Would you like a beautiful exposed aggregate concrete table, bench, or birdbath? You don't need big bucks to get it. The materials in that $800 round table above cost less than $20.
Years ago I designed and built all these pieces after learning how at a precast plant. They still - 40 years later - look great and have not blown away.
This instructable shows the basics, the special concrete mix, retarding the setup of the mortar skin, and fast stepping stone casting. The table instructable is my next one. If you are interested, let me know.
First we will make a stepping stone (The 4 piece planter above is really 5 attached stepping stones).
Then we will make a bird bath using a couple of bowls and paper cups. (and a coke).
Forms can be as simple as varnished 2x2s screwed to a piece of melamine. Exposed aggregate doesn't require perfect forms like smooth concrete, but all joints should be caulked with silicone.
You will need:
a small bag of portland cement
gap graded ( all one size ) rocks . You need enough to fill your form. Roofing rock works well, or you can find rock at landscape suppliers, or bagged, at HD.
sandbox sand, or masonry sand - not gravel
temporary use of a couple of large plastic or metal bowls
a cake pan
a coke, or sugar water
paint brush and optional concrete sealer
small garden shovel
5 gal bucket
running water and a place for your washed off cement water to go.
scrub brush (A wire brush can also come in handy.)
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Step 1: The Mix
A special concrete mix is necessary for cast exposed aggregate concrete.
*1 part cement by weight It can be grey or white. Add up to 5% pigment for color.
*1 part mortar sand or sandbox sand by weight - not standard sand/gravel used in concrete.
*3 parts gap graded stone. 1/2" is ok, 1/4" is ok, but not together. The mix I used has 3/8" rock my flat roof donated. Mixed size stones don't work because the smaller stones wash out leaving gaps and uneven surfaces.
I used the hardware cloth to sift out anything above 3/8 "
Round stones are easier to deal with than sharp ones, and the mix pours better.
The mix will seem rocky like the mix in the stepping stone pan above.
A wet mix will be weak and set up slowly. You should have to vibrate it with your sander to get the air out. If it pours, it is too wet.
Top surfaces can be heavily seeded like the path in Minnear Knives instructable (this contest). If your piece needs rock on a top surface take a look at his intstructable. Luckily you won't be doing a large area like him.
Step 2: Stepping Stones
An interesting thing about concrete is that sugar keeps it from setting up, even overnight. A piece of paper painted with a coke (or 7 teaspoons in 12 oz of water) will evenly keep the cement paste on the surface from setting up. Just paint it on computer paper and let it dry in the cake pan before scrubbing.
Pour, viibrate and flip it over on a flat poly covered surface, then pull the pan off. Your stepping stone will get hard overnight. Be sure to cover with poly so it does not dry. Scrub the paste and paper off with a stiff brush and water the next morning . If you use 1/4" stones, put less sugar in the water, or dilute the coke.
Step 3: Bird Bath Bowl
Making the bird bath bowl.
Paper and curved surfaces don't go together, so I mixed up sugar water and flour together and painted inside the larger bowl. The outside of the inner bowl- about 2 inches smaller in diameter, was oiled to give a smoother surface. Let set up overnite and the concrete will be hard enough to remove the bowls and scrub the outside to reveal the stones. If there are harder spots because your paint job was uneven, a steel wire brush can be useful.
Removing the form bowls is easier if they have a hole at the bottom. Then you can use a stream of air or water to "pop'' the bowl form off. I highly recommend inexpensive plastic bowls for this rather than drilling a hole in your spouse's stainless steel ones.
Step 4: Bird Bath Leg
I used 2-12 oz.paper cups to make the leg. Painted some more sugar paper and cut it to fit inside the cups. This seemed to be the most difficult part of the job until I cut a cup open and used it for a pattern.
A 6" x 3/4" dowel gets screwed to the center bottom of the cups. Wrap them in some paper, and then saran wrap so you can unscrew and remove it tomorrow. No base is needed, because you pound a pipe or rebar into the ground, and set your leg pieces over the pipe. The bowl gets glued on the leg with construction adhesive, gorilla glue, or urethane foam.
Step 5: Finishing Notes
All concrete, especially these small thin pieces like stepping stones need to be wet cured for at least a week to gain strength. Here in the dry west, a plastic cover is essential, maybe not in Florida
Cement paste clings to the cleaned rock, so a mild acid wash- white vinegar or diluted muratic acid will bring a little more color out.
A concrete sealer after a month will give it a wet look-much more colorful.
Table tops and legs need steel reinforcing, How much depends on the piece and abuse. Each is custom designed.
Like most new projects, the second try will be much easier and more successful, so make a stepping stone first, then a table.
Participated in the
Stone Concrete and Cement Contest