anhydrite

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Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium (baryte) and strontium (celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The Mohs hardness is 3.5, and the specific gravity is 2.9. The color is white, sometimes greyish, bluish, or purple. On the best developed of the three cleavages, the lustre is pearly; on other surfaces it is glassy. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to around 200 °C (400 °F) under normal atmospheric conditions. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits.

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  1. F

    Anhydrite / gypsum dust

    does anyone know if it contains silica in any volume ?
    • Flintstone
    • Thread
    • adhesive anhydrite canada dust gypsum screed
    • Replies: 9
    • Forum: Canada Tile Advice
  2. R

    Tiling Anhydrite screed with wet UFH

    Good morning, Gents I'd really appreciate the advice of experienced members here. I've been doing a small barn conversion in Kent for myself for the past 7 years and it's still nowhere near complete. I think I probably have OCD and this is only getting worse. The footprint of the building is...
  3. M

    Anhydrite Screed - Builder Nightmare - Which Hygrometer

    Should have walked into a job that was left"perfect" by the customers builder on Monday but its gone to pot. Long story short its been down for 6 weeks but the Laitance had not been removed. Builder had no idea what it was. Has done loads of these floors apparently. Also two substrates (old...
  4. Dannym80

    Anhydrite laitence removal

    Yes it's that damned gypsum screed! The builder assured me it's been sanded & laitence removed all bar one room. I'm on site today and they've got a guy using an electric hand sander with 80 grit paper. I don't think that's manly enough, how can I tell if the laitence has been taken down...
  5. J

    Anhydrite Screed Tiling

    Hi, I have got my kitchen extension floor to tile (6x3m). The floor is anhydrite screed which i had done about 6 weeks ago approx 40mm depth. This will be the first time i will have tiled on a gypsum based screed and after a bit of reading have come across all the possible problems (Mostly down...
    • J-a-m-e-s_7
    • Thread
    • adhesive anhydrite canada screed tiling
    • Replies: 36
    • Forum: Canada Tile Advice
  6. T

    Anhydrite laitence removal

    Hi Everyone This is something I have been doing a lot more of so I've upgraded all my gear so if anyone needs a screed sanded/diamond grinding please pm me for prices Thanks
  7. H

    Anhydrite screed & Laitance removal

    We had a 50mm anhydrite screed down over a DPM around 100 days ago. For the first 50 days the conditions were far from ideal for drying @1mm/day (early Feb, definitely no where near 20 degrees air temp, fresh plaster throughout, room open to elements). After around 50 days we comissioned the UFH...
    • Holster
    • Thread
    • adhesive anhydrite canada removal screed
    • Replies: 18
    • Forum: Canada Tile Advice
  8. Chris Gibbs

    anhydrite with ufh and porcelain

    I have a floor to put down and I'm after reassurance regarding procedure. Anhydrite floor with a 1200x600 porcelain tile on it. so.... prepare the floor with a machine to take the surface crystals off (about 2mm) then prime with a suitable anhydrite floor primer, ill probably use bal. lay ditra...
  9. J

    removing cement based adhesive from anhydrite screed

    got a job coming up where the stone floor has failed to a degree. anyway i have to take up the existing limestone which was bedded in cement based si adhesive. when doing a test some of the adhesive comes off anhydrite screed and some stays stuck to screed. i think best way forward is to take...
  10. P

    Looking for advice on slate floor on anhydrite screed.

    Please could someone tell me if I am doing this in the correct manner. The screed was laid mid may 2016, I have just removed the laitance layer with a STR 701 floor preparation machine and now have a lovely white floor. I plan to seal the screed with primer G, with a single coat of 1 to 1 and...
    • Playwrightpete
    • Thread
    • adhesive advice anhydrite canada floor floor tiling looking screed slate
    • Replies: 38
    • Forum: Canada Tile Advice
  11. G

    Force drying anhydrite

    How long do you think it will take to dry out this screed? Been down 90 days, 50mm thick so should have been dry at 60 days! Plastering has been going on so can't have helped? This is what the tramex read a few days ago. Got dehumidifier in and getting customer to get the pipe temp up to 50...
    • goz
    • Thread
    • adhesive anhydrite canada dry drying screed ufh
    • Replies: 9
    • Forum: Canada Tile Advice
  12. stone tiler

    Anhydrite Floor Sanding

    Afternoon everyone Just wondering what machines you guys are using to sand the laitance off these floors? I'm using a 9inch grinder at the mo with a dust shroud but its starting to give up on me. Before I go out and get something new I thought I'd check with you guys to see if there was...
  13. Element

    Anhydrite Screed Question

    I have a problem developing with tiles laid over water UFH in anhydrite screed. A few tiles are sounding hollow and are slowly becoming loose. The floor was 'scarified' using an orbital floor machine with a rotating disc with points underneath. The floor was then treated with a primer apparently...
  14. H

    Dural On Anhydrite

    Hello all. Got a large area of anhydrite that's having Durabase matting on it. Just wondering what adhesive you guys prefer to use with it. I'm thinking Granfix CSA as it's standard setting and i can mix a load at a time, as i said it's a big area. All input appreciated, cheers.
  15. H

    Basic Tester

    Hi all. Looking for a basic tester/meter to be used before a hair hygrometer on anhydrite screeds. Many thanks.
  16. H

    Won't Pay For Decoupling

    I've priced and got 200m2 of trav on a pumped heated screed. The client agreed to decoupling but has just sent me an email saying it doesn't need it according to the screeding company! I don't want to lose the job but not prepared to do it without the membrane. Can anyone point me in the right...
  17. H

    Tanking Alpha Hemi Hydrate Screed

    Hi all. I've got a wetroom to do with a pumped screed floor and wondering what would be the best method of tanking it. The floor has wet ufh and using silver trav. Thanks in advance.
    • hmtiling
    • Thread
    • anhydrite screed tank tanking waterproofing wetroom
    • Replies: 11
    • Forum: Tanking and Wetrooms
  18. S

    Anhydrite Screed

    Have to go look at a 90m floor on Monday..just came across this and as Webber recommend set plus for the adhesive I would always choose a slowsetting adhesive over a rapid set where possible, I've read many threads on here where it is advised specialist anhydrite adhesive should be used but no...
  19. AD Ceramics

    Tarmac Trueflow B

    Ay up Chaps Any of you guys tiled on to Tarmac's Trueflow B, I have read the bumf below Broken Link Removed but just wondered if any body has any experience with it the technical doesn't say anything about removing laitance. I have 360m² of stone to install on it first week January. Cheers Paul
  20. T

    Anhydrite Screed Prep

    Hi I know these questions have been asked time and time again but here goes ! I have a ground floor area of a house around 160m2 to tile, the screed is calcuim sulphate , the depth is 70mm, this was laid around 3 months ago , all i need to know are the proper steps to follow , ie how dry etc...
    • tubs
    • Thread
    • adhesive anhydrite aus floor prep screed tile adhesive usa
    • Replies: 13
    • Forum: Australia Tiling Forum
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