Damp problem in rendered Victorian property

[mikopaul]

Hi

we bought a rendered Victorian property about 9 months ago and had a full building survey done on it, which showed up no damp problems (one minor incidence of penetrating damp - apparently being caused by a faulty repair on an old air brick but nothing to concern us).

After buying it, while doing the internal decorations, it became apparent that there were a number of areas where there was damp present. The firm who had injected the damp proof course came out to check it and informed us that it was not the DPC (but they re-injected it anyway under the guarantee). A couple of the walls are damp at a height above 1m in a number of areas - with salt residue on the wall - no mould. The advice of the "DPC guy" was that the damp is interstitial condensation being caused by the impervious external coating.

When I spoke to the surveyor - he apologised verbally and said that he may simply have missed it (although I obviously have not managed to get this in writing). He has subsequently written to me claiming one area is rising damp and one is penetrating damp. I am not convinced by this as the incidences and damp patches do not appear consistent with that explanation.

I have just received a letter from a firm - Protectawall - who I have discovered applied the coating over 10 years ago. An article in the telegraph seems to agree with the assessment of my DPC surveyor - http://www.telegraph.co.uk/property...l&sSheet=/property/2006/08/09/ixpright12.html (bottom thread).

I would love it if someone could please provide me any advice on the following:

- Should my surveyor have noticed this? I paid c£1k for the survey and some of the damp patches were not hidden by furniture. If so, what action should I take? (I am not looking to make money, simply to make good and cover any significant costs)
- What treatments could be recommended? Any ideas on trustworthy / quality tradespeople who could help? Rough thoughts on costs?... it is a traditional 2 bedroom end of terrace property.

Any advice would be very gratefully received (and sorry for the long thread - it has been a frustrating problem!)

thanks in advance

mikopaul

 

[JohnD]

tell us how the house is ventilated

how many fireplaces and chimneys did the the house have when built, and how many are open now?

What sort if windows did it have when built, and what sort now?

where is outside ground level in relation to inside floors? what are floors made of, and what is underneath them?

how do you dry your washing?

condition of gutters and downpipes?

what is on the other side of the damp walls?

photos will help

 

[mikopaul]

There is a pozidry (positive pressure ventilation system) but to be honest we rarely use it. When looking at the property I now realise that it should have probably indicated some problem to me - but it just looked like an extractor outside the bathroom. Other than that - simply windows without many airbricks in the walls. UPvC windows - double glazed but not great.

There were two chimney breasts when built and now only one (still open) - but they are on the adjoining wall and the damp is all on the external walls and there does not appear to be any damp problems by the chimney breast.

Ground floor is raised about 1.5 feet off the ground at the front, but this reduces as you go back through the property and the back of the house is pretty much at grade (damp at front, middle and back of property).

Ground floor is old floor boards - we had the carpets lifted and the boards sanded about 8 months ago. Below the floor on the ground level is a dry basement - with a membrane tanking system.

Gutters recently replaced and the main damp is on the gable wall and it is very unlikely that they are the cause of the problem. Do sometimes in the winter dry clothes indoors, but try to open windows or turn on extractor or dehumidifier so I really doubt this is the cause of the problem.

Interestingly some days the damp looks worse than others but I have never managed to spot any trends on these days(ie rain / cold / drying clothes etc)

Along the gable wall there does appear to be some moss along the bottom of the house which suggested to me some resting water but we have never noticed any significant water at all.

thanks for the help - will try to get photos if it helps tomorrow ....

 

[JohnD]

remember the house was built with lots of draughts and chimneys.

50p says some or all of the damp is caused by condensation.

clues are: poor ventilation (PVC windows, removed fireplace, extractor not used in bathroom, clothes dried indoors

tape a piece of clear plastic tightly to a wall and see if moisture appears on the wall side or the room side

improve ventilation. start extracting from the bathroom all the time it is in use. best way to achieve this is to have the extractor come on with the lightswitch and stay on for a while after use. Open upstairs windows every morning. Use trickle vents in all rooms.

it is a clue that the previous owner spent money on ventilation.

never hang wet clothes indoors. you might as well throw buckets of water at the walls. buy a tumble drier wih extraction hose if you have a need to.

 

[AndersonC]

The advice of the "DPC guy" was that the damp is interstitial condensation being caused by the impervious external coating.

Did you ask him to define exactly what he meant by "interstitial" condensation? Interstitial is a term used in chemistry and materials science to describe atomic placement within crystallographic structures, not quite the term I'd associate with a bit of condensation in a house.

Or was he trying to BS his way out of something he didn't know the cause of?

 

[Brigadier]

My uncle is a plasterer of 40yrs' plus experience, and I asked him about this Protectacoat-type stuff ( I too have an old house that's rendered, and suffers damp without "management").

He reckons you can't beat old-fashioned render. It's been around for hundreds (if not thousands) of years, it's repairable when needs been, it moves with the building (if made with lime mortar), it lets the building breathe - in short, it's proven over a long period of time.

I'd not be surprised if these new coatings crack up and craze over 20 years or so, and then be a bit of a pain to get off and replace.

 

[JohnD]

interstital condensation is the term used when you have e.g. a wall which is warm on one side and cold on the other, the dewpoint occurs part-way through the wall and if it is not sealed on the warm humid side, condensation occurs inside the porous bricks but not on the warm surface. It is very common on walls round cold-stores.

It also happens in fibreglass loft insulation above steamy bathrooms.

I don't know about atomic crystals.

 

[mikopaul]

All

many thanks for the advice. My initial reaction was that the "interstitial condensation" was rubbish, but having looked into it I honestly think that it is the only explanation. Essentially, I believe that the Protectawall coating on the exterior of the house is like cladding the house in a plastic bag and therefore condensation enters the wall, but cannot escape outwards so shows up on the internal wall as damp. It shows up in isolated patches and the rest of the wall is dry - is this normal for this problem? There is no mould that you normally see with internal condensation.

JohnD - thanks - I will give the clear plastic trick a try and see what side the condensation shows up. However, there is not a lot of condensation in the house at all - we run an extractor in the bathroom whenever we use it. Although we do dry clothes indoors at times, we always open a window or run a de-humidifier. Not ideal I realise and we may well invest in a tumble dryer in the near future.

Does anyone have any advice on removing this sort of protectawall coating and re-coating (eg with a lime based render) - is it a massive job? Can you just remove the coating but leave the rendering so that all you do is re-coat outside existing rendering (rendering is in pretty good condition).

In terms of making good internally .... presumably it will not dry out but will require the affected plaster to be cut out, then allow the wall to dry and replaster... is this right?

many thanks again and I will try to get some photos in the next day or so in case that helps