Crumbling screed, possibly magnesite

[wgalyall]

We are currently renovating our kitchen in a 1930s flat. We pulled up some lino floor which was backed with sheets of MDF. When we started to pull up the MDF we noticed some kind of underlay / screed that had been painted green but with a red core. The screed is incredibly crumbly and looks like it will completely come apart once all the MDF has been taken out.

It is possibly magnesite, but after lighting a small lump from it, there was no glow as described on some online forums. Could this potentially be a sand cement or some kind of asphalt layer?

Any ideas and advice would be much appreciated!

 

[Dave]

It looks more like contamination or maybe some sort of patching material as its not consistent in colour etc. The amount of cracking is worrying as well. I would remove all the covering and then see how bad it is underneath. Then report back with further pics.