Failed Karndean subfloor repair

[desertrose]

Hi all,

The Karndean flooring in my south-facing porch started coming up at the joints after about 5/6 years, and it turned out the subfloor had failed such that large chunks were no longer stuck to the (apparently primed, given the yellow colour) concrete underneath. I am debating whether to try and repair using the same tiles or rip the lot up and go with something different.

Either way, I need to repair the subfloor, but I'm left with bits that come up easily and bits that seem pretty firmly stuck still, e.g.:

What would you do?!

Thanks in advance.

 

[dazlight]

Wrong screeding compound used and shouldn’t have been primed with that primer.
Floors with old adhesive down needs ardex NA.

 

[desertrose]

Good good! Always a pleasure to hear the professionals have done a quality job ... and reaffirm my preference for DIY.

How do I best fix it now?

 

[dazlight]

Without seeing it I’d say you need to take it all up and remove as much of the compound as possible.

Does the floor have a damp proof membrane ? How old is it? Before 1980 ?

 

[desertrose]

70s build. I don't know for sure about the porch but from other work elsewhere (e.g. garage) there seems to be some sort of see-through plastic membrane underneath the top layer.

 

[dazlight]

That’s good. But free 25 years they perish.
But anyway.
You need to get as much up as possible. Then do a full coat of ardex NA / fball 1200 / or similar

That looks like you have moisture suppressant on it. But needs to be an epoxy one.

 

[desertrose]

Thanks - really helpful. Arditex NA looks great, and even one of their pictures looks quite like my floor:

I've taken up more of the old tiles (and more of the old compound) tonight. Even what's left behind comes up relatively easily if you hit it in the right place. Annoyingly the skirting all needs to come off and there are pipes through it for a radiator too, all good fun.

It will be a bit of a job, but this advice is really helpful, so thank you again.

 

[desertrose]

As is often the way in DIY, things haven't quite gone to plan.

While removing the old compound at the edges, quite a bit of the original floor has come up up with it (pictures below). The edges break up very easily and the floor sounds hollow for up to around 3" from the edge. Seems to be the same on the side that meets an internal garage as well as the side that meets an external window (so maybe not caused by external water penetration).

Thoughts welcome, but a few options I can think of:

1. Dig out the worst of the loose material and concrete patch repair before Arditex NA over the top - although how far to go is a good question given the area that sounds hollow.
2. Pour some sort of resin over the loose material once exposed.
3. Don't worry and just go straight on top with compound, which seems to be what the 'professionals' did originally (!).

Thanks as always.