Is 50mm concrete slab strong enough for bathroom floor?

[JSLawrence]

Hi team,

I recently removed the 50mm screed layer from our bathroom and am seeking to fill the 50mm deep void with concrete reinforced with steel mesh. Can you advise if this is thick enough to avoid major cracks in the concrete? One of the concreters I’ve been speaking with is wary of doing the job as he thinks it will crack. If it’s on top of concrete though and the existing concrete is wet before pouring, won’t the new concrete bond to it and strengthen the whole thing? He has questioned whether I just use the existing concrete base and have a step down into the bathroom. I’d love to hear your thoughts please? My other problem is the concrete sheets on the wall have a 50mm gap at the bottom as they were installed before the screed was removed, so was planning to build the floor level back up to meet the concrete sheets. Thanks for your help. This is turning into a very painful job to try to manage with very few tradies who will come out to our rural property. So doing our best. Thanks for your advice and thoughts.

[Jewelleryrescue]

Hi @JSLawrence 

Yes  50mm is plenty strong  enough for a regular  garden  path.   75mm is the minimum  drive way thickness for  cars (not regular trucks parking though) 

Your 50mm is  super golden

I would  go as thin as 30 mm for regular concrete. Rare  hair cracks can be filled under tile  on top of the  original  slab they arnt an issue or weakness needing ripping up.

Worst  case senario a crack  forms.  Simply fill it with  regular cement no sand.

Make  sure you follow the bag mix ratios for general purpose cementing (do not put in extra cement as this will cause cracking for sure.)

Yes the steel  will help mid way into  slab thickness.

This step not really necessary as the new slab wont really move in situ as it is framed  by walls.  But In case of  future  jobs.

To intergrate the bottom slab  into the top slab use  a   lump  hammer / Impact chisel.  hit the old  slab and put dents/chips in to lock the two slabs together every 300mm or so.

Hope you get your project finish  with out to many hassles.