Cracked concrete floor prep for self levelling.

[baileyswalk]

I'm in the process of prep'ing a concrete sub floor. I just want to make sure I've done everything correctly before the self levelling.

The concrete has quite a few cracks in it, which are also high points. So I've been grinding these down which has opened them up a bit and they will now need filled. Can I fill them with regular mortar or do I need to use something else for better results?

Also, do I need to leave an expansion gap around the edge of the room for the self levelling compound or just make sure it's all sealed off so that the compound can't run out?

Last thing... should I PVA the floor first?

I've been reading around and I'm getting some conflicting opinions about the above.

The self levelling compound instructions don't really offer much help either. It's the No - Nonsense stuff from screwfix.

 

[cjard]

Little tip for the screwfix no nonsense stuff, take a look at the COSHH safety data sheet, it's linked on every relevant product on screwfix site. It will tell you who made the no nonsense box contents. In this case we see that NN leveller is actually norcros pro50. The data sheet also cites a phone number for the tech dept so if googling for info on the branded version of the name doesn't help, try phoning them

I understand why people say PVA, as if the leveller gets all the water sucked out of it by the concrete then it gets ruined.. The list of instructions on how to care for my poured screed self levelled floor slab were extensive. I imagine SL compound is similar stuff

 

[baileyswalk]

Thanks for that, found some more useful info after searching for the norcros stuff, they don't suggest applying PVA unless it has been power floated which seeing as it was put down in the 30's I doubt it.

 

[cjard]

I was very surprised to learn that the no nonsense expanding foam was made by soudal. significantly cheaper for the most part, I reckon screwfix must use their buying power to batter the makers of good gear down on price, then use that to give a reasonable margin on NN.

Handy things hose COSHH sheets, and I'll say one thing for screwfix, they might be a bit pricey on some stuff, but the convenience, quality and ease of returning surplus, plus the nice layout of the vat invoices makes them a sensible choice in many regards

 

[baileyswalk]

What about the cracks in the concrete - OK to use regular mortar or better off getting something specific for the job?

 

[dazlight]

Is the concrete old? Why is there cracks ? Does it have a damp proof membrane under the concrete.
Yes you should be priming it with the matching primer to the smoothing compound.