How to cut through concrete slabs or foundations


I’m am nearing the end of a never been done before job which involves cutting through concrete steps in order to create some flower beds when it got me thinking. Given my profession as a landscape gardener, I know exactly what to do. But what if someone else came up against this kind of work where you needed to cut through thick concrete, wouldn’t they need advice? And then after some more thinking, it’s not just thick concrete bases or foundations like the job I am currently on, but since the principles are the same, I will also give advice on cutting through concrete paving slabs for if you are thinking about laying your own patio. I actually did some looking around online to see what other websites have written about and I am looking at the advice and thinking ‘really?’. For example, lots of websites recommend using an electric circular saw which must take ages! Why not spend the same amount of money on a 9″ angle grinder? Anyway, let me give you my professional advice on the best way to cut through concrete, whether that be a concrete base, foundation or patio slab.

How to cut through concrete paving slabs

The truth is, whether you are cutting through concrete patio flagstones or natural stone, the method is all the same. The best tool to use is a 9″ angle grinder with a segmented diamond blade. Even the cheapest of blades will last a long time with ours costing around the £15 to £20 mark and lasting job after job! The 9″ angle grinder will give you approximately 3 inches of depth, large enough for even the deepest of concrete paving slabs.All you need to do is measure the size of paving slab that you need to cut, and mark it with a tape measure on each side of the concrete slab before running a line down it to make sure you have an even and correct line. You can use a pencil for this but make sure you have a pencil sharpener ready as they won’t stay sharp for very long when used on concrete or stone!

You then need to run the 9″ angle grinder down the line to make your initial indentation. If you don’t make this initial line first then the dust will cover the pencil line that you have made making it impossible to continue with a straight cut. Once you have made this slight cut, you can then proceed with cutting the concrete slab.To avoid breaking the concrete slab whilst cutting, I would recommend running the grinder back and forth until there is only 10mm of slab left before really going for it.

How to cut through a concrete base or foundation

We remove concrete foundations all the time, but until now, we haven’t had to cut through them. The reason we are cutting through them on the job we are on at present is to make flower beds into the concrete steps, but we immediately knew exactly what to do. You will still need the 9″ angle grinder, but in addition to this you will also need a breaker providing that the base is deeper than 3 inches which is most likely going to be the case.Using the same principles as above when writing about cutting through a concrete slab, using a pencil or marker pen, mark out the area that you want to cut before running the 9″ angle grinder to make your initial indentation on the concrete base or foundation. You will then want to cut as deep as you can using the grinder, which will take a fair bit longer compared to cutting through a concrete slab. Make sure you have a few segmented diamond blades available as we have gone through 3 on this job. They don’t last long when you are using them for a long period of time and cutting at such a depth too.

Once you are happy that you have cut into the concrete base or step as deep as you can, it’s now time to use your breaker. I would recommend using a pointed tip as this will break through the concrete much quicker than a spade bit. Starting from the center of the marked area, break your initial hole and once you have reached the earth or hardcore below, start to work your way backwards. Providing that you have cut a good 3 inches deep, you should avoid breaking any concrete beyond the marked perimeter.We had many steps to cut and break through on this job and only used a 9″ angle grinder but everything went well with no cracks beyond the marked area.

Tips on cutting through concrete

Firstly, make sure you use your protective personal equipment (PPE). For this work, you will need to use a dust mask as cutting through concrete with an angle grinder creates a large amount of dust. You may have noticed that some expensive petrol grinders spray water whilst cutting – This is to stop the dust. But for home use, it’s likely that your not going to be using such equipment. If dust is a worry of yours, then you could always have someone spray water (from a safe distance of course) whilst you are cutting. Yes we have had to do this on 1 or 2 occasions! As well as the dust mask, you will need goggles and ear muffs. Please don’t be lazy as you will get concrete shooting into your eyes and your ears will be ringing if you don’t protect them. I nearly forgot! Steel toe cap boots, heavy clothes and gloves!They may be a bit cheaper but avoid using a 4.5 inch angle grinder as they will only give approximately 1 inch of cutting depth when cutting into your concrete foundation, base or slab which just isn’t enough, although they might make life easier if your making awkward, hard to get to cuts. Our Mac Allister angle grinder broke down during this job (you will see in the pictures that the grinder changes from Mac Allister to an Einhell one) and were forced to use our 4.5″ grinder until we picked the replacement one up. We had a new segmented diamond blade on it which lasted no more than 10 minutes since you have more rotations the smaller the blade is, and the cut just wasn’t deep enough to safely use a breaker afterwards without cracking outside of the marked area.There are other sites recommending the use of circular saws and cut-off saws (also knows as chop saws) when cutting through concrete but I just don’t see the point. In my experience, circular saws just aren’t powerful enough causing them to loose power under pressure as well as the motor being at risk of burning out. Trust me, not long ago I tried to cut through decking with a circular saw and the thing started smoking like a chimney and smelt like burning plastic! I’m still waiting to find the time to write about it. And a bench saw doesn’t make sense to me since you would need to run a heavy concrete slab under it. Maybe I’m wrong, but I personally would recommend spending £40 to £60 on a cheap 9″ angle grinder for cutting through concrete as you can’t go wrong.The size disc needed for a 9″ angle grinder is 230mm but if you are worried that the cutting depth of 3 inches just isn’t enough (more for cutting through concrete foundations and bases) then there are larger grinders available which can take 300mm segmented diamond cutting discs although they come at a price, so it may be worth renting one. If you still aren’t sure then it’s probably best to get some quotes from a professional. Remember angle grinders and breakers are heavy equipment and in the wrong hands can do serious harm. Only use such a tool if you feel confident in doing so and always wear your PPE.

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