Floor prep..

[J Sid]

Unlike some I have no intension of picking an argument.
If I misread your post or misunderstood it, which can easily be done, I apologise.
The way I read it was, you were suggesting that getting it in writing, (an unrecommended fixing method) rather than verbally, you would have 'Some defense' if or when it goes wrong.
I take it that is not what you mean.

 

[Ian]

This job has no ufh, anyway none mentioned.
To many variables to answer.
Ceramic, porcelain or stone?
How much movement / bounce in wooden floor?
How new is the concrete?
Is it a new build?

I've seen floors tiled onto ply with the correct adhesive, apparently, and the tiles have crack along every joint within months,

I've seen job tiled over two different substrates as this post last years.

I'm sure you're seen the same Bri

Yeah absolutely, it's a tricky one to call. A bit like tossing a coin, it might last 20 years or it could last 20 days. My personal thought is, if it is over prepped ie, 22mm ply to the joists (with extra noggins), cement board over that with an overlap onto concrete side, slc concrete then ditra over the lot, it stands a fair old chance of surviving I feel.

 

[J Sid]

Agree, it would more than likely no fail, but at what cost.
Say, 15 m2 of ply + 11m2 of self leveling at 15mm to 18mm thick + 26 m2 of uncoupling membrane.
So what, about £800 to £1000 extra labour and materials to not have any expansion joint.

 

[Rich Midge]

Just to clarify my position on this.
I always recommend expansion strips.
If the customer is absolutely adamant they don't want them, I offer the prep discussed as an alternative option. Cost implications etc are always outlined in my estimate.
I cannot guarantee that at some point the floor may fail. This is nothing to do with my workmanship but because this isn't a recognised fixing method the adhesive suppliers etc wouldn't cover it. Again, this is all clearly written in my estimate.
If a customer doesn't want expansion strips and doesn't want to, or can't pay the alternative, I regrettably walk away.
I've yet to have a failure hence why I'm happy to share on here. Anyway, time for another beer in the Spanish sun! Adios amigos!