In this project we explain how to break up an old concrete slab. Examples of where you may need to do this might be where an old extension to the house is being removed or, the base of an old outbuilding, or a concrete base for an old garden building or shed.
Concrete floors are common and knowing how to break up the over site concrete and what tools to use will make the job easier.
Breakers and Demolition Hammers
The nature of concrete is that it is very strong and using a breaker is the only real way of cutting it up into manageable size pieces so that it can be cleared. There are a number of different breakers available or jackhammers as they are sometimes called. Typically a builder would use a hydraulic breaker as shown in the picture, or a pneumatic breaker powered by a compressor. For DIY, an electric heavy duty breaker would be more appropriate. These are readily available from tool hire shops and you should take the time to familiarise yourself with the operation of the particular tool that you hire. Hire shops will run through the method and provide you with instructions but, make sure you ask if you are unsure about anything.
Lighter weight demolition hammers can be used to break up concrete walls and the like but, you will need a heavy duty breaker for concrete slabs. These machines deliver around 2000 blows per minute enabling the slab to be broken up effectively. Machines are often 110 volt so you will be supplied with an appropriate transformer as well.
Breakers are supplied with points and chisels. For breaking up a concrete slab, the point is used. You should note that hire shops will charge for supplying additional points and may also charge for re sharpening. Changing the steel blade is a straightforward process. Making sure that the machine is switched off and disconnected from the power supply, open the chuck by lowering the lever. Remove the old steel and simply insert the new one as far as it will go. Close the chuck by returning the lever to its original position.
Breakers work by delivering a hammer blow to the top of the point or chisel then repeating the process hundreds of times per minute.
You will need to wear suitable ear defenders as the noise levels from these machines when breaking concrete are high enough to damage the ear. A dust mask should be worn to prevent you breathing in potentially harmful dust, and safety goggles to protect your eyes from flying debris. The same safety gear should be worn by anyone else working with you or in the immediate area. As with all machinery, wear suitable clothing avoiding loose items which may catch on moving parts. Wear work gloves to protect your hands and protective footwear.
Breaking up the Concrete
Before starting any work, identify potential risk areas. Determine if there any services such as electricity, water, gas, communication cables etc running below or near the concrete slab to be broken up. If there are any of these, or you are uncertain, you should seek the services of a professional. On the project in the image you can see what’s left of the incoming water supply to the old kitchen. Before breaking up the concrete it was obvious that there would be a water pipe below and the builders needed to work carefully to excavate the slab in this area without damaging the pipe. In this instance, the water main ran from the main in the street, under the house then out to this point in the original kitchen.
If the work involves anything which will affect a Party Wall, you will need to follow the requirements of the Party Wall etc Act 1996. The wall shown in the accompanying pictures actually sat within the boundary of the Client’s property rather than astride. The Architect on this job advised that it was therefore not deemed to be subject to Party Wall Agreements.
Work methodically so that the area can be cleared as you go and you will have a flat solid surface to stand on while you are working. Generally, working from the far side of the slab will allow you to do this. Look for any obvious weaknesses in the concrete such as cracks and work the breaker along these lines as it will make the job easier.
Making sure that the power cable is kept completely clear of the steel point, hold the breaker firmly and upright on the surface. These tools produce a substantial amount of vibration so be prepared. Switch on by pulling the trigger and allow the point to gradually mark the surface. The tool will try to wander if it is not upright or too much pressure is applied. Allow the tool to do the work in the same way as you use a hammer action drill - you shouldn’t need to apply much pressure.
Working to a grid pattern, break through the concrete at regular intervals so that you are left with manageable size pieces to lift out. Cut vertically and do not use the breaker in a levering fashion. If the steel point becomes stuck you should us a gentle pushing and pulling action to release it. You should never try to lever it out as this may cause damage.
When you have finished, or are taking a break, allow the machine to come to a complete stop before putting it down.
As you work, you need to be vigilant of any unexpected obstacles or services which may be buried in or beneath the concrete slab. If you find any of these, stop work straight away and assess what it is and whether it’s safe to continue.
The trick with breaking up concrete slabs is to take your time and allow the breaker to do all the hard work. If you try to rush it, it will be counterproductive and possibly lead to an accident.
If needs be, a long wrecking bar like the one in the picture can be used to break the concrete by using it as a lever in the holes created by the point of the breaker. The length of the bar means that a fair bit of leverage can be exerted and enable sections to be broken apart.
Once the concrete is broken up, it can be shovelled up and barrowed to a skip. If you have a skip with a drop front, it makes loading rubble from a barrow far easier. To maximise the benefit of this, barrow the rubble to the back of the skip first. If you’re planning to use the concrete as hardcore on some new work, you may need to break it up further so that it’s a suitable size, depending on the depth of the area to be filled. For example, if you need around 6” of hardcore, large chunks of concrete which are bigger than this will be no good. Otherwise, you will end up having to dig out to a greater depth so that the finished level is correct.
If materials can be re used, you might save a good deal of money. Take the hardcore scenario as an example: Barrowing the concrete to the skip takes time, and therefore money. Add to that the cost of the skip itself. Then, there’s the cost of buying in hardcore, which could be crushed concrete – the very thing that you got rid of in the first place. Of course, the time taken to break it up further may not be worthwhile, but it’s something to consider.