Uneven Concrete

[dobby1]

Hi Everyone,

We laid down a slab a few months ago. The readymix guy ran out of concrete and we had to get another one out to finish the job. This resulted in the last segment being about 10mm higher than the rest of the slab (due to thicker consistency). The slab size is 5600mm X 5400mm. The bit that is 10mm higher is about 1000mm x 5400mm. I would have screeded it, but the roof isn't very high and I don't want to take more head room away (2.2m), so I am consider using a concrete grinder to do the job.
Has anyone dealt with similar situations before? Will I be able to grind off the 10mm from that section with a grinder? or am I asking for too much? the mix itself was a C20.

 

[Doggit]

Depends how long ago it was done. Although it takes 28 days to reach full strength, it's pretty much there after a week, so it'll be a suck it and see job I'm afraid.

Can you add some SLC to bring the height up.

 

[tomfe]

You can grind it, it'll take a fair bit of time to take 10mm off but it's possible.
Buy your diamonds don't use the hire companies unless they have a decent price on diamond usage. You'll either need a vac or grind wet.

 

[dobby1]

Thanks for the replies guys.

Buy your diamonds don't use the hire companies unless they have a decent price on diamond usage.

Just checked, 50 quid per mm per plate, bloody hell! Am I really looking at 500 quid just for the plates here? Don't think I am willing to pay that much, I'm already spent way too much on the slab.

What do you think of using a grinding disc on an angle grinder? Something like http://www.screwfix.com/p/erbauer-double-grinding-cup-105-x-22-23mm/58310 - It'll be a bit risky, as I'll have to take the guard off, and I'm not a fan of angle grinders, but if it's saves be a ton of $$$ then it's worth a shot.

 

[Newboy]

What do you think of using a grinding disc on an angle grinder?

Not a hope in hell - even if the cup grinder could remove 10mm of concrete you'd be there for days (even more so with a 4" grinder) assuming your arms/wrists/back/knees/lungs held up long enough.

https://www.hss.com/hire/p/htc-gl450-grinder

 

[noseall]

What's the actual problem with the increased height?
If it is that contentious why not use a levelling compound on the remaining low part

 

[^woody^]

Scutch bit on a Kango is the traditional, no nonsnese way.

If you brush on some hydrochloric acid brick cleaner first, it softens the surface.

 

[garyo]

Is it a garage? I'd follow noseall's train of thought and try to ignore it. Could you put a run of 1 metre deep workbench down that wall etc...

 

[dobby1]

Thanks for the replies guys. I want to grind because the ceiling is already not very high, so using SLC/screed will only reduce it more. The area in at the entry of the garage door, so I can't put a workbench to conceal it alas.

If you brush on some hydrochloric acid brick cleaner first, it softens the surface.

That is a BRILLIANT idea. I'm going to do that before grinding that bugger.

You can grind it, it'll take a fair bit of time to take 10mm off but it's possible.
Buy your diamonds don't use the hire companies unless they have a decent price on diamond usage. You'll either need a vac or grind wet.

Will be using the DFG-400, the hire company charges £35 for 1mm per plate (that's 70 quid for both plates). How much wear do you think I will have on the plates for grinding 10mm on a 10m^2 area (C20 mix)?

 

[noseall]

That is a BRILLIANT idea.

Err....not really. Unless you wear a gas mask or are prepared for a wee bit of lung damage from the gasses given off.

 

[^woody^]

Err....not really. Unless you wear a gas mask or are prepared for a wee bit of lung damage from the gasses given off.

Hmmmm, is that what is printed on the can nowadays?

 

[nuzuki]

My slab for a garage came out a bit high. It was towards the back of the garage so ive told myself it was all part of the plan and will act as an inbuilt wheel chock to stop a car from rolling into the back wall

You could tell use the same theory and say its to stop cars rolling out the garage and damaging the door.

 

[333rocky333]

Wouldnt it be best to lightly kango and nibble the top off and then level if needbe.
Grinding without the quard sounds like an accident waiting to happen

 

[chappers]

.

Just checked, 50 quid per mm per plate, bloody hell! Am I really looking at 500 quid just for the plates here? Don't think I am willing to pay that much, I'm already spent way too much on the slab.

.

Its 50 quid for each mm of wear to the plate not the amount of concrete you want to grind.