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Discuss Turning on Underfloor After Tiling in the Tiling Forum area at TilersForums.co.uk.

  1. kiteboy

    kiteboy Active Member

    Location:
    Swansea
    Hi all

    About to turn of underfloor heating a month after we tiled the kitchen floor - (its cold) but i gather this should be done slowly and gradually up to the working temp and then turned back down again too

    Ive checked the control valve on the underfloor manifold and the lowest it goes too is 35 degrees which its set to now

    Looking for any tips really as I cant go lower than 35 anyway

    Thanks
     
  2. JulianSidney

    JulianSidney Billy no mates. Trusted Advisor Professional Tiler Top Contributor

    35 is good and will bring up floor slowly, make sure your wall sat is set low and not by a cold open door :mad:
    will help to monitor with one of these
    wp_ss_20190309_0003.png
     
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  3. kiteboy

    kiteboy Active Member

    Location:
    Swansea
    Argh I have one of them great - Ok - Ive set thermostat to 17 which is 1 above ambiant at the mo - its cold
     
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  4. Tile Fix Direct

    Tile Fix Direct Julian at TileFix Direct TF Official Sponsor

    Location:
    Aldershot
    Be careful if the screed is gypsum/anhydrite. If you turn the heating on and the anhydrite screed is still wet (the only way to check is for a screed test) then the remaining water in the screed could be forced out before the setting is complete which will cause cracking and reduce the strength of the screed and cause failure.
     
  5. kiteboy

    kiteboy Active Member

    Location:
    Swansea
    Im not too worried about the screen being wet - its been down 8months - thanks though
     
  6. Ajax123

    Ajax123 Tilers Forums Pro - Screed Advisor Trusted Advisor Professional Tiler

    Location:
    Lincolnshire
    WHAT!!! firstly the screed should have been checked before tiling commenced. Secondly the screed will be fully set regardless of any residual moisture present. Thirdly presence of any moisture or not wont affect cracking and finally turning the underfloor heating on with any residual moisture present will not reduce the strength of the screed. Too much moisture in the screed regardless of screed type can cause emulsification of primers and cause delamination of tiles...
     
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  7. Ajax123

    Ajax123 Tilers Forums Pro - Screed Advisor Trusted Advisor Professional Tiler

    Location:
    Lincolnshire
    so its had 8 months to dry out.... its also had 8 months to get wet... Screeds, regardless of type, should always be tested for residual moisture (%RH) before any tiling commences...
     
  8. Ajax123

    Ajax123 Tilers Forums Pro - Screed Advisor Trusted Advisor Professional Tiler

    Location:
    Lincolnshire
    you will only be putting water through at the 35 degrees C if the stat is calling for heat. if the stat is saying no heat please you will not be warming your screed. at 17 I would think it is not really doing anything.
     
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  9. Tile Fix Direct

    Tile Fix Direct Julian at TileFix Direct TF Official Sponsor

    Location:
    Aldershot
    Talking to BAL ref Gypsum screeds. If the screed is mixed with water in correct proportions that water is required for a chemical reaction. If that water is then forced out prior to the reaction being completed (i.e. the heating being turned on) then the gypsum screed will not reach it's full potential strength, and possibly fail.
     
  10. jcrtiling

    jcrtiling Trusted Advisor Professional Tiler TTA Member Top Contributor

    Location:
    Salisbury
    I was under the impression that a gypsum sulphate screeds could have ufh turned on after a week to help dry the floor is someone going to tell me this incorrect .
     
  11. Ajax123

    Ajax123 Tilers Forums Pro - Screed Advisor Trusted Advisor Professional Tiler

    Location:
    Lincolnshire
    misleading bolx. If you want info on gypsum screeds why ask a company that has absolutely no involvement in them. Ask people who make them...
     
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  12. Ajax123

    Ajax123 Tilers Forums Pro - Screed Advisor Trusted Advisor Professional Tiler

    Location:
    Lincolnshire
    You are quite correct. 7 days is the norm.
     
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  13. Tile Fix Direct

    Tile Fix Direct Julian at TileFix Direct TF Official Sponsor

    Location:
    Aldershot
    My initial post was clearly misleading, I have found the extract from BS 8204, see below. The point I was trying to make is that forced drying using a high heat can damage a gypsum based screed. Turning the heat up gradually after a week is fine, but do not ramp it up quickly or raise it to a high heat. It can also be very deceptive as to how dry a Gypsum screed is. The carbide moisture test is a very good way of establishing if the screed has reached the required moisture content.

    See the last sentence of the BS extract.

    Extract taken from BS 8204-7:2003 Screeds, bases and in situ floorings — Part 7: Pumpable self-smoothing screeds — Code of practice, regarding heated screeds including calcium sulphate based screeds;

    “6.8 Heated screeds
    Heated screeds are generally laid as floating screeds in conjunction with proprietary underfloor heating systems with the heating elements at the base of the screed. The heating pipes or cables should be fully secured to the surface of the insulation or to the base to prevent flotation during screeding. The manufacturer of the heating system should provide their installation details, but it is essential to ensure that the heating elements cannot float in the wet screed and that the wet screed cannot get between or under any insulation boards. The tying of heating pipes to a steel fabric will not provide sufficient resistance to flotation unless additional fixing is provided. The thickness of the screed should be as detailed in section 6.4 but also ensuring a minimum cover over the heating pipes or cables of 25 mm for a calcium sulfate based screed or 15 mm for a cement based screed. Cement based screeds should not be heated until they are cured and dried because of the increased risk of cracking. The manufacturer’s advice should be sought for suitable time-scales. Calcium sulfate based screeds may be heated once they are at least 7 days old, which can accelerate the drying of the screed.

    In all cases, the screeds should be heated very slowly to their operating temperature and maintained at that temperature for several days before cooling down to room temperature, but not below 15 °C, before installing any flooring. The usual operating surface temperature of a heated screed is about 27 °C; however, some locations operate at higher temperatures, e.g. 35 °C. Higher temperatures than this can adversely
    affect the floor covering and the stability of the calcium sulfate screeds.”
     
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  14. pdc

    pdc Only a Handyman... Trusted Advisor Professional Tiler

    I'm getting comfy.. 813B3KiPUML._SY606_.jpg
     
  15. Ajax123

    Ajax123 Tilers Forums Pro - Screed Advisor Trusted Advisor Professional Tiler

    Location:
    Lincolnshire
    The section you refer to is talking about the operating temperature for the screed once covered. I can see how this might be confusing so i will bring it to the attention of the standards committee to see if it can be clarified in the next publication.

    The maximum temperature for force drying is 55 degrees C as this is the highest flow temperature acceptable for these screeds. Temperatures above 65degrees can cause partial desiccation of the calcium sulphate molecule causing shrinkage but this will only happen if applied for a prolonged period of several months. To force dry calcium sulphate screed you should switch on underfloor heating flow at 25 degrees or the minimum allowed by the system e.g 35 kn this instance. Leave atvthag temperature for 3 days then increase by 5 degrees per day up to a maximum of 55. Leave it there for minimum 3 days before reversing the process. Once back down to minimum leave for 3 days before wpswitching off and testing for moisture. A 50mm screed treated this way in good drying conditions will be dry by the end of this process.

    If you switch on the heating too hot too soon it will indeed crack the screed just as it would any screed due to the effects of rapid thermal expansion or thermal shock as it is known.
     
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