Screed with central heating pipe duct

[Jackswan]

Just after some advice on what adhesive to use.

Screed laid about a year ago and running across it is a duct which carry the central heating pipes. Duct is made of external grade ply with a screwed down cover. It's roughly 125 mm wide and 2.5 metres long. Totally forgot about the duct until I lifted the hardboard protecting the floor tonight.

Porcelain tiles 500 x 500 are being laid on the screed and I have been provided with Tilemaster Rapid set adhesive. Should I use a flexible adhesive where the tiles run across the ducting?

Just another question should the screed be primed with anything first before laying the adhesive?

Any advice would be welcome.
Cheers

[Dave]

Hi and welcome..

That timber section is going to create some stress within the screed at either side, personally i would overlay with an Uncoupling membrane..

[whitebeam]

Does the duct need to be accessable

[Jackswan]

Hi and welcome..

That timber section is going to create some stress within the screed at either side, personally i would overlay with an Uncoupling membrane..

What is an uncoupling membrane?

[Jackswan]

Does the duct need to be accessable

No, there are no joints within the duct

[whitebeam]

What is an uncoupling membrane?

Underfloor Heating from Floor Heating Ltd

[Jackswan]

Ok I now see what is meant by an uncoupling membrane.
Also in the floor screed is a double seal inspection cover set at the correct height for tiles. If I was to fit this membrane the surface of the screed I assume would rise above the height of the inspection cover.


Above is a photo of the duct and the position that the tiles will take across it.

[whitebeam]

The decoupling is only 3mm thick

[Dave]

Is that a manhole cover...?

[Jackswan]

The decoupling is only 3mm thick

How thick would it be with the adhesive to bond it as well?
The room is approx 20m2 so I'm guessing that the cost would be around about £150 -£160 for just the materials alone, hell of a price

[whitebeam]

You could at a push use Dural/kerdi/homelux over the ducting and bring it 6" over onto the screed either side, then there won't be any hight issues and will cover for any movement you might get on the ducting

[Jackswan]

Thanks whitebeam, sounds good.
Just reading a posting on this forum
cracking screeds/tiles and underfloor heating
about cracks in screeds and how to repair them before tiles are fitted.
Using PCI PECILASTIC which apparently is only 0.8mm thick, but is it any good? This would be a good solution if it could just be laid say 6 inches either side of the ducting.
Where would I be able to obtain some of this from if it was suitable?

[whitebeam]

Pjc uses pci and rates it highly