Quick advice needed - bathroom floor

Hi folks,

Father has just started a bathroom reno and offered myself up as his gopher. It's an old bathroom (early 80s) so in desperate need of a makeover.

Lifted all of the floor tiles to reveal a very sandy concrete - soft and uneven. Around the vanity there were a few breeze blocks and probably a 4" drop to the pad (no sandy concrete inside vanity space - just a nice big hole).

My opinion is that we should blow away the sandy concrete and redo cement floor from scratch prior to anything else. Dad is keen to avoid the extra effort and cost and has suggested filling in the hole then going straight to a thick screed.

My view is it's worth getting rid of it and starting with the best possible floor surface so it lasts. Anyone willing to throw in an opinion from experience?

Cheers


EDIT: Also wanted to add the existing sandy concrete is not typical. Pale yellow, extremely sandy and soft. Almost like a sandstone.

How thick is the concrete ? My preference would be to knock it out and pour another one so you know what you are dealing with. There's nothing worse than doing all the work involved for a big reno and then having to re-do it a few years down the track because shortcuts were taken.
Is this a concrete slab on the ground or a suspended slab just in the bathroom area ?

Stewie

Thanks for the reply Stewie. Have just been round there doing some more work and had a closer look. The builders have put down breeze blocks onto the slab for the shower recess, vanity and bath - then rendered over it. The sandy concrete has then been dropped in on top of the slab, is 3-4 inches thick and only in the floor space that would be walked on. i.e. not under vanity, bath or in shower recess.

Have included img below (hopefully it works). I agree, best thing is blow it away and repour. Spend the time getting it right now so there are no dramas down the track.



Edit: Have since discovered water seepage in shower recess, so will have to cut out a large section and expose pad. Father still not keen on blowing the whole lot away - makes no sense to me given we need to grind 20-30mm off the top anyway. Oh well...take short cuts and pay the price later.