How to Make Aggregate Concrete
Aggregate concrete provides a beautiful and functional surface for driveways, sidewalks and decks. Because of the exposed aggregate, the surface won’t stain as easily as concrete. Another benefit to beauty and stain resistance is safety: Aggregate concrete’s surface offers more traction than concrete’s typical smooth finish.
Step 1 - Choose the Aggregate
Like selecting paint colors you'll need to choose the size and color of aggregate that you want your finished project to display.
Driveways need to support more weight than other applications so if that’s your project, the size of the aggregate will factor into your decision. The smaller the aggregate, generally, the more weight your concrete will support. Consult your concrete supplier for suggestions.
Step 2 - Sub-Grade Preparation
Remove topsoil, roots and other organic matter from your project’s site. Add stone or sand for fill, if necessary, then grade and compact. Ensure the finished, compacted sub-base is 3 ½ inches below the finished grade (the top surface of the concrete).
Prevent rain water from flowing toward or into your home. Slope the grade one inch for every one foot of concrete so the finished concrete’s surface will direct rain away from your home.
Step 3 - Build the Form
Using 2x4 stakes layout the shape your project will take. Use your square to ensure corners are at 90 degree angles. Screw 2x4 boards to the stakes to form the shape you desire. The top of the form boards will be the top of the concrete pour.
Ensure the form follows the slope away from your home recommended above. Use a six-foot level to check or, if your project is wider, rest a straight 2x4 across the forms then the level atop that board.
A 2x4 board is 3 ½ inches tall. You will pour concrete to the top of this board. This means that your concrete will be 3 ½ inches thick. If you desire a thicker pour, use a wider board to build your forms.
Step 4 - Pour the Concrete
Pour the concrete into the form. Use a straight 2x4 board to screed the concrete level by resting the lumber atop the forms then move the board back and forth in a sawing motion one end to the other until the entire surface is smooth.
Step 5 - Treat the Surface
Spray the surface retarder onto the top of the concrete to slow the curing process. Depending upon the ambient temperature and the surface retarder’s directions allow time for the concrete’s surface to cure enough to support your weight without displacing the aggregate below.
Use caution. Wait too long and the next step will become more difficult.
Step 6 - Expose the Aggregate
Wash the surface layer of concrete paste away with a hose (spray not stream) and scrub brush. Expose only the top 1/3 of the aggregate to prevent the rocks from becoming dislodged. After the aggregate is exposed gently spray the finished surface to remove any remaining concrete film.