Problematic Anhyrdrite floor!

[Spud]

question for Mark s and Alan, when I tiled on these types of screeds many years ago in germany when sanded they revealed an aggregate which seemed to have a high percentage of quartz sand ,when i recently tiled one over here I sanded the floor back a great deal only to reveal a "fly ash" very fine aggregate with hardly any decent grained aggregate ,i have been told that the anhydrite companies get subsidies to take industrial waste from incinerators to be used in the aggregate for these screeds my question is have the aggregates been changed over the years from quartz sand to some alternative and do you use toxic waste from incinerators in the aggregates for these screeds ?

 

[Ajax123]

question for Mark s and Alan, when I tiled on these types of screeds many years ago in germany when sanded they revealed an aggregate which seemed to have a high percentage of quartz sand ,when i recently tiled one over here I sanded the floor back a great deal only to reveal a "fly ash" very fine aggregate with hardly any decent grained aggregate ,i have been told that the anhydrite companies get subsidies to take industrial waste from incinerators to be used in the aggregate for these screeds my question is have the aggregates been changed over the years from quartz sand to some alternative and do you use toxic waste from incinerators in the aggregates for these screeds ?

Ok several questions in one so from the top when sanded the screed should resemble a sand cement screed in texture I.e. coarse but still sound. The sand usually is a grade m concreteing sand but obviously different sands from different quarries have different article gradings. some suppliers also use crushed rck fines which migh appear coarser dueto the particle shape. in the uk we use a lot of what is called river gravel whichs basically ancient river and sea beds but it still has to meet a suitable grading to make it suitable for a pourabe screed. There is deffinitely no fly ash in anhydrite screeds as this interferes with the hemi story in the most spectacular of ways. I am certainly not aware of any subsidies available in the uk for using or taking waste anhydrite, indeed it is a relatively expensive material to buy as the raw material suppliers know that the concrete manufacturers make money at it and charge accordingly.... If there is a subsidy then I don't know about it. Do we use toxic waste .... Absolutely not. The raw material is generally a bi product of acid manufacture. Not from waste incinerators. When you make certain acids you make anhydrous calcium sulphate as your waste material. This was sent to landfill or bulldozed into lakes and rivers many years ago but since it became a significant substitute for cement in the post Second World War period that landfill was turned into a useful material. there are no known significant risks to life or health from the material. It is highly alkaline and the binder is a fine powder so obvious precautions need to be taken but no there is no toxic waste in it..... Hemi hydrates which is the ther binder is much more modern in terms if its introduction to screed use and that is the material produced by calcining (heat treating) the waste from the flue gas desilphurisation process in coal fired power stations. This process was introduced to reduce the issues that such facilities cause with "acid rain" which is basically dilute sulphuric acid. More of this is now used in plasterboard than in screed in the UK.

 

[Ajax123]

Thinking about subsidies anhydrite is also used as a soil modifier in agriculture so there may be agricultural subsidies. It is often from the same raw material sources. I don't know for sure though

 

[Mark S]

Gary,
I see Ajax has answered your questions. I can only reiterate what he has put, the only thing I came across recently was the use of re-cycled crushed glass, as an aggregate, that had not been washed, and it smelt awful.
As far as we can tell ALL the major producers meet strict gradings of sand to make a good flowing screed, we are unaware of any subsidies.

 

[Master]

Hi, possible solution on this case remove the grout on floor/wall joint to relax the humidity of screed by sides
sorry for my English
Victor Spain

 

[Dan]

Just bumping some of the older popular (sometimes not so popular) threads. Probably wont be current discussion these days but I just need to do it. So just ignore the thread if it's not current for you.

 

[Joy1979]

Thanks Ajax...thats what I thought. As mentioned I didn't sand the floor as screed company said not to...I did try to sand and scrape a part but nothing came off...no dust...nowt. If moisture is the cause who is to blame? I don't do a bomb test and relied on dates given by customer and screed company who now say 120 days not 75 as previously. I told customer not to put up heating but he did so just my word against his. The heating to the travertine floors has been physically shut off for now so that if moisture levels are too high the floor can still breathe and hopefully be ok. Failed floors are porcelain. This type of screed obviously has some benefits...but not as regards tiling onto!!!!

Ironically unless you have anything in writing confirming floor was tested and passed all appropriate readings ready for installation of tiling, you the tiler will be at fault if no evidence to support, as you didn't get confirmation or check that tiling can commence, once you start fixing you can't go vack.