screed problem

[Beeboss]

I have a large floor to screed, getting on for 60m2. My problem is that it is a long way from the road to my new rear extension and my girlfriend (unpaid labourer!) has hurt her shoulder so I have to do the job by myself. I think I need some 4.5 tonnes of screed so it will be too much to have it delivered ready mixed and wheelbarrow it round and lay it in a day and I can’t find anywhere locally that can pump it round (even if I did have the money to pay for that) so my plan is to mix it up myself in batches and lay it over a few days doing maybe 15m2 a day. I am sure this isn’t ideal but I am wondering if it is a reasonable way to go? Am I going to cause any serious problems by doing it in this way?

The screed will be about 7.5cm thick on dpm and 100mm of jablite which sits on a reinforced concrete raft (150mm thick at minimum). Mix maybe 4:1, sharp sand : ordinary cement?

Any advice gratefully received.

 

[noseall]

You will need 8 tonne bags of screed sand to do 4.5m³ of floor screeding. Plus aboot 65 x 25kg bags of cement.

Screeding is one of the most difficult jobs in our trade and the mix is not easy to get right. Doing it in batches is ok, but on an unbounded surface, not advisable.

I use a company now for larger jobs. They have a machine that mixes it on site and pumps it into the building. They would do your job in a morning. Animals.

 

[Beeboss]

I would happily pay someone to pump it round but can't find anyone who has a pump for screed. If anyone knows of someone who can do this please let me know. I am between Brighton and Eastbourne.

Another possibility is to use tongue and groove chipboard (P5) instead of the screed, but I can't find out if I am allowed to do this or not. I did email buildings control and they have usually been very helpful but they didn't bother to reply this time, maybe it is something that is not covered by the regs and so they don't care, I have no idea. I would be quite keen to to this if I can - does anybody know if I am allowed to do this?

 

[clive12345]

Why not phone building control ,either first or last thing .
Leaving a joint when the screed is on insulation sometimes results in a small lip and a crack .
When you screed a room you put "screeds" all around the room for your levels . If you do it
in stages you will have to dig up the "screeds" each night . It really needs to be done in one .

 

[Beeboss]

Many thanks for your suggestions.
I am just wondering if I can use some sort of expansion joint and screed up to that and then the next day screed from there? Should I have an expansion joint anyway? (dimension of floor is approx 12.5m x 4.3m)
I am leaning towards getting ready mix delivered and then wheelbarrow it round but can't drum enough helpers to do it in 1 day. I could probably manage it in 2 goes though.
Do a few small cracks matter that much? Am I right in thinking that the screed doesn't really have an important structural function, and it will end up being covered with carpet or something anyway?

 

[theprinceofdarkness]

Insulation compresses when loaded with a weight. So the screed puts some weight on it to compress it a bit and when you walk on it the screed acts like a big sheet so it spreads your weight over a larger area, so it hardly compresses the foam any more. The weight of the screed and furniture also causes an overall settlement of the foam so it will drop slightly, or a lot (3mm) if it was not flat when laid.
I used foam then 22mm T&G P5 chipboard then 3" thick flagstones and it has not moved at all in ten years (beginners luck?). I would use formwork on your finished edge with straightened out stainless steel wall ties half in the old screed a and half sticking out to go into the new screed. So if you use 2 X1 roofing laths and screw then together trapping the ties in between. The problem is to keep this animal in place while finishing the first bit of screeding. More laths jammed against opposite wall and building blocks sitting on them? For belt and braces you could prime the old screed edge with SBR to help "glue" the two screeds together.
Frank

 

[Beeboss]

Thank you, that is very helpful.
I am a little worried about the insulation compressing because I have some heavy internal stud walls that will be resting on the top of the screed. I was considering putting in some timber supports underneath where the walls will go but I am not sure if that is a good idea.

 

[theprinceofdarkness]

i guess that the stud walls should run at right angles to any joint. How heavy are they?
Frank

 

[Beeboss]

I am building a room for playing and recording music so I need excellent sound insulation, the best way of doing this seems to be to build an entire 'room within a room', so stud walls covered with 2x12.5mm plasterboard (height is about 3.3m) and 8x2 rafters again with 2x12.5mm plasterboard for the ceiling. All in all that is going to be quite heavy. I guess I could work out the total weight and divide that by the area that would be in contact with the screed, would that help? I was wondering if there is a need to add some extra support for the walls underneath the screed but have never heard of anyone doing this. One point of concern is that the new stud walls will run along the perimeter of the room about and inch or so inside the newly built block wall but as I think I need to put in some strips of celotex as a thermal bridge around the edge of the screed, and so already the new stud walls would be very close to the edge of the screed.
Any thoughts kind people?