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Discuss Old question but still confused.... in the Adhesive and Grout Forum area at TilersForums.co.uk.

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  1. JimboD

    JimboD Active Member

    Location:
    Hampshire
    I’m tiling a 90m2 area with 600x600 limestone tiles, 12mm thick.

    The base is a poured screed (very level) which also contains the underfloor heating pipework.

    I appreciate I need a 100% coverage with the adhesive.

    I appreciate that the round notched trowels give better coverage (primarily as they leave more adhesive on the floor)

    From what I read, some folks state you need a 20mm round notch.

    What I am confused with is the size of the notches required to achieve a solid bed. I watched a really interesting video that highlighted how what is more important is the orientation of the adhesive ridges and how having straight lines are important rather than having wavy lines – if you bed the tiles in by moving from side to side perpendicular to the ridge lines they close up and create a solid bed (and don’t if you have wavy lines or grooves running parallel to the bedding motion)

    So, with this in mind, why does the bed need to be so deep? 20mm round ridges must compress down to about a 10mm bed so uses a huge amount of adhesive.

    In my situation, I have to ensure the tile bed is not too deep as they run up to a bifold door (ideally I need 3-4mm).

    So, my question is… Why wouldn’t a 10mm round (or square) notch, with grooves laid perpendicular to the tile bedding movement suffice in creating 100% coverage (especially if back buttered)?

    Second question…. In my mind, there seems to be a disconnect associated with the thickness of the bed that is left vs what people are claiming. The maths doesn’t make sense. For example, a 10mm notched trowel is claimed to leave a 3-4mm bed, but how is that possible? Imaging cutting the top 5mm off the top of each 10mm ridge and laying it in the 10mm deep groove next to it. You’d end up with a 5mm level base. So where does 3-4mm come from?

    The rounded trowels leave more material behind so would be even deeper, say 6mm for a 10mm trowel.

    Can anyone please help clarify things for me so I know what the best approach is.

    It would be much appreciated!

    Cheers
     
  2. pdc

    pdc Trusted Advisor Professional Tiler Top Contributor

    Because you don't hold the trowel at 90° so you don't have 10mm notch more like 7mm holding it at 45°.
     
    • Agree Agree x 2
  3. timeless john

    timeless john Moderator Staff Member Trusted Advisor Professional Tiler JOTM Winner Top Contributor

    Location:
    North East England
    90 sq mts for a DIY project seems a bit risky!
     
    • Agree Agree x 2
  4. JimboD

    JimboD Active Member

    Location:
    Hampshire
    Aha! of course. makes perfect sense :)

    So a 10mm rounded notch will give me the 3-4mm depth i am looking for but will i get 100% coverage? I'm hoping yes if i apply the straight line and perpendicular bedding motion. That video i eluded to was awesome - they bedded in clear glass tiles so you could see the impact on the grooves underneath and how they only close up properly if you use that technique.
     
  5. pdc

    pdc Trusted Advisor Professional Tiler Top Contributor

    "Poured screed"? Anhydrite? How long has it been down? Has the UFH been commissioned? Anti fracture membrane being used? You've a lot more to concern yourself about besides the physics of adhesive depths!
     
    • Agree Agree x 1
  6. JimboD

    JimboD Active Member

    Location:
    Hampshire
    I've tiles various floors in the past, so not too worried. But i am getting quotes for a pro to do it as well!
     
  7. impish

    impish Trusted Advisor Professional Tiler

    Location:
    Preston, Lancs
    You could use a 4mm mosaic trowel and achieve 100% coverage.
    IF (big IF) the floor is perfectly flat and the back of your stone is like glass, and the adhesive has the correct consistency, and you trowel, back-skim and bed them perfectly.
    I think guys shout about large notches because our floors are so bad, you have a better chance of good coverage.
    Personally, I won't use more than a 12mm trowel on floors. If it's so bad I need a 20mm round notch, I would prefer to straighten the floor.
     
    • Agree Agree x 1
  8. JimboD

    JimboD Active Member

    Location:
    Hampshire
    screed has been down 6+weeks. UFH being commissioned soon but wont tile until that has been ramped up/down etc. Wasnt going to use anti fracture membrane.
     
  9. impish

    impish Trusted Advisor Professional Tiler

    Location:
    Preston, Lancs
    I would insist on a membrane with 12mm limestone.
    Lateral stresses will easily fracture at 12mm.
     
    • Agree Agree x 2
  10. JimboD

    JimboD Active Member

    Location:
    Hampshire
    4mm might be pushing my luck. 10mm gives some wiggle room and as i now know, bed depth is 3-4mm which is fine
     
  11. impish

    impish Trusted Advisor Professional Tiler

    Location:
    Preston, Lancs
    You will really have to push and pull to get solid coverage, and make sure the adhesive is wet enough. And don't forget to back-skim!
     
  12. JimboD

    JimboD Active Member

    Location:
    Hampshire
    Good to know. will look into membranes.I was going to leave a gap round all the edges to accommodate expansion and obviously use a flexible adhesive, but didn't think lateral stress would then still be a factor.
     
  13. Adey1980

    Adey1980 Trusted Advisor Professional Tiler Top Contributor

    Location:
    Caerphilly
    Will you be trowelling the back of the limestone as well? I personally would with a smaller notch trowel
     
  14. JimboD

    JimboD Active Member

    Location:
    Hampshire
    yes, was planning on troweling (or at a minimum at least buttering) the backs.
     
    • Like Like x 1
  15. JimboD

    JimboD Active Member

    Location:
    Hampshire
    Just looked into membranes on Impish's suggestion. A few rolls of durabase seems the best bet but adds 3mm to the depth. Hmmm, need to do come careful measurements tomorrow as i think 3mm membrane +4mm adhesive + 12mm tile might be too high for then being able to run the tiles flush into the bifold door edging strip.

    Thanks everyone for the speedy replies!
     
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