20mm screed in a plain 1:4 cement/sand mix?
 

Quick sanity check:

I've just laid 20mm marmox in the bathroom and have left cutouts for the bog
and bath feet (wide enough to marry with most standard baths) as suggested
by Marmox technical as these are points of higher load concentration (bath
moreso but the bloke suggested both).

I need to infill these with screed to level tomorrow - then give it a week
curing and drying out time.

I *could* use an SBR mix, but I feel there is merit in allowing the
substrate under the marmox to breath slightly. Anyone see any problems with
a 1:4 basic mix at 20mm thick? It will be bonded to the substrate with
cement slurry.

Ta

Tim

20mm screed in a plain 1:4 cement/sand mix?
 

John Rumm coughed up some electrons that declared:

Tim S wrote:

I *could* use an SBR mix, but I feel there is merit in allowing the
substrate under the marmox to breath slightly. Anyone see any problems
with a 1:4 basic mix at 20mm thick? It will be bonded to the substrate
with cement slurry.

Bit on the thin side - but it will probably be ok. The other option
would be a self levelling mix with some sharp sand it it.


That's an option too.

I know an SBR screed will go down to 10mm - but then I considered that I
have random stuff[1] sandwiched between 2 impermeable layers (30mm bonded
SBR screed underneath and marmox on top). It's a bathroom - so it is
inevitable that water will get in sooner or later. So it seemed a good idea
to allow some paths for it to get out, even if it's very slowly via just
the grout lines.

[1] Random stuff is 10mm levelling compound (because I cannot dry screed
level!) and tile adhesive - neither of which is really rated for continuous
dampness.

I'm over worrying as usual but my philosophy is if a precaution can be added
for little effort, it's worth doing...

Cheers

Tim