rising damp

A lot is talked about rising damp from both sides

  • damp proofers and 
  • Independent damp surveyors.

Who is right?

Be independent, experiment, think it through. Make your own mind up! The cost of getting it wrong could be damage and a hefty charge for unnecessary treatment.

About rising damp

Water from all its sources rises where the force of absorption exceeds the force of gravity, which it always will do.

However, rising damp in the UK has a very specific definition.

Rising damp is the upward absorption of groundwater in a wall above ground level.

The reason rising damp is defined as coming from groundwater as because unlike all other forms of damp, such as rainwater in soil, groundwater is not always easy to remedy at source.

Water from all its sources rises where the force of absorption exceeds the force of gravity, which it always will do.

However, rising damp in the UK has a very specific definition.

Rising damp is the upward absorption of groundwater in a wall above ground level.

The reason rising damp is defined as coming from groundwater as because unlike all other forms of damp, such as rainwater in soil, groundwater is not always easy to remedy at source.

Water from all its sources rises where the force of absorption exceeds the force of gravity, which it always will do.

However, rising damp in the UK has a very specific definition.

Rising damp is the upward absorption of groundwater in a wall above ground level.

The reason rising damp is defined as coming from groundwater as because unlike all other forms of damp, such as rainwater in soil, groundwater is not always easy to remedy at source.

Water is absorbed by an absorbent material in all directions, including upwards, but it mainly falls downwards through gravity.

Kitchen paper is absorbent, and makes a very good medium for experimenting with and understanding the absorption of damp.

For example if you place water into the centre of kitchen paper, about 6 times more will be absorbed towards (fall) compared to absorption upwards.

falling damp
Falling damp from gravity

Groundwater is the water below the water table. Pores in the earth below the water table are saturated. There is 100 times more water in groundwater than in all the fresh water lakes and rivers of the world.

Groundwater has impermeable boundaries, therefore gravity can’t act to draw groundwater down. There is a capillary fridge which reaches to a height of a few millimetres with shingles to about 1M with mud.

A wall built in the capillary fringe will rise to the heigh of the capillary fringe. 

 

As is common in most cities around the world, groundwater is pumped out of the ground in London. It is currently about 65M meter ground level, below the level of the deepest tube.

rainwater defects

The Wikipedia image for penetrating damp correctly shows dampness entering a property through soil as penetrating damp. The solution being to lower the soil to its original level and improve drainage. The internal wall will then dry out – note it can take 10 months to dry out (the same time as damp proofing).

Understanding the difference

Rainwater in soil is in temporary suspension on it’s way to:

  • be used by humans, drain into the earth or join rivers,
  • be absorbed by plants and animals, or
  • evaporate into the atmosphere.

Below soil pores are unsaturated

Gravity drawn rainwater down. Some will eventually become groundwater, once it reaches the water-table. 

The pores in soil are unsaturated (unless water logged). The force of absorption causes the unsaturated pores to retain water in lower pores first, in preference to higher pores, according to the laws of gravity.

For this reason virtually no bricks sitting on soil dampened by rainwater. 

Below water-table pores are saturated

Groundwater is bounded by impermeable rock, like a vast tank. Water can’t descend, therefore unlike rain in unsaturated soil, water will rise within the capillary fringe.

Rainwater in soil is penetrating damp

Rainwater in soil is technically penetrating damp. If the soil is above the damp proof course, then the soil should be lowered to its original height.

Draining rainwater in soil

The best, easiest and normally the least risky and cheapest is to drain rainwater away from soil.

There are 4 common ways to test for rising damp:

  1. Desktop review, for there to be groundwater in contact with the property, you will need all three of these;
    • A high local water-table: Look local water table,
    • Rocks with aquifers below your property, and
    • A risk of flooding.
  2. Drill or dig below or near the house, making sure not to contact a gas, water, cable, drain, electricity etc. (use local area searches).
  3. Put a brick in the garden, under shelter.
  4. Test surface salts on the damp wall for nitrates. This merely eliminates groundwater as mains water and rainwater in soil also contain nitrates.

Rising damp proofer turned indie

Often rising damp proofers turn from contractors to independent surveyor.

Beware

In the early days of transitioning, there is temptation to continue to diagnose rising damp, because:

  1. old habits die hard,
  2. risk of being sued by former clients of diagnosed rising damp,
  3. PCA allow independent surveyors to make 15% of their gross income from damp proofing referrals. 
damp proofer turned independent
Peter MacDonald is key to the rising damp proofing story, but what does he say now?

Chain sawing an old house

Peter worked as the sales man for a damp proofing company in South London. The damp proof course was cut out with a chain saw. Interestingly the technique is still in use see a you tube video. Peter moved to high pressure chemical damp treatment in the 1980’s following a spate of chainsaw “problems”.

Epidemic of rising damp treatment

Rising damp treatment became something of an epidemic in the UK in the pre-internet days of the 1990’s. But high pressure chemical treatment was messy and there was no evidence that the treatment worked. Peter conceived the idea of a low pressure system.

DryZone

Safeguard Chemicals trialed and found a Japanese patent for reducing absorption in bricks, a silane/siloxane thixotropic emulsion, which they branded and now sell as DryZone. Peter ran Safeguard for many years. 

Poacher turned gamekeeper

About 10 or so years ago, Peter left Safeguard to consult as an independent damp surveyor. He didn’t completely loose his rising damp habits as he took over as the main teacher of rising damp proof surveyors at the Property Care Association (“PCA”)The chairman of Safeguard, chairs the PCA.

With a similar outcome to the Which! investigationPeter invited 3 PCA qualified damp and timber surveyors to inspect a three bedroom, semi detached housePeter writes:

None of us are perfect and I include myself in this but I was embarrassed that three fellow professionals in my industry had, in my opinion, completely failed to get correct what I would regard as a ‘bread and butter’ survey, which was able to be conducted with virtually no obstructions or floor coverings present to restrict access.

I had endeavoured to act in my client’s best interest by suggesting that reputable specialist timber and damp treatment companies should be invited to inspect the property and submit their reports and estimates for the work necessary but alas I was severely let down.

As no specialist company seemed capable of inspecting the property correctly the outcome was that I wrote a specification and met with general building contractors on site who submitted their quotations based on my specification. One of these building contractors will be instructed shortly and I have been requested to carry out periodic inspections as the work progresses.

BBC Raising the roof – on rising damp. 

Part 1.

BBC Raising the roof – on rising damp. 

Part 2.

Building Pathology – Mike Parrett Glasgow
Caledonian University

Part 1.

Building Pathology – Mike Parrett Glasgow
Caledonian University

Part 2.

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