# Has anyone drilled holes in Sandstone to make caves?



## audio (Jul 1, 2010)

I have started to try and make caves in my tank and was wondering if I was doing this right and if it is a good idea. Has anyone else done this? I know I could have just bought rocks with holes, but my whole tank is sandstone that I bought from the landscape shop for $5 and Im a teacher so money is tight.

My first rock.










post drilling.










In the tank...still a little murky...just put it in.










And another.










Anyone have any advice, comments, insults?


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## Mcdaphnia (Dec 16, 2003)

I have some sandstone that looks nice and flat like yours, but it's semi-metamorphic and has lots of iron in it. I have drilled it with quarter inch holes to use as bases for driftwood. Every once in a while I would hit a high iron pocket that instantly dulls a masonry bit. I bought a rock bit that has not needed sharpening so far. Use a cold chisel or star drill to naturalise the edges of the drilled holes. Even and old blade screwdriver will do.

Next time you look for rock, check out the possibilities. Tufa rock is the remnant resulting from an ancient coral reef that once dwarfed the Great Barrier Reef of today, running diagonally across the interior of North America that was once an inland tropical sea. Pieces of tufa, one of the lightest rocks, are much easier to drill than sandstone and most pieces come with great built in features. In some areas farmers have to pull this each time they plow out of their fields and make huge piles here and there on their farm. Unlike most rocks it "floats" up through the soil and collects at the surface. It is great at buffering Rift Lake cichlid, Central American cichlid, and even marine tanks.

Both tufa and sandstone are easier shaped and drilled with sand blasting than with drill bits and cold chisels.

I had a neat piece of tufa that I had hollowed out from the bottom then cut caves through front and back, but I offset them so that you could not see through the rock. It was sitting out in my yard in a rock garden area which is a great way to switch out rocks and get rid of algae but this time, my wife's neice visited this past weekend and when I looked at it, it had been smashed into a dozen chunks and thrown into the yard. At least I still have the others I made at the same time.


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## audio (Jul 1, 2010)

I will have to get a new drill bit, I killed the one I was using after just that one rock. The trick so far has been trying to make the hole/cave look realistic, while still being functional and looking good in my tank. The same basic problem I have had setting the whole tank. I don't have a chisel so I will have to grab one of those as well. Thanks for the help. Sorry to hear about the smashed rock. It is only a rock but I know how long it took me to get my first one just right. I have a kid and a dog...it might be safer to keep mine in my tank.


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## newfisher (Dec 20, 2008)

If the sandstone is quartz arenite (looks to be from the photo), then the matrix will have a hardness (mohs scale) of 7, whereas a carbon steel or high speed steel drill bit will at best have a hardness of ~6.5. Unless the arenite is loosely cemented, the rock will win the battle over standard drill bits every time. So if you're using a drill and bit, buy a carbide tipped bit. Depending on grade, tungsten carbide has a hardness of 8.5 to ~9, which should make it last several caves. Wrap the rock in a rag or use wood blocks to protect it, clamp it in a sturdy vice, put on safety glasses, then go at it with both hands hanging onto an electric drill. Drill several holes then chip out stuff between holes with a hammer and coal chisel. Have fun.


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## Mcdaphnia (Dec 16, 2003)

newfisher said:


> If the sandstone is quartz arenite (looks to be from the photo), then the matrix will have a hardness (mohs scale) of 7, whereas a carbon steel or high speed steel drill bit will at best have a hardness of ~6.5. Unless the arenite is loosely cemented, the rock will win the battle over standard drill bits every time. So if you're using a drill and bit, buy a carbide tipped bit. Depending on grade, tungsten carbide has a hardness of 8.5 to ~9, which should make it last several caves. Wrap the rock in a rag or use wood blocks to protect it, clamp it in a sturdy vice, put on safety glasses, then go at it with both hands hanging onto an electric drill. Drill several holes then chip out stuff between holes with a hammer and coal chisel. Have fun.


It is certainly true that you can't use drill bits for drilling in wood to drill holes in rock.

To get a better job and less risk of a rock splitting, soak it for a few days before drilling.
I use a cold chisel to finish off the holes and naturalize them.


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