Chiselling concrete floor

[OhGranny]

Hi Everyone
I am laying a new floor in my kitchen and the old concrete floor has been repaired badly with "humps" and "lumps" about 3/4" above the general level of the floor.
I would like to have a go at levelling it out a bit. I have tried a hammer and chisel but it is hard going.
Anyone recommend the best tool for chiselling the concrete level?
Also anyone know the best way to get off the old adhesive that was used for sticking down the vinyl tiles?

Thanks
Grannny

 

[^woody^]

Cheapest option would be not to use a normal cold chisel, but use a scutch chisel instead.

You can buy (or hire) a special diamond or Carborundum disc for a grinder for reducing humps in concrete floors. I'm sure screwfix stocks them.

Otherwise a scutch blade in a SDS drill with roto-stop, and then finishing with a hand block of Carborundum will do it.

Use a solvent, or heat gun and scraper for the glue - be careful with the heat gun though!

And remember, old floor tiles (normally the 9"x9" and pre-1970) are likely to have an asbestos backing - so avoid breaking too many and wear a mask and minimise dust when removing

 

[noseall]

the old concrete floor has been repaired badly with "humps" and "lumps" about 3/4" above the general level of the floor.
I would like to have a go at levelling it out a bit.
Thanks
Grannny

why not fill in all the troughs, and bing them level with the peaks with floor levelling compound?

 

[Aqua]

You say you are laying a new floor, what type ?

Concrete/cement screed, wood or something else.

To remove the high points of the original concrete floor you might hire a breaker (makita/kango) and use the spade attachment to level off the high points, will be less work than a hammer and chisel.

 

[OhGranny]

Hi Everyone
Thanks for the replies. I have been researching - anyone used a Concrete Planer such as this?
http://www.hss.com/g/6401/Concrete_Planer_C_w_Blade.html

I have lifted the old vinyl tiles and it looks like the floor slab has failed and someone has filled over the crack about 2.5 metres across the floor with too much material - in places I can see what looks like earth and muck in the cracks. I think it should have been dug out and then the floor levelled back to the existing level which I can see in places and which is generally - sound except for the crack across!!
I don't want to raise the floor level which matches with the adjoining hall. I just want to put Vinyl floor covering down.
I would like to get the cement / floor compound / concrete or whatever it is they have put down and try and get back to the original level - the biggest problem is that I want to fit a new door without hacking an inch off the bottom (like the present one) so that it will ride over the hump !!!!.

Thanks
Granny

 

[^woody^]

Are you sure that it is just a poor previous repair, or could it be progressive movement of the slab due to sulphate attack? Lifting of the floor slab (heave) in several places is a symptom of sulphate attack

If properties in your area do suffer from sulphate attack (ie ash used for hardcore infill) then it would be better to get this checked. Else it will continue to move

 

[Aqua]

Woody is correct, you might need to get it looked at before continuing.

If you are proposing to grinding alot of concrete off you might think about knocking the old floor up and laying a new concrete slab.

believe me ginding will make some real dust and mess.

 

[Nige F]

Guys, could old breeze blocks made from slag etc. and used for h/core have the sulphate problem

 

[noseall]

Guys, could old breeze blocks made from slag etc. and used for h/core have the sulphate problem

unlikely.

 

[JohnD]

I heard it's more often general builders rubble that includes gypsum plaster, combined with dampness. Possibly also bricks from old coal chimneys. (Power stations now use limestone filters to absorb the sulphuric acid fumes; it turns the lime into gypsum and has brought down the material price).

 

[noseall]

the biggest cause of sulphate heave is red ash or burnt ash being used as a hardcore infill.

this was widely used in mining towns as the waste slag from the pit or colliery was easily available. it was after a slag heap caught fire that the slag turned red and gave it the name red ash or burnt ash. this often happened.

dpm's help prevent sulphate ingress into the concrete and ultimately expansion of the concrete, which is so damaging. damp getting into the ash is also a factor.

coal fired power stations give off an ash bi product which is widely used in the building industry and is not related to red ash.

 

[OhGranny]

Hi Everyone
I've had a look at the schedule of defects when I bought this ex local authority house.
It states "Properties of this type of construction have been prone to expansion of the hardcore in the ground floor slab. This has been reflected in the valuation".
Also "The solid floor to the kitchen is crowning".
The living room which forms roughly 2/3 of the house is a wooden floor.
The kitchen and hall floors are concrete. It looks as if about a third of the kitchen floor is effected with a cross shaped crack with a definite crowning over about 2.5 metres square. The crown has been made worse by patching over but even removing the excess will still leave a definite crown.
The house is 1930's the walls are lath and plaster black lime so it seems likely they could have used ash infill especially as I can see through the cracked concrete slab what looks like black muck!!
My concern now is do I have take up the whole slab to cure it or just the effected part?
If I level it up and repair the cracks how long before it moves again?
I am going to renew the kitchen completely I don't want to have to rip it out again to fix the floor!!
On the other hand we have lived here for 5 years with no problem and I suspect the defect has been progressing for some considerable time before that.
Thanks
Granny

 

[Nige F]

Thanks, guys, sounds like my problem is the gypsum under the screed , I `d heard of this before but I`ve already had to dig up one floor and found breeze used as hardcore Strange thing is that these houses are loved by the estate agents ....and luckily punters too I was aware of most defects when I bought it and I`ve got 2 big strong sons to help ...........Granny, I would have your floor dug up and reinstated to modern standard with insulation and possibly have underfloor heating at the same time

 

[noseall]

agree with NigeF. dig up the floor, the affected hard core and re lay.

 

[OhGranny]

Hi
I'm getting worried now!
The walls in this house are of the cavity form.
Is it possible that the inner leaf of the wall is standing on the slab of the kitchen floor?

Or is the floor slab usually contained within the inner wall?
Granny