Is it normal that new Karndean floor in recently built extension is uneven?

Hi it sounds like your floor layer did a bad screed (latex) the karndean would need pulling up and screeding properly, sorry

Its obviously the floor layer and the screeder want to pass the buck, they want to take up another trade Peter

Hi I would say your original sub floor that was laid in the rain is the problem, this should have been pretty much level and then a latex screed added to this to make it smooth and any slight imperfections in level would have been sorted by the latex. What has happen is the floor layer has just poured a thin layer of latex over a very poor screed so the latex has just taken the same level of the screed. What he should have done was either to get you as the home owner to get the builder to sort out the poor screed or should have used more latex to actually level the floor. But because of how bad the level is, a deep base levelling compound would have been needed , as latex can only be applied to certain depths . As the answer above says only way to sort is to take up the Karndean and the level the floor correctly , not the answer you're looking for but the only way. Regards Jason @ J R FLoors