The Sinkhole: An Interesting New Hardscape – Part 1

By February 17, 2016 Blog 3 Comments

Header Sinkhole Prt 1
Whenever I consider creating a new enclosure, I think about how I might be able to make things more interesting by doing something differently. Whether it is the shape of the enclosure itself, the hardscape, the equipment/materials I am intending to use, or the inhabitants, I want to try and push the envelope just a little bit further with each build. This sense of adventure and discovery is what I believe helps us all improve our hobby, our own individual skills as hobbyists, and ultimately leads to amazing looking displays.


This vivarium build dubbed "The Sinkhole" was inspired by ZooMed’s new Skyscraper enclosure. The enclosure gets its name from its fantastic dimensions; Skyscraper has an 18” by 18” footprint and a height of 36” making for an incredible arboreal enclosure with unimpeded viewing provided by a single swing door. Skyscraper also utilizes all of the standard features of the original ZooMed Terrarium lineup.

When I saw the slender height of the enclosure, I immediately started formulating concepts on how to use utilize the dimensions in a new and exciting. With a small footprint and ample height, it seemed inevitable that there would be a lot of shading near the bottom of the enclosure from overlapping plants or hardscape structures. So rather than trying to fight it, I started thinking of various ways to incorporate the shadowing. After a few penciled sketches, I had stumbled upon what seemed to be a unique hardscape that would lend well to solving the issue of lighting, while increasing the usable space for the inhabitants. The concept started off with the simple idea of incorporating an underground component that is accessible through a hole in the center of the vivarium. I had not yet considered how I would create the platform that makes up the ‘ground’ of the hardscape, or what the underground section would actually look like. What I did know for certain is that I wanted the walls of the enclosure below ground to be completely filled in so that it looked dark and cave-like to contrast the lush green planted section above.

As the build progressed I put more consideration into what the ‘underground’ should look like. What would a hole in the ground look like in nature? Root structures, rocks, substrate, and maybe some leaf litter. The root structure underground lead me toward the idea of making a rotted stump above ground that would meld the the two sections seamlessly, while giving the viewer a chance to see a cross-section of the forest floor that is normally completely out of sight. This glimpse into a hidden world is what became the ‘it’ factor of the hardscape.

After some consideration, I decided to build the main platform that would later become the separation between ‘above’ and ‘below’ ground by creating a footprint out of a ½” Styrofoam sheet that would be held in place with silicone.  Before the platform was installed, the glass within the enclosure was prepared with a thin layer of black silicone to create a stronger bond between the foam and glass, as well as to create a clean look from the outside of the enclosure by hiding the foam from view. Expanding foam was then applied to the top and bottom of the Styrofoam, the entire rear panel, and the two side panels of the enclosure below the platform to create texture and bring the flat Styrofoam platform to life. The expanding foam was then carved to the desired shape for an overall natural feel.

The decaying tree stump is contructed of a few well placed cork tubes held in place by silicone and supported with expanding foam. Exposed joints were covered with Spyra, or Silicone and Peat. Once in place, the root structures were then put in place to match the stump, held firmly with more silicone and expanding foam.

Next, rock was placed in key positions around the enclosure. Three near the sinkhold at the top, one near the rear hole that allows some accent light to fall down the back wall of the underground section, then two underground on the side walls to add more texture. The remaining rocks were then place on the bottom pane of glass and held firmly with silicone.

To prevent the need for deep pots or substrate that would take up unnecessary space aboveground, I decided the best option was to utilize Folius Spyra grow fabric. This medium can be used to make every inch of the foam structure aboveground suitable for epiphytic plants and mosses while taking up virtually no space at all. The fabric is held firmly in place with Gorilla Glue, and in some spots, silicone. It is important to allow the Gorilla Glue time to set and become tacky before pushing the fabric in place so that the fabric does not unintentionally wick up the adhesive. This also means you want to try to be precise with your placement since removing the fabric once placed becomes much of a challenge. Personally, I found Spyra quite easy to work with.

The last step was to finish covering the expanding foam with silicone and peat moss, giving the underground section. The process was done in several stages, rotating the enclosure so that the surface I was currently working on was always face up. After 4 or 5 separate applications, the enclosure was then left to dry fully before being thoroughly cleaned of all dust, debris, excess silicone, and fingerprints.
Materials Used Equipment Used
Planting Plans

I intend to keep this enclosure focused on mosses and orchids, while incorporating some other small vines and flowering plants. I want to incorporate some of the vines around the mouth of the sinkhole so that they droop down into the lower section of the enclosure. I am also intending to create a natural drainage through the use of aquarium substrates that are designed for plants, so that some plants can be placed on the floor of the underground section where light bleeds through the sinkhole. I know this is somewhat vague, but I will be going into more depth with planting in part 2 of this blog series.

Frog Plans

As for frogs, I am hoping to get a good group of M. Laevigata for this enclosure, however, that won't be for quite some time as I want the enclosure to be well grown in prior to adding frogs. The availability of frogs at the time the enclosure is ready will ultimately dictate what frogs are chosen, but rest assured it will be an arboreal species of dart frog.


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