Gind misaligned concrete slab.

[JimDiGritz]

I've got a large 80ft area covered with 30+ year old concrete slabs. I've dug around them and they are c.6 inches deep.

The middle one is higher at one edge (by about an inch). I can only guess that a tree root has lifted it over the years (there is a 10ft eucalyptus nearby). The other end is still at the correct level.

I need to level the surface to put down a wooden workshop.

My initial reaction was to get the slabs broken up and have new concrete slabs poured. The problem with this is the cost, but more importantly I've been told it's probably too cold to guarantee the cement will cure properly. I'd really like the workshop to be up before Christmas.

I've just had a bodgetastic idea! Hire a Floor Grinder and level off the 'wedge' of concrete. I'm guessing for £100 and a days work I could get the slab pretty level!

Would this work?

Jim

 

[JimDiGritz]

Update:

I've re-looked at the middle slab - it's about 6 foot wide and 10ft long. The slab is 1inch higher at one of the 6ft ends.

I also wondered how much it would be to get a trench dug next to the raised slab end and lower it by lifting it and removing some material from under the slab? Seems like a job for a couple of guys and a mini digger for a day....

 

[r896neo]

No offence but both your ides aren't great. If the slab has lifted by a root then its probably going to lift more or crack. Grinding concrete is grim difficult work and you may end up damaging the slab. i.e sending multiple cracks through it.

Trying to lower it by undermining is also a bad idea. Unless the slab is well reinforced it may crack in the process and doing as you propose lifting and digging out some material will never work as the slab will most likely settle unevenly and crack or tilt even more.

The best bet would be replacing or if one of the slabs is big enough perhaps a screed to level it out?

 

[JimDiGritz]

Thanks r896neo, fair points - that's exactly why I posted here before heading out to HSS!

Since I've been unable to get a quote for re-leveling with a new layer of concrete (The builders I spoke to all told me that it wouldn't cure properly because of the frost) I guess my only 'quick' option is to rent a Kango, smash the hardstanding up and chuck it all in a skip. I would then probably build the workshop on concrete strips or paving slabs.

Seems a waste to dispose of 80sq ft of decent hardstanding...

 

[kazuya]

whats the workshop made out of? an inch isnt a great deal?
why not have a level course of blue bricks laid all around the edge where the workshop is being built, build the workshop on the bricks, then in the summer screed the inside

 

[JimDiGritz]

kazuya, the workshop is a large 36ft x 8ft version of this:

By blue bricks do you mean engineering bricks? I've not heard of them otherwise.

Surely an inch will make a big difference!

I could shim the other bricks with slate but THAT feels like a bodge to me... isn't it?

 

[kazuya]

ok its a wooden shed so forget the bricks,
and no i dont think an inch will make that much difference, and i dont think its a bodge to use shims, especially not slate, the slate will protect the the wood from the damp concrete, for the amount of time and effort its going save i think its your best option.
just spend some time getting the floor level using lots of packers, and how about getting some wooden strips cut that go from 1" down to nothing to attach under the floor, most timber yards will cut them for you.

 

[theprinceofdarkness]

Grinding is a no no. You will release several kilos of fine dust that will get every where. On this sort of scheme, cut the surface with a disc cutter into strips running across the slope, so they are 1/2" apart and vary from 1" deep to nothing. Knock them out with a bolster, you should get to better then +-3mm in an hour. If you cut some low, make good with a very rich mix of dryish sharp sand and cement, don't be too fussy, its shed base. Cover new work with as many empty plastic bags as you can find. A little plasticiser would help with frost resistance.
Frank