Is this some form of Damp Course?

[zappastix]

Hi

About to install a solid oak floor.

Pulled up the carpet to reveal a solid concrete floor.

The property was built around 1976, and it is 4" below sea level.

Around the whole property (chalet bungalow) is a wide concrete skirt,
which does flood on a heavy downpour (about 2" to 3") because the
ground around the skirt is mainly sand and it takes a while for the
water to sink away.

The property is a cavity wall system. Regular 9" bricks and very dark
grey blocks which although they turn to very fine powder when drilled,
do in fact holds things like radiators.

We have been here 6 years, and have not detected or smelt any
damp whatsoever.

MY QUESTION;

On the wall that is adjacent to the outside, there is a 10mm gap
between the solid concrete floor and the block work.

Is this some form of Damp Course?

i.e. is the gap there to stop damp crossing between the
block work and the floor?

There is a regular damp proof course inserted in the brickwork on
the outside, but as far as we can tell (after drilling down some way)
we cannot find a DPM within the concrete floor itself.

To be on the safe side I'll be laying a DPM (thick plastic sheet)
between the battens and the floor before laying the wood floor.

I would like to fill this 10mm gap - to help stop draughts etc.,
but I'm concerned that if I do I might be casing a lot of problems
down the line.

Should I fill this gap - or leave well alone?

Any thought or suggestions would really be appreciated.

Many thanks in advance.

Stephen

 

[cmother1]

Blimey! What's holding up the inner wall? You should call your house "Hogwarts"

Is there any sign of mortar on the bottom of the lowest course of blocks? If so it sounds like the floor has mystifyingly dropped. Can you poke a ruler (or the like) all the way to the outer wall?

 

[zappastix]

Thanks cmother1.

No there is no mortar, and I can't touch the outside bricks.

I can however slide a ruler between the solid floor and the BLOCK WORK.

Is this right?

Or should I run some cement along the gap to bride the floor to the plaster/block work of the cavity?

 

[cmother1]

You've probably guessed that I've never seen anything like this. If you can't get all the way to the outer wall how far in will the ruler go? It seems hard to believe that a whole wall could float with a 10mm gap below it without cracking up somewhere at least.

Could this be some sort of drainage device because of the danger of flooding? Anyone seen anything like it before?

 

[zappastix]

Sorry, I haven't made myself clear.

We are 4" below sea level because we are just a short distance from the sea.

I mentioned that because of the old build/lack of DPM in the solid floor.

There is nothing wrong with the cavities - brick work OR block work.

When I said I can get a ruler or even a masonary chisel in the gap,
I meant that the concrete floor stops 10mm or so BEFORE it touches the inner cavity block work - i.e. the floor does not meet the plaster work.

I was just wondering if I should/could I without causing a problem fill this gap in, before laying the wooden floor (onto battens)?.

Thanks for your help.

 

[Alastairreid]

probably shrinkage from when the slab was cast.......fill it up.

 

[cmother1]

Aaah - now I'm with you. Just fill it in and stop worrying.

PS. How do you get such an accurate measure as 4 inches below sea level?

 

[Alastairreid]

Aaah - now I'm with you. Just fill it in and stop worrying.

PS. How do you get such an accurate measure as 4 inches below sea level?

yeah, i was wondering about that

 

[r896neo]

the afore mentioned ruler i should think!

 

[zappastix]

That was what we were told when we moved here.

For miles around the area is flat, and is the natural flood plain for the sea.

The only thing that protects us are the high sand dunes, if (and not expected for 200 years) the sea level increased and broke through the lower footpaths. We are more likely to get flooded from the rivers, but thankfully they are led out to the sea.

Thanks for the answers.