White mould under floor - Property Care surveyor recommends extensive works!

[Marcia]

Hello, and thank you for accepting me as a member.

I live in a semi-detached house, built in 1905. The front wall is sandstone, the other external walls are brick, which has been rendered and painted. The kitchen extends out at the back of the house, is original to the house, and seems to have a solid floor. The floor is covered with laminate which I haven't lifted yet.

The house is built on a gentle slope, so at the front the floor level is about 50cm about the ground, with the ground sloping away from the house. At the back, the floor level is about 10cm about the outside ground level, which is slabbed. There is a slabbed path along the side of the house, and the strip next to the house is gravel. The kitchen and attached conservatory floors are about 10 cm above the outside ground level, as a low wall has been build to keep the higher ground in a border, with a gravel path about 50cm wide around the conservatory. The ground level is lower here, as closer to the house slabs have been laid.

In the main part of the house, the floors (original joists and board, mostly) is suspended about an earth floor. A couple of months ago, an electrician had to go under the floor in the living room, and he came back up covered in white powdery mould, and decided he didn't want to go back down there until I found out what it was, and if he needed to take any precautions. Anyway, he did all the work he could do above the floor, and still hasn't invoiced me for that!

I wasn't sure who to get to find out what this white substance was - looked like white floury crumble mixture (as in apple crumble). So, I asked the estate agent who dealt with the sale when I bought this place last March. They recommended a surveyor on the basis that he didn't charge for an inspection - I took this to mean he'd likely try to sell me something to make the visit worth his while - and I arranged a visit.

I still don't know what the white stuff is, but the surveyor has advised that there is wet rot on the wood at the front and rear wall, as well as under the shower, which may well be leaking. This news wasn't welcome, but really any great surprise. I've already had to replace joist ends and floor boards at the front door, and the shower although new-ish, hasn't been very well done.

However, he then told me that all the floorboards would need to come up (in the hall, front room, shower room, and back living room) so he could put down plastic (?) sheeting which would then be covered in concrete. This, he said, is because the wooden joists etc are constantly sitting in a damp atmosphere and will all rot if nothing is done. He also said that having no damp proof course is a problem, as well as the bare earth under the floor.

Anyway, that was on Thursday, and he's going to send me a quote detailing the work he recommends.

Now, I do need to fix the wet rot, and based on other issues I have with the plumbing, I can quite accept that work will need to be done to the shower. However, having done a bit of reading, and looking at the house, I think the other problems are due simply to there being inadequate ventilation under the floor. There is one metal grille on the front wall, which is clear and lets air in under the floor. I'm pretty sure I remember seeing a similar grille or air brick when the floorboards were replaced at the front door, but the doorsteps are poured concrete, so that source of ventilation is blocked off.

At the rear of the house, I suspect there is no ventilation from the kitchen and the terracotta air brick in the living room wall is above the level of the floor, and although clear is then blocked off by wallpapered plywood.

So it looks to me that I need to improve the sub-floor ventilation, and not put down sheeting and concrete. At the back of the house I'll need to remove the slabs and lower the ground level. What will I do then to ensure that space doesn't simply fill up with rainwater?

Also how easy is it to insert new air bricks or ventilation grilles, and who would do that, and do it properly?

All advice, questions and thoughts welcomed. Thank you!

 

[88v8]

Hello and welcome.
You've done your research very thoroughly.

The freeboard at the back, 4" is not ideal. Rather than lower the ground I would start by replacing a line of slabs - assuming they are rectilinear - with a couple of inches of gravel so as to eliminate rain bounce.

Wet rot.... there was some bad building in the past... it's not just modern builders.... the joists may be sitting on the wall or even set into the wall. So, with no dpc, they get damp and eventually they rot. Not difficult to fix, but quite disruptive as the floor around the perimeter has to come up. Are the boards t&g? Hopefully not...
How to fix it... put the joist ends into hangers
http://www.builderdepot.co.uk/speed-pro-masonry-joist-hanger-100mm-x-125mm.html?gclid=CMClh4mD888CFUwW0wodvkQEwQ
See? The top angle is set into the wall and the joist is no longer touching the (damp) wall.

Where the wall is masonry, this apparently simple task may be slightly complicated by lack of a continuous joint at the right height. In which case the hanger can be chased in with an angle grinder or pointing chisel.
Alternately, surround the ends of the new joists with dpc felt to isolate them from the wall.

The joists may also be supported under the floor by sleeper walls
http://fet.uwe.ac.uk/conweb/house_ages/rtf11_lr.jpg
See how it's honeycombed to maintain good air flow.
Ideally these sleeper walls should have a dpc. But if they don't they don't. Unless the underfloor is very damp, just good ventilation can be sufficient. However, check that the sleeper walls are not themselves blocking the airflow.

The damp earth. Yes, in later years, say WW1 onwards, it became the practice to cover the sub-floor with a layer of weak cement so as to keep the damp down. But to do this retrospectively would be very difficult, and to incorporate a dpm (plastic sheet) as suggested would be ridiculous. The damp will not be banished - it will simply move under the dpm, to the perimeter where it will rise up the walls.
The palliative, as you indicate, is copious ventilation.

In our previous house, there were insufficient air vents. I added another three at the front, and three or was it four, it was 30 years ago... at the back. Where a solid floor was in the way at the back of the house, I piped the air bricks through the floor, but that was a new floor and obviously this is impractical when the floor is already there.

Draw a floor plan. Mark the air vents. Now look where there are gaps, dead corners with no airflow. That will show you where you need more vents. Front, back, side.
Also, peer under the floor and see if there are solid walls between front and back - there is little purpose in inserting vents if there is a solid wall in between, and in that case it would be necessary to make some holes by knocking out a few bricks.

You cannot have too many vents!!

Terracotta air bricks are useless. The free air space is too small Cast iron is what you want. Paint them before insertion.

Here's an antique - a standard brick size - 9x3" in English.
http://www.ebay.co.uk/itm/Vintage-Style-Cast-Iron-Air-Vent-Brick-Trivet-suits-reclaimed-bricks-beam-fire-/332006466930?hash=item4d4d20a572:g:gQgAAOSwTapV7Usn

And here are new ones
https://www.vintagedoorknobs.co.uk/products.asp?code=CDC-SGLEAIRBRICK&name=cast-iron-single-air-brick&gclid=CM-s-M2I888CFdaRGwodXuwJuw

To insert more, basically knock out a brick, insert vent, mortar in. It's easy. Although where you only have 4" of freeboard, the vent will be rather low.
Again, with the masonry wall it's not so easy as the sizes may not suit a standard 9x3" air vent, but it's still a matter of knocking a hole and sticking a vent in there, any competent builder could do the job.

Indeed, the whole job is one for a competent builder. Or DIYer.
See
https://www.youtube.com/watch?v=k7MmiCSBgoY
They make rather heavy weather of it with their ear protection and diamond saw.... your bricks will be set in lime mortar which is easy to knock out with just a chisel.

So, now, all you need is a good builder.
Edit your Profile to chow your location, in case someone can recommend.

Ivor

Ummm, your white powder might be sulphation. Just a guess.

 

[Marcia]

Good evening, Ivor, and thanks for your comprehensive reply and the links. Lots more reading for me!

I think I'll spend a bit of time under my floorboards this weekend, with a good torch! The floor boards aren't tongue and groove, fortunately, and there are sleeper walls, but I don't know yet if they are solid or have spaces for ventilation.

There are new houses being built across the road from me, by a local company owned by a husband and wife. The wife's father and my father are cousins, so I might wander over, mention the family connection and see if any of their builders would have the experience necessary to do the work I'm looking for.

 

[mje2k]

Hi, I'm no expert but I've seen something similar to your white powder before. If it's the same, it could be efflorescence - the salts left behind when mineral-rich water evaporates (e.g. water which has seeped through your foundations), or just white mold (I've even found that under the carpets of leaky cars). Either that or a previous occupant was trying to emulate Breaking Bad

 

[MikeG]

.......Terracotta air bricks are useless. The free air space is too small Cast iron is what you want. Paint them before insertion.......

I have never understood why manufacturers don't fit insect mesh, leaving the builder to bodge something in if he can be bothered. It can be a bit of a fiddle. If you don't have mesh, then not only will wasps and bees explore under your floor, but the holes are plenty big enough for mice too.

 

[Flyfisher]

Terracotta air bricks are useless. The free air space is too small Cast iron is what you want. Paint them before insertion.

Surely that depends on how many are fitted?

Also, are there any building regulations covering how the required 'free air space' should be determined for adequate underfloor ventilation?

 

[88v8]

The more the better. The free air space in a terracotta brick is very small.
http://forterra.co.uk/chimneys-roofing-flue-systems/red-bank-product/list-no-350-square-hole-air-brick-215-x-65mm
1290 sq mm (whatever they are) for this 9x3"

Contrast with
http://www.brassairvent.co.uk/services.htm

Their Grid3 at 5000 mm
and Max3 which we used at 7800 mm or four time as much as terracotta !
http://www.brassairvent.co.uk/services.htm

A lot of good information here, including a section on damp
http://www.brassairvent.co.uk/services.htm

Interesting point about bees n wasps n mice. Never had that in 30 years of unmeshed iron vents - the only time anything got in was through a vent that someone had broken to put a pipe through - but in one year of unmeshed holes in chimney stack we have bees!

Ivor

 

[Flyfisher]

I agree with all that in principle, just being pedantic really. If a grating admits 4x the air of a conventional airbrick, then 4 airbricks should be just as good (arguably better as their ventilation will be more diffused). In other words, not 'useless'. Indeed, in some applications a conventional air brick may be more suitable if you prefer such things to blend into the brickwork rather than stick out like a black sore thumb. In other circumstances, a black iron grating may be more appropriate. Horses for courses really.

 

[88v8]

Mmmm, yes. I used two Victorian terracotta gothic vents under our conservatory, although their air opening was quite good.

It's also the number of vents. There need to be sufficient to eliminate dead areas where there is no airflow, especially in corners.

And they don't have to be black, although usually they are. Can be the same colour as the paintwork, so ours were green.

Ivor

 

[Flyfisher]

Good point about corners. It's not always possible but ventilating a space using air bricks on different sides of a building is supposed to be more efficient as the wind creates slight pressure differences around a building, which aids air flow through air bricks.

As for colour, you're right of course. Our white limewash with black woodwork exterior decor tends to dull my imagination.

 

[Marcia]

I've now received the quote from the guy who came and had a look.

Here's what he's proposing:

1) Sections of floorboards will be removed from areas indicated on the attached sketch (the entire ground floor apart from the kitchen and conservatory) for access to the solum. and sub floor timbers.
2) Decayed sections of joist and wall-plates will be cut back to sound timber and removed as required.
3) Sub floor walls will be injected with a chemical DPC just below wall-plate level.
4) The solum will be cleared of all debris, treated with a fungicidal fluid, a DPM will be laid over solum surfaces and sealed with approximately 100mm of pumped concrete.
5) Using treated timbers new sections of wall-plates, joists and floorboards will be fitted. Joist bearing ends and wall-plates will receive a coat of bituminous emulsion and a physical DPC laid along wall heads. All retained floor timbers will also receive a surface application of a fungicidal fluid.

The grand total for this work to be £9442.80 inc VAT! He hasn't provided any breakdown of the costs for different aspects of the work, just this whopping great total! If I did go ahead with this, which I am not, I'd have actually to move out and put my furniture in storage.

Nope!

I'll see about increasing the sub-floor ventilation, get the shower fixed or replaced if need be, and get a local joiner who's done work for me before (and whose parents live round the corner in a house about 10 years older than this one) to replace any timbers which are actually rotten.

Does that sound like a plan?

There is no smell of damp in this house at all. The only time I've smelt anything has been after someone has gone under the floor to do work, and that was a slight mushroomy smell which cleared in a day or so.

 

[TheRoost]

Confused at how/why your surveyor would lay plastic sheeting then concrete over joists? It sounds like you already know this is a bad idea.

In our loft where woodwork has become damp for a short period of time, a white powdery mould has appeared when dry.

Our subfloor space is very dusty and white in places with the original builders leftover lime/stonedust/crumbly lime mortar etc on the ground, is it possible your electrician has got covered in this stuff rather than something growing on the walls/woodwork? Just a thought.

 

[88v8]

I think you are wise to be dubious of some elements of this programme.

A dpm would push the damp into the walls, and although it is proposed to isolate the floating floor with a dpc, that does nothing to protect the perimeter walls, so I would skip the dpm and the oversite concrete.
If the earth is very damp I might consider concrete alone. That would allow a modicum of breathability - concrete is not wholly impermeable - whilst keeping most of the damp down. 2" would be ample - the 4" he proposes is more suited to clog dancing.

Injecting the sleeper walls might actually be effective, but if there is access to do that I would thought it equally possible to cut away the mortar and insert a physical dpc of felt. However, unless the subfloor is very damp, it seems not worthwhile. The additional ventilation should take care of that.

It should be a matter of routine that any new timbers are isolated from the wall by inserting a layer of dpc around the ends.

You could spray the underfloor timbers with the extended wand of a Killaspray, and Cuprinol 5 Star. Bit smelly, but effective.

Should have mentioned previously, have you actually checked the humidity level? One or two of these
https://www.amazon.co.uk/Digital-Hygrometer-Humidity-Thermometer-Temperature/dp/B00E3JOQ3Q/ref=pd_lpo_60_tr_t_3/254-3118679-7594218?_encoding=UTF8&psc=1&refRID=26D1V43MWF8S4KK87MFB
will give you a now and then by which to measure the effectiveness of your rectifications. Keep a record, as there will be seasonal variation.

Ivor

 

[Roger H]

3) Sub floor walls will be injected with a chemical DPC just below wall-plate level.

:shock:
Can you get a physical damp proof membrane between the joists and the sleeper walls? I.e. slide some plastic under. Don't waste your cash injecting.

 

[Hazel7000]

This isn't a technical reply - more instinctive and based on experience of mould. I would just replace the wood floors with hardwood and put more airbricks in And check nothing is leaking under the floor to make the soil wet. Hardwood doesn't succumb to rot the same - killing mould spores isn't that easy - ventilating if you have mould spores or dry rot under the floor can make them proliferate. Having said that - if you're talking quite a few rooms and a lot of expense - and it doesn't bother you - maybe just do nothing.

 

[Matt Green]

This isn't a technical reply

This is.

There's no need to use a hardwood, decent quality pine will fair well enough. Isolate the joist ends and any other timber in contact with masonry with DPM.

It's probably not mould at all- far more likely to be sulphate salts. A rake and stiff broom should deal with that if you are worried. Don't put any sheeting down, don't concrete it. By all means improve the ventilation if your house isn't listed and it's reasonable to do so without smashing lumps out of the walls but the 'lack' of ventilation if there is one isn't causing the joists to rot.

Actual problems you are experiencing:

1) leaking shower
2) potential high ground levels in walls with load-bearing timber pockets (should be 6" below the suspended floor at least
3) a panicky electrician
4) a commissioned salesman thinking of solutions in terms of the product range they sell, not what would actually solve the problems

If your floor isn't collapsing and the electrical work is done: fix/investigate the shower and then lower the ground levels and improve the ventilation. once that's sorted, take the floor up and see what's going on.

 

[Hobden]

Some general advice, from a relative of mine who used to be a builder (he's long dead) - "don't mess around with little holes". I've always remembered this. By it he meant, don't try keyhole surgery. Clear the room(s) out, get the carpets up and lift all the floorboards, carefully if you think you'll reuse them, else with a demolition saw for speed! That way you can see what's there (half the battle) and if you need to fix sleeper walls, replace wall plates/joists, add DPC under a new wallplate, fix something you hadn't even thought of, it's easy to do so. You can also clear out the existing airbricks, if there are any, and look to see where it's best to insert new ones. Existing water pipes can be insulated if necessary. Your electrician could even do his wiring without worrying about getting zapped by anthrax or whatever else he thinks the white powder might be (as others have suggested, I'd go with efflorescent salts).

If you have the time, and the energy(!), it's something you might be able to do yourself rather than paying a builder to do. Or you could do the "demolishing" bit yourself and pay somebody else to install new stuff. Or you could twist a friend's arm to do the work for you )

H

 

[MatthewC]

lift all the floorboards, carefully if you think you'll reuse them

... and don't let your tradesman do this job. Don't ask me how I know. :evil: