removing hump in concrete floor

[markio]

I'm about to lay a large laminate floor and having removed the carpet, I've realised that the concrete floor underneath has a shallow hump in the middle.
I don't want to raise the rest of the floor, as it's open plan and would require raising the floor all the way through.

I'm wondering what the best method of flattening the hump would be? It's a couple of square metres that needs "shaving off", as it were.

 

[noseall]

are there any cracks around the hump?

does it sound hollow when tapped?

 

[markio]

That's a perfect description of it. Is it caused by water?

 

[noseall]

it could be attributed to 'sulphate heave'.

do you live in an old mining area?

 

[markio]

No mining around here I'm afraid. Can you elucidate?

I think the concrete floor is no more than about 20 years old, although the property is much older.

If it is sulphate heave, what should I do to level it, or would it need to be replaced completely?

 

[noseall]

for any degree of success, the floor will need to be removed as well as any contaminated hard core beneath.

replace with m.o.t. type 1, 30mm-dust granular stone hardcore. if the sub floor make-up is particulary deep compact in 150mm layers if necessary.

use a damp membrane.

i would imagine there are drilling tests that can be carried out to determine whether your floor has sulphate gas present or if it is just a structural fault.

you will have to make some local enquiries.

do you know if there is a d.p.m. present under the current floor?

 

[markio]

No idea if there's a DPM, but I have a chartered surveyor friend, so I'll ask him for some pointers on sulphate heave.

Thanks for your help.