Laying external porcelain tiles - what primer? Screed ok?

[oranjeboom]

Hi All, 

 

Hoping to complete the patio in the next few days. Concrete slab  needs a bit of levelling and ensuring slope is sufficient so will need to add a semi dry screed prior to laying the 10mm porcelain tiles.

 

 

Some questions:

 

1) Screed okay with one part cement to three to five parts sharp sand? How long before I can tile on top of that?

2) What adhesive should I be using for the porcelain tiles? Would this Mapei  Porcelain adhesive be okay? https://www.toolstation.com/mapei-stone-porcelain-adhesive-20kg/p57343?store=C5&utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=s_dc&pcrid=515847200306&pkw=&pmt=&gclid=Cj0KCQjwqKuKBhCxARIsACf4XuH2yjuBtJrOJesLRv1RUFPg47RO8EjPIgKZh6OrNZAwt7-1Ysm7mJ8aAg9bEALw_wcB&gclsrc=aw.ds

3) I've also read that priming the tiles would be a good idea - anything specific I should aim to get?

 

Thanks in advance.

 

 

 

 

[Nickfromwales]

How thick will the screed be? It’s a can of worms putting a thin layer over existing outdoors. Water ingress + frost = ?

[Dave Jones]

where is the cill for those bifolds ?

[nod]

I would just put a self leveling on that 

Then tile it the following day while it’s still green 

Then leave it a week to dry out before grouting 

[oranjeboom]

5 hours ago, Nickfromwales said:

How thick will the screed be? It’s a can of worms putting a thin layer over existing outdoors. Water ingress + frost = ?

 

I have plenty of depth to play with. The doors are still a bit too high and there's a slope in the base already. So what's the min thickness, Nick?

 

5 hours ago, Dave Jones said:

where is the cill for those bifolds ?

 

Doors sit on foamglass. External cill will lip onto the door frame but not fitted until slab is done.

 

4 hours ago, nod said:

I would just put a self leveling on that 

 

Problem is that there is already a slope in the current base, so levelling is going to be an issue surely? 

[Adsibob]

On 22/09/2021 at 14:59, Nickfromwales said:

How thick will the screed be? It’s a can of worms putting a thin layer over existing outdoors. Water ingress + frost = ?

I'm laying sand and cement screed externally with the intention that it will be coated with a special microcement product. The manufacturer of the microcement initially gave us various options for how the screed should be laid, all of which included a vapour membrane underneath the screed.

When we queried what the difference was between the options, they said it actually didn't matter as long as we could guarantee that the screed was solid, wouldn't move and would have a humidity content of less than 16%. Is that realistically achievable, even with a vapour membrane? Will i need to keep it dry whilst it fully cures (which could take a couple of months!)

 

[Nickfromwales]

26 minutes ago, Adsibob said:

I'm laying sand and cement screed externally with the intention that it will be coated with a special microcement product. The manufacturer of the microcement initially gave us various options for how the screed should be laid, all of which included a vapour membrane underneath the screed.

When we queried what the difference was between the options, they said it actually didn't matter as long as we could guarantee that the screed was solid, wouldn't move and would have a humidity content of less than 16%. Is that realistically achievable, even with a vapour membrane? Will i need to keep it dry whilst it fully cures (which could take a couple of months!)

 

Nobody is saying how thick the screeds are! ?

[Dave Jones]

On 22/09/2021 at 20:43, oranjeboom said:

 

Doors sit on foamglass. External cill will lip onto the door frame but not fitted until slab is done.

 

 

 

 

how will that be watertight, they look like bog standard bifolds ?

[oranjeboom]

2 hours ago, Nickfromwales said:

Nobody is saying how thick the screeds are! ?

Well, I could get away with 70-80mm and still retain the required 150mm clearance below the DPC as required by BuildRegs.

 

2 hours ago, Dave Jones said:

 

how will that be watertight, they look like bog standard bifolds ?

 

Not bifolds. Just french doors that open outwards.  Watertight? As in damp, or water ingress from rain etc?

[Nickfromwales]

6 minutes ago, oranjeboom said:

Well, I could get away with 70-80mm

Use a dry concrete mix then with 6mm aggregate instead of screed.  

[gc100]

I’m getting my porcelain  tiles laid on a newly poured concrete slab I did last week. The tiler wants to out dita mat down under to stop water being pulled up from the ground to reduce chance of the tiles popping off In frost etc. Anyone heard of this been done outside ?

 

I agreed to it as I have lots of dita left over anyhow but still seems a bit odd. 

[Adsibob]

2 hours ago, Nickfromwales said:

Nobody is saying how thick the screeds are! ?

In my case the microcement manufacturer suggested a 100mm, but my architect queried this as excessive, and the microcement people said we could go down to about 70mm think.

[gc100]

Mines 100mm as well 

[Nickfromwales]

8 hours ago, gc100 said:

I’m getting my porcelain  tiles laid on a newly poured concrete slab I did last week. The tiler wants to out dita mat down under to stop water being pulled up from the ground to reduce chance of the tiles popping off In frost etc. Anyone heard of this been done outside ?

 

I agreed to it as I have lots of dita left over anyhow but still seems a bit odd. 

I’ve done a good few pool / hot tub surrounding areas with tiles, and always over a decent ( 80-100mm minimum ) concrete slab. Never had any comebacks. 
The preparation must be right before tiling, or the tiles are doomed, as if the slab cracks so will the tiles. “Excessive” may be some people’s wording, but skimp there and reap the rewards! Costs a lot more to do it twice

 

I’d put mesh in if it were mine as it’s cheap and makes concrete work ridiculously robust.

IMO the Ditra would cause more issues than it’s supposed to solve, as there are more cavities to fill or for water to the bury into and freeze, but it would give some protection against tiles cracking on a regular screed / thinner concrete base. As in all things, if you’ve a good trade on site the job is more likely to succeed and they can mitigate by making sure the perimeter has a continuous run of adhesive to prevent water getting in. 

[Nickfromwales]

8 hours ago, Adsibob said:

In my case the microcement manufacturer suggested a 100mm, but my architect queried this as excessive, and the microcement people said we could go down to about 70mm think.

Side with the manufacturer over the architect!! 100mm is much better. How much area? What costs uplift are we looking at to add the 30mm?

[Dave Jones]

9 hours ago, oranjeboom said:

Not bifolds. Just french doors that open outwards.  Watertight? As in damp, or water ingress from rain etc?

 

as in the doors are not sat on cill so how is water being stopped from getting inside ? Are they a proprietary frame with built in drainage?