Concrete and screed - in sections?

[JuneW]

This may be a daft question, but do not want to discover the hard way what not to do! Hope someone can help (unfortunately I'll be offline Sat-Tues so please won't be able to respond immediately if you need clarification).

The question is about a conservatory base and how to go about the concreting/screed stages. The area is 2.5m x 4m, with the long side against the house wall, so the plan is to mix and pour concrete in sections 2.5m x 1.5m (ish) for ease of tamping.

Can I pour the concrete then top off with a screed mix, then tamp down, or should I tamp down the concrete then wait (if so, how long?) before adding the screed and tamping that down? Or should the screed be applied across the whole base in one go?

And...how quickly or not should I place the adjoining section? Should I be aiming to finish the whole base in one day, removing the shuttering once the concrete has set enough to stay put and moving across to the next section? Or should I wait for one section to go off, then do the next section the following day? (will be using a cement mixer rather than having ready-mix delivered)

I was planning to put the DPC beneath the concrete, but could it go between the concrete and screed?

The plan is finish the floor, eventually (!), with ceramic floor tiles.

All advice gratefully received.

 

[HuwRoberts]

Not sure how to answer the pouring stages but for the size of the bay it would be easier to pour in one.

In respect to the DPM, it all depends on where your insulation lies?

If between the slab and the screed then the DPM can be installed under the isulation, however; if installed under the slab then the DPM should be under the slab.

 

[JuneW]

Thanks for the reply Huw.

Regarding pouring the floor, I didn't envisage doing this in one go as the area is too wide (I thought) for ease of tamping. 4m is quite a stretch! Thought I'd be more successful with sections.

Or were you referring to the concrete and screed ie pour the concrete, tamp it, and then top off with screed immediately?

Cheers

 

[PrenticeBoyofDerry]

If you are insulating the floor, which would be recomended. I would have DPC below and above the insulation.
I would also consider doing it in one pour too, instead of stages.
Work out the volume you need, it maybe worth getting ready mixed and delivered.

 

[HuwRoberts]

Thanks for the reply Huw.

Regarding pouring the floor, I didn't envisage doing this in one go as the area is too wide (I thought) for ease of tamping. 4m is quite a stretch! Thought I'd be more successful with sections.

Or were you referring to the concrete and screed ie pour the concrete, tamp it, and then top off with screed immediately?

Cheers

As I said earlier I am no expert when it comes to concrete or screeds but this site below is very informative and should give you the answer you require.

http://www.homeinstitute.com/pouring-concrete.htm

Also with the double DPM answer, I have heard of this being done but any large contractor would dismiss this as overkill and has never come into any of my designs, however; the choice is yours.

Hope Ive helped.

 

[JuneW]

Hi again

Getting ready mix is not really an option due to the site constraints. So I have to use a cement mixer, and will have to do it in sections to tamp it down successfully as I only have access to 3 sides of the base (house wall in the way on the long side).

I've looked at that link (thanks for that) but I still don't know if you can add the screed mix straight on top of wet cement, or whether you have to wait, and if so, for how long? I know you can put a screed on dry concrete and old bases, but have yet to find any info on how quickly you can do it.

Cheers.

 

[PrenticeBoyofDerry]

wait until the concrete slab is cured/dry before screeding.
If you are mixing in seperate batches, be careful to measure the mixes to near exact as you can, this includes water content, if not the concrete will have different strengths and cure at different rates, which can cause cracks.
I would also recomend that the following day, you pour water over the base, this will help toughen it up.