which to do first - render wall or insulation and screed

[unclebob1]

Good afternoon, in the process of tidying up my home, at present i have got a concrete floor ready for insulation, underfloor heating pipe and screed to go on, (so original floor height - 170mm) and ive taken off the render off the walls.

Question is, what goes on first. the sand/cement render + finishing OR insulation, pipes and screed?

for info the concrete base already has had DPM put in under it.
And a new ufh manifold needs to be installed along with new boiler and DHWT

 

[Ashworth1]

Do your insulation/ufh/ screed first . If your using liquid screed they will normally only specify up to 50mm so use thicker insulation .

 

[unclebob1]

screed will prob be sand/cement mixture, insulation will be 100mm, screed will be 50mm, and 10mm for tile.
Just a bit concerned on how to mount the manifold to pressure test the UFH while no plaster on the wall, or is it a case of test, screed, then take the manifold off again for plaster?

 

[mointainwalker]

I don't understand :

1) Why you are testing the circuits ? Have you been wearing spikes on your work-boots ?
2) What is the point of testing - other than just pressurising the system - once the screed is laid ? What does that save you ? If there is a leak you will have to repair anyway and you won't be able to locate the leak until the screed is dry and the leak then shows up as a wet patch.

 

[tomfe]

When you commission an ufh manifold you fill and pressure test the pipe work before during and after installation of the flooring. It allows to to check that the pipe work has no damage before you screed and then after to check it sill has no leaks. It's not that daft if you had someone in to screed the floor you could potentially come back to them and say you put a hole in the pipe, unlikely they would do anything but it does mean you don;t have a shock when you try it for the first time after you've plastered all the walls etc.

You can mount the manifold on the wall in the correct position and then just take it off again to render behind it.

 

[cjard]

Good afternoon, in the process of tidying up my home, at present i have got a concrete floor ready for insulation, underfloor heating pipe and screed to go on, (so original floor height - 170mm) and ive taken off the render off the walls.

Question is, what goes on first. the sand/cement render + finishing OR insulation, pipes and screed?

It doesn't matter which you do first, because the screed and the render(you also referred to it as plaster; they're not quite the same thing) should not be in contact with each other. The perimeter of your room should have a strip of insulation, 25mm kingspan for example, that the screed will run up to

You won't get any screeder worth his salt to lay a sand and cement screed at 50mm; it's too thin and will break. 50mm is ok for liquid screeds (I still have no regrets about mine despite many people saying "don't do it") and with additives they can be 40mm if needed but a sand cement screed will be more like 75 mm. If you're having underfloor heating, put as much insulation in as you can, and make it kingspan, not polystyrene. Your floor is your radiator, it needs thermally disconnecting from the ground below as much as possible, otherwise you're paying to heat the mud under your house

Officially, underfloor heating pipe work should be pressurised with water before a screed is laid on top of it, and it should be at a pressure beyond what it will be run at when in service. This will highlight any leaks or damage, and it will ensured the pipe is expanded slightly more than what it will when in service, minimising the risk of damage to the screed. Hard as it is to believe, the pipe expansion can be enough to break the screed when the system is pressurised

As has been noted, the uh manifold can be put in place temporarily, then unscrewed, bent out of the way(the pipes remain flexible, the manifold should be around half a metre off the floor) and the wall rendered behind it. Alternatively, render first, even if it's just the one wall where the manifold is.. Saves your 500 quid manifold getting covered in mortar

 

[unclebob1]

Thanks cjard, Will try and squeeze more screed on, concrete base went down 2 weeks ago, wish i'd asked earlier now!
Kingspan is def choice - and looking to effectively line the room floor - even isolate each room as each will be its own zone with own thermostat. The UFH pipes and screed will be isolated from the building walls/subfloor for defo.

And i may just do that with manifold/render on that wall. it will be a smallish wall so may give it a go myself.

 

[cjard]

www.secondsandco.co.uk sell battered/misshaped kingspan for anything between a huge discount and a wacky surcharge. As it's going below a floor you can cope with the odd bit of damage/warp/wedge shape. Be sure to work out the £/cubic metre of what youre buying though, as their stuff is priced pretty much on a "ooh, that's a big pallet of stuff, £200", "this pallet looks smaller, call it £150" basis by people wandering round a yard. I found prices anywhere between £33 and £190 a cube. Straight Grade A kingspan is around £100/cube. They also had a thing a while back to get rid of all their accumulated ****e that noone wanted to buy - free kingspan, if you collect from the yard (in Wales). No idea if that's still an offer

 

[unclebob1]

Cheers for the tip - i'd been keeping an eye on their stock for a while already - currently looking at:
their 100mm rebated - £26 for a 1.2 x 2.4 sheet. but need to work out my floor space, and the normal price of a sheet to see how much of a bargin it actually is!
http://www.secondsandco.co.uk/#!product-page/c1n8h/b97dcf8c-1762-4194-220b-761ea92871bf