can we talk, calcium sulphate screeds

[Diamond Pool Finishers]

as a substrate, please any top blokes can write about it for us to read someone like ajax/DAVE???? i dont know much about them myself only they have been around a long time, and they are pump and almost liquid thanks for replies guys

 

[david campbell]

since i know the bare minimum about them you can read away here until your little hearts content-http://www.gyvlon.co.uk/

 

[The Legend; Phil Hobson RIP]

I have tiled on Anhydrite ( calcium sulfate) I think if you stick to the technical advice. You should be OK. Anhydrite screeds are a mixture of screeding sand and binder.

I think the last job I did, we had a tech guy mesuring the residual moisture content in the floor. I think it should not exeed 0.5% But we were using ditra, so we got away with 2%. We primed with epoxy, but I believe you can sand depending on maufacturers advice. Hope this helps

 

[DHTiling]

THe new Gyvlon screeds are the nuts compared to others...

Some info to follow..

 

[TT Tiling]

good screeds when layed right ,been laying on them down here for years ,you dont find many that are flat ,but when you do they are spot on ,make sure you epoxy or it will be up in no time , take a very long time to dry ,i nom get the guys to put the underfloor on to dry it out prop,before tiling

 

[Dan]

Best guy for this will be Ajax mate I think.

 

[Diamond Pool Finishers]

yes i hope ajax see this when he is on!? HAS DAVE got some info to share? its just for general knowledge for all of us really !!!

 

[Ajax123]

Is there anything specific you wanted to know Gooner.

In very laymans terms......

Calcium Sulphate screeds are a mixture of clean water, grade M sand and calcium sulphate binder which can be made from anhydrous calcium sulphate or from alpha hemi hydrate calcium sulphate.

The binders should be manufactured in accordance with BS EN 13545 and are usually made by third party accreditted manufacturers such as Knauf and of course my own company Lafarge (When I say my own - I wish - I mean the company I work for)

The binder is a blend of milled raw calcium sulphate in our case harvested as a waste product from the acid production industry. approx 150,000 tonnes of this used to go to landfill. We take some to make into screed binder and some goes to agricultural applications. Because it is a waste material it is classed as recycled when talking about things like the code for sustainable homes and BREEAM etc but in reality as it has not previously been used it is not truly recycled but as I say is a waste material that would previously have gone to landfill. When you land fill calcium sulphate and it begins to degrade anaerobically it produces a number of noxious gasses such as hydrogen sulphide amongst others so taking it out of landfill is great for the environment and the ozone layer. The raw material is mixed with very small amounts of additives which help to stabilize things like the pH, setting time and shrinkage etc. This material is then delivered in bulk to readymix suppliers. We supply quite a few readymix producers nowadays. For every 1 tonne of our binder used 980kg of landfill is saved.

Alpha Hemihydrate is made from the waste material resulting from the operation of coal fired power stations. Much of this waste goes into plasterboard manufacture as well. The issue is that when it comes out of the powerstation it is a composite material comprising calcium sulphate in several forms. To use this as a binder would lead to a great deal of instability and unpredictability in the final screed performance so it is processed to make wither Thermal anhydrite of alpha hemihydrate. Thermal anhydrite is the same chemical as the acid production stuff but it has been through a thermal process. The alpha hemi is made by a process called calcination and occasionally by autoclaving, ie heating up under pressure with steam. This process has to be controlled in such a way as to partially convert the calcium sulphate to gypsum. This again is supplied to the readymix manufacturers. I do not know the ladfill savings for this material but as it is temperature processed it could be argued as being not quite as environmentally freindly.

If you think of the binder as a special type of cement that is in calcium sulphate screeds you are not too far off the mark. We just refer to it as binder cos it binds the sand together to make it hard.

Next installment to follow......

 

[Ajax123]

chapter 2

Once the calcium sulphate binder is manufactured it is delivered to the readymix producer where it is stored in bulk untill time for use. The readymix producer will have a variety of mix designs available depending on the specific requirements of the screed. e.g. standard domestic screeds will generally be C20F3 or C25 F4 in strength whereas screeds over timber floors (used for accoustics and thermal mass systems) will generally need to be stronger. The screed mortar should be manufactured in accordance with the requirements of BS EN 13813 which makes incumbent upon the manufacturer certain testing regimes to ensure that the screed meets things like flexural and compresive strength criteria in a similar way to concrete manufacture. Compliance to a third party accreditted batching system is essentially optional but mos suppliers in the UK do comply to these systems. Some also carry CE marking and in a very few cases specific NHBC approval. The screeds are not usually BBA Certified these days because the thrid party accreditted QA systems make this un-necessary. The batching will be one of a variety of methods but essentially all of them aim to place binder, water and sand into the barrell of the readymix truck ready for delivery to site. The screed installer, who will usually have been on a training session to learn the technical side of the material, takes delivery of the material. The screed should be tested upon delivery for flow (like a mini slump test) and presuming it meets the required flow specification it will be discharged into a screed pump which should ideally be of the worm and stater or continuous flight auger type. This enables greater controll of the mateiral at the placement end of the pump. It can be pumped considerable distances. One of the advantages anhydrite has over hemihydrate is that the rate of reaction (setting) is slower and more predictable so allowing the installer more time to work with it on site.

The installer should foolow the guidelines within BS8204 part 7 but as we all live and work in the real world this does not always happen.

next bit to follow later cos me fingers are now aching.....

 

[doug boardley]

have we got an epilogue??:lol: