Underfloor Heating, Screed and Tiles

[Ed_MK]

Hi all,

 

I have been offline for a month or so ...struggling to get the exterior of the house complete ...

almost there ...will the weather catch up with me for 2018 ....sadly i think it might (sigh)

 

But anyway we have been cracking along with the internal ....boarding upstairs is done 

and the electrics and plumbing are done on first fix ...

 

I DPM-ed, vapoured and insulated the Beam and block and then finished with a slip sheets

and last week the Plumbers installed the nu-heat UFH system and tested it ...all good so far!

 

the screeders are coming wednesday and they are laying a grit sand and cement screed

I have 16 tonnes of sharp and 80 bags of the grey stuff standing by !!

 

But it has got me thinking about tiles ! ..well i KNOW the wife is looking at basically the ENTIRE downstairs 

tiled in large 300x400mm tiles that are 9mm thick ...

 

Now ...I have had various advice ....stuff like

 

• use special grout
• use special adhesive
• use a separation or decoupling membrane
• dont tile for 2 months as it needs to dry
• as rooms are different zones it will CRACK at door openings and you need "gaps"

 

Is there any truth to any of this ....and what can you advise

 

PS

Floor is Beam and Block with 1200 micron DPM, 500DPM Barrier/Slip, 90mm Kinspan TF Insulation with
60mm external and 25mm internal upstands and screed is set to be at 70/75mm

 

PPS
Those are temporary stairs (in case you are puzzled)..that is actually a solid wall the REAL stairs will run in from the hall

Edited November 4, 2018 by Ed_MK

[nod]

I’m suprised the screeners are mixing there own

Ive done lots that way but the ready mix is so much quicker 

You need to allow a day per mil for the screed to dry out 

You are better with a decoupling mating 

Though I’ve tiled lots without 

Our own buiild I have tiled the entire downstairs 150 sq metres 

and used Ditra matting 

One long espansion joint and all doorways 

Its worth asking your screeders to put a joint int in each doorway 

Just a piece of twinwall plastic 

Cavity closer or simalar 

Flexi adhesive 

Flexi grout 

and filling or straightening needs to be done before the matting goes down 

Jist 5 mil to stick it down 

6 to 8 mil gap around the edges 

[lizzie]

I have tiled 180sqm in 600x600 porcelain. used ditra matting, flex adhesive and grout as Nod.  Have "invisible' expansion joints at doorways. Good prep is key again as Nod says..

 

 I don't have a screed my ufh is in the slab  and we tiled straight onto slab so it may be different for drying, my slab had been down for 6 months or so before we tiled.

[Ed_MK]

thanks for the advice.

its quite open plan..so the only internal doors are wc..utility and lounge. .

 

what do you suggest I ask the screeder to put in again...I take it it goes in all the depth of the screed ?

 

and ofc I will have to cut it around for the ufh pipes

 

as the entire floor is surrounded by insulation. .will this help to absorb movement...as ofc ot has play vertically

[Temp]

13 hours ago, Ed_MK said:

• as rooms are different zones it will CRACK at door openings and you need "gaps"

 

Is there any truth to any of this ....and what can you advise

 

We have stone tiles on our ground floor kitchen and living room. Both slabs shrank towards their respective centres (very slightly) causing a crack where they meet at a doorway. This crack propagated through the stone. The crack was curved slightly more in one room than the other. This happened despite us having fibres in screed (recommended by builder) and him covering the screed with plastic to control the setting process and waiting more than the recommended drying time (1 day per mm).

 

So yes. If you plan to screed and tile through door ways I would form a deliberate crack (expansion joint). It might be possible to tile over this gap once everything has settled but I would use a threshold strip/tile that can be replaced in case there is any movement later.

 

It might be different if you are screeding before building internal stud walls on top.

Edited November 5, 2018 by Temp

[Ed_MK]

Well the screed went in today....at last

 

I took the Building Controllers advice and tied some wire mesh supports in doorways and across the crossovers

where the UFH zones change ....and the screeders left a 4mm gap in these places as well ...just in case of cracking.

 

Lovely job they did ....flat as a pancake !!

all in all 6 hours and they were away 

 

Really nice lads and best of all a good price

 

So..... a shameless plug for anyone wanting screeding doing in the Luton, Bedford or MK area's

Give Ian a call at Alder Screed !

 

 

PS

I took a few peoples advice in the end on the expansion joints ...and the BCO told me as the areas were not Overly large

and due also to the open-plan kitchen that heat difference cracking would be limited (most likely none at all ) ...even without

mesh and extra fibre in the mix....but if i DID put in lower expanders ...they would definitely need to be continued to the top ...

and the wife hated the idea of all these rubber strips breaking it up...so that kind of sealed it !

 

So now i will wait 2 months at least before i can tile ....I have lots to be getting on with !! ...once i can get back in !!

 

I have been reading a LOT on this Ditra 25 matting and flexible adhesive...and sadly (as its dear stuff) ..it looks like i will need to go for it..
unless their is a cheaper alternative ...

 

Tiles going down are large porcelain (imitation riven slate)  600x400x10 ...so i dont fancy these boys tenting or cracking ..as they are not cheap either