anhydrite

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. W

    Floor Tiles Lifting On Anhydrite Screed

    Been working alongside a plumbing and bathroom company on a job and the owner told me he'd had a failure on anhydride screed. He said they sanded the floor primed it with suitable primer and tiled it with benfer solo flex gypsum adhesive. The screed had been down over 6 months. The tiles have...
    • wayne
    • Thread
    • adhesive anhydrite aus debonding floor floor tiles floor tiling lifting screed tile tiles usa
    • Replies: 30
    • Forum: Australia Tiling Forum
  2. S

    wet room and anhydrite screed

    Hi I am after some advice on the following, I have been to look at a job which had problems in a wet room, i removed the floor tiles (very easily) which were fixed directly to the Anhydrite underfloor heated screen. I say its anhydrite as i have laid screeds before but this seems a lot finer...
    • shick
    • Thread
    • adhesive anhydrite aus room screed usa wet wet room
    • Replies: 8
    • Forum: Australia Tiling Forum
  3. M

    Anhydrite screed question

    Hi All I have a couple of questions regarding tiling prep for Anhydrite screeds and was hoping someone here might be able to offer some advice? A few months back i quoted for a floor tiling job for a wet underfloor heating system. The screed the builder decided to use was a gyvlon thermio+. I...
    • Matthew77
    • Thread
    • adhesive anhydrite anhydrite adhesive aus screed usa
    • Replies: 31
    • Forum: Australia Tiling Forum
  4. F

    Prepping Anhydrite Screed

    Hi All, I have a floor tiler coming in in a couple of weeks time to lay ground floor tiles on an Anhydrite screed. He’s going to do it properly and has tiled to this surface before. We have to clean up and lightly sand the surface to ensure there is no more laitance etc. What sanding kit...
  5. B

    anhydrite floor screed

    We are our wits end ,, We had an Anhydrate Floor screed laid at 40 mm and was left for 6 weeks to dry ,, the problem we got is the tiler laid the porcelain tiles on the floor he primed it ,and use rapid set flexi adhesive, followed all the correct procedures . The plumber ,then turned on the...
    • barno101
    • Thread
    • adhesive anhydrite anhydrite adhesive aus floor floor tiling screed usa
    • Replies: 37
    • Forum: Australia Tiling Forum
  6. J

    The best primer and Adhesive for anhydrite screed

    Hi, I have a 60sqm floor to lay on Anhydrite screed, I am using 800mm x 800mm porcelain tiles and Ditra matting. What is the best primer to use, and adhesive to fix Ditra matting. And finally what is the best adhesive to bed the tile with.
    • Jase-tiler
    • Thread
    • adhesive anhydrite anhydrite adhesive aus best primer screed tile adhesive usa
    • Replies: 33
    • Forum: Australia Tiling Forum
  7. K

    Wetroom Prep on anhydrite floor

    Evening All I know the briefest of details but I'm off to see a customer tomorrow where by the sounds he is having wet trays set then the screed poured to the required height. Has anybody any experience of this, pit falls, tips, waterproofing, etc. Apologies a bit lacking in detail but should...
    • kaharrison9
    • Thread
    • adhesive anhydrite aus floor floor tiling prep screed tanking usa waterproofing wetroom wetroom tiling
    • Replies: 11
    • Forum: Australia Tiling Forum
  8. S

    Advice needed turning on ufh with anhydrite screed

    Hi u lot. I tiled 100 odd sqm of 450x900 porcelain onto anhydrite screed which has a water ufh system. It's all been commissioned before tiling and the screed tested. I have been told the ufh can not be turned on gradually as it's lowest setting is 30 degrees C (water temp) so I'm worrying that...
    • stusgsx
    • Thread
    • adhesive advice anhydrite aus needed screed ufh usa
    • Replies: 6
    • Forum: Australia Tiling Forum
  9. F

    Advice please on primer and adhesive for anhydrite screed

    I am seeking help on recommended products for use on dried and sanded anhydrite screed with low temperature UFH. I need to stick 18mm plywood to the screed for some floors and porcelain tiles for some others. I know I need to have flexible adhesive and a compatible primer and adhesive, but would...
  10. High Peak Tiling

    Anhydrite Screed (gypsum based)

    Hi guys. All the Anhydrite screeds I have done, have UFH (wet) I have always lathered the floor with Weber PR360. Then applied Ditra with cementious addy. I have never had any issues, and all the jobs are perfect now as they were when i left. I have even monitored the drying of addy on the...
  11. F

    Advice please - natural sandstone - indoors on anhydrite screed

    Hello, I am pretty new to this forum and would like some help please on laying sandstone indoors. I’ve read up everything I can find that looks relevant first so as not to waste your time :smilewinkgrin: I have a 3.2m diameter circular floor area with anhydrite screed finish and am a laying...
  12. K

    Anhydrite with electric mat

    Good Evening. Looking at an anhydrite conservatory floor tomorrow but with no wet UFH around 35/40m2. I have a formula for anhydrites with a wet system but this is a first where there is to be an electric ufh system. Usual anhydrite prepping then was thinking of insulation boards put down...
    • kaharrison9
    • Thread
    • adhesive anhydrite aus electric screed usa
    • Replies: 18
    • Forum: Australia Tiling Forum
  13. M

    Anhydrite screed advise

    I'm tiling a 36 metre floor next week it's dried out and the builders are putting 3 coats of this blue primer on it I've ordered anhydrite adhesive but been told I don't need it as it's been primed and can use rapid flex should I still go for my anhydrite sticky and will it be ok on the primer
  14. D

    anhydrite adhesive/concrete screed

    okay a bit of a hypothetical question, we all are aware of the potential pitfalls of using a cement based adhesive on an anhydrite screed, but what about using an anhydrite adhesive on a concrete screed?, I was mulling this scenario over the other day when I was skimming a sand and cement...
    • Dougs Third Go
    • Thread
    • adhesive anhydrite anhydrite adhesive aus screed tile adhesive usa
    • Replies: 11
    • Forum: Australia Tiling Forum
  15. Aspect Tiling

    1st Anhydrite screed ?

    Hi all, Not yet seen this job which is as good as mine but I'll put all the info I have from a brief conversation with the customer and update when I've seen in person. 75m2 anhydrite screed layed by Lafarge approx 4 weeks ago. 1 room (originally layed through 2 rooms with a wall since...
  16. High Peak Tiling

    In a spot of bother... Anhydrite screed!

    Hi guys, I have a site meeting tomorrow with the customer and father inlaw (architect) so I bringing my dilemma to you guys. A quick run down on the problem and why.. I priced a job up a while ago which entailed hallway and kitchen tiled in black Riven Slate onto concrete screed. being a brand...
  17. K

    Anhydrite not dry

    Good Evening All. Had been making plans to hopefully start the tiling of a anhydrite floor at the end of the week but the first readings from the digital hygrometer is it floating between 87-90 rh. The screed went down in December and has different depths the deepest I believe is 90mm so quite...
    • kaharrison9
    • Thread
    • adhesive anhydrite aus dry not screed usa
    • Replies: 25
    • Forum: Australia Tiling Forum
  18. Andy Allen

    anhydrite in a bathroom..

    did I read somewhere that theses type of floors are not recommend for bathrooms..? im on about a bathroom..(bog, basin, bath and separate shower tray and shower door) not a wetroom..
  19. P

    Proven anhydrite methods

    Just wondering what everyone's adhesive/primer combo is for tiling on calcium screeds without a decoupler and if you have faith in your system?
    • Peter
    • Thread
    • adhesive anhydrite aus screed usa
    • Replies: 33
    • Forum: Canada Tile Advice
  20. R

    Tiling on anhydrite

    Customer has karndean on ground floor of his house. All over floor are small blisters in karndean (like screwhead). Floor has been sanded, primed ( dont know a products used) but selflevel is also debonding in places. It is going to be replaced with tiles.I think that issue is a moisture in...
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