few examples of the many types of pattern sheets available. I started by acquiring an assortment of different pattern sheets from various sources.

Although a specific pattern sheet may be found online, its availability is certainly hit or miss, especially when searching for G scale items. But that seems to be a common theme for anything G scale. The next obstacle is finding suitably sized pattern sheets.

Patching a mold together across multiple pattern sheets is problematic at best, creating a “parting line” effect in the casting. To avoid this, I chose to start with a 15″ x 15″ square brick pattern sheet. The resulting casting will cover one side of a concrete block, roughly 8″ x 8″ x 16″ in size.

Why a concrete block? Because it is immediately more puppy proof than just a thin casting. This technique also calls for an embedded wire mesh frame to provide strength for the brittle casting. The issue becomes how to manage parts that require multiple castings to complete due to their shape or size, a pitched roof casting for example.

For a pitched roof, only one face or the other can be cast at once since the mold must be level. But the mesh must be formed at an angle across the roof peak, with the other half protruding from one side’s casting until it cures. The other side can then be cast, but this presents the unique challenge of fixturing, somehow propping the previous casting in place while the new one hardens.

There is no easy way to cast a four sided building using a single piece of wire mesh. The challenge of keeping the first wall standing and squarely aligned while casting the second wall is difficult enough, but consider trying to hold three walls in place as the fourth is cast.

That last wall would also require somehow connecting the ends of the mesh together, either from the start, or allowing enough to extend from the first wall to fasten to the other end of that last wall. Extending the thought of somehow connecting the ends of the mesh together, just folding up the edges to leave about half an inch of the mesh exposed should do the trick.

Mesh Insert
Wire Mesh Insert

The Pour

With everything pinned together and the mesh cut to size and in place, it’s time to mix up the concrete patch and pour. Having never done this before, the consistency of the mix is in question. “Pancake batter” can range from runny to thick enough to require a ladle, so opting for somewhere in between seems the best bet. A dedicated mixer is recommended, so opting to hand mix presents its own challenges.

While the mix slacks, everything is sprayed with the mold release agent, WD40 in this case. Although the “batter” seems to be thoroughly mixed, the patch wants to settle out to the bottom of the mixing bucket. The closer to the bottom of the mixing bucket, the thicker the consistency becomes. Working around the inserts is difficult with the thicker mixture and even a small trowel isn’t helping much.

The Pour
The Pour

Once poured, the mix needs to be vibrated into place to remove any trapped air bubbles, like real concrete. A handheld jigsaw was recommended, minus the blade of course, but a palm sander will do in a pinch. The idea is to vibrate all around the mold, and for long enough to allow the bubbles to float to the surface and burst. Now all that remains it to let it set up for 24 hours then remove it from the mold.

The first attempt at removing the bubbles proved to be an exercise in futility. While the plywood bench all around the insulation base was vibrated, many bubbles remained trapped. And while all those minute voids in the casting can be filled, it’s more trouble than it’s worth. The take away is next time, the mix must be thinner, and the mold itself will be vibrated directly.

Once the casting had cured a few more days. it was painted. And a nice brick red it is. The air bubbles still show, but aren’t discernable from a distance. The “Five Foot Rule” is in full effect on this first one, a learning experience for sure.

Another lesson learned is to wait until the casting is no longer “green”, that is, fully cured before fiddling with it… let alone flexing it or the exposed mesh along the edges. The missing edges where the casting fell apart because of that flexing are much more noticeable than those tiny voids in the brick face from the bubbles.

The Final Product

After painting, the casting was secured to the concrete block using thin set mortar. The missing edges were filled in as well, to look like a “repair” of sorts to crumbling bricks along the edge of the building. Now all it needs are windows for the upper floors and display case windows and an entrance for the ground floor.

Our First Building
Our First Building

All in all, our first building casting for the downtown marketplace is a success. Is it perfect? By no means, but it certainly looks more like a three story building than a bare concrete block does! Some “window dressing” and other details will make it an even more believable model.

Lighting is another consideration, and by extension, how to power the lighting. But all that will wait for another installment. We started working on the downtown marketplace back in June of 2019, so there is plenty more to come. Stay tuned!

If you have any questions, or you would like to see more detail, leave us a comment.