Author Topic: Best length SDS max chisel? (breaking a concrete top floor)  (Read 2066 times)

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Offline threesixright

  • Posts: 119
Hi All,

Need remove a top cement floor, roughly 100 m2. It's 7 cm concrete (top layer). It's pretty soft and not reinforced.

What woud be a decent length for a SDS Max Chisel?

FYI. It's not a rush job, I have 8 weeks (and a Bosch GSH 5 CE). So im thinking a few hours a week, no interest in wrecking my back  ;).

I'm guessing the longer the better? But maybe some of you have experience and can give me a good tip (other then, let someone else take care of it  [big grin] ).

Thanks!



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Offline awil66

  • Posts: 148
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #1 on: November 13, 2018, 07:18 PM »
100m2? You don’t think that’s a big job for one person? Who’s removing all the material from the room? Anyway, a 6” chisel might do the job but you will be close to the ground. Get a longer one to help your posture.

Offline aloysius

  • Posts: 332
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #2 on: November 13, 2018, 07:22 PM »
5 Kg & 7 odd Joules of impact are both pretty small figures for breaking slabs.  It'll do it of course.  Dripping water will wear away stone too.  Eventually.  But it'll also wear away at you.

Hire a big 'un for a half-day.  Just a few Quid at most.  Either a big AEG/Metabo/Milwaukee/Kango 1700w, 20 Joule, 12 Kg or equiv Bosch GBH 12 combi or even better a bigger, harder hitting GSH hex type dedicated breaker  (Bosch, Makita, DeWalt, Hitachi-Koki, Hilti, Wacker Neumann et. al.).  This is one of the few tools where weight is actually a distinct advantage, making it easier on the operator.

While you're at it, grab a longer steel with a 25mm chisel tip.  Moil points just don't tend to last in tough going I've found.  You can readily touch it up (with a fairly "blunt" grind) with a flap disc on a grinder provided you keep it cool.  Say about 600mm length works well with L-shaped combi-hammers or maybe a slightly shorter 400mm or so for longer inline machines.  You can always drag the tool around on the chisel tip if it's getting a bit heavy @ the end of the day, but a longer bit minimises that terrible bent back in use that can do real, lasting & permanent spinal damage.

Make sure it's the tool doing the work, not you.  Work backwards away from the face, just as if you were shovelling a trench or tilling a garden:  the opposite of working with a pick or mattock.  This is where the greater mass & impact of more powerful tools becomes relevant.  Such a relatively small volume of concrete (7m3 +/-) is merely an hour or two's work for a bigger breaker, but the better part of a week (or more) with such a small tool as you've suggested! 

Whilst I don't doubt that Bobby Bosch's smallest breaker is ideal for such small tasks as removing wall tile from a shower alcove or splashback, I know without a shred of doubt which tool I'd be using on a floor.
« Last Edit: November 13, 2018, 08:34 PM by aloysius »
FOG-wit since '95:  Some say since birth...

Offline aprato

  • Posts: 5
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #3 on: November 13, 2018, 11:38 PM »
I second renting something bigger. I just took out a little bit for a new footing and even though it didn't have any bar it still took some work. Especially because there was a previously unknown footing right where i tried to open it up.

Offline w802h

  • Posts: 221
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #4 on: November 14, 2018, 09:38 AM »
If you have adequate ventilation for the space, you might consider renting a walk behind concrete wet saw.  You could turn the slab into a grid of liftable squares without any jarring jack hammer impact to your body.  Not a lot of dust with a wet cut either.  Of course you will still need to do some work around the edges of the room. 

Offline Holzhacker

  • Posts: 904
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Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #5 on: November 14, 2018, 10:15 AM »
Doesn't matter how much time you have. If using a less than ideal tool the job is always a PIA. Renting a bigger machine should be considered.
However, you say its not reinforced. Depending on the substrate and mix this might come up easy. If it were me I would take the machine I have and do a test area and decide from there what tool to use. I've done large floor areas with a small SDS like that one. If the concrete is a very sandy mix, once you cut out a trench it can be very easy to get a spade bit underneath and use pop it all up and apart. All depends on the mix.
Don't take 8 weeks to do it, its not worth it.
"The Code is not a ceiling to reach but a floor to work up from"

Offline RJNeal

  • Posts: 364
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #6 on: November 14, 2018, 10:45 AM »
I agree with Holzacker. Try and area.
Just remember try not to beat yourself up to save a few bucks.
Rick.
Have you walked your saw today?

Offline jimbo51

  • Posts: 451
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #7 on: November 14, 2018, 12:03 PM »
Gee, nobody suggesting a sledge hammer and a hand chisel.

I helped dig some post holes in very rocky (shale) ground. Using a small machine to break up the rocks became very tedious.

We used a wet saw to cut the initial holes in the concrete slab where the posts needed to go. It is a bit messy and you will have a good deal of water to clean up if you go that route inside a room.

Offline threesixright

  • Posts: 119
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #8 on: November 14, 2018, 02:52 PM »
HI, All,

Thank you for the replies, much appreciated!

Let me clarify the situation a bit better. I do understand bigger is (in general better (yes phun intended  [tongue])
When I said 8 weeks, I meant more  I have a few weekends to take care of it. We are basically waiting for the permit, and it would be a miracle if it comes before 1 February. Point here:, it doesn't need to be done in a single weekend.

Thats said. I also feel its good to put a but a bit blood, sweat and tears in your own house  [eek]. Makes you enjoy it the more ...

1. There are a a few rooms with a bit of glass, I as afraid that bring in the big guns would lead to debris flying all over the place causing damage.
2. The top floor feels (as someone note pretty) sandy. I tried a bit with a hand chisel and was not that bad at all.
3. I also need a chisel to clean some cement and tiles form the walls (guessing 60 m2). For hat the Bosch would be perfect I think.
4. Rental is kind of a PIA, since I 100 KM (roundtrip) from a rental place.

The Bosch had a good reputation and its clear it will take a bit longer. But I could also use it for the walls (in a later stage). Looking at the chisels I thought of going for a 400 or 600 mm?  Not sure what would be better (and if the length leads to any performance issues).

Making a test is the best answer I think, and then take it from there.

Again much obliged!

Offline aloysius

  • Posts: 332
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #9 on: November 14, 2018, 07:52 PM »
Don't quite understand what you're asking, or maybe inferring.  You'd use a purpose built tile chisel for tile or thin veneers of topping compound, with the tool tilted to about 100% (45 deg) to the substrate.  Short is good for waist height & above, providing a modicum of control.

The relative weakness of these small "baby" hammers helps here too, preventing inadvertent damage to deeper layers & ejecta, and the light weight of a tiny tool & short chisel allows longer sessions before fatigue demands cessation.  Your little hammer will be ideal for this.

But to use a tile-hammer for heavy floor breaking is seriously questionable.  I'd be driving to the hire shop instead, even if it is 550km each way, or at least get the tool dropped off &/or returned by your local bus service or freight company.  They (the hire shop) will supply the proper (25mm floor) chisel for the job too.

In regard to breaking a 100m square slab by hand:  yes, it can be done, but only a fool would try when there's such a variety of superior, inexpensive alternatives available.  Firstly, you simply can't use a mason's chisel & sledge simultaneously.  I'm astonished, with all due respect to the poster, why somebody would suggest such an impossible task.  Simply put, a 10 or 12 lb sledge with a 2-3' handle cannot be wielded, let alone accurately swung, one-handed! 

You'd use a club hammer (1 or 2 lb only) with a mason's chisel:  something that can be swung safely & accurately single handed!  But it would be slow and pretty useless.  I've done sufficient hand chasing to realise that hammer & chisel work is only suited to basic, small scale carving & chasing applications.  Bigger tasks require mechanical hammers.  It's pretty clear to me that suggestions to break a slab with a sledge & chisel so are not just impossible to do, but also dangerous & ill-informed.  Don't do it.

Even a sledge (swung alone) is hard work too.  My first ever (holiday) job as a schoolboy was breaking rocks on a roadway & drilling with an Ingersoll or Atlas air hammer in a quarry for blasting quartzite gravel.  You're absolutely GUARANTEED to burst most if not all your windows with such a coarse and crude tool from fly-rock.

To saw up a floor with either 2-stroke or electric floor saws will be impossibly messy, slow, noisy & expensive, esp. if it's an upstairs floor in a house!  Maybe a remote hydraulic-drive saw might possibly work, but what will you do about all that slurry draining unpredictably downstairs through the building's each & every available orifice?  Plus it's going to be ludicrously (if not insanely) expensive too.

By all means ignore my advice:  but please be aware that I at least am talking from a modicum of experience.  I've been using hammers for a variety of tasks for half a century.  I've jackhammered & broken multiple thousand tons of concrete & stone, cut, gouged & chased literally kilometers of floors & walls with hammers, chisels, gouges & diamond saws, cut, chiselled and sculpted everything from concrete to granite, bluestone, dolerite, marble & sandstone for construction, renovation, installation, land & water-scaping& even on occasion art, & bored several kilometers of fixing holes for a million odd masonry plugs & screws.

I've used dozens of different types of mechanical hammers, owned nine of my own (currently have six), still using them (but irregularly these days) for all the expected tasks, plus quite a few "unusual" applications like gardening, post-driving, tilling & small-scale excavation.

Yes, I have a bad back.  Yes, I have an acute susceptibility to Carpal Tunnel Syndrome & white-finger.  Hardly surprising considering all those hundreds of hours of use, misuse & abuse done to my body over the decades at the hands of mechanical hammers.  Size the tool for the task.  Get, & use, the correct tools for the particular task or suffer the long-term consequences.


Addendum:
I forgot to mention that your proposal to use a short, wide tile chisel in a small-sized L-format chipping hammer to break up a floor will inadvertently force you to work on your knees.  Good luck with that!

Here's a possible alternative:  self-levelling mix-n-pour screed straight over the top of your undesirable slab.  A perfect surface in a day or 2.  No jackhammering at all!
« Last Edit: November 14, 2018, 10:07 PM by aloysius »
FOG-wit since '95:  Some say since birth...

Offline Cheese

  • Posts: 5606
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #10 on: November 14, 2018, 09:00 PM »
I have to agree with aloysius. About 15 years ago I decided to take out a 3” thick sidewalk that was 3’ wide and 35’ long. I decided to take it out on a holiday weekend when the rental places were closed. I used a 2# sledge, a 12# sledge and a couple of hand chisels.

The side walk had been installed 50 years ago and there was no rebar so I figured it was a piece of cake. Well after 2 consecutive 12 hour days it was finally gone.

Lesson learned...I’d never, ever, ever try that again.

You crack the cement with the 12# maul but the concrete pieces still need to be chiseled out one by one. Sometimes it’s a 1” piece, sometimes it’s only a 1/2” shard that gets ejected. You smile when a LARGE 4” piece can be pried loose. Drive that chisel too deep into the concrete and there isn’t enough power to break that piece so you have to then remove the chisel and try to chew off a smaller amount.

I’d suggest you purchase a chisel/bull point, put it on the Bosch and test drive it yourself to see what you’re up against.

Offline threesixright

  • Posts: 119
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #11 on: November 15, 2018, 05:11 AM »
Don't quite understand what you're asking, or maybe inferring.  You'd use a purpose built tile chisel for tile or thin veneers of topping compound, with the tool tilted to about 100% (45 deg) to the substrate.  Short is good for waist height & above, providing a modicum of control.

Thank you for your elaborate answer.

My core question is what is a good length for a chisel, ergonomic wise, when using the Bosch style hammer for floor demolition work.

Maybe the thread got a bit derailed because of my choice of word. I wrote concrete top floor, but its a cement top floor. Which consists of just cement and sand. Something different then concrete. Please forgive me for the poor choice of words [embarassed].

Whats the difference in m2 / hour between a 8 J and 20 J hammer?

TBT I'm not after a 4 weeks of back breaking work either. But if it takes 4 hours with a 20 J hammer, or 2 days (spread over the 2 months) I would be fine with that.

Not trying to be a wise-, I'm sure many of you know what you talk about and take all your advise to hart.
« Last Edit: November 15, 2018, 09:37 AM by threesixright »

Offline aloysius

  • Posts: 332
Re: Best length SDS max chisel? (breaking a concrete top floor)
« Reply #12 on: November 15, 2018, 06:17 AM »
"The core question is what is a good length for a chisel, ergonomic wise, when using the Bosch style hammer for floor demolition work."

An absolute minimum of 400 x 25 mm.  That's still going to be hay-erl to work with due to the short length of the tool.  For comfort's sake the handles of your jack should be @ about the midpoint between belly button & nipples, maybe a tad higher.


"Whats the difference in m2 / hour between a 8 J and 20 J hammer?"

M2 per hour isn't an appropriate measure for a chipping hammer.  Sort of like graduating a motor car's speedo into parsecs.  Guessing here, of course, but maybe a factor of 10?  The difference of maybe 10 kg/h to 100 or so.
« Last Edit: November 17, 2018, 06:21 PM by aloysius »
FOG-wit since '95:  Some say since birth...