How to Make a Fake (but Realistic) Rock Cave!

I have a hot tub under my porch and was sick getting dripped on when it rained, so I wanted to make a fake rock cave to both shelter it from the rain and to make something that looked better than sitting under a porch! I was originally looking to use shot-crete, but being concrete it would be permanent and very expensive to remove if needed. I loved the look though because it was so natural! I was also going to use styrofoam because people used it for indoor applications and it looked great when carved.. but mice love chewing into it so that was a no-go.

I ended up figuring on a kind of paper mache hybrid. I hadn't seen anything like it before so wanted to share it on here so people can save time and avoid the mistakes I made!

Overall I probably put in over 100 hours, and it cost me about $800 in materials, a lot of that was due to change-of-mind or mistakes along the way! I used 3 jugs of resin which is the most expensive part. I used 2 rolls of screen and 2-3 rolls of landscape fabric. I hope you like it!

I used a pond liner, some scrap wood, metal screen, screws with large washers, landscape fabric, construction glue, automotive fiberglass resin and paint. Other tools were wire cutters, needle nose pliers a drill, respirator (for fiberglass).

The first thing I did was to create a rain-barrier shell by taking up a pond liner. I also put up some wood in different angles inside of the 'shell' that I would be able to screw into later without having to put holes in the pond liner shell.

Next, I started affixing the wire mesh to the wood, making sure to pinch the prongs of one piece into the one next to it to create a single solid mesh. I used needle nose pliers and wire cutters for this. I made sure to take my time when working with this to make sure the shape was good and not just smooth mesh.. I pulled and bent it into shape and secured it with long screws. I even created a few extra shapes out of wire mesh that I added in, like a shelf for drinks.

Once the wire mesh shell was in place and the shape was what I wanted, I started cutting up the polypropylene Landscape fabric and using the construction glue to stick it on the wire mesh, essentially like paper mache for adults!

I cut up the pieces about 12" square.. and some smaller ones as well that I found worked well to cover the corners of the bigger pieces because the sharp edges were kind of a pain and tended to fold out from the mesh. It's best if you can make sure all the edges are glued in nicely. It will save you A LOT of time later (you can already see my mistake in the last 2 photos)! Another tip is when you put the glue on the back of the landscape fabric, don't get in the habit of doing a design like lines because it will show through and become the texture of the rock! I think the best thing to do is put dabs or dots on the fabric, that will look consistent and like rock. You can always go over it later though if you decide you don't like the look.

At this stage I used automotive fiberglass resin, which is a 2 part mix. A small hardener and the resin. I used a painting tray and roller and once mixed I had 12 minutes to work at around 20 degrees celcius. It hardens really fast! Also you'll need a good respirator. I poured the resin in the tray, squirted in the hardener, mixed with a chopstick and then started rolling the walls immediately. I did about 1/3 can of resin each time I worked because anymore than that and you'll run out of time! I pointed out that the landscape fabric I used was polypropylene, Which most is, but it's also important because it binds with the resin! Usually you would use fiberglass cloth but its more expensive and because I am not making a car, it doesn't need to be that durable. This is a cheap option and is still sturdy.

A good tip is to try to work when the temp is more like 15 degrees or less. Then you can roll for as long as you want and it won't really harden until you blow some hot air in there with a heater. be careful not to use any flames though because the resin is highly flammable at this time.

At this point I put on a bit of primer but found that some of the edges of the fabric that were not glued down all the way were creating little gaps and I needed to fix this before painting. You can see I had quite a lot to fill, and this is why I said earlier to take your time and glue those edges down!

So to fix this I used automotive repair putty. It is red and comes in a toothpaste tube and can be rubbed into the cracks with gloves.

Now that that is done, you can prime with a really thick shag roller. I used a primer that I tinted with Ranchwood for a more natural base and then actually went over it with a grey because I didn't like that color!

I found that the best natural look for me was to use a grey base, then roll on some of that creme ranchwood on the protruding points to make a bit of an accent color. it doesn't look good at that point, but I then got a grey and bronze spraypaint (both Matte) in each hand and blended that creme color in by spraying the lows and high points. It ended up looking pretty well how I wanted it! I also used a clearcoat spray at the end to seal it in a bit.

While that was all happening I also made a rock that could sit next to the steps and cover the side of the tub. This is photos of that rock from start to end which I tended to use to test spray paint colors and things like that because it was smaller and I could take it in the sun to see it better. So here is a condensed version of the entire process!

Enjoy!