The soil underneath your subbase is called your subgrade, and your concrete is only going to be as strong as your subgrade. [2] X Research source Think about it: If your subgrade shifts, craters, or otherwise moves, the integrity of your concrete is going to be compromised. Make sure your subgrade is properly compacted and stabilized before adding the subbase. [3] X Research source Many professionals choose open-grade stone or closed-grade fine-grade stone for their subbase. Open-grade stone lack the smaller stones, giving water a way to pass through. Plus, it’s less expensive. On the downside, it doesn’t really compact as well as finer-grade stone. Finer-grade stone is compactable but tends to be more expensive. [4] X Research source Lay a 4–8 inch (10. 2–20. 3 cm) thick subbase with your chosen material, and then compact it with a hand tamper or a plate compactor. Plate compactors can be overkill for small, DIY projects, but offer more power in the compacting process.
For square or rectangular forms, make sure that your corners form 90 degree angles. Take a tape measure and measure both diagonals of the square or rectangular; they should correspond to one another exactly. If they don’t, it’s back to the drawing board with your form. Also make sure that the forms have a slight slope to them. If they are completely level, you can expect water build up in the middle of your beautiful concrete. To eliminate this possibility, create a slight slope of 1" for every 10 feet. [5] X Research source
Wire mesh will help guard small cracks growing and spreading, as well as offer stability across two axes (wire mesh is welded, where rebar is often tied together). Rebar may offer better structural integrity, and be better for higher load-bearing surfaces. On the flip side, it doesn’t do much to minimize the appearance of cracks that do appear.
In a concrete mixer, add the determined amount of water and then the concrete mix. You can also mix this in a wheelbarrow with a shovel. Use as little water as possible. Water makes the concrete more maneuverable but it also weakens the constitution of the final product. [7] X Research source A drier mix makes the concrete more crack resistant. Turn on the machine. The mix will become smooth and consistent. Shut off the machine. Always wear a ventilated mask, safety glasses, gloves, and long sleeves and pants when mixing concrete. [8] X Expert Source Gerber Ortiz-VegaMasonry Specialist & Founder, GO Masonry LLC Expert Interview. 10 March 2020.
Work your way from top to bottom, gently screeding until you have a flat surface. Your concrete surface won’t be finished yet, but it will begin to look more complete and professional looking at this point.
Use a large floating device, also known as a bull float, to press down aggregate and help the cream (gravel-free concrete) rise to the surface. Do this by moving the bull float away from you, keeping the tailing edge slightly elevated, and then moving the bull float back towards you, keeping the leading edge slightly elevated. Use a magnesium hand float to go over the surface. After some of the water bleeds to the surface, use long sweeping motions with your hand float.
If moving the broom over the concrete causes clumps of concrete to aggregate on your broom, it’s too early to broom. Move over the concrete again with the magnesium floater to smooth out the pattern left by the broom, then try again later.
Sealing concrete will prevent it from absorbing liquids and staining. [9] X Expert Source Gerber Ortiz-VegaMasonry Specialist & Founder, GO Masonry LLC Expert Interview. 10 March 2020.
