Prep for 10mm floor tiles on Indoor/Outdoor Concrete Slab

nowImonboards

I'm in the process of preparing for pouring a concrete slab for an indoor/outdoor patio area (veranda with glass sliding doors).

I want to tile the floor using 10mm indoor/outdoor porcelain tiles, similar to what you would use for your kitchen bathroom floor. These are not the 20mm porcelain tiles that would usually be used for paving a patio or driveway. I have a particular tile in mind and they are rated for both indoor and outdoor use, slip resistant etc, so all that part is sorted. However, I'm not sure how to best plan the concrete pour so I end up at the correct level.

Initially I was planning to pour a concrete slab on top of a hardcore base covered with DPM and pour to 20mm below the planned final level. This would leave 10mm to account for the tile itself plus 10mm for the tile adhesive. However, after researching various articles and videos I see that sometimes a screed layer has been put on top of the concrete floor. I'm not sure though under what conditions this is required. If it is needed, I'll need to pour the slab at an initially deeper level to leave room for the additional screed layer. If I do add the screed, I'm not sure whether the DPM is then placed between the slab and the screed insteawd of under the slab itself or whether there are actually two layers (one below the slab and another between the slab and the screed.

As this is an outdoor floor (covered most of the year) I wanted it to finish at ground level to match the height of an existing (permanently outdoor paved patio). I'm wondering what I need to take into consideration to account for our extremely varied Irish weather, particularly in relation to damp and frost.

If anyone else has tried or had experience with a similar project I would love to hear what you have done or planned to do.

Thanks to all for any input.

Mellor

Outdoor patios are not typically 20mm porcelain. FWIW

Is the slip resistance appropriate for wet floors? Is the area drained? Have you considered falls? Is the threshold level? Is it drained?

A screed is placed in order to have a suitable substrate for timing. It’s not necessary. But the tolerance for placing a concrete slab is greater than a screed. Whether you need you would depend on whether falls are needed, and how good you are at laying concrete.

For the outdoor slab, what is the purpose of the DPM?

nowImonboards

Hi Mellor,

My comment on the 20mm patio tiles was due to the fact that 99% of the many articles and videos I reviewed were specific to 20mm patio tiles. It is very difficult to find any info (specifically localised to Ireland/UK) that use 10mm tiles outdoors. The 20mm tiles are rarely laid on a concrete base (at least from what I have found in my research and heard when speaking to paving contractors). However, 10mm tiles seem to require a concrete base. I was just trying to make sure I had distinguished that early on so I don't waste peoples time.

The purpose of the DPM is to stop the ground moisture making its way up under the tiles. I also need to minimise the risk of frost uprooting them. Is there a reason why I shouldn't use DPM? The end result should be just like the existing kitchen floor (just at a lower level to match the existing outdoor patio). In the summer it will be open patio and in the winter it will be closed and act as an extension of the kitchen and will be treated as such, e.g. I'll be mopping the floor in the same way I would the kitchen floor.

It won't generally be directly exposed to rain so I wasn't planning to add falls. I was aiming for level.

Rows Grower

It's important to butter the back of each tile before laying it onto the ridged adhesive so that each tile is on a solid bed of adhesive. Even doing this and using a 10mm trowel you'll probably end up with less than 10mm height of adhesive as when you press the tiles into place they will flatten the ridges made with the trowel.

Be sure to use a "flexible" adhesive.

nowImonboards

Thanks very much for the input Rows Grower.

One thing on that note. When I was looking for tiles, one of the vendors advised to make sure there were no gaps beneath the tiles to avoid water getting in and freezing, uprooting the tiles. Is it possible he meant not to use a ridged trowel or is that even possible? Perhaps he just meant to butter the back of the tiles like you suggested. Any thoughts on that?

Rows Grower

https://www.boards.ie/discussion/comment/122535904#Comment_122535904

He's dead right, they should be laid on a solid bed of adhesive to stop them popping after a freeze. You can do this with a ridged trowel by buttering the back of each tile and then when you fit the tile press it into place. This will flatten the ridged adhesive into a solid bed. The 10mm deep trowel will have a 10mm gap between the teeth so in reality you will end up with about a 6-7mm solid bed of adhesive underneath each tile. When you are doing the job it's no harm to lift a tile you've just laid every now and again just to check it was lying on a solid bed.

GreeBo

https://www.boards.ie/discussion/comment/122535904#Comment_122535904

This just means not to lay tabs on "daps" of concrete/adhesive

a) they will likely lift

b) if you drop something on a cavity it will crack/break

c) incredibly weak edges/corners

10-10-20

Also the adhesive ridges should run perpendicular to the longest side of the tile. ie - so that the air has the shortest path out from underneath. Use a good quality tiling primer on the concrete too, none of that PVA stuff.

Rows Grower

https://www.boards.ie/discussion/comment/122536098#Comment_122536098

No, it means lay them on a solid bed.

Tiles haven't been laid using the dabs method since the last century.

Water has very narrow shoulders and most grout is water resistant but not actually waterproof. If water did find it's way under tile it will expand in freezing conditions and at least weaken the integrity of the adhesive if not cause the tile to pop. A solid bed of adhesive will prevent this from happening.

nowImonboards

Thanks All!

That definitely clears a few things up on the tiling. All makes sense :)

The tiles are actually hexagonal (of course it couldn't be simple) so no long side as such. I'm aiming to avoid any air pockets if possible though as mentioned above. I'll ensure the initial ridges align with any fall if there is any (although I was thinking to make the floor level).

I was looking at some different types of adhesive. I see a few on screwfix.ie which mention that they are suitable for outdoor use. However, they don't all specifically mention frost-resistance. I would have assumed that the outdoor variants would have taken frost into account….. until I seen the one that specifically mentioned it. Has anyone had any experience with these:

The first one what was recommended to me was UltraTile ProFlex SPES Standard Set Tile Adhesive. However, this doesn't seem to mention frost.

I did see this Mapei Keraquick Wall & Floor Rapid-Set Flexible Tile Adhesive which does specify frost resistance but only has one review.

There is also one very reasonably priced option that has reviews ranging from brilliant to terrible. I'm guessing the results depend on skill level.

Any experience with either for outdoor use?

Also, should I be looking at some kind of uncoupling membrane to help with cracking / frost protection?

10-10-20

hexagonal

Saints on skateboards, you like a challenge.

I think it's the jointing compound that most needs frost proofing. Had you decided on a joint width? AJ recommends a jointing compound here with resistance, but they need ~10mm joints.

https://www.pavingexpert.com/a-joint_01

Also, should I be looking at some kind of uncoupling membrane to help with cracking / frost protection?

Never heard of it being used externally, not sure it's needed unless you're putting in an expansion joint into the slab or are covering a join, or are expecting elephants.

nowImonboards

https://www.boards.ie/discussion/comment/122536357#Comment_122536357

It wasn't my choice believe me. For some reason, not matter what the possibilities are, my better half always seems to choose the most complicated version without knowing.

The slab is 6m x 3m so I was planning an expansion joint.

I was planning a standard 5mm joint width. I thought the jointing options on AJ's site, (as well as the rest of his tiling advice), was aimed at 20mm paving tiles. I wanted this to be like an internal floor.

I have seen the separation membrane recommended here.

I have also seen a recommendation for a waterproofing membrane (RedGard) here.

I don't think either or these have taken Irish weather into account but something like the RedGard seems to make sense.

Most other countries seem have it easy when it comes to outdoor living spaces.

Had our glass box built on a composite deck mounted on screwpiles which I built. Thought about a slab but the complexity, cost and potential for things to go wrong changed my mind.

Cost about €2K for the 3mx4m deck and took me about a week to build.

nowImonboards

Thanks Shoog,

That was an option I was considering but was unfortunately over-ruled :-/

I have it dug out anyway and waiting for the pour. I just need to make sure I have brought the sub-base up to the right starting height to make sure I don't mess up my levels after all this work.

Tiling aside, I'm just wondering which of the following layer arrangements I would be better off aiming for:

Option 1		Option 2
[10mm] Tile		[10mm] Tile
[~7mm] Adhesive – Flexible, frost-resistant		[~7mm] Adhesive – Flexible, frost-resistant
[?mm] Tiling Primer		[?mm] Tiling Primer
[130mm] Concrete Slab		[?mm] Sand/Cement Screed
DPM (under slab)		DPM (between slab and screed)
[20mm] Sand Blind		[130mm] Concrete Slab
[150mm] Hardcore		[150mm] Hardcore

Mellor

https://www.boards.ie/discussion/comment/122535827#Comment_122535827

20mm tiles should still have she sort of bed. 20mm Pavers would not. With pavers would expect movement and joints are not grouted. Tiles, as they are grouted should be stable.

I asked about the DPM as it sounded like it was an outdoor patio. In which case it would be wet anyway. If enclosed it go with DPM.

But I’d also then consider, if it’s a heated space, thermal envelope, cold bridging to kitchen, and step/level junction at kitchen.

Lumen

Can you clarify what you mean by these statements?

...indoor/outdoor patio area (veranda with glass sliding doors)
...this is an outdoor floor (covered most of the year)
... In the summer it will be open patio and in the winter it will be closed

If the roof is permanently fixed, then it's not ever an outdoor space. Just because it has sliding doors doesn't make it outdoors - my kitchen has sliding doors and it's very much indoors.

You said you have an existing outdoor patio to match levels with (presumably at the threshold) so it can't be the case that you're putting new tiles outdoors.

Is the roof moveable or something?

This distinction is important because it affects how you're dealing with rainfall. If the roof is fixed but the doors are closeable, you don't need a fall and can rely on sunshine to dry off the tiles from small amounts of wind-driven rain and close the doors in the case of a torrential downpour.

I'd have thought the roof would have a bit of overhang anyway.

What's going on here?

nowImonboards

https://www.boards.ie/discussion/comment/122537659#Comment_122537659

My understanding is that 20mm tiles would normally have a mortar bed whereas the 10mm tiles would require a concrete slab in such an environment to minimise the chances of cracking/popping off. If that is not the case I have been misinformed but I'm going with the slab anyway as it allows any kind of surface updates in the future.

Any instructions you can point me to on the cold bridging and step/level junction would be appreciated.

Thanks again for your input.

nowImonboards

Hi Lumen,

This is a glass veranda with each wall fully retractable. The supporting structure is made of a few aliminium posts with everything else being glass. It is neither fully indoor nor fully outdoor. It can be both. See the following pic.

In my case the grass will go right up to the front of the new slab and the paved area on the right is the new tiled patio I put in during the summer. This is the existing level I need to meet.

Apologies but I don't understand what you mean when you say "it can't be the case that you're putting new tiles outdoors".
I have already put new 20mm porcelain tiles on a mortar bed as the fully outdoor section (to the right of the structure in the above pic) of the patio area. I'm simply trying to get the layers (and therefore finished height) correct for the new slab/floor and tiles for the indoor/outdoor section so it meets the existing level of the patio and grass area.

So if, for example, it would be recommended to add a 50mm screed on top of the slab, then I'll have to finish my sub-base layer 50mm lower than I would if a screed is not recommended.

Does that clarify things at all?

https://www.boards.ie/discussion/comment/122539747#Comment_122539747

These are outdoor spaces so issues of cold bridges don't really come into it. Myself and my wife play the game of what to call it, it's not a room, it's not an extension, it's an outside space with glass screens. We tend to call it the box or the glass box.

Its consistently warmer than outside but it's not an outside room so when the temp drops it's not usable as a living space. We get to use it when no one else is outside in their gardens and can stay out late into the evening when it's mild.

It's a covered in patio and that is it's function.

Mellor

https://www.boards.ie/discussion/comment/122539747#Comment_122539747

20mm tiles should still have a slab if they are to be grouted imo. Pavers can be laid without a slab.

If the patio is unheated/outside the thermal envelope you can ignore the bridging. Threshold detail depends on whether you want a level doorway

nowImonboards

I was thinking to have an electric heater out there (similar to the ones you would find in a beer garden in winter). When do you need to consider bridging? Wouldn't that be more of a concern for the existing kitchen? Are you just talking about putting a slice of insulation between the slab and the structure of the house?

I don't want to get too far off track but I appreciate info an anything I need to consider.

The main thing for me right now is the levels though. I want to start compacting the sub-base today and filling it it to the height it needs to be. From what I understand so far, there is no real need for a screed layer so still going with option 1 from above at this point. Feel free to shout if you disagree.

Thanks to all for responses so far.

https://www.boards.ie/discussion/comment/122541692#Comment_122541692

How do you intend to level your finished slab. With these types of big tiles it needs to be razor flat in all directions otherwise it will be a complete mess in the finished tiles.

nowImonboards

https://www.boards.ie/discussion/comment/122541711#Comment_122541711

I have someone helping me who has the floats etc. He was going to do it by hand. As long as we can get it to withing a 5ml tolerance I would have thought the bed of adhesive would have helped deal with anything that falls within that. Am I wrong?

https://www.boards.ie/discussion/comment/122541850#Comment_122541850

Its a skilled job floating a floor but if your friend has the experience then it should be OK. Best way would be to hire a hover float - they do an amazing job of leveling.

nowImonboards

https://www.boards.ie/discussion/comment/122541949#Comment_122541949

Thanks Shoog, that's my fallback option the help falls through.

Just to clarify though, when I mentioned my immediate concern was the levels, I wasn't referring to the flatness of the finished surface. I was referring to the thickness (height) of each layer. If I need a screed it would potentially add 50mm (or whatever the thickness of the screed layer is) to the height. If I don't need a screed layer I need to bring my base layer up 50mm higher in order to meet the existing level. The two options I am trying to decide between are:

Option 1 - Without Screed Layer
[10mm] Tile
[~7mm] Adhesive – Flexible, frost-resistant
[~3mm] Tiling Primer
[130mm] Concrete Slab
DPM (under slab)
[20mm] Sand Blind (Plastering sand)
[150mm+] Hardcore layer

Sub-base layer would then need to finish 170mm below the existing patio level

Option 2 - With Screed Layer
[10mm] Tile
[~7mm] Adhesive – Flexible, frost-resistant
[~3mm] Tiling Primer
[50mm] Sand/Cement Screed
DPM (between slab and screed)
[130mm] Concrete Slab
[150mm+] Hardcore

In this case the Sub-base layer would then need to finish 200mm below the existing patio level

This is the immediate concern right now.

https://www.boards.ie/discussion/comment/122542006#Comment_122542006

Screeding is the standard method of getting a tileable floor surface. The issue with concrete by itself is that it is difficult to know how flat it will be because of inconsistency in the mix which will result in differential drying with low and high patches developing as it dries. Also without regular reference points how do you know what your levels really are across a big floor. People wouldn't go to the trouble of screeding if it wasn't a known issue. Its a bit like when plastering with skimcoat - you always use two layers to get the final finish.

Just my opinion though.

nowImonboards

That's great info Shoog. Thanks very much. I didn't know the levels change as it dries. Do you happen to know the range of difference we are talking about? It's only a 6m x 3m slab. I'm wondering would I get away with a layer of self-leveler at the end if I aimed to leave about 5mm for it.

Also, if it tends to raise in spots as it dries, why would a power float make a difference?

Mellor

https://www.boards.ie/discussion/comment/122541692#Comment_122541692

Bridging is only a consideration if the new slab connections to the existing slab. Including at doorways. Not a concern where it abuts the outside of the house wall.

A screed is essentially fine concrete. There’s no need for a screed. But it is harder to pour a concrete slab as accurately or as level.
if the concrete is uneven there is only so much you can make up in the adhesive. If it’s out my a significant amount then the tile won’t be level.

depends on how confident you are in the concrete. Commercial I’d always allow at least a little to level the slab.

nowImonboards

Thanks Mellor,

As you mentioned doorways above, the slab will run along the back of the house, outside the back door about 150mm below the bottom of the door frame. Does that change anything?

Regarding your last sentence - when you say "Commercial I’d always allow at least a little to level the slab", are you talking about screed or leveler here? If screed, how much would you allow for? Is 10-20mm too little?

Thanks again for input

https://www.boards.ie/discussion/comment/122544935#Comment_122544935

Self levelling compound is both expensive and quite hard to use unless you are aiming for a continuous layer over the whole slab. It's also weak compared to the concrete. It's a bad sticking plaster.

It would be far cheaper to go for the hover float and get the slab level at pour time. A power float amalgamates the surface reducing unevenness but it also covers a relatively large area in each pass. It's how pros lay industrial floors and the results can be very flat.

nowImonboards

https://www.boards.ie/discussion/comment/122545252#Comment_122545252

Thanks again shoog. If I went for the power float and managed to get it super flat, wouldn't it still be affected by the differential drying you mentioned above?

I do find the whole process pretty interesting and just trying to better my understanding so apologies for the followup questions.