Hi Paul, Hope you are well. We are there UK Distributor for Fix-A-Floor and also members of the UK Tile Association where Fix-A-Floor won the Best Innovation Award for floor repair this year.
Fix-A-Floor will work on all types of substrates including concrete and even those with underfloor heating as it cures with elastomeric properties which means it will cope with any fluctuations in temperature without de-bonding. It's been specifically formulated to flow freely underneath the tiles via holes drilled in the grout-lines and literally it will fill any gap or void it encounters along the way which is exactly what you need. Once it fully cures it will provide a long-lasting extremely strong bond holding the tile in place and providing a permanent fix.
Predominantly it is used in situations where removing or replacing isn't necessarily an option, this is especially true on areas that have underfloor heating as potentially lifting and replacing the tiles could cause damage to the heating system underneath. In terms of drilling holes in areas with underfloor heating we suggest that you mark the drill bit to the depth of the tiles as you just need to reach the area directly underneath the tile opposed to drilling into the floor underneath that.
In answer to your question with reference to 2mm, If your grout-line is wider then a larger drill-bit would be preferable anyway. The Customisable tip that comes with Fix-A-Floor can be either cut very finely at the top to fit smaller holes (2mm) or you can cut to fit much larger holes which is better as it increases the flow.
If you have any other questions or need advice we are a UK based company and are more than happy to discuss any concerns or questions you may have with regard to Fix-A-Floor and using it. You can also call us anytime at the office on 0121 270 8883 and we are always happy to advise or help where we can.
As members of The Tiling Association we are finding more and more tradesmen and contractors are successfully using Fix-A-Floor in situations where removing or replacing tiles aren't an option, Loose tiles can be caused by thermal shock in areas with underfloor heating or even areas where anhydrite screed has turned to dust and tiles have loosened as a result
Adrian