Quick drying concrete.

[mallyplumbob]

Has anyone had experience of a fast drying concrete, 100mm slab, which can be laid prior to tiling a wet room
(Porcelain tiles over Marmox insulation board) floor. Needs to be quick drying.
Someone’s mentioned Cemscreed which is a Tarmac product.
Thanks

 

[Ian H]

The quickest is the Extra Rapid in the yellow/green bags.

 

[mallyplumbob]

Hi Ian. Is that a concrete or adhesive.
And what make.

 

[JohnD]

do you mean quick drying? Because of damp?

Or do you mean quick setting or quick curing, because of frost or need to walk on it after a few days?

Concrete does not harden by drying.

 

[mallyplumbob]

Hi John.
Quick drying. I need to put a new concrete slab down, 100mm approx and then fix the Marmox insulation board using tile adhesive, lay the Warmup heating element and then lay the porcelain tiles. I need the concrete slab to “dry” as soon as possible so that I can carry on with the rest of the procedure.
I’ve been told a standard concrete mix would take 1 day per millimetre to dry.
So I’m looking for a “quick drying” mix.
Tarmac Cemscreed, which is added to the ballast/aggregate, instead of cement, apparently dries quicker than the standard mix.

 

[^woody^]

You need to reduce the water content of the mix do that there is just enough to make it workable and for the cement to react.

Cemscreed is for screed not concrete.

There is a vacuum moisture extraction process for rapid drying of concrete, but that's probably a bit too extreme for a little wet room.

You could add mesh to control cracking and then use fans or heat and ventilation.

 

[Ian H]

It's a cement available from any builders merchants. It sets fast but no idea about drying.

 

[mallyplumbob]

Ok thanks

 

[JohnD]

if your concern is damp concrete making the floor finish wet, apply a DPM over it.

 

[tomfe]

Why the rush?
Concrete you can work ontop of concrete after a couple of days.
If you use a flexible adhesive and grout and wait 7 days you should be fine.

 

[mallyplumbob]

I’m concerned about locking the moisture into the concrete slab.

 

[Blagard]

I’m concerned about locking the moisture into the concrete slab.

Woody has already told you the most sound bit of advice - reduce the water content of the concrete. You can get concrete to set fast sure, but that is not dry fast. The water locked into the mix needs to work itself out, so the less you put in the less to evaporate. once the concrete has cured to a reasonable strength I would suggest a week, then put a heater and dehumidifier into the room to accelerate the drying out. The figures you have are for natural drying out. You may be able to decide when to carry on by the amount of water the dehumidifier collects each day. But if for instance you put heat and humidifier in too early, it could cause the concrete to crack because you have not given it enough time to cure. That is why contractors put mats over concrete in the summer, to keep the moisture in until the concrete has sufficiently cured.

Since you are doing a wet room your grouts are going to be waterproof at least to some degree. So long as the title adhesive does not degrade with the dampness you lock in, you should be OK as the moisture will usually find a way out but over a much longer term. But I would still try assisting the initial drying out before doing the tiling

 

[JohnD]

I’m concerned about locking the moisture into the concrete slab.

Why?

 

[badgeraudio]

Hi John.
Quick drying. I need to put a new concrete slab down, 100mm approx and then fix the Marmox insulation board using tile adhesive, lay the Warmup heating element and then lay the porcelain tiles. I need the concrete slab to “dry” as soon as possible so that I can carry on with the rest of the procedure.

Could you not change the build up?
Say 50mm celotex, then the warm up element. Then a 55-60mm screed then the tiles?
you only have screed to go off then rather then the concrete and insulation board adhesive before applying the tiles..

Note I am not qualified in any way but its what I would consider!

Mike