Introduction: Concrete Rocks and Sculptures
This is an overview of how to make concrete rock sculpures and electrical boxes.
I started using this technique to do a concrete pathway...rather than have something too different from the rocks and style of our japanese style garden I tried to do something a little more random and natural looking.
Step 1: Rock Structure
stack togother concrete blocks, bricks, rocks and your storage box / conduit if you are adding electrics.
You can use lots of different things like foam boxes, square plastic containers etc... the idea is to build a base that you can wrap your chicken wire around and apply concrete to.
Step 2: Special Note for Electrical Boxes and Lights.
( the 2nd and 3rd photo show the end result after the door has been made)
If making an electrical box or lighting stone you have a few options after you have made a space inside the form,plastic containers work well even an upside down bucket or drum works, run the electrical source cable up into this cavity and you can send out empty condiuts to power exterior feature such as lights and fountains.Remember the access opening must be concave so the door can be removed. Here are 2 ways to do the door.
1.Foam tecnique - create an access to your electrics by using a piece of foam the size of the desired trap door then removing the foam once cement sets and redoing the door in mortar. When finishing you can bring the final coat up to, or below the level of the foam, keep the edge irregular because when you come back to redo the door you will make it irregular to match.
2. Diamond disc technique - add a piece of foam to the face of your cavity, but for this way you will actually be covering the foam with a equal layer of mortar, not too thick as you will be coming back once it all sets with your diamond disc on a grinder to cut out the door. The foam will act as a buffer so that you have more chance of cutting through the mortar
Step 3: Stuff You Will Need
apart from the concrete products, chicken wire depending on rock size the following is advisable
1.Gloves good thick rubber and safety glasses
4. Extra cement. Fatten up the mix
5. plastic sheets protection
6. sponge and brushes for getting work area wet
sculpting process / tinting process
1.Large dry brush
2. spoons, twigs , trowel wire, anything to help or that works
3. plastic sheets and some drop sheets
4. powdered oxide, for colouring
1.diamond disc and grinder
Step 4: Protect Around and Beside the Rock.
Its a good idea to put some plastic sheet or bags around the base of the rock to catch any falling mortar, you can reuse the fallen mortar as you go. The whole process can get messy so protect nearby plants and walls.
Step 5: Make a Solid Structure
If you can mortar the bits together it helps later. I even used a little polurethane expansion mouse to get the pieces to stick to each other then return once the mouse has set to wrap the chicken wire.
Once the pieces are together applying the concrete will be much easier because the base will not move so much.
Recycle old cement products
To get the base solid you can use any cement based product... tile glue , tile joint, old cement, mortar etc.... mix them all together and fill any large holes, or stick your concrete/rock bits together. The consolidation of the base is the not as important as the chicken wire and final coat of render/concrete so don't be afraid to use old bags of cement product that may be a out of date or even have hard bits due to humidity damage.
Wrap the chicken wire around and stitch or tie it together. The less the wire moves the easier it is to apply the concrete.
Step 6: The Concrete /mortar Mix
For this project there are 3 types of cement products you can use.
*Concrete - Sand , cement, gravel and stones. Good for base and base coat.
*Mortar - sand, cement, (lime). Used to join bricks together and good for final coat because in general there are no stones or at worst coarse sand. I add a little cement to this to get it stronger and easier to work.
*Render - Sand fine grain, cement and lime. In general more expensive but easier to work use for final coat.
Any gravel or stones will be a problem once you start working and sculpting the rock details but you can use this type of mix for the base coat then cover with a final coat of mortar/render.
I used mortar mix and added more cement to get it really strong or "fat", try to avoid concrete with stone or gravel in it... or if you make your own 2 parts sand to 1 part cement should be good.
I have even used cement render mix which is good because you can trowel finish if you want to turn your rock into something more sculptural.
Step 7: Cover the Base
You will need to wear gloves, good thick rubber gloves. DO NOT USE YOUR BARE HANDS OTHERWISE YOU WILL REGRET IT.
I have a concrete mixer, but you can mix it by hand, remember if you have a large rock... borrow or rent a mixer... try and save your energy for applying the render / concrete.
Smear a coat that covers the chicken wire, use whatever technique you can to get themix to stick. I try to cover the whole rock an chicken wire before building up the features patting / slapping down my mix till it penetrates well into the chicken wire.
A good coat of 3 to 5cm will work and then add your features in general the mix will stick better to the bits that have already started to set especially for vertical or overhang bits, wet the surface with brush before slapping on extra mortar , brush around the edges to blend it into place.
Step 8: Optional Plastic Wrap
The objective here is to give th rock some veins and random forms.
Using whatever plastic you can find bunch it up to form bands and wrap it around the rock, you may wand a little help to hold it in place while you wrpa of cloth drop sheet around.
The ensemble can be wrapped in string as well. I try and get the plastic to leave a good impression by patting and pushing it into the mortar.
The more random the better, leave this in place until the mortar starts to firm up.
Step 9: Define the Rock.
Take of all the sheets and plastic, you should now have some veins ànd shapes to start with. Dont worry if the veins did not come out as deep or as you wanted, because they serve as a guide as you define the rock.
Use anything you like to make details- trowel, wire, sticks, spoon etc to dig out forms and veins. Using a dry brush sweep out excess mortar from the cracks and crevises created. The mortar needs to be dry enough to be dry brushed without just turing your work into a flat blobs.
As you finish clear out the fallen mortar from the foot of the rock to give it clean finish and add to the illusion.
Step 10: Colour the Rock.
I dry brush oxides to get general colour of the rock first. Then use hand sprayers with yellow or green oxide mixed with water to give a splatter lichen effect... this is the very last step as you can't work the rock any more after. The spray lichen effect can be done after the rock has set also
Step 11: Wet the Rock.
In general cement gets strength from keeping moisture / prolonging the drying process so keep your rock wet by spraying it with water and covering for the next few days. You can also spray some oxides mixed with water to get a more natural effect, the rock will take the colour better when it is dry, but you can spray oxide on a wet rock if you want a dark oxide to run in the veins and cracks.
Step 12: How the Rock Ages and Weathers....
Depending on exposure to sun the rock will bleach out a bit, but hopefully as it weathers it will get its own aged patina and moss. I have heard people mixing dirt and moss with water to make a paste/soup and painting it on to get some moss kick started, some say painting yoghurt helps green up rocks.
I have also painted clear stone sealer/ paver sealer on some of my rocks, this helps deepen the colour but can inhibit the natural moss and lichen process... you want to do this when your absolutely happy with the colour as after the sealer is applied the staining oxide technique is not effective
here are some samples of how other rock finishes have weathered.