Screed info please

[happyhero]

Hi sorry to bring this subject up yet again. I have been on here about this job before but I was just wondering if someone could clear a few things up for me please.

Basically I have a downstairs extension which had a wall in it dividing it into two halves. It has parquet floor on hardboard sheets laid on the floor.
I have removed the wall and it has left a trench which I have removed anything loose from and this trench varies from about 3cm to nearly 5cm, most of it being about 4cm. The floor is out by about 1cm either side of this trench so I was going to peal away at the parquet until I can lose the difference in a gentle unnoticeable slope if neccasery.

I was going to screed the trench to just below the lowest floor level which would make the screed closer to 3cm. Then peel back the floor until I get something acceptable and then use some of the Ardex k15 leveller to level from the top of the screed to the face level of the parquet.

Thing is the more I read the more I get confused. Some suggest 3 to 1 mixture and some 4 to 1, can someone tell me which one is best and why please?

Also as this screed is quite thin for screed what should I do with it, ie what should I put in it, PVA (how much if so), expanded metal, anything else?

How thin can a screed be and get away with it?

Also by the wall the removed wall was joined to, I can see there is a membrane under this floor. In the trench you cannot see this, just concrete so I am assuming that this is a layer of concrete over the membrane. Do I have to do anything to this concrete to make my screed stick better to it, ie PVA it?

Any advice or recommendation appreciated.

 

[Fluffster]

Go for a stronger mix however at that depth you could use a bag of self levelling latex if the area is not too big.
Pete

 

[happyhero]

Go for a stronger mix however at that depth you could use a bag of self levelling latex if the area is not too big.
Pete

But isn't it a bit too deep for that at 3cm plus?

Can you explain about what difference the 2 mixes make, eg someone told me that sometimes the stronger mix will be too brittle or something like that?

 

[bobbler]

Hi,

What you have to remember here is that screed is something that you use to just level off a floor. All screeds crack after time and most delaminate from the concrete below.
Screeds also need to be at least 50mm thick to be effective as this is where the strength comes from.
In this case to get over the problem, in the areas that are 25mm or deeper, I would mix a clean grit sand (suitable for concrete) with cement at 1:4 by volume. I would then not add water but mix in Styrene Butadine admixture (SB) until the material is just damp and definately not sloppy. I would not use PVA as some of these are as useful as chocolate fireguards! Then where you are to lay the screed, paint a coat of SB into the hole and before it drys fill with the screed and level off. In the thinner areas use a self leveling compond. The screed will set like bell metal and the SB will help it to bond.