Sand cement Floor Screeds

[widler]

Re: Floor Screeds

alan just out of interest ,if you have an outdoor screed, that is exposed to the rain ? how will this dry out, on outdoor pools we tend to leave it three weeks then carry on mosaic tiling when its dryish obviously we use mainly water soluble adhesive and can only tile if the surface of the screed is not ringing wet , and in the main we tend to cover them in more nowdays

i supose its the same with rendering,i rendered a supermarket front years ago and tiled it within days,big buggers as well,still drive past it,and still looks the same,well apart for grout being a bit darker

 

[Tile Marble Granite]

Re: Floor Screeds

The way i do it (US standards) I can lay tiles on it the very next day. It dries over night

 

[Ajax123]

Re: Floor Screeds

The way i do it (US standards) I can lay tiles on it the very next day. It dries over night

No Detroit .... It sets over night.... It does not dry overnight .... There is a big difference.

 

[Fliselege]

Re: Floor Screeds

I used 2 new products last week, will take photos of it Monday and post back, one was a hey'di self levelling "turbo", you can tile on it after 4 hrs, the other was a PCI ready mixed normal "?" screed, tile on it after 5 hrs, I walked on it after an hour and it was solid as a rock. Christ knows what additives they put in it, viagra maybe. It was supplied by the builder, now we've worked with it once, we'll never work with it again.

 

[Ajax123]

Re: Floor Screeds

There are loads of screeds availale tha will set very quickly. Most have hydraulic binders which tie the residual water up in crystals of one sort or another. They have a place in the market Most deffinitely it realistically they are relatively pricey and your timing needs to be good. I have seen a few issues with some of them due to cracking. Not yet convinced of their long term stability against long term shrinkage but they satisfy a demanding some respects. Really though most projects are not tiled within 5 weeks let alone 5 hours so the advantages are limited ...... That is my opinion anyway.......awaits barrage of contrariness

 

[Ajax123]

Re: Floor Screeds

By the way these screeds are not "dry" it is simply that the moisture is locked in.

 

[Diamond Pool Finishers]

Re: Floor Screeds

very interesting what are the BS STANDARDS ON EXPANSION JOINT BAY SIZE?,in screeding ( just to enlighten some peeps ) you would have thought that they would match tile bay size? i love talking screeds/render and potential faults

 

[Fliselege]

Re: Floor Screeds

You're probably right in most cases but we work mostly in peoples houses with only 1 bathroom so it's screed floor 1 day, spend 2 days tiling the walls then start on the floor quick as poss, and if the grout lines on floor have to match the walls we do the floor first. The product we use the most is hey'di B20, hey'di is a brand name and B20 is the mix, loads of manafacturers produce it but hey'di is the best, saying that not impressed with their self levelling gear. It's become the norm for me now, but when I first started here I thought it was a lazy cheat, I'd only ever done screeding in U.K with a labourer on a mixer pump, shovel in hand with a pile of sand on one side of him and a pallet of blue circle cement on the other!

 

[Ajax123]

Re: Floor Screeds

very interesting what are the BS STANDARDS ON EXPANSION JOINT BAY SIZE?,in screeding ( just to enlighten some peeps ) you would have thought that they would match tile bay size? i love talking screeds/render and potential faults

Bs8204:1 which covers sand cement screeds does not actually give any specific guidance on bay sizes which is always a bit of a bone of contention amongst screeders and tilers alike.

The generally accepted rules are though that Traditional unmodified sand cement screeds should be split into bays of no larger than 6m in length with an aspect ratio of no more than 2:1 so the max bay would be 6mx6,. This fits in with the acceptable limits for concrete as well. Some will say the max bay length should be no more than 40times the depth.

When it comes to heated screeds I usuall offer the advice given in the NHBC handbook chapter 8 which says sand cement bays should be o more than 15m2 or room size whichever is the smaller.

The standards do go on today that sand cement screeds tend to crack uncontolledly.......

Calcium sulphate screeds are covered in a different part of the standard BS 8207:7:2003 which says that these can be laid to bays much bigger 1000m2 unheated and 300m2 but it does not give advice on aspect ratios so we say unheated 8:1 and heated 6:1.

In both screed toes there are guidelines on additional jointing e.g. Door thresholds and independent heating zones as well as areas of high thermal gain......

The tiling standards then conflict by saying 40m2 in all cases which is about ok for cement but is not even close to correct with gypsum. Trouble is all the standards are written by differentcomittees comprising different "experts". Trouble is the comittee members often have vested interests at some level so it is really difficult to remain objective when looking at the requirements of the standards. The other issue I find is that some of the standard tolerances allow interpretation and you can drive a bus through some of the tolerances.

My view is that BS are for guidance only and should be over ridden by manufacturers requirements. Bit of a nightmare really........

 

[Diamond Pool Finishers]

Re: Floor Screeds

god that is a minefield of as you say conflicting committees ,with that old chestnut vested interests , they should be based on scientific facts,but as you say alan BS standards are only recommendations ,that i presume would not even have any weight in a court of law ? should we not all be adopting european standards anyway !!? a bit like imperial/metric systems that will be dragging about for years to come ?

 

[Ajax123]

Re: Floor Screeds

British standards should reflect best practice but this is best practice in the opinion of the comittee writing them. D they stack up in a court of law, sadly they probably would because a judge would not be an expert and wild take a view that he standard shold reflect best practice.

Where products exist which are outside of national standards there are other systems in ace which allow manufacturers to warrant that they are fit for purpose. Additionally manufacturers can self test. We do this sometimes at Gyvlon where we develop new systems which have no standards available to cover them. A good example of this is the thermoplane system which is a new underfloor heating sytem or the soundbar system which was developed as a screed to go in a timber frame building. these are proprietary systems tested to destruction by third parties to demonstrate compliance with the requirements of the applications.

 

[Diamond Pool Finishers]

Re: Floor Screeds

yes i would agree that they might stand up in a court of law if the judge was a lay person ,but i understand that the judge would seek an expert advice ,ie a building surveyor ,or specialist expert ,someone like yourself
ALAN , THERE YOU GO A NEW SIDE LINE FOR YOU LOL!
i thought the BBA would test most systems and be a good source of compliance that a material /system is fit for purpose .
i hate these peeps who don't have any real accreditation for a product/system ,but just come to market anyway, usually leaving a wave of failures in there wake .

 

[Fliselege]

Re: Floor Screeds

This is the gear I was on about. Looked at the additives, no viagra.

 

[Ajax123]

Re: Floor Screeds

Bit like some of the ones over here. Ardex done and so do Mapei.

 

[c1432666]

Re: Floor Screeds

Bit like some of the ones over here. Ardex done and so do Mapei.

Sorry to resurrect such an old thread, but it seems this is the appropriate topic and has been replied to by those with the knowledge I seek.

I have a 8m x 2.6m room (~20m2 internal space), with a standard 100mm sand/cement screed (no additives other than poly fibers and retarder to work with it for the initial lay) going on top of UFH pipe, on a floating floor of XPS insulation.

I intend to do the recommended full 1mm/day dry out period ~100days, and do a couple of full heating cycles in the last week prior to tiling, as I have 15mm thick granite tiles going on top and do not want any thing propogating through.

During the drying out period, I will be doing lots of work completing the room, boarding out, 1st and 2nd fix electrics and lots of walking on the surface. So when it comes to tiling the floor surface will need a deep clean before laying down any adhesive. I have some bondit branded, cement based flexible adhesive (product name: CTA Flexible).

My question is do I need to do any other preparation to the surface prior to laying tiles, is an SBR required? Anything I have missed?

Thanks in advance,
Kev