I've just removed some super old tiles from my bathroom floor.

Most of the now exposed concrete is in decent condition. However the cement is a little soft / sandy around the drain area (it's an old terraced house with extension over drain).

I'm laying tile backer boards over the floor before the tiles.

What should I do about this slight sandy area. Would it be ok to level with tile adhesive or should I try something else.


enter image description here

enter image description here

  • By "the adhesive" do you mean thinset mortar? How deep is the decomposing concrete?
    – isherwood
    Mar 20, 2019 at 19:43
  • Added some images Mar 21, 2019 at 0:00
  • And updated text - meant: tile adhesive Mar 21, 2019 at 0:07

2 Answers 2


You have to get rid of the sandy area/sand. If there is just a thin layer and you have solid flooring under you can use a filler like a floor leveler - there are other options but I would need to see pictures. If there is a thick layer or no solid flooring you are going to have to pour concrete or frame (which may be impossible).

There are solutions like floating a floor over the sand but these would break down over time - probably a lot faster than you think. This is maybe an alternative in some climates and some situations.

  • Thanks for this! I'll get some pictures taken tomorrow. Mar 20, 2019 at 22:52
  • Added a couple of images Mar 21, 2019 at 0:00
  • Can you clean up the sand then take pictures? It is hard to tell what is loose or solid in them. From what I see it doesn't seem that bad but want to be sure.
    – DMoore
    Mar 21, 2019 at 3:03
  • That’s about it. The rest is ok. The depth of the recess is about 50mm max. Mar 22, 2019 at 0:03

I will clean and pour concrete if necessary I also will add fiber to concrete or solution to make it stronger. You need a solid foundation to begin.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.