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Concrete can Be Sprayed, poured, troweled, & pumped into place. There are pump trucks that can reach over a house to the back yard, line pumps that can pump high up to buildings or ran around obstacles where a truck can not reach. And of course, the least expensive option, the good old fashioned wheelbarrow powered by human labor.
There are two different methods of spraying concrete. Gunite and shotcrete.
Shotcrete is applied by attaching a nozzle to to the end of a concrete line pump. A large air compressor jets air through the nozzle where the concrete exits and sprays it onto the desired surface. It pretty much has to be done all in one shot because the line can clog if left sitting for a any length of time.
Gunite is a similar process except the cement mix is pumped dry down the line and wetted at the nozzle. The obvious advantage is the nozzle operator can stop and start as he pleases without the concern of clogged lines and the end clean-up process is much simpler.
Both methods create a superior bond to whatever they are blasted against and are quick methods of application for large vertical and overhead areas.
The nice thing about artistic concrete in the form of artificial rocks and sculptures and such is that the concrete can be mixed by the batch in a mixer and applied at a leisurely rate without having to worry about cold joints unless it involves a pond or water feature.
A cold joint is a line where you stop your project and begin again the next day. The new concrete up against the old concrete can leave an invisible crack which under the pressure of a pond can leak. If you're building a pond be sure to keep a “wet line”. A wet line simply means that you start at one end and work fast enough to continue placing wet concrete against wet concrete before it begins to kick over or cure wherby avoiding the cold joint.
large projects can be done with just wheelbarrows and trowels if you have a well built armature and the right amount of help. Even larger ponds can be built this way if you order your concrete by the truck load.
THE BASE COAT
The base coat gives the project added structural strength when necessary. You would want a base coat for a structure of any size or a load bearing structure, whether it be a load of water, people or machines. Also in climates where the ground will move in freeze thaw climates or earthquake areas you would want a base coat.
In a situation where there is no load, and the potential of small cracks is unimportant such as ornamental boulders, a base coat is probably not necessary.
For the base coat you will want to use regular, strong cement mix with aggregate. I use a 5 to 1 mix, 5 parts 60-40 sand/gravel to 1 part portland cement. Simply smear concrete through the outer layer of chicken wire to lay on the inner layer trying not to loose any through the inner layer. An inch of concrete with the rebar encased in the center is quite strong.
A guy mixing the concrete, a guy carrying buckets to the site and a guy applying it works well.
I’ve found a heavy rubber glove and a careful hand so as not to cut through the glove and into your flesh on a sharp wire, is the best way to apply the base coat.
CAREFULLY MAKE IT ROUGH
A rough surface and some chicken wire showing through makes a much better surface to bond to than smooth concrete and can save you a lot of hassle on vertical and overhead surfaces.
Just remember those sharp little wires will cut right through thick rubber gloves and into your hand if your not carefull.
SQUARED OR SHARP EDGES
It can be really difficult to create an unrounded square edge on a rock. The way I solved this problem is to use folded hardware cloth to create sharp rock edges and embed it into the base coat to shape the texture coat on.
For small scale projects such as pagodas, bonsai pots & trays, application is best done with your hands and trowels. Be sure to wear gloves because the lime in concrete will dry out and burn your bare skin. You will not feel or see it happening until later in the day after your project is finished.
The video below shows the process of applying the mud to a small columnar basalt armature and I will refer you to my columnar basalt project page for a detailed written description with photos.