When I've had to troubleshoot mesh installations, the majority of the problems seem to occur with one-step applications...installing the mesh, then thinsetting and tiling all at once.

The installer just doesn't fully bed the mesh in thinset, leaving myriad voids that eventually result in broken bonds and crunchy grout and tiles.

We've had radiant heat in our bathroom (2 years), kitchen (1.5 years), and sunroom (3 months) with no grout problems. Sounds like your GC may be doing something wrong on the installation.

Thanks, Mongo, that makes sense. Weedyacres, thanks for telling your experience - it may be that GC doesn't do it correctly but I had the impression he just has seen alot of bad installs - and hasn't done that many himself - because of what he has seen. I'll have to have a more extensive conversation with him about it.

julie, yes and no.

If it's done correctly, you don't need Ditra. But Ditra can absorb some sins. But if the mesh still isn't filled with thinset and then it's covered with Ditra, problems could still occur.

Like most areas of employment, there's a fair amount of ignorance and apathy in construction. Sometimes it doesn't affect things, other times it can cause problems.

Faster and cheaper often takes longer and costs more.

The whole trick is not to energize the system until the grout has set for about a week.

anyone can mix up some thinset by themself, and spread it out to cover the heat cables.
You can do this in several passes.

Then the pro can come in to set tile.
You do the invisible part, and the pro handles the part that you will walk on and see.

Is your bathroom floor on a wooden subfloor, or on a concrete slab?
What climate / insulation / cold corner / situation do you have?

HTH

Now I’m nervous. We are concrete slab, new construction, super small area (25 sq ft) and planning on penny tile, which means lots of grout. Should we do thunder ourselves? Will save $ as less trips for the tile people.