Dry vs Wet screed for UFH

[ab12]

Having UFH for 3 rooms: a kitchen , a bathroom and a living room.

 

In the bathroom I will be having a walk in shower in the shape of a rectangular box  dimensions 165cm long and 90 cm wide but without a shower tray. Worried shower trays break easily and also I think it will more cost effective to create the falls needed in the shower area with dry screed.

 

On one of the longer sides will be a fixed glass screen running from external wall with a gap to walk into the shower space and on the opposite side is the internal wall.

Shower head and taps will be affixed to external wall on one of the shorter sides of the rectangular box- see diagram attached

 

I will make a small rectangular partition in the floor where the shower space will be if I use wet screed so can get the falls for the drainage.

 

Floors will be finished with tiles.

 

I am in 2 minds about Dry vs Wet screed. Dry Screed will be cheaper but a bit more laborious which I don't mind. Wet will off course be a quicker install but cost premium attached.

 

For Dry I will go with 75mm thickness and for Wet I think the recommended is 60 -65mm thickness.

 

Considering it's a DIY project which screed finish would you opt for?

 

Are both types of screed equally effective for UFH in terms getting the space warmed up quickly and avoiding cold spots?.

 

I suppose the thicker the screed the more time the slab will take to warm up but equally I suppose the more time that heat will be stored in the slab.

 

BTW I have no prior experience with living with UFH so not sure about which direction to proceed.

 

[JohnMo]

57 minutes ago, ab12 said:

Are both types of screed equally effective for UFH in terms getting the space warmed up quickly and avoiding cold spots?.

Both will be equally slow, which is the whole idea of UFH. Unlikely to be any cold spots - but a floor well put together isn't hot either. Many because most if not all the time it's actually cooler than your body so will never feel hot.

 

I assume you have thought about and installed plenty of insulation under the UFH pipes?

Edited 5 hours ago by JohnMo

[ab12]

14 minutes ago, JohnMo said:

Both will be equally slow, which is the whole idea of UFH. Unlikely to be any cold spots - but a floor well out together isn't hot either. Many because most if not all the time it's actually cooler than your body so will never feel hot.

 

I assume you have thought about and installed plenty of insulation under the UFH pipes?

In terms of insulation I will putting 150mm PIR even though 100mm will suffice. Going with the extra insulation hopefully should be better. Initially though plan was to fit 100mm and so I purchased most of the boards already. Now have changed mind and will be ordering the 50mm boards.

So I will be laying 50mm PIR first and them 100mm on top.

In hindsight I should have ordered 150mm board.

 

Other option is to use use 50mm Polystyrene such as Jabalit and then 100mm PIR on top- Cheaper option.

Watched a you tube video about this  and learnt the following: Polystyrene boards break easily and can be a bit more tricky to cut but I don't have prior experience so basing everything on what I saw in the video.

 

Have you worked with Jabalite? Is it fairly easy to work with?

 

[JohnMo]

14 minutes ago, ab12 said:

I will be laying 50mm PIR first and them 100mm on top.

In hindsight I should have ordered 150mm board.

Good - go with 150mm. But stuck with 100 and 50mm. 150mm are a pain to install well. Stick with PIR at that depth. You 50% more depth of polystyrene boards for the same U value as PIR. 

 

A blunt saw is good for cutting PIR. Foam in any gaps. Stagger joints between layers

[Nickfromwales]

1 hour ago, ab12 said:

Worried shower trays break easily and also I think it will more cost effective to create the falls needed in the shower area with dry screed.

It requires a methodical approach, and a lot of careful execution. 
 

Shower trays don’t typically break easily, more like mechanical damage or accidental dropping of things onto them. 
 

If you’re not having a shower tray then maybe consider a wet room former? You just set this in place with tile adhesive, test the drain for leaks, then screed to it. 

[saveasteading]

1 hour ago, ab12 said:

should have ordered 150mm board

But laying 2 layers allows the staggering of joints.

Having recently done 2 layers I'd  be thinking of having the thinner layer below, as the top one will be stiffer to resist bending under load (if there are any voids).

Jablite is much softer and the saw doesn't get stuck in thck boards. But for 50mm of either, a saw is fine.

 

Both are easy with a machine.  We had a contractor do the floor. He used a recip. saw and long blade. Fast but approximate.

I've been doing some wall stud infilling. It's a pain. I'm using a jigsaw with 4" blade which only cuts 2". Then repeat other side.. so is slow.  With a long blade it wanders wildly.

 

I think ideally with pir I would cut first with a jigsaw then complete the cut with a recip.

 

Also, eps makes lots of dust, pir much less but nasty and needs a mask.

 

Another option.. pir has aluminium foil on both faces. It cuts by stanley knife and so for 50mm you can cut both faces and get a snap-off cut... and it ux marked in 100mm squares.

Yes eps snaps rather roughly.

[saveasteading]

also of note. I have been a hater of expanding foam for years as it is used freely to hide bodges.

But Soudal with a gun is another matter as there is control of quantity to some extent, and the nozzle can be extended into voids. BUT NB it acts as a solvent with EPS so must be used with caution. I have learned to squirt in a small amount as adhesive, then a sparing amount, then a 'top coat'. Not fast but a proper job

[Russell griffiths]

You say diy project 

does that mean you are laying the screed, what sort of area do you have. 

[saveasteading]

Continuing this drift from the original question.

We have had a difference of opinion with the BCO. Any advice will help, either technical or to my behaviour.

 

 

I am personally infilling between timber studs at an isolated area where the architecture requires that we add some insulation. 50mm of rockwool would meet the numbers required.

 

Because we have some 150mm eps and pir left from the floor works, I am using that. Obv this far exceeds the requirement.

 

I wasn't there during the routine inspection, maybe as well.

BCO isn't happy to see  different materials being used. There is PIR and EPS, and even that looks like different products because batches have different amounts of the black specks from graphite additives.

He also doesn't like where I have used 2 or more pieces butted within a section of wall. It is all sealed at edges and any joints with aluminium tape.

 

Why have I used more than one piece? Economy and avoidance of waste. Sometimes because there is a nail sticking out so I've cut it for ease of adjustment, or there is a pipe behind and I have used 2 pieces, cut for exactness.

 

And some are where eps has snapped, as mentioned above.... I have used it but taped the junction.

 

In family discussion I suggested we tell him where to go / ask him on what grounds there is any suggestion of a problem / submit proof that this exceeds regs /  sign it that I have a degree in Building Science.

 

Pragmatically we are avoiding a row as it isn't worth it. So I've gone back to address the worst and there actually isn't anything that bothers me. I saw one panel where I'd used 3 bits so decided to pull that out and redo. Then I saw why I had done it. The sparky had inserted a noggin so I had pushed what I could down the back of that, in 2 bits to get a good fit. Then I had done the front, with a gap at the noggin but used eps and pir. The boards are so well fitted that one won't come out

 

So I decided to reduce the quality to please the man. I've cut 30mm off one of the blocks, but 30mm off it and joints and placed 25mm board over for better aesthetic effect.

 

 

Lowering standards to get approval... Grrrrrr.

 

I'm thinking of peeling the aluminium face off PIR and gluing it over any panels with joints. But no, I will not lower myself to that.

 

 

Thanks I feel a bit better now.

 

 

 

 

 

 

 

 

 

 

we have had a difference of opinion with the