Hi all really hope someone can help me out. So I messed up when casting a concrete hearth. I tried to finish the top 40mm with a grit sand mix to achieve a smother finish but I got the mix too weak. I've now hacked the top layer off. So basically I need to reapply another layer to add the thickness back. I've no idea what to use. Originally I was thinking a dryer floor type screed but I've now been advised that this probably wouldn't work so worried that I'm going to have to chop it all out and start again I've put a photo of what it's currently like