Please reassure me on my adhesive choice

[lerence]

I have a concrete floor with a small 200mm channel of MDF for plumbing services.

The old tiles I have just removed had cracked grout along the area of the MDF underneat. Would it be advisable to use BAL rapidset flexible?

I take it most kinds of flexible adhesive would be suitable for concrete?

 

[gcol]

You don't need a flexible adhesive to tile on concrete.
Sounds like there's a bit of movement in the MDF cover. How is the MDF supported and how is it secured to the floor?

 

[lerence]

It seems to be a channel in the floor for services. Its screwed down to what I imagine would be baton in the channel. I haven't lifted it up but there are definitely screws in it.

I'd rather just buy the flexible stuff even if its only to ensure the tiny bit of wood I'm going over will not cause problems.

 

[Softus]

I'd rather just buy the flexible stuff even if its only to ensure the tiny bit of wood I'm going over will not cause problems.

MDF isn't wood, and shouldn't ever be used for flooring, especially under ceramic tiles.

 

[gcol]

It seems to be a channel in the floor for services. Its screwed down to what I imagine would be baton in the channel. I haven't lifted it up but there are definitely screws in it.

I'd rather just buy the flexible stuff even if its only to ensure the tiny bit of wood I'm going over will not cause problems.

Using flexible adhesive is not the answer. As Softus says, you're going to want to be replacing the MDF. Replace with a suitably thick piece of WBP ply and screw it down. Then you can use your flexible adhesive if you like - no need to go to the expense of using Bal flexible adhesive as the floor is mainly concrete.

 

[lerence]

Damn, wasn't expecting that.

I'll see what I can do. Thanks for the advice.

 

[lerence]

So, I've replaced the offending part of the floor that was actually water resistant chip board and not MDF.

I now have some lovely WBP ply on it. I've screwed it 200mm centers likes I've read on here and its pulled it down wonderfully. But the entire channel is around 5-7mm lower than the rest of the floor.

Could I use self levelling compound on it to make it lovely and flat or shall I just leave it and heap on the adhesive more there?

The adhesive manufacturer recommends a 10mm max notched trowel (if i remember rightly). Which is what I have. Would it cause problems to just slop more adhesive in the areas its needed? I understand the setting time would probably be longer, but is that the only pitfall of putting more adhesive down?

Thank you for your advice so far. Been very helpful.

 

[gcol]

You can screed over the recess with tile adhesive if you like. We know it's 200mm wide but what length are we talking about?

 

[lerence]

Its 1200mm.

Yes, 1.2 meters. Its only a small bathroom.

Nothing much really but I wanna do it right. Doe the length affect much?

 

[lancenotalot]

The length isn't that much of an issue,I think gcol is thinking of your pocket.Shouldn't take too much adhesive to fill it,a trowel is plenty wide enough to bridge the gap,use the back edge to get a nice flat finish

 

[gcol]

I think gcol is thinking of your pocket.

Indeed I was.