# Forum Home Renovation Demolition  Breaking rocks

## OBBob

I've (frustratingly) come across some 'floater' rocks in a trench I'm digging. They are hard. I can cut lines into them with a diamond disk on an angle grinder and if I really whack them with a crowbar sometimes I can break a small piece off. I'm wondering if I need a full blown jackhammer ... or is it worth trying a rotary hammer drill? I'm asking because found an old thread on here suggesting one for this purpose instead of the JH. Additionally, the Ozito one below would be similar to the hire cost of a JH but I'd get to keep it.  
Finally, there are only three of these rocks along a 6m trench ... but being a footing, they have to go. If one of these is capable of chipping away at them it might be worth a go - don't really want to do both though.  :Smilie:     Ozito 1500W SDS+ Rotary Hammer Drill | Bunnings Warehouse  
Edit: so reading elsewhere the suggestion is drill holes, then change to chisel bit and crack it apart?

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## justonething

No, not a rotary hammer drill, you need a demolition breaker/jack hammer. Buy a 2nd hand one and then sell it afterwards.
I remember using that rotary hammer drill to dig out the concrete around a few fence posts, It took a whole day, with a jack hammer, it would have been done in minutes. Also hammer drills don't usually have a long enough reach into the trench..

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## OBBob

The trench is only 400mm deep and 300mm wide,  so getting in there isn't an issue. Two rocks are just poking in by about 100mm, so the edge just needs to come off. One is larger and goes across the trench... but I don't think it's that thick.

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## johnc

1/2 inch masonry drill and an sds bit in a rotary hammer. Drill a few holes in a line and give it a belt. If you can borrow some splitting wedges (pin and feathers) even better

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## phild01

Put this in the other post you mentioned it in:
>"Don't hire, buy a cheapie. Gone through 3 already but far cheaper than hiring." 
Always wanted to try the feathers but never got to do it, not sure why as I was drilling 50mm holes at the time.

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## Marc

Drill a couple of holes in it and fill it with Dexpan. 
or 
Buy something like thishttps://sydneytools.com.au/thump-thudem-1500w-16kg-demolition-jack-hammer-breaker?fee=4&fep=5926&gclid=COe_ysbow8wCFYGavAod2  SYCMA

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## OBBob

I'm guessing you can't get that in Bunnings.

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## Marc

Expando, Expansive Mortar, Non Explosive Demolition Agent Used For Rock, Concrete Breaking  DEXPAN

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## OBBob

Thanks you. I think that's a little more than I require (I hope).  
I'd prefer to get onto this tomorrow, so I'll either need to hire a breaker or buy the rotary hammer. Note really getting a definitive vibe ... but my aching shoulders are suggesting a lighter tool might be the go (sigh).

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## OBBob

> Buy something like thishttps://sydneytools.com.au/thump-thudem-1500w-16kg-demolition-jack-hammer-breaker?fee=4&fep=5926&gclid=COe_ysbow8wCFYGavAod2  SYCMA

  That's a pretty good price ... pity it's ion Sydney.

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## OBBob

Hmm ...  Rockwell ShopSeries Demolition Hammer - 1700 Watt - Supercheap Auto Australia

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## webtubbs

> Hmm ...  Rockwell ShopSeries Demolition Hammer - 1700 Watt - Supercheap Auto Australia

  That looks almost identical (different colours) to the Full Boar unit I got from Bunnings. Half the price though. If they are similar, go for it. Mine has done plenty of work breaking up concrete without missing a beat.

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## johnc

That should do it, about the right price as well. When you consider the cost of an SDS drill and pin and feathers (about $25 a set and you need a few sets) seems the cheapest option. Your problem is probably that the ground is absorbing some of the crow bar strikes, floaters are a real pain.

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## PlatypusGardens

> >"Don't hire, buy a cheapie. Gone through 3 already but far cheaper than hiring."

  
Wouldn't 3 cheapies = one decent?  
Or are you taking them back on replacement warranty....?

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## PlatypusGardens

Personally I'd rather spend a few bucks on getting a mini excavator or bobcat in and have them do the hard work    :Wink:

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## OBBob

> Personally I'd rather spend a few bucks on getting a mini excavator or bobcat in and have them do the hard work

  Well ideally I'd prefer to have someone do the whole job for me ... but that's just not what I tend to do - @@@@ knows why! It always seems easier on paper.  :Smilie:

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## PlatypusGardens

Wish I still had a photo of the sleeper retaining walls a mate built.....dug all holes by hand and mixed all the gear in a barrow. 
20-odd holes from memory, maybe closer to 30... probably 800 deep at least.   
Not because he had to but he "enjoys getting stuck in to it" 
Bugger that I say   :Smilie:

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## OBBob

Well the last one for me was 56 holes ... dug with an auger but then all refilled with mud that I dug out by hand. You're missing out, that's all I have to say on it!

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## PlatypusGardens

Nup been there done that... built fences by hand, dug all the holes, cut the posts and rails with handsaw, hand nailed palings on and mixed concrete in barrows all day long.  
These days I tend to use things with electrical cords, batteries, air hoses, hydraulics and petrol/diesel engines to do the hard work whenever possible.    :Wink:

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## OBBob

> Nup been there done that... built fences by hand, dug all the holes, cut the posts and rails with handsaw, hand nailed palings on and mixed concrete in barrows all day long.  
> These days I tend to use things with electrical cords, batteries, air hoses, hydraulics and petrol/diesel engines to do the hard work whenever possible.

  No end to what can be powered and automated these days.  :Smilie:  Qantas Club - Japan.

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## phild01

> Wouldn't 3 cheapies = one decent?  
> Or are you taking them back on replacement warranty....?

  First one was a second hand Hilti until the hammer failed and no parts available.  Second one did more than the Hilti until the cast handle broke, still goes though.  Last one has been the best and still goes great.
Thing is, I never realised from the outset how much I would use one.  Also on my fourth rotary, last one is a Makita, lesson learnt.

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## Godzilla73

If you do buy a cheap one, keep up the grease on the bit you have in it. Just helps reduce the wear and tear, they also need a bit of a running in period so take it easy at first.

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## OBBob

Well. I'm glad I didn't go the hammer drill. I hired a Hitachi H65 because I found it at a good day rate.  
The first thing the guy said was 'your area is renowned for floaters and this won't do it. I have a big arsed hydraulic one and that probably won't do it either'.  Well I said,  I have to try.  
First rocks cracked straight into four easy pieces! But then all the others were amazingly tough... just chip little bits away. It took all day.  
So for future reference it depends on the rock. I can see the hammer drill working on some... but not all.

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## justonething

That must have been fun  :Smilie:

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## OBBob

Yep a real blast. It's raining now.

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## toooldforthis

> I've (frustratingly) come across some 'floater' rocks in a trench I'm digging... [snip]... 
> Finally, there are only three of these rocks along a 6m trench ... but being a footing, they have to go. [snip]

  so, just a question.
if the rocks are substantial
what's to go with just drilling some holes and 'gluing' in some anchors for the footing to grab to?

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## OBBob

> so, just a question.
> if the rocks are substantial
> what's to go with just drilling some holes and 'gluing' in some anchors for the footing to grab to?

  Yeah,  well I asked the building surveyor and he said I had to remove them. At the time I didn't realise quite how difficult they were going to be. If I had have realised I might have considered arguing that option a little more carefully.

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## OBBob

So I moved over the other side to start on the floor stump holes. Of course the first one, 200m down and rock across the full area of the hole.  
I wonder if they'd accept start bars and a small footing on top? Can't really eye this happening... they probably want to know how bit the rock is.

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## Optimus

Where abouts are you? 
If we come across floaters (restumping) we are instructed (by the building inspectors) to stump on top of them..  
Might be different considering we have a house over our heads so its quite difficult to dig them out

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## OBBob

I'm in Northcote. What's your stumping on top process? There's not much height at this part of the house.

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## Optimus

There's not much room under most houses in Northcote.  Horrible ground to dig in too.. 
Just expose the floater approx 400x400 wide and hang the stump over the top.. preferably at least 150mm crete under the stump. 
If not possible to get 150 use starter bars and get some formatube and create your pad out of the ground

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## OBBob

Thank you! Not much else I can do with that hole today, so I'll cross my finger's I can get surveyor to accept that.

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## OBBob

It's going right next to existing stumps to extend the bearer... I could also bolt the new bearer to the old. A new stump seemed better before I discovered rock!   :Biggrin:

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## phild01

> Thank you! Not much else I can do with that hole today, so I'll cross my finger's I can get surveyor to accept that.

  What do you mexicans call the people who use tripods, levels and a surveyors staff? :Wink 1:

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## OBBob

Surveyor... it's confusing. Sigh...

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## Optimus

Whats this for? An extension? 
If its butting up to the old bearer can't you just notch out 50mm over the top of the existing stump and place your new bearer on that?

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## OBBob

Small extension between house and boundary. I have the strip footing dug (hopefully)... just four stumps next to house. So far it's one all on the stump holes (one rock, one looks ok).

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## Optimus

Show us a pic

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## OBBob

Hmm, not sure pictures are very helpful. This rock is down 200mm at deepest section. Stumps are protruding 150-200mm at this point  of the existing house.

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## Optimus

Sorry  i meant pics of the bearers joining. Can you not butt the bearers as described in my post above. 
Or if its running the other way can you nt just sit the extension joist on top of original house bearer

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## OBBob

Oh, didn't see the second part of the post. Possibly. Do you cut 50mm off the full depth of the bearer?

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## Optimus

You can join the bearer using whichever joint you choose. But for simplicity the butt joint described would be the one i would use. Yes just cut half way  (approx 50mm) with a recip saw and sit your new bearer on existing stump.. Saves doing one of the 4

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## Marc

> Where abouts are you? 
> If we come across floaters (restumping) we are instructed (by the building inspectors) to stump on top of them..  
> Might be different considering we have a house over our heads so its quite difficult to dig them out

  I was thinking the same. A boulder like that would make a better footing than some pitiful bit of concrete.

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## Marc

> What do you mexicans call the people who use tripods, levels and a surveyors staff?

  Depends which part, some call it a "Topografo" others an "Agrimensor" ...  :Smilie:

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## OBBob

So I won (generally) on three of the four. I will have to see what's considered acceptable on the tough one.

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## OBBob

Just to conclude this, the building surveyor was happy with my proposal of adding starter bars to the rock and then pouring a mass footing, although he said "don't worry about the starter bars". When the inspector came to look (different guy) the first thing he said was "you should whack some starter bars in that rock"! Anyway, I was thinking that was a good idea and had planned to do it after the inspection anyway, thus I was prepared.  :Smilie:   
He signed it off yesterday and I poured all the footings today. Yay!!

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## justonething

So are you drilling into the rock to put the starter bars in?

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## OBBob

That's what I have done and chemset them, Yep.

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## OBBob

The starter bars are just for the one stump hole that was completely rocked out ... the rock in the strip footing and other holes was removed.

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