600 x 600 marble tile joints

[jaluka]

I made a post last night but it seems to have dissapeared :yikes: ill try again

i am laying 600 x600 marble tiles on a fibre screed which has kingspan and piped underfloor heating under
The screed has been layed for about 3 months and the heating has been on.
there are joints about 8mm at the threshholds, they could be shrinkage cracks i am not sure!

I was unsure as to what spacers to use i thing someone suggested 3mm?
Someone mentioned using uncoupling matting to try to prevent lateral movement and cracking of the tiles.
I had asked for help on sourcing the matting and just logged on to check for replies and the link to the thread could not find the thread :incazzato:

I checked the adhesive today while i was there it is all crated and adhesive and grout packed with the tiles.
The adhesive is Stonefix (flexible) i did write down the details but cant find the paper, i can get them if needed.

I also remember being advised to put the tile joint at the thresholds over the joints in the screed.

the floor areas are approx 6.5 x 5m leading into a hall about 4 x5 with a 3 x 1.5 corridor then into a maintence room 4 x 2 then another room of the main about 4.5 x 2

to summarise

What spacers is recommended?
Where can i source uncoupling matting (about 75m2)
Any general advice appreciated

thanks

Mark

 

[Ajax123]

Hi Mark

I not a tiler so will leave the pro tilers to sort out the joint spacing etc. My specialism is the substrate.

Firstly the screed being heated should be jointed at the door thresholds, between independently controlled heating zones, at areas of high thermal gain e.g. lounge to conservatory, areas where a large change to aspect ratio is observed e.g. an L shaped room or corridor and where the linear length of any bay exceeds approximately 6m by 6m (BS says 40m2)

On that basis the threshold joints which should be between 5mm and 12mm sound spot on assuming they are preformed using a compressible fill material. Bear in mind these are expansion joints not shrinkage control joints so if they are just part depth cut rather than full depth isolation there could be some problems later on. You may also want to just double check with the client the need for further joints. If they are not in place a decision needs to be made as to how to proceed.

An uncoupling mat is not an absolute necessity

Cement based screeds can be prone to curling which causes "lips" at the joint interfaces. If the screed curls post tiling an uncoupling membrane will not cope with this vertical movement and the tiles will crack if the bridge the joint.

If you have a joint in the screed you should have a matching joint in the uncoupling mat and also the tile face. This would normally be a cold joint (ungrouted)which is then filled using a flexible sealant - usually Silicon to match the grout. If you place a rigid fill in these joints they will fail. You should not bridge joints in the screed with tiles as the screed movement both vertically (curling) and horizontally (expansion and contraction) will crack the tile.

If you go down the route of uncoupling there are numerous to choose from. The most common are Ditra from Schluter and Dura Ci from Durabase. Most good tile suppliers will be able to get hold of these. They are available from Gemini products (G Mat) Uzin products and BASF although I don't know the brand names of the latter 2. There are probably others as well. I guess it will come down to best price because they all perform the same function. Don't expect them to accomodate all screed movement though because that is not what they are designed to do.

The other issue is how dry the screed is. Based on the facts that it is 3months old does not mean it will be dry. Screeds will only dry once they stop getting wet and it is important to ascertain this before tiling commences. If it is still wet there are one or two damp proof membranes you can put on top but most manufacturers steer away from DPM's on heated screeds. It is also impossible to tell visually if a screed is dry. I agree that if the building is complete and the heating running for a while it is likely to be though. I would just do a quick moisture test (most adhesive manufacturers are able to do this if you comit to using their materials. Alternatively (non science lesson) I always test screeds initially using the polythene bag test which simply involves putting a sheet of polythene down on the screed about 1mx1m and putting something on top to hold it in place. Leave it there for 48 hours snd then lift it. If there is moisture under the polythene the screed is not dry enough. You can do this test whilst the screed is heated. You cannot do a formal test on a warm screed's

As for spacers size - sorry not sure so that for the tilers on here to answer.

Hope this helps and best of luck with it.

 

[DHTiling]

we lost some posts from yesterday...sorry for that and hopefully the advice you got yesterday will be repeated.

 

[jaluka]

Thanks for the quick reply regarding the missing post Dave

Ajax123 that makes some interesting reading, the joints are definetly not filled with any flexible substance ( i remember putting fibreboard in concrete slabs years ago when groundworking, is this the sort of fill that shoud be in the joint? )
Can i create these joints now as these joints seem to be very important, is there a mastic or simular substance i can fill the joint with?

regarding the screed and damp i have a Protimeter Surveymaster will this be surfice in giving me a reading to rely on (will try the plastic sheet too as i have three days left on the bathroom yet)
I will also tell the customer to get the heating on as much as possible before starting next week.

regarding the uncoupling matting i will wait for feedback on this and work on their advice.

thanks for the info ajax most helpful

 

[Ajax123]

Thanks for the quick reply regarding the missing post Dave

Ajax123 that makes some interesting reading, the joints are definetly not filled with any flexible substance ( i remember putting fibreboard in concrete slabs years ago when groundworking, is this the sort of fill that shoud be in the joint? )
Can i create these joints now as these joints seem to be very important, is there a mastic or simular substance i can fill the joint with?

regarding the screed and damp i have a Protimeter Surveymaster will this be surfice in giving me a reading to rely on (will try the plastic sheet too as i have three days left on the bathroom yet)
I will also tell the customer to get the heating on as much as possible before starting next week.

regarding the uncoupling matting i will wait for feedback on this and work on their advice.

thanks for the info ajax most helpful

Yep the protimeter device will give a reasonable reading on this type of screed....for future reference though it won't work on ahydrite. I usually suggest the poly bag test as most people I talk to in this type of work don't have suitable test equipment.

With the joints it is not so important at this stage that the joint in the screed is filled with mastic. It is more important that it is a full depth isolation joint. In my experience it is easier to form these with preformers than cut them and fill them afterwards. Additionally there are heating pipes within the screed. If you think about it the screed will expand when heated. It needs somewhere to expand to so if the the joint is not full depth the screed cannot expand at this point. It would be wise to cap it with a flexible mastic before tiling though because you may drop addy in the joint and then it bcomes no longer an isolation joint. It will also prevent dust and debris getting into it.
The fibre board joints you talk of in concrete whilst old fashioned (sorry!) they are for the same reason. They are compressible and allow the concrete to expand and contract without restraint thus preventing cracking.

Heated screeds are much more sensitive than unheated to this movement and cement based screeds significantly more susceptible to cracking than anhydrite but the rules are very similar for both materials.

Are these actually formed joints in the screed or are they cracks. If they are cracks you need to be wary at this point because the screed is cracked due to movement. This movement may pop or break your tiles and if it is not straight it is difficult to form your joint in the tile face accurately. Where these cracks are randomly formed I usually recomend the cracks are repaired with epoxy and then reformed by cutting a straight line across the threshold very carefully as you don't know the depth of the pipes. This is by no means an ideal solution but it is the best of a bad job.

These joints are very often ignored by screeders and builders alike who shoud know better.

 

[White Room]

I agree with the joints Ajax but have seen very large areas of screeded floors without a single control joint anywhere.

The walls are a different issue with movement joints between concrete and block walls, perhaps they only think the walls will move but the floors won't.

 

[Ajax123]

Thanks for the quick reply regarding the missing post Dave

Ajax123 that makes some interesting reading, the joints are definetly not filled with any flexible substance ( i remember putting fibreboard in concrete slabs years ago when groundworking, is this the sort of fill that shoud be in the joint? )
Can i create these joints now as these joints seem to be very important, is there a mastic or simular substance i can fill the joint with?

regarding the screed and damp i have a Protimeter Surveymaster will this be surfice in giving me a reading to rely on (will try the plastic sheet too as i have three days left on the bathroom yet)
I will also tell the customer to get the heating on as much as possible before starting next week.

regarding the uncoupling matting i will wait for feedback on this and work on their advice.

thanks for the info ajax most helpful

Bu**er - just typed a long reply and the internet kicked me off.....Now where was I.

For the joints to do their job they need to be isolation joints. The screed will expand as it is heated and it needs somewhere to expand to in an unrestrained manner. If the joints are preformed they are likely to be this type. If however they are saw cuts installed after the screed has set the bottom 2/3rds of the joint will be locked by aggregate bridges and the two sides of the crack will be virtually touching hence no room to move.
Whilst very old fashioned (sorry!) the fibre board idea in concrete is for exactly the same reason to provide a compressible material for the concrete to expand against preventing restraint cracking. You probably used to put the same sort of joints around stanchion posts or pillars etc.

Forming joints in heated screeds post installation can be difficult because of the danger of cutting pipes so if they are not in place then it would be unwise to do this yourself. Where you do have threshold joints are they preformed, saw cut or just cracks.

If they are open joints they need to be topped out with a flexible sealant to prevent you dropping addy in them and restraining movement and also to prevent loads of dust and debris getting in and doing the same thing.

If they are cracks and not straight I would usually recomend they are repaired using epoxy and immediately after repairing a new straight line saw cut placed to give you a nice neat cut to form your tile joint over. This is by no means ideal but it becomes the best of a bad job so you need to be carefull obout contractual legalities and warranties etc.

If they turn out to be preformed isolation joints jobs a good'un and oyu can just seal them with mastic and tile as normal placing your joint directly over the top.

Your protimeter is ideal for this type of screed but for future reference it will not work on anhydrite screeds. They need a different test. Post if you come across that and I'll help with advice accordingly. I usually suggest the poly bag test because I come across so many people who do not have the necessary equipment to do the testing.

In terms of heating the screed 2 things to lok out for. DOn't over heat the screed because you could thermally shock it and that will cause it to crack. Secondly in terms of drying the screed heating it will only work if you also ventilate the area above the screed in order to get rid of the moisture driven out of the screed. If you don't ventilate the screed won't dry...

Lots to think about I guess but if you have the right infomration you can take the right actions in response can't you....

 

[jaluka]

I will have a close look at the joint/cracks across the thresholds tomorrow, they are straightish but definetely not sealed.

Fibre boards Very old fashioned now that makes me feel old

If i sent you a plan could you recommend where joints should be, if possible i would like to create these joints.
Would it be practible to cut out say 100mm strips and build it back up to a gap between 5mm to 12mm as recommended with epoxy (how long would that need to dry)
I will find out the construction tomorrow to see how the floor is built up and what is over the pipes.

Regarding the uncoupled matting do you think it is worth installing if these joints are not correctly prepared?

 

[Ajax123]

I will have a close look at the joint/cracks across the thresholds tomorrow, they are straightish but definetely not sealed.

Fibre boards Very old fashioned now that makes me feel old

If i sent you a plan could you recommend where joints should be, if possible i would like to create these joints.
Would it be practible to cut out say 100mm strips and build it back up to a gap between 5mm to 12mm as recommended with epoxy (how long would that need to dry)
I will find out the construction tomorrow to see how the floor is built up and what is over the pipes.

Regarding the uncoupled matting do you think it is worth installing if these joints are not correctly prepared?

Sorry about the fibre board dig

I could make some suggestions as to where I think the joints should be but this is really the domain of the heating installer along with the screed supplier. It should be based on the requirements of BS8204 and BS1264. I have copies of both but then I am a bit sad sometimes :smilewinkgrin:

If you cut out 100mm and then refill it you are actually going to create 2 joints - one either side of the 100mm strip so I would not recomend this as an option - it will also be a reall ball ache. I would certainly consider the uncoupling as an option. Obviosly it is not what they are designed to do but they will give some protection against movement.

 

[jaluka]

spoke to builder he said pipes are between 50 to 90mm under the screed so trying to makes the cracks into a joint is not going to happen

The cracks where they are are due to the screeder putting his trowel edge across the doorways thus creating a weak point.

I have explained to the customer my concerns based on info recieved and he has opted to go for the uncoupling matting, it cant make things any worse.

the uncoupling matting is this a well known application as tile giant have never heard of it harris tiles never heard of it i did get a price off my usual builders Hews gray and they quoted about £1000 for 80m2 is this a sensible rate, if not any suppliers near Chester?

just ordered a dewalt 24000 mk2 as my wet saw only cut 400mm max
So ready to go nearly :drool5:

Nice to get info from people who know what they are talking about :hurray:

 

[DHTiling]

just ordered a dewalt 24000 mk2

From Trade tiler i hope..:smilewinkgrin:

 

[Ajax123]

spoke to builder he said pipes are between 50 to 90mm under the screed so trying to makes the cracks into a joint is not going to happen

The cracks where they are are due to the screeder putting his trowel edge across the doorways thus creating a weak point.

I have explained to the customer my concerns based on info recieved and he has opted to go for the uncoupling matting, it cant make things any worse.

the uncoupling matting is this a well known application as tile giant have never heard of it harris tiles never heard of it i did get a price off my usual builders Hews gray and they quoted about £1000 for 80m2 is this a sensible rate, if not any suppliers near Chester?

just ordered a dewalt 24000 mk2 as my wet saw only cut 400mm max
So ready to go nearly :drool5:

Nice to get info from people who know what they are talking about :hurray:

Tile Giant not heard of uncoupling mat????????? Schluter Ditra, Dura ci, G-mat gemini systems etc etc - I am certain tile giant will have heard of Ditra Matting - maybe you were talking to the trainee :lol: Uncoupling is talked about on here all the time and I have seen thousands of square meters so yes it is a common option...

Not sure about price - last price i got for Dura ci was £7.40 per m2 plus adhesive to stick it down. that about £640is for 80m2 so £1000 a bit OTT but it is possibly in the right ball park.

Maybe someone on here from tile giant can help point you in the right direction.

 

[Matt]

Tile Giant not heard of uncoupling mat????????? Schluter Ditra, Dura ci, G-mat gemini systems etc etc - I am certain tile giant will have heard of Ditra Matting - maybe you were talking to the trainee :lol: Uncoupling is talked about on here all the time and I have seen thousands of square meters so yes it is a common option...

Not sure about price - last price i got for Dura ci was £7.40 per m2 plus adhesive to stick it down. that about £640is for 80m2 so £1000 a bit OTT but it is possibly in the right ball park.

Maybe someone on here from tile giant can help point you in the right direction.

I know of uncoupling membranes, but, I must admit I didn't know alot about it until I joined TF. It is not something we sell alot of at TG. Some stores sell alot, others not so much

 

[jaluka]

It was tile giant at chester i asked about the matting, i will speak to them again in the morning.

Matt i asked for a price for keraflex maxi today and the best they can do it for was £24.69 inc for 20kg is that right as i have heard of cheaper prices on here?

Sorry Dave put in my account at builders as tile trader showing no stock

 

[Matt]

It was tile giant at chester i asked about the matting, i will speak to them again in the morning.

Matt i asked for a price for keraflex maxi today and the best they can do it for was £24.69 inc for 20kg is that right as i have heard of cheaper prices on here?

We sell Ditra Matting. Ask them to look it up on the computer and they will find it.

Members of the Tilers Forums Arms have special discount. If you are in the trade and can get into the Arms, then you are entitled to the discount. You would need to gain access to the arms (PM Dave on how to) and fill out the form that is in there