Six common mistakes to avoid when pouring concrete

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We all do it . Make mistakes that is. Though concrete, despite being the second most used commodity in the world, is probably the most unforgiving. Once it starts to set and harden, its all over. Therefore if we can minimise the mistakes we make on the day of the concrete pour, our concreting project can succeed, as opposed to fail dismally. With this in mind here’s half a dozen of the most common mistakes made when pouring concrete.

1. Preparing your concrete slab

The ground and surface area under your concrete slab needs to be prepared adequately. An even layer of crusher dust, manufactured sand or compacted stone is there to absorb moisture and prevent contamination of your slab from underlying soil and sub surface materials. One of the most common mistakes made is failure to hose down and dampen the sub surface in hot weather. A hot dry sub surface can lead to plastic shrinkage and even separation cracking in your slab if fresh concrete is poured on the warm, dusty surface below. Another mistake made is failure to check your sub layer levels. If they are all out of kilter you may find you either over or under order the amount of concrete from the plant, not to mention mess up the level of your slab on pour day.

2. Organising your concrete pour

Preparation and sound organisation are the key to making your concrete pour a successful one.The second common mistake made on pour day is the failure of the concrete or slab owner to organise all the players in the pour effectively. Timing is everything in a concrete pour. You need to have adequate placers and finishers, a pump that is set up on time in the right location with enough line on board to meet your requirements, and the concrete plant needs to know what time to send the first and second trucks to ensure everything runs smoothly. Failure to line up all these dots and cross all your T’s when it comes to organisation is the second most common mistake made which can easily be avoided through forward thinking and good organisation.

3. Placing your concrete

Most good concreters will tell you “it’s easier to add water to concrete than to take it out”. Wet concrete can be easier for many of us to move around and place on site. It isn’t as heavy and cumbersome as dry concrete, and we can rake and shovel it with relative ease. Though wet concrete takes longer to set and when it finally does harden, the surface is often weaker than dry concrete. Water flows to the top and once evaporated can lead to a powdery surface that is dusty, weak and susceptible to cracking. Therefore avoid adding water on site wherever possible. The third most common mistake is to add too much water on site.

4. Finishing your concrete

Concrete takes time to hydrate, set and eventually move from a plastic (i.e., wet) to hardened state. During this process it is important to let the particles and substances within the concrete do their thing. They need to knit together and connect as it were. The fourth most common mistake made is to get on your concrete slab and commence finishing the surface too early. Closing off the surface before this hydration process has occurred effectively shuts down the evaporation and hydration process, not allowing all important bleed water to come to your surface and ensure the entire slab sets evenly. Efflorescence, scuffing of the surface, delamination of the surface and dusting or even cracking of the upper concrete layer are all potential side effects of “getting on you surface too early” and not allowing the hydration process to run its course.

Another common mistake made during the finishing of your concrete which should be avoided is the need to over finish your surface through excessive troweling. Try not too over do it, as it were. too much work on the surface can produce imperfections when your surface finally hardens.

5. Curing your concrete

Leaving your concrete exposed to the elements without adequate curing is the fifth most common mistake made when on concrete day. Whether it is tarps, water or aliphatic alcohol, a curing compound, hessian bags or water from your garden hose remember your slab needs to be

protected against the elements. Heat, wind, rain and humidity can all all have negative effects on the ultimate result of your concrete pour, therefore ensuring your slab surface is protected against these elements is a good way to avoid these adverse effects on pour day.

6. Cutting you concrete

Even when your concrete slab has been poured, placed, finished and cured, there is still work to be done. The sixth most common mistake made in a concreting project is failure to have your slab professionally cut with a concrete saw in real time. And by real time we mean within 24 hours of finishing your surface. On or around 24 hours (i.e., during the following day after pouring) is ideal. Concrete cracks where and as it wants to. Unless you cut your concrete in real time it may well start to crack wherever it wants to.

If possible and affordable ensure your concrete slab is professionally cut. Small cracks, chipping and a breaking away of the concrete surface can occur in and around your saw cuts if they are not cut evenly, at appropriate depth and with a sound concrete saw.

Now you know what to avoid on pour day, happy pouring!

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