Expansion joints in screeds and tiles

[jonnyc]

I'm looking at some plans for a large terrace about 1600.00 sq mts.
The current proposal is to use rhomboid shape tiles locking up to each other.
the tiles themselves will have different coloured glazes when each tile is split colour wise in two .ie two triangular colour shapes per tile.
the mix of ten colours and permutations will give a pattern of sorts when viewed from above.
expansion joints will be needed but the pattern could be ruined by these if expansion laid in rectangular or square bays .

I had a thought that if screed laid in one go,then perhaps expansion joints could be cut in screed following day when I could accurately mark out rhomboid bays reflecting an area of multiple of tiles.
this way the expansion joints would become part of joint pattern and not cut through tiles.
my question is , would this compromise the strength of screed in any way.
it would be far too difficult to ask a screener to set perfect bays as rhomboids as they lay screed.
also I have used schluter expansion trim between tiles before but do you think this is really so much better than just a Silicon joint above expansion joint in screed, which would be less unsightly.
screed will be 100mm thick over drainage layer over 240mm insulation on 200mm RCA deck laid to falls.

 

[Ajax123]

What sort of screed are you thinking of that you will lay 1600 square metrs in on go?

 

[jonnyc]

Sorry,you are right I was not thinking.
i am so used to doing domestic jobs where the largest single room ie kitchen/breakfast would be done in a day and that would not be more than 120sq mts max.screeder puts a day joint in doorway before going in to other rooms.
so yes this 1600sq mts will be split in to various areas on different levels.
the largest will be approx 700sq mts.
i think what you are suggesting is that no one will screed that area in a day which is understandable and therefore my question should be I suspect is:would a specialist screed company be prepared to take responsibility for laying specific bay sizes laid as rhomboids to a very accurate measurement given ,having obviously factored in their extra time needed in costing. Or would it be expected that contractor or myself set out bay lines for them.
I know from viewing previous posts that you are the oracle on screeding Ajax.
Any advice you can give would be very much appreciated
I apologise for posting such a daft post . I am actually very specialised in my field and probably concentrating too much about other aspects that I am au fait with.
I am just hoping that I can glean a bit more understanding of trades before me and reasonable expectations before I present some of my ideas for what is actually a very prestigious project in London.

 

[jonnyc]

Sorry, should have added ,screed is I believe sand/cement with fibres .
there are various walkways that have to have specific falls and quite steep inclines where pattern of tiling needs to run from one level to next .
i truly believ that the success of project depends on not just right product being used through whole process but mainly the screeding being done to a very high standard which will assumedly be cost premium.

 

[Ajax123]

I assume this is anoutdoor terrace. If it is indoors my first thought would have to be anhydrite screed butif it is outdoors this is not appropriate

Assuming i am correct I think you wouldbe better to use a concrete rather than a screed in this instance personally. Some of the self compacting products wold be perfect for this type of thing.

I do not beleive that a sand cement screed is appropriate for this sort of area at this sort of depth if you intend to doit properly.


100mm should be laid in two layers and split into bays of no bigger than 36square meters and the bays should be as square as possible. each layer wold need to be levelled and flly compacted and realistically you cold expect maybe 80 or 90 square meters a day maximum. Taking prep Ito account and curing and jointing this process cold take well over a month to complete

If you go for self compacting concrete you can lay much larger areas in one go and you could add steel fibres to reduce cracking which would allow youto return within 3 days and saw cut joints as appropriate. I reckon with a self compacting product ou wold be looking at two weeks

I think you would deffinitely be better to use a specialist. If you want to give me a call at work on Monday I can put you in touch with the people who can spec this up properly for you and install it if you like. My number 07545 932723.

Only issue I see is that bay sizes need to be controlled to avoid random cracking dueto shrinkage and as there are some falls there will probably be two different products involved. it is all doable though given the right expertise. It is deffinitely not a jobbing screeder project though. I think if you do it with the right products to minimise labour the costs will probably surprise you,in a good way.

 

[Richard Edwards]

Hello Jonny

I know that Ajaxv works for Larfarge and is a well known authority on liquid / gypsum bases Anhydrite Screeds and I am posting this message as I want to see what he comes up with. [I respect this man's opinion most highly, always worth taking a call]

That said, if you are sure that its going to be conventional screeds - morter based albeit with added fibre for strength, then if you are planning to lay these rhomus tiles point to point then you will have a straight line to roughly at 30 deg off the centre line[depandant on the actual rhombus dimensions which can vary a lot by definition] So, tecnically I can see no reason why you should not cut the screed in this line by measuring the centre line of each room or area and place one or two cuts right through to the slab or substrate and then you could start the tiling from that joint.

The only thing I would say it that some manufacturers of expansion joints will supply a narrow exp joint - typically 2-3mm and colour coded inserts which I think would be infinately better than a Silicon joint. So with this small joint you might be able to set the grout joints in the tiles to match the Exp joint.

 

[Richard Edwards]

Just read Ajax's reply - There you go -blo''dy marvel than man.

Is it outside or inside and is the area split up into different rooms of is all one but split level, ?

 

[Ajax123]

Rhombuses..... Or is it rhombi....... Are not the best shapes to cut or indeed to lay screeds or concretes into because the level of lateral stress at the acute angled corners is far higher than that at the obtuse angled corners. This dan lead to high levels of shrinkage cracking.

I personally think this task would be better with a self compacting concrete containing steel fibres. That way the lateral stresses at these corners will be transferred across the joints thus minimising the risk of cracking. He joints can be saw cut to one third the depth of the concrete a day or so after laying (provided bay/pour sizes generally are suitably controlled). This way the propensity for curling is also minimised as the fibres transfer dimensional stresses throughout the depth of the concrete and also across joints.

If it is indoors anhydrite would be far better. One joint only required.

 

[jonnyc]

What sort of screed are you thinking of that you will lay 1600 square metrs in on go?

It is virtually all outside with one area in covered cafe area.
there are viewing areas under terrace area
thanks for responses. I will try and come back with more info tomorrow.
this screeding prep part is very interesting to me .
Prep is the key and I would not entertain getting involved with prep work or tiling aspect if I could not give the very best job.

 

[jonnyc]

Ok this is getting very technical and very interesting as I thought would be the case I will come back with as much info as poss in morning .thank you