How many hands?

[Jegero]

Hi,

I am about to pour a thin concrete slab over an existing one. The volume of this slab will be approx 7000mm x 4000mm x 50mm. Is this a job I can do on my own (with a powered mixer), or should I try and get some helping hands?

I plan on doing a 1:2:4 mix... Should I use any additives to slow the curing process?

Ta

 

[RonnyRaygun]

At 50mm thick you could do it yourself.

Use a proprietary bonding agent and prepare the existing surface to get a good bond, else it will debond and crack in no time.

 

[Jegero]

Thanks for the reply...Do you think it will still crack if its on top of an existing slab thats 2-300mm thick?

 

[RonnyRaygun]

Thanks for the reply...Do you think it will still crack if its on top of an existing slab thats 2-300mm thick?

Sorry, edited my reply, see above.

 

[Jegero]

Bonding could be an issue anyway... I was planning to lay a DPM over the existing slab and pour on top of that...?

 

[RonnyRaygun]

Bonding could be an issue anyway... I was planning to lay a DPM over the existing slab and pour on top of that...?

Well, concrete screeds are usually 75mm thick. It’s not unheard of for them to be 50mm, so you might get away with it on an existing solid surface.

 

[Jegero]

Well, concrete screeds are usually 75mm thick. It’s not unheard of for them to be 50mm, so you might get away with it on an existing solid surface.

It is pretty solid... I'll give it a shot I think... Thanks for taking the time to reply

 

[^woody^]

Concrete or screed?

You'll need mesh in screed, and concrete is not the right stuff to lay if this is for a floor finish.

 

[Jegero]

Concrete or screed?

You'll need mesh in screed, and concrete is not the right stuff to lay if this is for a floor finish.

Thanks Woody, I was planning to use a self leveling liquid screed on top as the finish??... Is there a better product I should use?

 

[RonnyRaygun]

Concrete or screed?

You'll need mesh in screed, and concrete is not the right stuff to lay if this is for a floor finish.

Good point. At 50mm I’d put fibres in it. Not impossible to float a concrete screed, but not necessarily a DIY job.

 

[^woody^]

Good point. At 50mm I’d put fibres in it. Not impossible to float a concrete screed, but not necessarily a DIY job.

Fibres only control initial shrinkage, and do not reinforce generally.

 

[RonnyRaygun]

Fibres only control initial shrinkage, and do not reinforce generally.

True, but that’s what mesh is for in a screed too.
It’s on a solid slab so not subject to bending forces.

 

[^woody^]

Thanks Woody, I was planning to use a self leveling liquid screed on top as the finish??... Is there a better product I should use?

Well, as long as you are aware that you'll need to use self leveller.

The other concern is that 50mm may be too thin for a concrete mix, due to the stone sizes. It's a risk IMO, may work, may not. Perhaps a modified mix, of some sort, but then it's just guessing.

 

[Jegero]

How would a smaller aggregate like pea shingle work out?

 

[^woody^]

True, but that’s what mesh is for in a screed too.
It’s on a solid slab so not subject to bending forces.

But if there are subsequent temperature and humidity changes - normal or seasonal, the mesh deals with those but fibres won't.