Damp survey

[cf-leeds]

I have an internal damp issue on the driveway side of my 1930s semi. There's efflorescence on the enclosed under-stairs area, which also has exposed brickwork on that triangular under-stairs wall section.

In a small adjacent toilet cubicle, there's also some efflorescence on the outer wall area. Neither area is heated and I'm wondering if this is possibly condensation related. Worryingly, under the stairs, there's black mortar powder at the bottom of the outer wall, so some process is making the old original mortar deteriorate.

I called a damp specialist company recently and they said the original chemical DPC of 25+ years ago should be replaced and limelight plaster should be re-applied to a certain height on the affected walls. They provided an expensive quote for this obviously.

I've done lots of reading on damp over the past few days and TBH, my head is now spinning.

I am now suspecting that the original white painted pebbledash render on the outer side of the wall is compromised, as I can find small points (ie. smaller than a penny) where a pebble is missing and the exposed original render seems moist and crumbly underneath. Maybe the rain is penetrating the render and causing the issue.

Maybe re-rendering the affected area is the best way forward (?), though what I'd really like is an honest survey by an expert (happy to pay for that). I.e. someone with no vested interest, who can maybe provide good advice, without immediately suggesting a chemical DPC. Do such people exist ?

Any constructive advice will be gratefully received.

Thanks

c.

[Tim Lamb]

In message [e-mail], cf-leeds [e-mail] writes

Would a 1930's semi not have a conventional dpc if only slate.

Is the exterior level high compared to the inner flooring. Two of our previous houses suffered from rising/penetrative damp where concrete paths had been laid in contact with the outer wall leading to rain splash penetration. Both fixed by creating a 6" gap filled with pea shingle.

[alan_m]

Is the driveway higher than the DPC?

[The Natural Philosopher]

1. If you have damp higher than about a foot above ground level it's not

*rising* damp and a damp course wont fix it.

1. Driving rain can get behind damaged pebble dash and soak a wall, but is the wall cavity or sold? driving rain doesn't normally get to the inner leaf. The easiest way to fix this is to get a mortar sealer and then repaint. but of course the wall wont breathed after that so it neds to be dry to start with

2. Usually these issues are internal condensation and are best fixed by dehumidifying and then adding internal vapour barrier and insulation.

[cf-leeds]

Many thanks for the responses.

The original DPC is a couple of courses above drive level and visible still outside the house. It was put in as a condition of mortgage about 25 years ago.

The house has 9" walls with no cavity.

I'm kinda sceptical about rising-damp, as the under stair area has efflorescence a couple of foot from the ground, with non really at ground level. If I thought replacing the chemical DPC would help, I'd take that on myself, though IMO that would be the last thing to try.

My theories are:

Condensation - The areas affected are in non-heated spaces and I reckon humid air from the kitchen has found its way into the spaces over time and condensed on the walls. We were not in the habit of using the extractor fan in the kitchen, unless windows started to steam up - yes that was a big mistake.

Penetrating damp through the weak old external render reaching the brickwork. It seems that the original mortar in the wall is quite absorbent. Not sure what it's called, but it's kinda black and friable. I'm therefore planning to point the affected internal areas, where possible, as a starting point. I'll have to get someone to do the external render, which needs replacing, whether or not it's causing the issue. Maybe the exterior can be repointed at that time, while the brickwork is exposed.

So right now, a possible plan of action is:

Point brickwork internally in affected areas Replace external render Re-plaster affected areas with renovating plaster - maybe add a vapour barrie (I need to research that one)(?). Add heat sources/ventilation to the affected areas. I should have installed a mini-rad in the toilet years ago, but maybe it's also an idea to add a mini-rad under the stairs, to keep it at a minimum warmish temperature and just stop the area getting freezing cold, as it tends to.

Thanks in advance for any comments c.

[Steve Jones]

My understanding is that efflorescence is not caused by condensation but water rising to the surface and taking salts with it so its either rising or penetrating damp

[The Natural Philosopher]

Its the evaporation of condensed water that can have the same effect, so while I agree that efflorescence is salts leaching out of a blockwork wall, how the water got in there in the first place is the issue.

But in this case it might well be driving rain

[Nick Odell]

If what you'd really like is an honest opinion from an expert with nothing to sell beyond their expertise, I'd suggest that you could do worse than call in a property surveyor - one that has RICS after their name.

Nick

[Animal]

The cause is almost certainly condensation due to the cold. Air can hold an amount of water vapour proportional to temp, and indoor life increases interior vapour wrt outdoor air, so when the indoor air cools it dumps condensation. Rain penetration might or might not be adding too it. A dpc is an irrelevance. Rising damp diagnoses are false in >99% of cases. Damp remediation sector is relatively scammy.

You could solve the problem 2 ways:

1. heat the space
2. use a desiccant wheel dehumidifier, not a refrigeration type.

Crumbly black mortar is a known problem in some old builds. Any crumbly should be replaced. 'Sealants'/coatings of various kinds are mostly unhelpful & often exacerbate damp trouble.

[Jeff Layman]

Why? See background information on humidity starting with

. Then look at Chapter 3 (at ). The OP's damp area is inside his house, where the ambient temperature would be expected to be well above the 8 - 12°C range where a desiccant dehumidifier would be recommended. Quote: "Above 12 °C, however, their energy balance becomes worse and using them is no longer reasonable from an economic point of view."

[Animal]

It's an unheated indoor area. Who knows what temp it is. If the op can guarantee 12C all year, great. IMLE people that don't choose to heat areas indoors often don't stay above that.