Help identify floor construction, next steps

[njx]

Hi.

Renovating a single room extension (c1980s I believe) attached to a c1800 stone house. I intend to install a laminate floor, and because of some undulations need to level the existing base.

When lifting carpet grippers (tacked down but also glued in places) parts of the floor lifted with them. There seems to be a very thin (~1mm) screen over a soft sandy aggregate (~50mm deep)? Digging down, there looks like a concrete base with a clear polythene membrane underneath. Pic attached.

I don't know much about floors, but this seems wrong to me?

Can anyone offer any advice...

1. What type of aggregate is this?
2. Why this type of construction (dry soft/easily breakup aggregate with a very thin screed over concrete)?
3. How to I move forward - do I remove everything down to the underlying concrete and build back up?

thanks for the help

 

[dazlight]

Sounds like a bag screed mix.
I'd grind floor a bit to get loose stuff off.
Then go with Uzin PE425 which will strength the screed.
Then prime and screed with a smoothing compound.

 

[njx]

Thanks dazlight.

After looking further, it appears its been used over the entire ground floor of the house. It takes hardly more than a tap with a lump hammer to break it up and it reverts to grit. Then I can just shovel it away and start again, the concrete underneath seems good/solid.

Just seems bizarre to me.