DIY cement rocks

[DragonFish71]

So we're going to be making our own rocks for my mbuna tank, and I have one question: making the mold.

We figured play sand, however, I want the rocks to look real. Any ideas on how the get natural looking holes and the general craggy look of a real rock? We're basing the molds off of lace rock.

 

[mfdrookie516]

rock salt is supposed to be good for that. i tried, i failed, end of story. the rock salt "melts" and leaves the tiny holes, etc... mine just fell apart (never claimed to be a good mason)

 

[mr_X]

use sand. fill a box of sand about 1/4 the way then add some portland, then pour sand around it and add more..the sand is your mold. be creative with the hole you make for the cement. in a few hours you'll have a cool looking rock.
make sure you cure it in water for a few weeks at least, changing the water regularly. this will make your ph crazy until it's cured.

 

[DragonFish71]

rock salt is supposed to be good for that. i tried, i failed, end of story. the rock salt "melts" and leaves the tiny holes, etc... mine just fell apart (never claimed to be a good mason)

Ahha! rock salt! Great idea. My fiance brought up snow, but since we are well into spring with little snow left, that idea went out the window.

 

[DragonFish71]

use sand. fill a box of sand about 1/4 the way then add some portland, then pour sand around it and add more..the sand is your mold. be creative with the hole you make for the cement. in a few hours you'll have a cool looking rock.
make sure you cure it in water for a few weeks at least, changing the water regularly. this will make your ph crazy until it's cured.

Yeah, we have the mold problem figured out, it was just getting the natural look that we were having the issue with. Sand alone isn't going to give the craggy look or natural looking holes. And yep, I read about the curing. A few sites suggested curing it in a vinegar/water mix then soaking in plain water. Any thoughts on that?

 

[mr_X]

how big are these rocks? i have heard of curing them in the toilet tank if they are small enough....a water change with every flush.
i don't know if vinegar is goign to balance things out like you'd want it to. you might want to ask a chemist something like that. i only pour and finish concrete. i don't know much more than how to put a finish on it.

 

[DragonFish71]

They will be all sizes. I want to start with larger ones in the back, making caves with extra holes for the cichlids to swim around in then moving to smaller ones in the front. We have tubs to set up outside for curing. Just getting them to look natural is the biggest concern.