Removing concrete

[MarkSmith]

Hi,

I'm doing a cellar conversion and I need to remove a "slice" of concrete from the floor. I'll try to explain.

The original cellar construction had a sloping "floor" to take account of the house being on the side of a hill. I've tried to show here:

Original construction

• MarkSmith
• 2 Sep 2009
• 1

Original construction showing the front wall of the house (underground) and the sloping concrete...

Later, someone came along and levelled off that part of the floor (I presume because that makes it more usable) by adding a polythene sheet, building a little retaining wall and back-filling with concrete.

How it is now

• MarkSmith
• 2 Sep 2009
• 1

How it is now: someone has built a breeze-block wall, put down a polythene sheet, and...

I want to lower the top of it a bit. I am willing to live with a "step" at the back as it will be behind seating anwyay. I need to lose about 10-15cm height.

How I want it

• MarkSmith
• 2 Sep 2009
• 1

How I want it: lower the raised section a bit, so there will be a little step in it. Note: not...

I'm not sure how to go about this. My thinking is to angle-grind the line near the main wall where I want the step, angle-grind across the front of the retaining wall, perhaps grind a criss-cross pattern into the concrete to aid breaking, and then set about almost carving it out with a cold chisel. Ultimately then level the new surface with some more concrete or self-levelling compound or similar.

Is there a better way? That's going to be a LOT of very hard work.

Thanks!
-Mark

 

[Deluks]

That's how I'd do it, but if a large area I'd be thinking of hiring something with a bit more grunt. How wide is this section, maybe you can get a floor cutting saw in there, which would cut full depth.

 

[MarkSmith]

It's about 3m wide and about 1m deep.

Just googled for a floor cutting saw and it looks like it's worth further investigation - thanks!

 

[MarkSmith]

OK, bit of an update on this.

I took off part of the wall and it turns out the actual construction is a bit different to what I thought. It's something like this:

How it really is

• MarkSmith
• 17 Oct 2009
• 1

I dismantled it a bit and the actual construction is more like this.

The top layer of concrete varies quite a bit in thickness but it's broadly around 10cm. I actually need to remove it and redo it, because the damp proof sheet (shown in blue) is rubbish - it's a load of old building sand bags and bin liners, and there's a big damp patch. Ideally I'll rebuild it a bit smaller, possibly from wood rather than concrete. Anway...

I have got a concrete breaker to take apart the top layer, but it's really really hard work. I got a brand new pointed bit, drilled three holes, and it's now completely blunt. An hour of really hard work later I have removed about 1 square foot of the concrete.

Hard work!

• MarkSmith
• 17 Oct 2009
• 1

Using a concrete breaker to take off the top layer

A lot furthe to go!

• MarkSmith
• 17 Oct 2009
• 1

There simply has to be a better way - at this rate we're looking at 200 drill bits and about a week of solid work. Not going to happen.

Any suggestions?

Am I using the right tools? Pointy bit rather than a chisel or a flat one? Is the breaker big enough? How long would one expect the bit to stay sharp? I could cope with getting through a few bits but 3 holes is ridiculous...

Thanks!
-Mark

 

[Thermo]

the breaker is more of the sort of breaker id expect to use for brickwork etc. you need a decent size concrete breaker. Looking at that concrete it would go through it in no time.

 

[MarkSmith]

Thanks Thermo. OK, so I'm looking at one of the sort of stand-up ones?

Actually I just tried the low-tech approach: sledge hammer and crowbar. Got twice as much done in 5 minutes as I did in an hour with the breaker - it helps that I have hollowed out a lot of the sand from underneath so the concrete can "fall away".

Doing the lot is still going to be hard work with a sledge hammer - do you reckon it's worth getting a bigger breaker, all things considered?

Thanks for the reply!

 

[Thermo]

if its hollow underneath a sledge hammer and pry bar under it will do well. If not you want a decent jack hammer, although youll need an electric one because of the ventilation. Best to work a line across the concrete about 8-12 inches from the free edge. It should just start to crack away from the main mass as you go then. Once you get going its fairly easy.

 

[MarkSmith]

Sledge hammer does seem to be the way forward:

Untitled

• MarkSmith
• 17 Oct 2009
• 1

Thanks!