Cure Concrete
Curing concrete is the term used for stopping freshly poured concrete from drying out too quickly. This is done because concrete, if left to dry out of its own accord, will not develop the full bond between all of its ingredients. It will be weaker and tend to crack more. The surface won't be as hard as it could be.
Steps
- Leave the form work used to create the concrete formation. The form work itself, if left in place, or on the underneath of a suspended slab, or around a concrete column will stop the concrete drying out too quickly, and so can be said to be a curing agent.
- Use ponding, which as illustrated in the photo above, is done by forming a dam wall of sand around the concrete formation and then flooding with water. This method has the following disadvantages:
- It takes a fair bit of work to do, and then quite often a breach occurs and the water runs off the slab.
- Usually this can only be done for a few days as it inhibits other work and the pressure is usually on to get the walls up.
- A possible drawback of this method, especially if soil or clay is used, is the chance of staining the concrete.
- Spray water onto the formation. A simpler way is to just keep water sprayed onto the slab with garden sprinklers or hand held hose pipes. Following are some disadvantages that you need to consider if you intend to use this method:
- This method is very wasteful of water
- Again, it can only be done for a short period usually. If you hand water, it should be wet all the time, that is you should not let it dry out at all, almost impossible to do.
- Use some sort of cover that holds and retains sprayed on water, like a sand layer or hessian. The sand cover or hessian has to be kept wet and if they do dry out they actually aid in sucking moisture out of the concrete.
- Use a plastic shield, which basically is a plastic sheet laid on top of the slab to stop the evaporation process. This is one of the most efficient methods of curing concrete. Usually a spray from a hose pipe is used to wet the surface and the plastic is laid on, with generous laps at the joints. Use timber or cement blocks to keep the plastic in position, rather than taping the joints. To a certain extent the plastic can be used a few times. A major benefit of plastic is that it does not stop other work, like building the walls, and so it can be left in position for weeks if need be.
- The photo shows concrete columns that have had the form work stripped (for further use) and then wrapped in a clear plastic film. The evaporation from the concrete condenses on the inside of the plastic and the surface of the column remains moist.
- Use concrete curing oils or curing compounds. These compounds and oils now come in a variety of types. Used the water soluble waxy emulsions that can be sprayed onto the fresh concrete with a hand pump type spray. They are milky white when used but dry into a clear waxy film. They have the advantage that that they can be sprayed onto footpaths and the like even before the concrete is set enough to walk upon. Another major use is on concrete walls. They remain on the surface for weeks and finally break down in sunlight. Be hesitant to use concrete curing oils on internal floors, on the off chance that any residue would stop the full adhesion of ceramic tile glues etc.
- Other types of concrete curing compounds are PVA based, chlorinated-rubber or resin based. They can also be obtained In coloured versions that fade over time.
Tips
- Hot or windy weather makes the drying out process quicker.
- You have spent a lot of money buying a good product, and you can lose a lot of the value in that product by not curing it.
- Even on a small slab for a garden shed, we are wasting good money and ruining good concrete by not curing it!
