Although it does take time making your own rocks can be great fun and you can get exactly the kind and color of rock you want. You can create shapes and looks that are just not possible with real rock.
Click image for a wider view.
It's easier than it looks, actually it's hard to go wrong. Take some cement mortar, shape it a bit with your hands or a trowel, sprinkle on some color and even your first try will look like a rock from a few feet away.
The Cement Recipe
60 LB bag of mortar mix
1 gallon bucket of Portland Cement
1 gallon bucket of "Mortar Clay"
1/4 bottle of concrete color, optional foundation color
The recipe isn't exact and you can add more or less of each item.
The "Mortar Clay" can be hard to find. Try "Building Materials" in the yellow places. If you can't find it no big deal. The mortar clay just makes the mortar smoother and easier to work with.
Mixed together the dry ingredients in a wheelbarrow with a small garden hoe. Then add a small amount of water and mix. Add the color before all the water has been added. Add as little water as you possibly can, much, much drier than you'd think. As dry as you can. Seriously dry. If it's too wet it won't hold its shape as you form it. If that happens you must add more mortar mix.
If mortar is left unused in the wheelbarrow for more than 30 minutes or so it can start to setup, get hard. Just stir to some more with the hoe and it will go back to being workable. You can add a few Teaspoons of water but don't add too much.
The above recipe can cover about 3 to 5 feet of pond edging depending on width of course.
The foundation color isn't absolutely needed but is a nice safety net. We generally mix in about 1/4 as much as the directions say but you can add more if you want richer color. Stick with the browns, tans and blacks. Stay away from red. You can also mix different colors if you like.
Whatever "recipe" you come up with write it down as you go. You'll need to mix later batches basically the same so it all matches.
Forming the Rock
Your first thought might be to use molds. We don't like them for lots of reasons. Expensive, slow, actually harder to make good looking rock but mainly we can just do more things free form.
Two basic ways to form the rock, your hands and a trowel. Hands to make round type rocks, trowel for flat types.
Wear latex gloves.
Just like making meatballs. Gather up a big blob of mortar and set it where you want it. Poke it, round it, flatten it and smooth it. The trick is more to make it not look like cement than it is to try and make it look like rock. If you look at it and see a part of the rock to be that looks like cement mess with that part. You can press plastic food wrap or tin foil onto the blob and then work it with your hands and pull off the wrap when ready. The wrap can give you a smoother finish. The wrap does slow you down a bit, we don't normally use it.
Change the size of the blob you start with or the rocks will be too uniform. Don't be afraid to really mix up the shapes, flat, round, cracks, rough, smooth.
To make sandstone and flagstone type rock you need a pointed cement trowel. Blob some mortar mix where you want it. Use the trowel vertical and horizontal to the ground to flatten edges. Just keep repeating this motion until the mortar is smoother and smoother. Be careful not to add too much detail. It takes longer and although it make look good up close where you're working it gets lost when you step away and view from a normal distance. Make rocks larger than what you might first time to do.
Click image for larger picture.
The goal with the trowel is to smooth all the little grains of sand into the mortar so they don't show. The sharper the edges the better. Think of flat sides like facets on a diamond.
Getting good with the trowel takes some practice. If you don't like your first try rip it out and try again. Mortar is petty cheap.
Top Color - The Magic
As soon as you're happy with the rock's shape it's time to add the top colors. We use Color Harder from Brickform Rafco Products which is normally used in concrete stamping. We use 3 to 4 colors. Color Harder is a power that just needs to touch wet mortar to stick and become part of the mortar.
One color is chosen as the base color, the color the rocks will basically be. This can be a light or dark color. Take a pinch between your thumb and two fingers and throw it at the still wet rock you've just made. And/or rub the color The more base color you add the more the rock will end up being that color. Generally I like the base color to cover 50-90% of the surface, but not too thick, just a dusting.
The next 2 or 3 colors are highlight colors. Just a little of highlight color is needed. You can also throw the highlight colors on but throw from further away so a lighter dusting hits the rock. Or the safer method is to just sprinkle from about 12" above the rock, very light, like putting salt and pepper on your food.
Don't try to smooth or "fix" the rock or color once applied. It smears and doesn't look natural. If you really need to "fix" it you can use a spray water bottle to wash off some or all of the color dust and try again. The water trick may not work. You may also like the look after just spraying a bit of water.
You're done. Just let the rock sit. If you keep working be careful just be careful not to hit the still wet rock. Give the rock at least a week to cure, a few weeks is better. You can apply a concrete sealer to the rocks but we really like the natural look that happens over time with stains and dirt when no sealer is added.
Is Cement Safe for the Pond?
Yes, it's fine.
When I first started ponding I read the pond chat rooms on the internet. In those days pretty much everyone said cement, even the smallest amount, would leach lime into the water and kill everything. I was afraid to put any of this poison into my pond. But one day I need something to put a plant on and added a new concrete block. I worried all night. I measured pH daily ready to adjust the deadly lime. But a funny thing happened, the pH didn't change. I added more blocks, no change. Then I did some research and found that up until really just a few years ago most ponds were made completely out of concrete. Today many ponds in the far east are still concrete. Far from deadly.
My next experiment was to drain a small 100 gal pond and cover its liner with concrete. I waited 30 days for the concrete to cure. I filled the pond with water and let it set for another month. At that point the pH was 9.0. Not bad considering we have 8.0+ pH out of the tab. My liner only ponds have always been 9.0 pH without problems so I didn't see the concrete pond as being any different.
Most of my ponds are now mortar and mortared rock over liner and have been that way for several years. I've never seen any creeping up of pH and the fish have been fine.
It's really unfortunate the cement myth has been repeated over the years like many of the myths spread in chats. This myth has been slowing going away in recent years thankfully.
Cap rocks can be made in an "L" shape to hang over the top of a wall and down into the water.
The result is a wall that appears to be made of solid rock.
Cap rocks are made on a form made from wood. Two pieces of wood are fasten together at 90 degrees and the laid on the ground pointing up. I like to build the form as long as the wall so all the rocks can be made at once and joints can be tight.
A sheet of plastic is laid over the wood to keep the mortar from sticking.
For each rock a piece of 1/4" plastic mesh fencing is cut to the rock size and laid on top of the form. Then mortar is laid over the mesh so the mesh is embedded. This will keep the rock together if it cracks. This is the only application where I use any kind of reinforcement. The mesh contains no metal and can be purchased most hardware stores.
The mortar must cure at least a few days, a week is better. Be gentle when lifting the rocks off of the form. If the rock sticks fast to the plastic the plastic can be cut.
In applications where the top of the wall isn't wide enough to support the vertical part straps can be embedded into the mortar. The straps can be anchored into the soil to hold the rock in place.
Scrap liner or underlayment can be placed over the pond liner before placing rocks to protect the liner.
Hanging cap rock work really well in freezing climates because they can be flipped out of the pond in the fall and flipped back into position in the spring. And if straps are used even that isn't needed. These rocks aren't super strong, some may break. Howvever I did walk on the ones in these pictures many times over several years without damage. Should one break you'll know how to easily make a replacement.
More pictures of fake rock.