What is this product?

[Duck_Tape]

Dear Everyone
I own an old house, the space between the floors has ash-deafening as a noise suppression.
I have a basement area below the main living rooms, the basement area is street-level, and there are steps up to the main house.
I am having the basement area renovated. The space consists of a toilet area, a kitchen area and a living room area.
I wanted down lights in all the areas. All the ceilings are old lath n plaster. I removed all the plaster in the kitchen area back to the joists
and as expected there were straps holding up the boards keeping the ash-deafening in place.
There is quite a bit of rot on the joists and the straps so a lot just fell away.
I now have an unknown substance between the ash-deafening material and the boards holding it in place.
I am worried it is an Asbestos product.

I will get it tested but just wanted to know if it is something you lot have seen before
Cheers Duck Tape

[Duck_Tape]

The testing kit was ordered yesterday, delivery, maybe tomorrow Saturday, or probably Monday
almost definitely AIB (asbestos insulating board) going by all my online searches.
Probably ££££ to remove maybe more.

This puts the project on hold. Project cash is diverted to asbestos removal.

[big-all]

it needs to get in your lungs to be dangerous
iff the only holding point is each edge then it may come out fairly whole
so wet spray and ott mask then double bagged
but no expert

[dewaltdisney]

It is difficult to correctly identify this but I would suggest that it is a concrete mix made up of clinker perhaps, and cast insitu. It looks like the impression of timber shuttering form work on the underside evidenced also by the parallel line marks made by the planks used. I doubt asbestos went into the mix, as it would if it were then it would suggest it was factory-made sheets instead. Cast concrete would have been cheap and created a fire break of sorts. Just an idea.

DWD

[Grendel]

On an old building it could also be a lime ash mix. That is put in in the same way concrete is and dries to a hard structure that seems and looks an awful lot like concrete. That said testing it won't do any harm.

[Duck_Tape]

I got the test results back, and DWD hit the nail on the head: white concrete with no asbestos. I breathed a big sigh of relief.
As DWD said " by the parallel line marks made by the planks used" The planks were laid, and then the concrete pour went on top.

Cheers to all that answered or commented