Concrete floor problem

[poynton phil]

I'm going to be tiling a concrete floor soon, that was laid in October 09. The problem is that i can scrape up to a cm off the surface of the concrete, of what looks to me like cement, that turns to powder as i scrape it off. The company that done the job, said in cases like this they just cover it with slc, and then it'll be ok for tiling. Now i'm thinking, will a slc put this right, or is this company just trying to fob me off. Any advice on this will be appreciated, thanks.
PS, I have included a couple of pics below.

 

[Ajax123]

This looks like laitance to me. IT could be mixed up with a curing compound of some sort but not sure. It will need to be scraped back as much as possible to hard concrete and then I suggest treating with a consolidating epoxy such as PHS from Flowcrete or PSRS from Ardex. This will leave a reasonably hard surface onto which you could pour a smoothing compound to which you could tile.