WORKING WITH CONCRETE

22 Aug WORKING WITH CONCRETE

Concrete is key when it comes to foundations. A well-designed foundation is the key to the stability, safety and durability of any building.

Solid soil is just as important as the footings and foundation that lie upon it. It’s a good idea to have an engineer examine the load-bearing quality of the soil you are building any cement foundation upon. It is also wise to consult your local building department about the average frost depth in your area. Concrete slabs and footings should be built on undisturbed virgin soil or compacted soil that is uniformly graded and well drained.

Concrete is a mixture of Portland cement, gravel or crushed stone (coarse aggregate), sand (fine aggregate), and water. It hardens into one of the strongest of building materials. Determining the right mix is the key to making it strong and durable. Too much water weakens the concrete, but too little will render the mixture unworkable.

The wet concrete is poured into moulds. These forms, as they are called, are commonly made of lumber and plywood sheathing, and shape the concrete as it hardens. They must be strong enough to withstand the force of the concrete pushing against it as the mixture dries. Concrete footings support foundation walls and should be set below the frost line to avoid frost-heave damage.

Given the quick-drying nature of concrete, it’s important to work as quickly as possible, and handle it as close to the job site as possible. Begin pouring the concrete into the farthest corner of the forms. Each new load should be placed against the previous one and a shovel or hoe can be used to spread the mixture evenly.

Air bubbles can easily form, so you should keep tamping them out by jabbing a shovel or hoe in and out of the concrete.

In order to keep the concrete moist during the curing process, it’s important to spray water on it from a garden hose, and then cover it with large plastic sheets or waterproof paper to prevent evaporation. The application of a curing compound to the damp surface is another way to keep moisture in.

The form-work can be removed after about a day. But be sure to do it carefully in order to avoid damage to the concrete. It will take about a month for the concrete to cure, so it’s advisable not to hammer or pry against it during this period.

As for concrete repairs, small cracks can be fixed with a crack sealer, preferably a ready-mix material that can be set in place using a trowel. The sealer comes in liquid or a caulk-like form. Larger cracks may need to have weak spots chiseled out in order to widen out the bottom of the groove. Repairs can be carried out with a cement-and-sand mix.