Damaged damp proof and cracked concrete floor

moklo

Hi all,
I am hoping someone can help.
I have found that i have multiple cracks in the concrete floor of my kitchen that is adjacent to the outside wall on the inside.  The concrete floor has gone done, which has caused the crack.
I bought the house 2 years ago.
I removed some of the damaged concrete to reveal some holes / rips in the clear plastic sheet that goes underneath the concrete foundation.
I am worried about damp.

I have 3 questions please:
1 - how to repair the damaged / cut plastic sheet to prevent any possible damp?
2 - What should i use to fill the holes in the cracked concrete? a screed / concrete filler or resin based hole filler?
The holes are about 40mm deep, 500mm long and 110mm wide.
3 - Can i get away with just filling the hole or is there alot more work involved?

Thanks for any help.

stuart45

Did you mean the floor has gone down as in sunk? Sometimes happens when the fill is too deep.
It's the screed that cracked. Flooring sharp sand and cement 3/1 should be used. Mix not too wet. 
Clean area and damp down, or you can use a bonding agent such as SBR mixed with cement. Instructions are on here.
SBR-BONDING-AGENT-TDS-29.pdf (sovchem.co.uk)
You could tape some plastic to the ripped sections.
The external air brick won't be doing it's job properly.

FreeBear

Half an air brick on the outside wall - The paving level is too high. Ideally, it wants to be ~150mm below the DPC (which is just above the air brick).

But, an air brick with a concrete floor ?.... Do you know if it is a block & beam suspended floor or was there originally a timber floor in there ?

moklo

stuart45 said:

Did you mean the floor has gone down as in sunk? Sometimes happens when the fill is too deep.
It's the screed that cracked. Flooring sharp sand and cement 3/1 should be used. Mix not too wet. 
Clean area and damp down, or you can use a bonding agent such as SBR mixed with cement. Instructions are on here.
You could tape some plastic to the ripped sections.
The external air brick won't be doing it's job properly.

Thanks Stuart, i will look into this product. 
Sorry, Yes, i meant that the floor had sunk.  It has also lowered the kitchen units.
I am going to have to prop up the units and drill them into the wall rather than relying on the feet.

stuart45

I would guess the slab was original as the DPM is lapped between the DPC and the blockwork.

stuart45

moklo said:

stuart45 said:

Did you mean the floor has gone down as in sunk? Sometimes happens when the fill is too deep.
It's the screed that cracked. Flooring sharp sand and cement 3/1 should be used. Mix not too wet. 
Clean area and damp down, or you can use a bonding agent such as SBR mixed with cement. Instructions are on here.
You could tape some plastic to the ripped sections.
The external air brick won't be doing it's job properly.

Thanks Stuart, i will look into this product. 
Sorry, Yes, i meant that the floor had sunk.  It has also lowered the kitchen units.
I am going to have to prop up the units and drill them into the wall rather than relying on the feet.

The slab looks like it's dropped an inch or so. Have you got a timber floor at the front?

moklo

stuart45 said:

moklo said:

stuart45 said:

Did you mean the floor has gone down as in sunk? Sometimes happens when the fill is too deep.
It's the screed that cracked. Flooring sharp sand and cement 3/1 should be used. Mix not too wet. 
Clean area and damp down, or you can use a bonding agent such as SBR mixed with cement. Instructions are on here.
You could tape some plastic to the ripped sections.
The external air brick won't be doing it's job properly.

Thanks Stuart, i will look into this product. 
Sorry, Yes, i meant that the floor had sunk.  It has also lowered the kitchen units.
I am going to have to prop up the units and drill them into the wall rather than relying on the feet.

The slab looks like it's dropped an inch or so. Have you got a timber floor at the front?

Yes, the front of the house is timber floor.
Do you think i need to remove from the inside wall any of the plaster above the DPM?  If so, how much and what should i apply on top?

stuart45

I would be more concerned about the air bricks being blocked. These are to allow an air flow through ducts to the timber floor at the front of the house. There should be some air bricks at the front as well. 
It looks like when the area was paved half of the air bricks have been blocked off. Without a decent air flow under the timber floor you can can problems with it.
As the floor has dropped it may have affected the ducting system as well.

moklo

stuart45 said:

I would be more concerned about the air bricks being blocked. These are to allow an air flow through ducts to the timber floor at the front of the house. There should be some air bricks at the front as well. 
It looks like when the area was paved half of the air bricks have been blocked off. Without a decent air flow under the timber floor you can can problems with it.
As the floor has dropped it may have affected the ducting system as well.

Thanks again Stuart.  One further thing.  In regards to the SBR, do i use it as a primer on the concrete floor and walls, or just in the concrete mix or both?  Also, in regards to the wall, shall i replaster or do i need to break away the existing plaster and fill with something else.

stuart45

Use the SBR as a bonding agent by mixing with cement for form a paste. For thin screeds 1.5 inches or less SBR can be added to the flooring mix as well. Polymer floor mixes can go much thinner than traditional screeds. As it only a small amount of screed if you have enough SBR put some in the mix as it add strength. Generally not used in a normal screed because of the expense.
Used on it's own mixed with water isn't needed here, as this is only to reduce suction, and the use with OPC as a bonding agent will do that anyway.
With the plaster just cut off any rough bits with a bolster and make good any difference once the screed is down, although the skirting will probably cover this.
On site the plasterers would take the plaster down to within a couple of inches of the concrete floor, then the screed would cover the gap, then the chippies would 2nd fix the skirtings.