Discuss Hollows over underfloor heating in the Tiling on Underfloor Heating area at TilersForums. The USA and UK Tiling Forum (Also now Aus, Canada, ROI, and more)

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Hi All
I am after some advice please. We have a retrofit undefloor heating system ( Robbens Profilow 15) which was laid on a rather uneven floor. We had 4 rooms knocked into a large kitchen dining living area approx 50 sq m. I can tile myslef to a reasonable standard and have used this forum over the years to help me ( small ensuites , bathrooms etc) but this floor was was to big for me to tackle hence calling in a professional.
We asked our tiler if we should have more slc applied to level out the floor but he said not to worry, he would build it up with tile adhesive where necessary. He visted three times to discuss the job & knew full well the floor wasnt very even. He assured us all would be well so we booked him. His price was similar to other quotes so not overly cheap by any stretch. The job commenced and he ended up using 75 bags of adhesive over the 50 sq m. He used ultratile adhesive (pink bag) which I noticed had a 3-20mm recommended thickness. With hindsight I feel he should have stopped and used slc to build up the floor then carry on tiling. He was unable to grout before he went on holiday for 2 weeks so during this time we cleaned the tiles by hand and my wife noticed a few hollow sounding tiles. We then started to tap test each tile (800x800 8mm porecelain) and found well over half the floor with hollow spots in the tiles and particulary around the edges of the room there appeared to be very little adhesive. After a week of the adhesive curing and under the advice of Robbens we slowly recommisioned the heating starting with a flow water temperature at 25 deg c and incremented it by 5deg c / day up to 45 degrees. The single zone room stat was set to 30 deg c to ensure the system stayed on 24/7. we then did a hand touch test on the tiles with hollows and found several cool spots. I bought a flir one pro iphone thermal camera to see what was going on. It looked like there were multiple cool areas. I turned down the heating and as the floor cooled it was easier to see which areas remained warm the longest. We revealed several dots/dabs under the tiles. When the tiler returned to grout last Friday we asked him about the hollows and how unhappy were were especially as Robbens stated that their system should have 100% adhesive coverage on top to aid heat transfer. They said the varying thickness fo 10 to 40mm in places wasnt an issue as long as there were no air voids. The tiler denied any wrong doing and after an hour of discussions he went away ( grouting suspended for now) . He asked to return today to discuss further and try to come to an agreement. He brought his own ufh installer who basically trashed our system and said that any heat loss through voids wasnt an issue of any significance and we shouldnt worry. He has know the tiler 20 years and has every confidence in the quality of his work. They both maintained that the tiles would not crack due to any hollow areas. The tiler maintained that he had to dot and dab as there was no other way given the thickness of the build up and that he has vastly underestimated how much adhesive he would need. The floor looks goos tbh but my wife is distraught at the clip clop hollow noises as she walks ove the floor ( in hard shoes). we would like the hollows to be gone but the tiler refuses to lift any tiles maintaining there are no hollows and how can we be sure? He is worried about damaging the retrofit ufh pipes. Without lifting at least one tile we can't be certain what is going on underneath. The tiler then claimed that lots of floors sound hollw and its nothing to worry about in day to day use.

Are we being too picky or is the tiler simply trying to steer us to accept the hollows and move on as it wil clearly cost him time and money to rip up and replace what could be upt to 40 tiles.? We are curently at an impasse as he refuses to consider any kind of compromise. I am inclined to take a core dril to a tile that wil be under our island and see if ther is a hollow void or not. My wife is in bits and very distressed by the whole episode. It also doent help that the tiler ( who actually had a good reputation in the area) is our next door neighbour! they are a lovely family and we really dont want to fall out with them. What should we do?


Apologies for this long post.
 
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As an aside, are there any circumstances where there is an accepted ( industry standard) percentage of a tile that may contain a void?
 
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I decided to drill a 1.25” inspection hole in 3 tiles - 2 will be under a kitchen island and one under a corner base unit. Each hole was drilled over an identified hollow spot and revealed … no adhesive
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underneath. Just a 25mm+ deep void.
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As an aside, are there any circumstances where there is an accepted ( industry standard) percentage of a tile that may contain a void?
some allow 5%!

I've just seen your other two posts, this is bad practice, you need as much coverage as possible between tile/adhesive/substrate. IMHO, these tiles will crack when something falls on them.
 
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some allow 5%!

I've just seen your other two posts, this is bad practice, you need as much coverage as possible between tile/adhesive/substrate. IMHO, these tiles will crack when something falls on them.
You are spot on. I’ve replied to your other reply, good suggestion of yours btw,. The whole floor is coming up now.
 

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Its the kitchen but you are right. I did wonder if the thin back buttering stuck to the dabs but came away from the tile.

I saw the video link in one of your posts about trowelling and back buttering. Its very informative. Our guy has done everything the video says not to.. even down to swirling the notched trowel & then dabbing the tile in places.
 

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