Damp in wall adjacent to busy road

[frednelson203]

I have an 18c property which has had several attempts over the past 4 years at resolving damp problems on an external wall next to a fairly busy road. Three years ago we had all of the plaster removed inside and out and had it replaced with lime putty and painted inside and out with lime based paint. After the first attempt failed we tried again and included an injected dpc and a french drain

We repeatedly get flaking plaster and salty deposits despite all the work being done by reputable builders and under the supervision of a local well respected surveyor

I am about to buy a dehumidifier to try to solve the problem and will probably take off the interior plaster up to about 2 feet for a year to see if we can dry out the wall

Does anybody have similar experences and therefore helpful advice

 

[Lime]

My immediate reaction.
Has enough time been given for the wall to dry out?
What was up against the wall prior to a french drain being put in?
..and a pity about the injected DPC.

 

[Pford75]

The other point to consider is road splash...we had this problem with a flint wall around our garden.

We contacted Highways...who came and resurfaced the section of road to prevent pooling and subsequent splashing

 

[Nemesis]

It would be interesting to know how long was given for drying until it was deemed that the solution was a chemical DPC - which I agree probably wasn't the answer.

Also - what was done alongside the DPC? What sort of plastering took place after?

Is the wall subjected to splashing from the road? Is it below, internally, the exterior level?

 

[frednelson203]

Thanks to Nemesis, Pford75 and Lime for their responses to my post re Damp on wall adj to road

To answer the key questions - very little drying out time was built into the works. We had an initial piece of remedial work done (using Lime plaster and appropriate paint) in 2003. The plaster came off inside and out via flaking - there was and is now no damp feel to the wall just flakiness and salty deposits. There was no additional/replacement dry lining done. On the second occasion we had remedial works done in 2005 we removed the first lot of plaster, had the dpc injected (on advice from a reputable Surveyor), replastered and repainted with limewash (many coats)

The interior and exterior levels are virtually level (Im aware it would be better if outside was lower. The road abuts our property with the french drain being the last 6 inches or so between tarmac and wall

 

[Nemesis]

Well, reputable or not surveyors don't always know how to treat period buildings.

What was the wall plastered with after the injection?

 

[MdB]

(caveat - I'm not an expert in this)

It sounds to me that you have a wall which will have a high water load every time it rains due to road splash. As you have a breathable wall, this moisture will get into the wall but more importantly it can easily get back out again. This is leaving you with a dry wall which is more than a lot of people get.

The problem with salty deposits is a general problem with all walls where there is a lot of moisture movement. The moisture brings the salt to the surface and it is left behind when it evaporates. I recently removed a cement render from a modern (1970s) block wall which was very wet. Within a couple of weeks I had a salty fur about 10mm thick in a number of places where the moisture had evaporated from. Now that this wall has dried out, it is no longer a problem. In your case, salt coming to the surface may reduce in the future or it may be something you have to live with.

The flaky lime suggests it wasn't put on properly but I'll leave it to others to comment on this.

 

[frednelson203]

Thanks for additional replies. Accept that not all Surveyors are expert on old buildings but we do have a lot of old stuff around here (Suffolk) and the guy I used has extensive experience. The plaster relacement was lime putty and sand (not sure of mix ratio)

Good feedback on the salty deposits thanks. I believe what we will go for now is leave the areas inside to flake over the winter, get the wall dry thru dehumidifcation and see where we are next spring

 

[Nemesis]

It's a great pity you did the injection. It may be part of the ongoing problems and a waste of cash! Also, it's usually carried out in conjunction with other works including plastering with a cement based render - belt and braces.

The situation is complex, but I can't think 'rising' damp was the main cause of the damp here really.

You may find the lime is sacrificial.

What is the wall constructed from?

 

[Matt Green]

The situation is complex, but I can't think 'rising' damp was the main cause of the damp here really.

Really? Why not? The ground levels are equal inside and out and the interior surface has a nice warm atmosphere around it and a breathable coating to move through. I bet there was/is some groundwater rising through the base of the wall.

Equally, I bet no one tested the wall before the injection to determine that either. :?

Regardless, if traffic is spraying water over the DPC it's installation was purposeless. The wall needs to be invasively tested to determine the water source to diagnose the problem.


Matt.

 

[MdB]

Fred, I may not be an expert in this but Matt is and is worth listening to. (Follow the www link below his post.)

 

[Nemesis]

I agree with Matt - bet no-one tested, and the fact the road is being sprayed with water could well have been a major cause of the damp. So hard really to know.

I'm never totally convinced by the instant and all too ready diagnosis that all damp is rising. And how far it rises (and even if it does...) is a cause for controversy in some circles still!

 

[frednelson203]

Great responses thanks. What does Nemesis mean by "maybe the lime is sacrificial"? As Im no expert Im not sure what the wall is constructed from - also of course I dont know what has been added/taken away over the years. I have been told that I must use a lime based plaster and "breathable paint". I have done all this and still have a problem. I think the splashing is a real issue and agree that if the traffic splash hits the wall above the dpc then no wonder the wall is struggling.

I agree that further invasive testing of the wall to confirm/understand the source of the water ingress is worthwhile. Im getting more and more convinced that it is traffic splashing as it is only on this wall I have the problem. I have a basement that has no damp problems - the basement does not extend as far as the road

Great exchanging views with you guys - wish I had found ppuk years ago

 

[MdB]

I'm never totally convinced by the instant and all too ready diagnosis that all damp is rising. And how far it rises (and even if it does...) is a cause for controversy in some circles still!

I wish I could find the links to the experiments I have seen (on TV) and read (linked from here somewhere) where various walls have been built with their bases standing in water to see how far the moisture rises. All were brick or block with various types of mortar. The worst had damp to around 200mm to 300mm with most being half that (if I remember correctly). None had any form of render if I remember correctly which may suck water up further and / or stop the evaporation process from the surface.

I don't doubt though that rising damp is diagnosed far too often.

 

[Nemesis]

Well - is the wall brick, stone, wattle and daub...

What sort of plaster / render was there before? What condition was it in externally?

 

[MdB]

I have been told that I must use a lime based plaster and "breathable paint".

What do you use as "breathable paint"? Paint that had "breathable" on the tin or paint that was recommended by someone who new what they were talking about? Unfortunately, some manufactures put breathable on the tin when it actually only allows a very small amount through. You mention lime wash which is a good covering to use so hopefully you should be OK. Distemper, clay paints and silicate paints also get recommended by people here.

 

[Juju]

I've found this discussion very useful. I've posted before about a similar problem of rain splashing up the house and through the letter box! We've got similar nobbly salty deposits on our internal wall - I was wondering if it's lack of ventilation though so we've just removed the solid secondary glazing panel and as it isn't too noisy or draughty, the next step is to remove the complete fittings which the previous owner fitted across the little bit of window that opens... I'm hoping that getting some fresh air in(despite traffic fumes) should help a bit.

I would be very disheartened if we paid out to re-render the house in lime and re-plaster the interior, only to find the problem continued!

 

[MdB]

We've got similar nobbly salty deposits on our internal wall - I was wondering if it's lack of ventilation ...

Salty deposits are due to evaporation. More ventilation will produce more evaporation so potentially more deposits. I don't know any way around this.

 

[Matt Green]

As MdB says, salt deposition may increase with more ventilation.

Remember: salts mean water travelling through the plaster and depositing desolved minerals on the surface - not condensation. ventilation means more evaporation and more salt deposition. This may not be a bad thing: if the source of water has been idenfied and fixed, the wall will dry faster and the problem will sort itself out lathough you may need to (and it may be a good idea to) replaster.

Condensation is water deposition on a cool internal surface which can result in mould growth (mould is inhibited by salt, so you don't usually find the two together). Ventilation helps move moisture laiden air away from the surfaces reducing the possibility of condensation.

Now I hope you've all noted that down.
:wink:

Matt

 

[Nemesis]

Engraved on my heart Matt.