Existing base vs new extension

[an203888]

Hi all,

I have built a 40m2 extension with a beam and block floor, 100mm insulation, and layed some ufh pipes. Will be sand and cement screeding this week. We will be bringing the screed up to the two rooms we have knocked through into.

I think we are going to want 600x600 tiles layed in the extension and into the existing room. What floor prep/drying is required before I tile?

Some of the existing room is going to want some filling/levelling but have been doing some reading and a paintable DPM is mentioned (Sach as the ones in the stickies in this forum). Presumably this is to allow you to use the newly screeded floor quickly rather than having to wait months to dry? Is this correct?

So looks like a dpm and then a layer of self leveller before tiling is required? Doe stgis sound right?

 

[Notch7]

If you have old screed meeting new and tiling over, I would recommend using ditra mat.

I'm a bit confused, I presume you want liquid DPM for old floor not new.

Liquid DPM doesn't provide a shortcut to screed drying time.

Personally for new screed over UFH and to reduce curing time I would use Mapei top cem which improves thermal conductivity for UFH and reduces drying time for cementitious screed from 8 weeks down to 3 days or less.

Using ditra mat decouples the tiles from substrate movement and if you are butting new and old screed it's Def worth it.

So are you having new screed with UFH butting up to existing screed with no UFH? - I'm not sure if that creates a prob.

Don't forget your expansion foam around where the new screed is going

 

[an203888]

I thought a liquid Dpm can be applied before screed is fully dry so that a leveller and finished floor can be added. I've read that it can speed up the process.

I already have the cement so not going to use Mapai Top Cem plus its about 4 times the price!! Might as well use a flow screed if you were going to use that. The old floor has some low profile ufh set into it too.

What do you mean by expansion foam? What can be used for this?

Ditra matting seems like a good idea. Does it add to the height much? Don't really want any extra height on the floor?

Do traditional screeds need to be fully dry before tiling over?

 

[dazlight]

I wouldn’t put a liquid Dpm over UFH myself. I’d get the pipes on low after 2 weeks to force dry the screed

 

[an203888]

I wouldn’t put a liquid Dpm over UFH myself. I’d get the pipes on low after 2 weeks to force dry the screed

I think I read somewhere that the heating on a new screed can come on after 30 days.
I was thinking of turning heating on after 30 days and installing tiles after 60 days. Does this sound reasonable? I think most tile adhiesives can be used directly on a screeded floor after cleaning

 

[dazlight]

Didn’t realistic it was ceramics. So yes 60 days will be fine.

 

[foxhole]

The longer the screed takes to cure the stronger it will be.