Block and Beam Screed

[Jamie25]

Hi folks. Been lurking on here a while but first posting today.

I've recently built a 6x 7.125m extension to my bungalow and being on a sloping site I went with B&B for the flooring. Having just re-roofed the bungalow I've finally opened the doorway from old to new and the next step is to lay the insulation, UFH and floor screed.

The floor finish will be tiles directly on top of the screed. I'm concerned about getting the screed level, particularly because of a 25mm drop on the B&B from front to back - entirely my fault for reasons I won't go in to out of embarassment!

The screed is to be between 60 and 85mm thick but I'll be leaving a small chanel out of this for services. This gives around 3 cube of screed required so I'm looking at a readymix. The walls are already built but the screed could be pumped through the window opening.

Should I just be looking for a wet mix, then tamp and float it myself. Do you think I'd get theis level enough? Concerned about screeding the normal way with battens because of the size of the room and the slope of the floor. Maybe screed just below required level and finish with a self leveling compound? I don't know how this might react with the UFH.

Would a self leveling screed be suitable for this and would it make it any easier. I guess it'd be a lot more expensive?

Sorry for the myriad of questions but it's all new to me!

 

[Cindysotherhalf]

Ready mixed screed tends to be quite dry and has a retarder in it so you have plenty of time to lay it. I tend to run sufficient screed around the perimeter of the area I'm working in first and form bays with more rows of screed. Providing these are level you then fill them in pushing down on the screed and levelling as you go. I use an aluminum straight edge 2400mm long and drag this over the screed that forms the bays thus filling them in. I also use a plastic float rather than steel as the steel ones bring the water to the surface and this makes it more difficult to get a good finish. Hope this helps.

 

[noseall]

I've not used the wet pumped stuff but i would imagine it requires a watertight sub base.

Don't go down the additional floor levelling compound route as you can get an excellent finish with regular screed.

Floor screeding is bloody hard work though and requires reasonable skill. These dryer screeds can be pumped in also. You level roughly with the shovel, pull it level with the featheredge, work the surface with a polyfloat and trowel finish with a steel floor trowel.

Not a job for the faint-hearted.

 

[Jamie25]

Thanks for the replies folks. Does anyone have any experience of the self levelling screeds? Would they make this job easier and would they be suitable?

I'm concerned about laying screeding battons becasue of the UFH and the sloping B&B.

 

[PaulJR]

I have worked on jobs where we have used "self levelling" mixes.
It isn't self levelling, it just has a plasticiser in it so that it flows more easily.

Noseall pretty much hit it on the head, all I can add is that pumped mixes will also use a plasticiser to ensure it can be pumped, and it will stay workable for a decent period - but remember cementitious mixes cure faster in hot weather.

If you really haven't got clearance for any sort of rail then you could use a notched tamp and set the rails above finished floor level.

 

[theoldun]

Will gladly give you some pointers, but first, flowing screed is not for you, whether you had it in mind to do it yourself or have some one in to do it for you. Flowing screed lads are looking for 1000m2 a day. You have approx 42m2 Even if you could find some flowing monkeys to do such a small area, they would charge you approx 4 to 5 times the price of a sand and cement screed.
If you try to lay flowing yourself with screed, pump, dapple bar and level tripods. Will cost you approx £1300 plus VAT. When finished it will be cat and look cat with tide marks everywhere.
Sand and cement. Materials including fibre and mixer hire will cost you approx £420 plus VAT. If you have never run screed through a drum mixer before then the gauge will come out like a. barrow full of marbles and will be as strong as a sheet of paper. If you are doing it yourself and never laid screed before will take you 2.5 days, so you will have two day joints that will require reinforcing with D49 mesh or fish tail end wall ties.
If you have ready mix screed you will not lay 42m2 in a day so you will require two drops which will cost you an arm and leg. Once again if you have not laid screed before it will look cat and be cat.
Suggest phone around and chat around and find either a 1 and 1 or 2 and 1 gang of floor layers (screeders) who have a paddle mixer pump. You supply materials and for labour only, cash in hand they should do 42m2 for between £10 to £15 metre square. It’s a handy little earner for them to fill 3 hours in. If they have their own mixer pump then it is 95% positive that they are floor layers and not scally wags.
If you have a P/A of .5, you will need 70mm of Celotex FF4000. This is designed for wet UFH. Round external perimeter 20mm Celotex TB4000.
You do not leave chases for services in screeds. You do not require any radiator runs with UDF, but it you did to comply with Water Byelaws they should be run in pipe in pipe, domestic hot water should be run pipe in pipe, domestic cold water should not be run in a UDF screed. Electric services dropped from above.
Sorry to have spoilt your day.
Regards oldun