Concrete floor concerns

[Ambergreen45]

I live on the ground floor of a small block of flats built in the late 40's. I want to put a laminated wooden floor in the lounge but by taking the carpet and underlay off first I noticed the screed had a few cracks. Wanting to repair that first, I used a cold chisel and club hammer to remove the cracked mortar (hard work and a lot of banging) but what intrigued me was a hollow sound on some areas when I hacked with the chisel. Having removed the mortar screed from the affected areas, I then realised one corner of the concrete itself had a similar hollow sound when I tapped on it with the cold chisel. It appears fine, no cracks but I've been trying to find out, out of interest what could be causing it in that particular area only. Is the concrete floor likely to be resting on a solid surface or could it be a suspended concrete floor? I hope I haven't damaged anything. Could somebody enlighten me?
Many thanks.

 

[russellsmiler]

Have a look externally at low level, If there are air vents the chances are you have a suspended floor.
Another possibility (but unlikely for a late 40s build) is that there is insulation beneath the floor, In new build were insulation to sub floor is compulsory there is a hollowish feel to it when struck.

Another possibility is that it is settlement from uncompaction, which is potentially problematic, however if its not broken do not fix it.

Hope this may give you a clue!!

 

[Ambergreen45]

It is a solid ground floor (no air vents). I thought maybe when the concrete base was originally laid it could have been done in layers rather than in one go, meaning that a section of one layer perhaps may not have completely "glued" to the other layer, therefore creating that hollowish feel, all within the scabbled concrete floor (prior to laying the screed).

If not, I have to conclude there is settlement from uncompaction in that corner of the room (about 1.2 sq metre), but since it is not broken, I will leave it.

Thank you.

 

[Static]

It may have an insulation layer directly below the screed..

 

[Ambergreen45]

What I can see of the floor is Vinyl tiles, DPM (bitumen paint that must have been used to seal the tiles), mortar screed, then scabbled concrete base.

 

[^woody^]

What I can see of the floor is Vinyl tiles, DPM (bitumen paint that must have been used to seal the tiles),.

If from the 40's those tiles will most likely have an asbestos content, and wont be vinyl

 

[Ambergreen45]

Thank you. Useful piece of information. I've had to break a few tiles, which are brown and brittle. I need to find more information, hopefully I'll be alright...

 

[Nige F]

You`d have to try very hard to release enough asbestos from those "Marley" tiles to be a real danger