Fresh Concrete Slab Uneven

Saddens me when peeps can't lay concrete level,it isn't difficult to level slab.

I would think insulation will compress enough with weight of screed on top of it.

 

I suppose you could run over the slab with a grinder & remove the high spots.

 

I'd be tempted to get the 'oles who laid it to grind it away - with their teeth.

Isn't it ok to lay a sand screed on top, level this orf, and then place the insulation down? Obviously the sand would have to be contained so's it cannot move out from the sides.

I cannot see insulation sheet - even the polystyrene type - compressing that much - not unless you got an elephant to walk over it; it'll be such a smooth and gentle height change that the sheet will be well supported and won't compress. A wee 'chip' sticking out would be ok - that would embed itself in the sheet, but a 'flat' surface, I don't think so.

Ah - I think KIAB means it'll 'conform' to the sloping surface, and not actually 'compress'? Good chance it will, tho' it'll depend on the thickness of the insulation and what type - how rigid.

I guess try laying the insulation on top, see how flexible it is (will the weight of the screed 'form' it down) and take it from there. If it will, then fine, if it won't - if it 'bounces' - then a thin sand screed down first to level the slab?

I'M SURE PRO BUILDERS WILL KNOW EXACTLY WHAT TO DO HERE. WHERE ARE YOU?!

 

All depends on the thickness of the screed & insulation, some will compress just enough,others not a smidgen.
The insulaton will take the shape of the slab, & with the screed, you might get away with it.

 

The insulation will be much more likely to bend and form if it's made up in layers rather than one thick sheet.

(This thread could run and run...)

 

Polystyrene boards would most likely deform/compress just enough, whereas with Celotex it's solid, just looked at sheets here, it's solid, no compression at all.

 

We walk on Celotex in floor construction and don't leave footprints so it is highly unlikely that 65/75 screed will push it down uniformly. The finished job will likely sound hollow and may move over time. Get whoever did it to put it right: as KIAB says it ain't rocket science.

My preference is always to put the Celotex under the concrete for a variety of benefits:

1. Heat storage within the insulated zone
2. More weight on the Celotex to hold it in place and reduce chance of
3. Second chance to get floor dead level when screed goes down
4. Less screed

 

Alway perfer Celotex or simalar under the concrete, but some BC's prefer it under the screed.

 

Unfortunate as it is, its not uncommon, after all the oversite is just that, not a finished layer, 20mm in 2 metres is only 1% out so isnt the end of the world, you could make up some of the lowest areas with self levering compound to bring them to within 10mm, this then shouldn't cause any problems.

 

Poo through the letterbox of the person that did the work?

 

Agree with Phil the Paver above, latex(levelling compound) the outer edges to build up near to high point if it's that much out of level, let go off, then proceed as normal, insulation and screed. The alternative is chiselling out the high point which is time consuming, soul destroying and mess creating.

 

A floor grinder is about a £100 a day to hire, I would be tempted to just grind off the high spots and then let the insulation and screed make up the level

 

Agree, cheaper option to levelling compound.