Is this salts or mould in subfloor void?

[Adam78]

I have a subfloor void in a room which has a unused fireplace of a 1930s semi in the north west of england. There is lots of white deposit on the subfloor void and when I dig the floor the ground is like clay. Is this deposit mould or salts? I cant see any on the underside of the floorboards its just on the ground?

The external walls had cavity wall insulation done back in 2007 according the 'supposed guarantee'. The vents to the subfloor appear to be full of the cavity wool stuff but there is still some airflow.

The walls holding the subfloor joist does appear to have the old dpc. Whilst the external walls which had cavity wall insulation appear damp free the internal walls especially on the chimney side which is a party wall has what appear to be rising damp up to a meter from the floor and areas where furry deposits are forming on the lime plaster.

The external floor level has also been raised very high by whoever did the paving. You can see the dpc layer is on top of the first course of bricks from the paving right along the line with the door step. I'm thinking of removing the line of block paving bricks touching the wall and diggin a trench 150mm below the dpc level, lay a geotextile membrane and back fill with pea shingle up 100mm leaving a gap of 50mm between pea shingle and dpc layer or do i need to leave a gap of 150mm between dpc and peashingle? in which case i'd need to dig 250mm trench?

Also how would i stop the edging of the blockpaving from shifting overtime?

Any advice and steps to remedy.

 

[foxhole]

Chimneys most likely cause of damp , has it been capped and/or left unventilated?

 

[Adam78]

Chimneys most likely cause of damp , has it been capped and/or left unventilated?

Chimney has a vented cap, has been swept and is fully open from the bottom so its breathing plenty.

 

[foxhole]

Chimney has a vented cap, has been swept and is fully open from the bottom so its breathing plenty.

But is it in good condition at roof ? Damage may be historic .

 

[ree]

OP,
1. The white crystal stuff over the soil is harmless, its a result of lack of through ventilation from front elevation to rear elevation.
2. The air brick I can see is set too high to be useful.
3. With your high ground level you will probably need Telescopic air vents every 1500mm to 1600mm.
4. All subfloor pipes & cables should be clipped to the joists.

5. Why not post pics of the damp defects along the chimney breast/party wall?
6. Do you have an external path or is it a patio?
7. FWIW: Your pointing needs re-doing. The overflowing gulley needs cleaning out.

 

[Justin Passing]

Periscope

PER3 Periscope Vent Duct and Windsor air brick - Cast Iron Air Brick Company

Periscope Vent Duct supplied with a telescopic sleeve and 1 Cast Iron Air Brick with choice of finishes, bare as standard or painted black ( + £5) Use of periscope ducting is particularly useful where outside ground levels have been built up over the years. It is, and has been, over the last...

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even.
Possibly what Ree 3) meant.

 

[Adam78]

Here are some pics of the damp areas on chimney and alcoves of chimney breast.

 

[Adam78]

OP,
1. The white crystal stuff over the soil is harmless, its a result of lack of through ventilation from front elevation to rear elevation.
2. The air brick I can see is set too high to be useful.
3. With your high ground level you will probably need Telescopic air vents every 1500mm to 1600mm.
4. All subfloor pipes & cables should be clipped to the joists.

5. Why not post pics of the damp defects along the chimney breast/party wall?
6. Do you have an external path or is it a patio?
7. FWIW: Your pointing needs re-doing. The overflowing gulley needs cleaning out.

I've added some pics of chimney breasts.

 

[foxhole]

Definitely looks like source is chimney , damp then runs down from chimney around corner .
Any underfloor vents?

 

[ree]

OP,
Whats your final purpose with the chimney breasts?
1. There are obvious signs of a previous attempt to treat the damp. I suspect it failed because the render that was used was too hard, it didn't allow the wall to breathe - so it "drove" the damp further up the wall?
2. Remove all skirtings on that wall, & hack off to, say, 600mm above the last damp signs.
3. Damp might be showing on the neighbour's side of the party wall?
4. Damp could be rising from soil filled hearth fender walls - & common rising damp in the alcoves.
5. Go back under the floor & check, by probing, all joist tails resting on the fender walls - & in wall joist pockets. Check for soft or rotten timber.
6. Re-position the electrics away from the chimney breast - set plates a min of 450mm above the floor.
&. Where are the air bricks you mention?
7. If you come back I'll suggest how to make good?

 

[Adam78]

Definitely looks like source is chimney , damp then runs down from chimney around corner .
Any underfloor vents?

There are subfloor vents but the property had cavity wall insulation done using the woolly stuff, and some appear blocked. I've pulled out what i can from the subfloor and there is some air flowing but not a great deal. I'm going to use a hygrometer to double check the humidity down there.

 

[Adam78]

OP,
Whats your final purpose with the chimney breasts?
1. There are obvious signs of a previous attempt to treat the damp. I suspect it failed because the render that was used was too hard, it didn't allow the wall to breathe - so it "drove" the damp further up the wall?
2. Remove all skirtings on that wall, & hack off to, say, 600mm above the last damp signs.
3. Damp might be showing on the neighbour's side of the party wall?
4. Damp could be rising from soil filled hearth fender walls - & common rising damp in the alcoves.
5. Go back under the floor & check, by probing, all joist tails resting on the fender walls - & in wall joist pockets. Check for soft or rotten timber.
6. Re-position the electrics away from the chimney breast - set plates a min of 450mm above the floor.
&. Where are the air bricks you mention?
7. If you come back I'll suggest how to make good?

The air bricks are at the front, back, and gable end side of property. The chimney breast in the pics are on the party wall side so no air bricks there. The joist are sat on sleeper walls with wodden packers underneath. The joist tails do appear damp close to wall joist pockets. I will come back with more pics. I know there is dpc membrane on the external walls but i can't see any such membrane on the sleeper walls.

 

[foxhole]

Pics of chimney externally would help .