New Concrete Slab - Dilemma

[cornish_crofter]

BAL say you can use it as soon as the screed can be walked on.. but concrete is 7 days .. So you want to use it on screed..?

Basically, the plan was always that the former would go down directly onto the concrete. The screed would be laid on the area of concrete that the former doens't occupy, butting up to the former. Bearing in mind if it were an existing concrete floor I would have removed the screed in the area that the former would be going in so that it sits level with the screed.

As it's a new floor, former, with screed butting up to it was my plan.

I was looking to use the Greenscreed to bed the former down onto the concrete, which I will have to wait 7 days to do even if I use Greenscreed. Then my plan was to put down the screed using your idea of slurry mix or Alan's idea of SBR. Then the decoupling membrane the next day or as soon as time will allow using something like the Greenscreed. Then finally tile on top of the former and screed (all one level) using a flexible fast setting adhesive.

So you're right in a way. 7 days before the former goes down using BAL GREENSCREED, then 24 hours minimimum after laying the screed (which I'll be able to do after laying the former) for the decoupling membrane onto the screed again using BAL GREENSCREED.

 

[DHTiling]

That's it..🙂

 

[cornish_crofter]

My response in Bold

Alan

Thanks for that post.

The only other idea I had was to batten off where the former is due to go (leaving an inch or so to make laying the former easier, which can be backfilled with adhesive later)and lay the screed up to that, then wait until the concrete has been down for 7 days before fitting the former. This would

a) have the screed down earlier, meaning that the screed will be on the way to being down for 7 days before laying the membrane.

b) would reduce the total lead time on the job - screed and cement are curing simultaneously.

For example. The concrete went down on Friday. Hanson reckon as early as poss for the screed whilst there is still moisture in the cement. Screed would go down on Monday up to where the former would go. Then day 1 for the screed curing would be day 4 for the concrete. I would then leave it until Friday to put the former down using the Greenscreed, level with the new screed. By then the screed would be 4 or 5 days old. Then leave it until the following Monday to lay the matting on the screed.
Does that make sense to you?

 

[cornish_crofter]

OK, now I need to lie down! :LOL:

 

[DHTiling]

Can you not screed your own former? then you can do it all in one go..

 

[cornish_crofter]

Can you not screed your own former? then you can do it all in one go..

I see where you're coming from Dave but I like these formers. Cast your mind back to 2008 when I used one on an existing concrete floor, OK I had to dig a bit of the concrete floor out as the former was thicker than the screed that was down.

The thing with these formers is that the fall is basically worked out for you. It's a Tilux as supplied by Wetdecs - again.

I did have to replace a small area of concrete underneath the floor then. Having said that I seem to remember only using about 1 mixer full. Most of the area under the former was old concrete.

I recently got in touch with the customer I did that job for to ask him how they were getting on with the wetroom. His response was along the lines of "You would have heard from me if there were any problems." They use it regularly. His GFs father, who is wheelchair bound and their 6 dogs benefit.

 

[cornish_crofter]

With this job starting again tomorrow, I am considering laying the screed before fixing down the former.

The approach would be:

1) Trim and position the former. Mark off where the former would end and the screed would need to begin on the floor. Remove the former and place out of the way.

2) Batten off the floor in the marked position at the correct height.

3) As I'm having to run 15mm pipes in Denso tape down both sides (heating and hot and cold water) use 3x2 battens to facilitate this and to help me level out the screed. One batten each side.

4) Coat the area to be screeded with a slurry mix (SBR and cement 1 to 1 with water). Refresh/add as screed progresses. Backfill former waste channel with screed mix as much as possible at this stage, bearing in mind that some flexibility with the plumbing will be needed for fitting the former.

5) Allow screed to dry and remove battens.

6) At this stage the screed should only be walked on when protected by suitable ply etc. Hence it is feasable to start to lay the plumbing for the towel rail and the hot and cold supplies. All this while the screed is drying out as is the cement slab ready for day 7 for when the former can go down using BAL Greenscreed.

7) After plumbing is in, tested and suitably protected, backfill those channels with flexable tile adhesive (Greenscreed not necessary, just a normal fast setting flexible adhesive will do)

8) After a MINIMUM of 7 days has passed since the original concrete slab was laid, fix the former using BAL Greenscreed. Backfill the channel for the waste and any gaps between the former and the screed with the same adhesive.

9) When this has set lay Dural/Ditra decoupling membrane (decoupler and waterproofer - right?) onto screeded area (including where plumbing is) only. Use BAL Greenscreed for this, even though the screed may have been down for a few days at this point.

10) When the Dural/Ditra has set, I will then need to run some tape on the floor/wall joints either side of the room. This will allow any tanking on the walls to effectively join the floor.

11) After the Greenscreed under the former and the DuralDitra has cured I am now in a position to tile when I am ready - ie after boxing in the plumbing for the shower.

How does that read to you?

 

[cornish_crofter]

Thanks Dave, I take it you approve 😉

 

[DHTiling]

Yep.. happy screeding..🙂

 

[cornish_crofter]

Well, got on with it today and on the whole it went OK, apart from the sharp sand had frozen!

I didn't use hot water to mix as I was worried about it curing too quickly and not bonding, though afterwards I realised that this probably wouldn't have made any difference and may have helped me.

I managed to do most of the area I had set out to do. Though I did start to wonder why I bothered when there's the plumbing to go down. The only benefit I can see with this approach is that the battens I had laid onto the floor helped me to get a near perfectly flat floor - running towards the position of the former and away from the door.

I had measured and cut the former before I started then left my inch then battened off for the screed. My guess is that I won't be able to do much tomorrow as the screed will still be setting. It's taking a lot longer for everything to set in this weather.

The SBR slurry went down a treat. I also applied neat SBR into the channels I backfilled as well.

When I can next get onto that job I'll be laying the plumbing for the heating and water along the floor, ready to cover and backfill. I'll probably put down a suitable length of DPC, lay the pipes on that then cover with denso tape, sticking that down onto the dpc as well as the pipes. I uncovered a similar arrangement on another job and it seemed to work well for 20 odd years. The pipes were only leaking where they had come into contact with screed or concrete.

It'll be well over 7 days before I can do the former I think - which was part of my plan 😀