Replies

1. 
   DanH | Apr 16, 2014 06:29pm | #1

   If you feel you need to remove it, either heat or chemicals will likely work.  I've used both to reasonably good effect (aside from the blaring smoke detector).

2. 
   deadnuts | Apr 16, 2014 10:27pm | #2

   skim it

   If your bond of old adhesive (who knows what it is) is that tenacious, then you probably don't need to worry about it. IMO it's not worth the agony of the fumes or dust.  I would recommend flat troweling the entire floor with latex modified thinset and let that completely set up (overnight is a good idea) before proceeding with your tile installation steps. Flat troweling is quick and easy...and cheap insurance for a good substrate bond.

   You might question "what's the difference between flat trowling (skimming) versus going ahead with a regular bed coat for the isolation membrane."  I feel that you get a better bond because skimming allows only a chemical bond betwen the old adhesive and the thinset; not the old adhesive and the isolation membrane. When it cures you begin the same process in reverse with a know compatible substrate. I believe this phenomena is similar to the theory of only applying cellular PVC glue to a single surface of two PVC components being glued together instead of putting the adhesvie on both at the same time. I don't know why the chemical reaction is different (I'm not a chemist), but they say it is. This is fundatmentally different, for example, than when you glue two pieces of wood together with alphatic resin adhesive (carpenters glue) where you can smear it on the faces of both materials being joined and get a superior bond.

   Anyhow, you can check the next morning on your skim coat and see that hasn't reacted in any way with the old adhesive and that it is just as tenanious a bond as your old adhesive residue. If it is, then your good to go. If you're in doubt, you can start with a 2 sq ft trial area to test your leariness about having to remove TWO adhesives. If it does prove succesful, then you've just minimized any dissimilar chemical reactions between your decoupling membrane installation (which BTW, you'd just have to trust buried in your isolation membrane installation otherwise) and your old adhesive. I've used this skimming method over old adhesive (well bonded) for over 30 years with no failures. In fact I've seen billard balls bounce off some of the tiles I've installed in this manner over similarly prepared concrete slabs decades ago to no ill effect.

3. 
   mikeljon | Apr 17, 2014 07:53am | #3

   more questions about this

   I've got cutback that's well-bonded, but asbestos, so options limited.

   Has anyone here used Tavy thin-skin in these situations? Supposed to stick to anything and stay stuck. Then thin-set over that.

   Alternately, what are the best modified thin-sets for use over cutback. A lot of them say that at most there should be only the faintest of cutback residues.

   Thanks...

1. 
   deadnuts | Apr 18, 2014 10:16am | #4

   Latticrete if non water soluable cutback

   Latticrete makes thinsets that are compatible for tiling over cut-back adhesives that aren't water-based. Use LATICRETE Floor N’ Wall thinset mortar mixed with laticrete 333 super flexible additive. You can check solubility of your cut back by placing soapy water on a small area and then agitate that area. If it dissolves the cutback, then don't tile over it. If it does dissolve it, then there's your answer to removing it.

1. 
   mikeljon | Apr 19, 2014 08:34am | #5

   Thanks!

   Thanks--already know it is not dissolvable and that it contains asbestos (had it tested)