Floor screed

[Grassman]

I am installing a heated floor and need to screed over the pipes.
Has anyone any experience?
Do the self levelling screeds work and is it something I can do myself?

 

[Pan mixer]

I am installing a heated floor and need to screed over the pipes.
Has anyone any experience?
Do the self levelling screeds work and is it something I can do myself?

I did a bit indoors in an old fireplace, blo*dy stuff ran everywhere, dead level.

Then it cracked, a million times, under the carpet so not worried.

 

[Pond digger]

I believe the self levelling screeds have the advantage that they flow fully around the pipes, resulting in better heat transmission. Not sure I'd want to do the job myself as a newby.

 

[Pan mixer]

I believe the self levelling screeds have the advantage that they flow fully around the pipes, resulting in better heat transmission. Not sure I'd want to do the job myself as a newby.

I have laid acres of real concrete - literally, the fireplace was the only bit of self levelling I had done, it was alarming.

Try a bit somewhere private for a start.

 

[Grass And Grain]

Did some in August, not for ufh though.

Need to get the slump correct, tested with the cone thing. If it is too stiff then the aggregates come to the top and leave a terrible surface. But perfectly level if you get the correct slump.

It has cracked badly and the surface was sprayed with curing compound. Turns out the fancy curing compound was just a pva solution!

And I believe that drying times can be several months, so research this if you were having any wooden floors.

 

[Will Blackburn]

When they did our house they used a dry mix type to screed over the UFH pipes, worked well. The tiler should have sealed it before he laid the floor tile though!

 

[acorn]

Also make sure you get your plumber to pressure up the pipes, it will help stop them collapsing and if the pressure drops you will know you have damaged one.
One other thing, use as big a bore pipe as you can, at leased one size bigger than the "experts" recommend....

 

[Lofty1984]

Be careful once it's layed if you fire up the heated floor too soon it will feck the screed up

 

[Grassman]

Òh heck. This is sounding like a minefield!

 

[jamesy]

Did a couple of floors for air to water ufh. Was meant to be 60mm screed, I went to 75mm & used readymix with particle size no larger than 10mm with fibres mixed in. Worked fine.

 

[David.]

When you see it on Grand Designs, it looks like just very wet pre-mix almost like grout. What is actually special about its composition?

 

[Pond digger]

When you see it on Grand Designs, it looks like just very wet pre-mix almost like grout. What is actually special about its composition?

I think you'll find It's a completely different animal to concrete, and I doubt there's anything better for ufh.

 

[nickf]

Just had two floors laid with anhydrous screed, self levelling over under floor heating.

Get your threshold levels accurate and the sub base level and it is fantastic when laid by a good gang. Mirror finish perfectly level across the site. Karndean tiles can be glued (with the correct glue) straight to it.

I think it dries at 1mm per day, but after a couple of weeks you can put the underfloor heating on to speed things up a bit.

I would not lay a large area myself, I would use a professional.

 

[Ditch clipper]

What size of area have u needing done? And what depth is it? Self levelling floor screeds are pumped, id doubt anywhere would hire these as its a specialist piece of equipment and to be honest it wouldn't be that easy done. There are two types of screed, traditional (sand cement), and liquid (self levelling). Sand and cement will work out far cheaper and will be just as level as liquid if carried out by a good man. It won't retain heat as well although adding a small stone to the mix will help it a bit. Flo screed is semi self levelling and has to be dappled and persuaded to level. It will also run through any holes or joints in the DPM and insulation so the costs of prep work are greater.It will also need to be scarified or sanded before tiling as tiles can have a hard time adhering to it. The difference in price will be considerable.

 

[YELROM]

@Ditch clipper Is there anyway of scarifying a smallish area of flo screed with out hiring a scarifying machine.
Do you just have to remove the flakey top of the screed of or is it the dimpled affect the scarifying machines leave that makes tile key to the screed

 

[Ivor Cornfield]

We used conventional screed with glass fibres. Were not in a rush, so left for nearly 12 months before floor tiling.
Priority with ufh is 100mm insulation (taped joints)on top of slab, and 12 to 15mm ish insulation around outsides. Pipework upto cold pressure before screed. Left then to cure for minimum 7 to 10 days, before any heat. Longer if you can. Once fire up heating, gradually increase up to reccomended temp.
We did a lot of prep ourselves, but got a guy in for screed. I do have a contact for him somewhere.
We were thinking same as you when researching, and was thinking liquid would give better contact area.
I would not hesitate to do exactly the same again, as our floors work amazingly well.

 

[Ditch clipper]

@Ditch clipper Is there anyway of scarifying a smallish area of flo screed with out hiring a scarifying machine.
Do you just have to remove the flakey top of the screed of or is it the dimpled affect the scarifying machines leave that makes tile key to the screed

An orbital sander would do the job.. You want to remove the flakey, smooth top and expose the aggregate bellow.. It should resemble sand and cement plaster that's been rubbed up if that makes sense.. It is quite dusty and all this dust will need to be swept, then hovered to make sure the surface is dust free before applying primer.. Hope this helps!