General Advice Please

[alexhackett]

Hi everyone,

I'm getting towards the end of a major renovation that has taken 4+ years so don't want to make a mistake with the tiling that will be throughout the entire property. 300sqm on the floors. I've also got a couple of guys that are going to do the work, who have done lots of tiling before, but not with the large format tiles we have bought, so advice and hints and tips are very much welcomed.

The Floors

The majority of the floors have wet UFH and a cemfloor screed. Unfortunately, there was an issue in the main space so it has all been levelled with Bal Level Max. It was primed properly before the main relevelling, and primed again before the secondary relevelling of c. 3mm. All in accordance with the Bal technical advice chap we spoke with. The floor was heated up slowly and cooled down prior to doing it, and the main floor has been down for 6 months so is absolutely bone dry.

There are a few cracks as to be expected.

The Tiles

All the floor tiles for most areas are the same type from the same manufacturer. Cerdisa Reden Dark Grey and are 800mm x 800mm.

Plan and Questions

We are planning to use the Ditra Mat throughout. Is there an adhesive better than the Ardex AF200, or a better tool than the standard 2mm v groove trowel? I was also going to get one of the rollers to press it down, but recommendations are welcomed.

The guys have asked for a non rapid set adhesive and plan on using a 10mm notched trowel. Can you receommend a suitable adhesive to buy in bulk that is flexible and suitable for use with UFH. I think i read somewhere about it needing to take a certain amount of weight with the larger tiles. And do the tiles need to be back buttered? They also wondered whether there are any pre-mixed adhesives to save time?

As one of the areas is a big open plan, we are planning on breaking it up into 6 areas of circa 20sqm (roughly 4.25 x 4..25m) using expansion joints. Ideally i'm looking for tight grout lines, so don't really want to mess up the look with the 10mm wide rubber expansion joints, and it's unlikely the colour would match the grout. We had intended on 2mm/3mm grout lines throughout, and i wondered whether simply leaving a 5/6mm gap and filling with the colour matched Silicon would be viable? I appreciate that the Silicon may not be as hard wearing as the rubber expansion strips, and that i might need to redo on occasion, but we're a pet free shoes off house, so i don't think it will have too much abuse. There will be at least 10mm gaps/voids under all the skirting. Basically, i'm looking for something really minimal, but have no idea how much porcelain tiles expand in the real world residential environment with UFH and sun light. I obviously don't want them cupping or cracking, but genuinely can't see them expanding that much with a flexible adhesive and grout. Happy to take all advice.

I also want to make the job as easy as possible and was planning on utilising the Raimondi rls tile levelling system. Reviews on here suggest it's the best. Any alternatives that are just as good/better?

I said i would stump up for a rubi roller seat if it works and helps them. Does it actually roll on the ditra mat, or are there any other ways of keeping everyone healthy?

I'm sure i've missed a few things, so would be very grateful for any advice to help me and the guys get the best result.

thanks in advance.

Alex

 

[Ajax123]

I'm curious to know why you are needing the advice. Presumably the tilers are qualified to lay the tiles. Surely any advice should be from them?

 

[alexhackett]

I'm curious to know why you are needing the advice. Presumably the tilers are qualified to lay the tiles. Surely any advice should be from them?

Hi Ajax123, to answer your question , it's because they aren't tilers by trade. One is a very good chippy, and the other a plumber and general hand. Between them (and me) we've reroofed, walls back to a shell, built an extension etc. They do a lot of bathrooms and kitchen refits, and i've seen tiles they've laid in my neighbours house, but they were smaller.

They're good guys, but no one knows everything and we're all looking to learn something to make sure it goes as smoothly as possible.

 

[Ajax123]

Hi Ajax123, to answer your question , it's because they aren't tilers by trade. One is a very good chippy, and the other a plumber and general hand. Between them (and me) we've reroofed, walls back to a shell, built an extension etc. They do a lot of bathrooms and kitchen refits, and i've seen tiles they've laid in my neighbours house, but they were smaller.

They're good guys, but no one knows everything and we're all looking to learn something to make sure it goes as smoothly as possible.

Ah I see. Fair enough.

In terms of advice the only thigs I will say are that all movement joints in the screed must reflect through the tiles. your idea of a colour matched Silicon is fine and movement joints should be between 5 and 12mm wide. I'll leave the tilers to advise on the rest.

 

[alexhackett]

Ah I see. Fair enough.

In terms of advice the only thigs I will say are that all movement joints in the screed must reflect through the tiles. your idea of a colour matched Silicon is fine and movement joints should be between 5 and 12mm wide. I'll leave the tilers to advise on the rest.

Thanks Ajax.

Am i right in assuming movement joints in the screed are different from expansion joints in the tile layer?

Regarding the movement joints, what we have down stairs is basically a piece of the expansion foam in the doorway between the hall and the main open plan space. This effectively creates two separated areas. All the edges had the expansion foam installed prior to screeding. There are no other joints in the screed. It's been down 6 months+, actually probably 9 months, and its been heated and cooled a few times etc. There aren't any cracks other than 1 or 2 hairline ones which we were told would happen.

Upstairs, there are wider cracks emanating from the door ways which happened a month or so after the screed was laid and it dried. Some spaces i.e. between landing hall and rooms had foam between them, others didn't. Again, these floors have ufh and the screed is c. 50mm cemfloor. All bone dry now, well probably 8 months ago. Heated and cooled a few times. This is not a quick renovation!

Because these cracks aren't straight across the doorways, more of a bow type shape, there's no way a tile will follow them. There's no movement in the vertical plane as far as we can tell. For info, the house was built in the 1960's and first floor is basically concrete slabs between steels. We then insulated with 25mm celotex, tanking sheet, ufh and then screed poured. So, the actual structure of the house (sub floors etc.) is as stable as it's ever going to be.

So, with these cracks do we simply run the ditra mat over them, but still have a neat Silicon joint in the doorways, or is the Silicon joint in the doorways unnecessary? My understanding is that the ditra mat effectively means that the tile floor is separated from the screeded floor, and the expansion joints in the tile layer are simply there to allow the tiles to expand. But, do tiles really expand that much bearing in mind there will be at least a 10mm gap around all the perimeters under the skirting.?

 

[Ajax123]

Thanks Ajax.

Am i right in assuming movement joints in the screed are different from expansion joints in the tile layer?

Regarding the movement joints, what we have down stairs is basically a piece of the expansion foam in the doorway between the hall and the main open plan space. This effectively creates two separated areas. All the edges had the expansion foam installed prior to screeding. There are no other joints in the screed. It's been down 6 months+, actually probably 9 months, and its been heated and cooled a few times etc. There aren't any cracks other than 1 or 2 hairline ones which we were told would happen.

Upstairs, there are wider cracks emanating from the door ways which happened a month or so after the screed was laid and it dried. Some spaces i.e. between landing hall and rooms had foam between them, others didn't. Again, these floors have ufh and the screed is c. 50mm cemfloor. All bone dry now, well probably 8 months ago. Heated and cooled a few times. This is not a quick renovation!

Because these cracks aren't straight across the doorways, more of a bow type shape, there's no way a tile will follow them. There's no movement in the vertical plane as far as we can tell. For info, the house was built in the 1960's and first floor is basically concrete slabs between steels. We then insulated with 25mm celotex, tanking sheet, ufh and then screed poured. So, the actual structure of the house (sub floors etc.) is as stable as it's ever going to be.

So, with these cracks do we simply run the ditra mat over them, but still have a neat Silicon joint in the doorways, or is the Silicon joint in the doorways unnecessary? My understanding is that the ditra mat effectively means that the tile floor is separated from the screeded floor, and the expansion joints in the tile layer are simply there to allow the tiles to expand. But, do tiles really expand that much bearing in mind there will be at least a 10mm gap around all the perimeters under the skirting.?

Movement joints are the proper name for Expansion joints (I'm a screed tech guy so a bit pedantic on naming) screeds and of course tile expand and contract so the joints are there to mitigate risks of failure due to movement in both directions.

from the screeds perspective there should be movement joints across all door thresholds, between independently controlled heating zones and where heated meets unheated screed. These are standard requirements and your screed installer should have installed these as a matter of course. These should reflect through the tile face.

if the joints have been omitted you can get shrinkage restraint cracks (exactly as you have described) as the screed shrinks. This is more pronounced with cement based screeds than with anhydrite based screeds so joints are more important. If the screed does crack at these points there is a risk that a tile, bridging the crack, will be subjected to differential stress as the screed moves during thermal cycling at different rates in the areas the door separates. Running Ditra over them is not a technically correct way to do it. The right way would be to repair the cracks with a suitable resin repair and then retro install a suitable movement joint (saw cut to 1/3rd the depth of the screed). this can then be properly reflected. It would be for Ditra to offer an opinion as to whether it would work or not but it may work as long as the screed does not curl. Cement based screeds are prone to curling and this is common where such cracks occur. This leads to vertical movement and if this happens ditra most definitely will not work to bridge it.

and yes tiles expand quite a bit. When you look at the numbers it does not sound much but if that expansion bay to bay is sufficient to overcome the modulus of elasticity of the adhesive used then the tiles will pop. Also if the grout gaps are not big enough to allow for expansion tile to tile then the tiles will have no where to go but upwards leading to tenting.

 

[alexhackett]

Movement joints are the proper name for Expansion joints (I'm a screed tech guy so a bit pedantic on naming) screeds and of course tile expand and contract so the joints are there to mitigate risks of failure due to movement in both directions.

from the screeds perspective there should be movement joints across all door thresholds, between independently controlled heating zones and where heated meets unheated screed. These are standard requirements and your screed installer should have installed these as a matter of course. These should reflect through the tile face.

if the joints have been omitted you can get shrinkage restraint cracks (exactly as you have described) as the screed shrinks. This is more pronounced with cement based screeds than with anhydrite based screeds so joints are more important. If the screed does crack at these points there is a risk that a tile, bridging the crack, will be subjected to differential stress as the screed moves during thermal cycling at different rates in the areas the door separates. Running Ditra over them is not a technically correct way to do it. The right way would be to repair the cracks with a suitable resin repair and then retro install a suitable movement joint (saw cut to 1/3rd the depth of the screed). this can then be properly reflected. It would be for Ditra to offer an opinion as to whether it would work or not but it may work as long as the screed does not curl. Cement based screeds are prone to curling and this is common where such cracks occur. This leads to vertical movement and if this happens ditra most definitely will not work to bridge it.

and yes tiles expand quite a bit. When you look at the numbers it does not sound much but if that expansion bay to bay is sufficient to overcome the modulus of elasticity of the adhesive used then the tiles will pop. Also if the grout gaps are not big enough to allow for expansion tile to tile then the tiles will have no where to go but upwards leading to tenting.

Thanks again, that's really helpful, and pretty depressing the screeder hasn't done what was needed.

I want to do everything properly, so it sounds as though we are going to need to do what you have suggested.

Can you recommend a suitable resin repair product?

I'm guessing the width of a cut would be about 5mm (diamond blade on small angle grinder). I am nervous about slicing through an ufh pipe, and can't guarantee how deep the screed is over the pipes. I appreciate your advice is a 1/3rd deep, but if i don't know for certain how deep the pipes are, then if it was say 8-10mm then do you think it would still serve the purpose?

Do you put a product in the new saw cut, or is it just left as a void?

I'm not sure i understand the screed curling part. If it is flat either side of the existing cracks at the moment, and after 9 months, are you saying that one or both sides could still move (curl) up when the heating is turned on and off?

Assuming i over come the above issues, then regarding grout widths and popping tiles, is there a generally accepted grout width that is the sweet spot between tight grout lines (ideally 2/3mm) and wide enough for a flexible grout to take the strain?

Again, thanks for time and advice

 

[Ajax123]

Thanks again, that's really helpful, and pretty depressing the screeder hasn't done what was needed.

I want to do everything properly, so it sounds as though we are going to need to do what you have suggested.

Can you recommend a suitable resin repair product?

I'm guessing the width of a cut would be about 5mm (diamond blade on small angle grinder). I am nervous about slicing through an ufh pipe, and can't guarantee how deep the screed is over the pipes. I appreciate your advice is a 1/3rd deep, but if i don't know for certain how deep the pipes are, then if it was say 8-10mm then do you think it would still serve the purpose?

Do you put a product in the new saw cut, or is it just left as a void?

I'm not sure i understand the screed curling part. If it is flat either side of the existing cracks at the moment, and after 9 months, are you saying that one or both sides could still move (curl) up when the heating is turned on and off?

Assuming i over come the above issues, then regarding grout widths and popping tiles, is there a generally accepted grout width that is the sweet spot between tight grout lines (ideally 2/3mm) and wide enough for a flexible grout to take the strain?

Again, thanks for time and advice

ok firstly the resin... there are loads but one I use a lot is KR516 from Uzin. you n find it on google. There are loads of others and they are all pretty much of a muchness so go for the one that gives you the best deal once you know what you are looking for.

you need to be extra careful if you don't know the depth of the pipes. not sure how you deal with that but it is certainly a risk.... were it me I would look to do a guaged depth cut maybe 2 or 3 mm at a time. hopefully the pipes are properly installed and secured so that they remain a good 25mm plus below the top of the screed.

you can fill the joint with a simple Silicon just to keep out the dirt and dust or you can leave it open. properly formed they contain a compressible foam former which stays in. What ever you put n needs to be flexible. I am surprised that the screeder didn't mention this as its a cement based screed and is much more important than would be with anhydrite.

curling is a phenomenon associated with Portland cement based materials. It is caused by 2 mechanisms which lead to the top of the screed shrinking relative to the bottom of the screed. The first happens in the short term the fist happens in the short term due to over Rapid Drying (which i don't think you have suffered) and the second which is more long term and is caused by Carbonation. Atmospheric CO2 penetrates the top of the screed (that's the bit that's in contact with the air) and reacts with the reaction products of the cement to cause the same phenomenon ie. shrinkage from the top.

with regards to the grout lines I cannot remember the minimum but think for large format it is 3mm. that the minimum based on perfect conditions. only you can decide if the conditions are perfect. I'm sure one of the tilers will be along to confirm or correct the 3mm width though.

 

[Kevbos]

Hi everyone,

I'm getting towards the end of a major renovation that has taken 4+ years so don't want to make a mistake with the tiling that will be throughout the entire property. 300sqm on the floors. I've also got a couple of guys that are going to do the work, who have done lots of tiling before, but not with the large format tiles we have bought, so advice and hints and tips are very much welcomed.

The Floors

The majority of the floors have wet UFH and a cemfloor screed. Unfortunately, there was an issue in the main space so it has all been levelled with Bal Level Max. It was primed properly before the main relevelling, and primed again before the secondary relevelling of c. 3mm. All in accordance with the Bal technical advice chap we spoke with. The floor was heated up slowly and cooled down prior to doing it, and the main floor has been down for 6 months so is absolutely bone dry.

There are a few cracks as to be expected.

The Tiles

All the floor tiles for most areas are the same type from the same manufacturer. Cerdisa Reden Dark Grey and are 800mm x 800mm.

Plan and Questions

We are planning to use the Ditra Mat throughout. Is there an adhesive better than the Ardex AF200, or a better tool than the standard 2mm v groove trowel? I was also going to get one of the rollers to press it down, but recommendations are welcomed.

The guys have asked for a non rapid set adhesive and plan on using a 10mm notched trowel. Can you receommend a suitable adhesive to buy in bulk that is flexible and suitable for use with UFH. I think i read somewhere about it needing to take a certain amount of weight with the larger tiles. And do the tiles need to be back buttered? They also wondered whether there are any pre-mixed adhesives to save time?

As one of the areas is a big open plan, we are planning on breaking it up into 6 areas of circa 20sqm (roughly 4.25 x 4..25m) using expansion joints. Ideally i'm looking for tight grout lines, so don't really want to mess up the look with the 10mm wide rubber expansion joints, and it's unlikely the colour would match the grout. We had intended on 2mm/3mm grout lines throughout, and i wondered whether simply leaving a 5/6mm gap and filling with the colour matched Silicon would be viable? I appreciate that the Silicon may not be as hard wearing as the rubber expansion strips, and that i might need to redo on occasion, but we're a pet free shoes off house, so i don't think it will have too much abuse. There will be at least 10mm gaps/voids under all the skirting. Basically, i'm looking for something really minimal, but have no idea how much porcelain tiles expand in the real world residential environment with UFH and sun light. I obviously don't want them cupping or cracking, but genuinely can't see them expanding that much with a flexible adhesive and grout. Happy to take all advice.

I also want to make the job as easy as possible and was planning on utilising the Raimondi rls tile levelling system. Reviews on here suggest it's the best. Any alternatives that are just as good/better?

I said i would stump up for a rubi roller seat if it works and helps them. Does it actually roll on the ditra mat, or are there any other ways of keeping everyone healthy?

I'm sure i've missed a few things, so would be very grateful for any advice to help me and the guys get the best result.

thanks in advance.

Alex

I never liked ditra mat, durabase is better , use 6mm trowel to fix the membrane and I used to rub it in with a grout squiggle!! Mapei keraquik is great adhesive !! But bit worried about your tilers asking for a premixed adhesive , I'd get someone else

 

[parkerfresh]

3mm is meant to be minimum grout joint for floors. Ditra is superior to durabase in my opinion. durabase definitely lays better and doesn’t wat to curl up like ditra, however, I feel ditra is more robust & can be fitted with both AF200 or powder depending on the substrate. Like kevbos said, knee pads on and push it down with a grout float.

Ready mixed is only really suitable for small ceramic tiles with a maximum equivalent area of 300x300mm, I believe some higher end ready mix like Ardex D20 can be used on small porcelain wall tiles. Ultimately, don’t use ready mix on floor.

Don’t use rapid adhesive if you don’t need to. If your fitters aren’t used to it, it will catch them out and be going off in the bucket. Get something good quality like ‘Bal flex one’ or Ardex X77. I almost always use a 12mm notch as standard on all floor tiles and back butter… lucky to get 3m2 per bag on ditra.