Levelling interior concrete

[nordita]

Ive poured a concrete slab floor awhile back and unfortunately it's not entirely level with it declining around 30 to 40mm over 5m.

What would you recommend for levelling it?

I have a half ton bag of ballast and half ton bag of builders sand left over I was hoping to use. I'm tempted to use the builders sand but I know that's not recommended.

 

[Deluks]

What's going on top?
Ideally you'd screed it using sharp sand, if you could sieve the big stones out of the ballast and mix with the building sand 3:1, that could make a reasonable substitute. But all that effort for the sake of buying a few bags of sharp sand.

 

[nordita]

I haven't decided yet. Probably something like laminate wood flooring. Yes I will likely load my car up with sharp sand.

 

[noseall]

I haven't decided yet. Probably something like laminate wood flooring. Yes I will likely load my car up with sharp sand.

Be careful with floor screed. It can not be laid thinly. You need a minimum of say 50mm over the whole floor.
It will not lend itself to say being feathered out to 20mm or less. It will just break up.

 

[Ivor Windybottom]

Could you do a rough job with cement screed then liquid self-levelling over the lot?

I mean make up the big bits to just under finish level, nothing on the higher bits, then liquid over all of it.

 

[23vc]

Or mix sharp sand in with floor levelling compound. But that’ll obviously cost more.
If attempting to screed using normal sharp sand and cement where it’s thinner, using a good bonding agent (I’d probably use SBR) will be key (pun intended)

 

[nordita]

I've reached the point of my floor which the depth to make up is at least 50mm. I have half a ton bag of ballast left over. Any problem if I coat the first 25mm with mixed up concrete and then finish the top with the sand cement screed (immediately after the other)?

Will save me £££, a trip to B&Q and lugging bags up the garden.

 

[Ivor Windybottom]

Probably not a good idea, the aggregate will be about the same size as the thickness so you'll be building in weak points.

All IMO.

 

[nordita]

I've done a bit more work today without concrete and I'm almost done. I'll finish the rest with sand cement and then buy some self levelling material.