Damp Proofing – How Much Should You Pay?

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We hope you can save money off your damp proofing and repairs by exploring this page.

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Damp can cause considerable damage to plaster, timber, render, wallpaper and carpets and if left unchecked can lead to health problems such as respiratory illness.

Unfortunately, many modern treatments involve sealants that mask the symptoms of damp without solving the underlying issues.

This can push the moisture into other areas leading to additional damp repair costs at a later date.

Bubbling plaster to damp wall

4 Most Common Causes of Damp

  1. Condensation – this is almost always at its worst during the cold winter months. Modern houses are constructed with insulation in mind; sealed airtight double or triple glazed windows, loft and wall insulation and airtight doors all create an environment where moisture cannot escape. Hanging wet clothes on radiators, cooking without lids on pots and bathing/showering without adequate ventilation can all combine to create a moist property, as soon as that moisture comes into contact with a cold surface, it will condensate and form water droplets that can soak into walls and floors resulting in mould and damp patches.
  2. Wet external walls – the external walls of modern houses are designed to cope with rain. House bricks soak up water but then dry out very quickly. If however, an external wall is subjected to moisture for a prolonged period of time, it may penetrate through the outer wall and onto the inner wall. This usually happens when rainwater pools at the base of an external wall, the end result is damp penetrating into the property and rising up the internal wall, plaster then becomes soft and crumbles and redecoration is required. Common causes of damp walls are insufficient drainage in the garden.
  3. Leaks – the most common type of leak is from the roof; chimneys are often the highest point of a house and are sometimes pounded by windswept rain which can penetrate through the bricks or around lead flashings. Broken tiles and leaking or blocked gutters can result in rainwater splashing onto an external wall, or even worse running down a cavity. Pipes can also leak and cause isolated areas of damp although these should be fairly easy to locate.
  4. Damp below ground – this is the most expensive to solve and can be caused by several issues, rising ground water levels are notoriously difficult to work against.
evidence of damp

Damp caused by condensation

Case Studies – With Costed Solutions

The following case studies are all real and emphasise how important it is to locate the cause of the damp before going ahead with a damp treatment program.

As there are so many causes of damp,  it may seem as though not all of these will apply to you but we suggest you read them anyway. The solutions are often affordable and quick:

Case 1 – Claire in Frimley Surrey

We were contacted by Claire from Frimley during a particularly cold spell of weather during the month of February.

She was very concerned at the rapid onset of damp patches on the plastered outer walls of her first-floor maisonette.

Along with her partner, Claire had lived in the property for three years and they had never experienced damp or mould before. They were particularly concerned as they had a new born child and the walls were showing signs of mould growth.

On initial inspection there appeared to no damp rising up from the ground, we had a quick chat with the owner of the ground floor maisonette and they didn’t have any issues, neither had they any in the past. A visual inspection of the roof didn’t reveal any broken tiles and the gutters were in good working order with no blockages. There didn’t appear to be any internal piping near the damp walls either.

A chat with the homeowners revealed the cause of the damp issues.

After the birth of their first child, they had made some lifestyle changes which led to a build-up of moisture in the house:

  • they kept all windows and doors closed to keep the house warm for their baby.
  • clothes were washed daily and dried out on the radiators.
  • bottles and other equipment were frequently sterilised in hot water in the kitchen, windows were not opened due to it being cold outside.
  • showering and bathing were done in a bathroom with the window closed and the extractor fan, which was partially clogged, was rarely used.

None of the above caused a visible damp issue until the outside temperature dropped below freezing and the walls of the house become cold. The warm moisture then condensed, soaked into the plaster and damp mouldy patches appeared.

We advised the homeowners to make the necessary lifestyle changes to reduce the build up of moisture; only use radiators to dry clothes if a window can be left partially open. Open all window trickle vents. Keep the kitchen door closed and the window partially open when boiling water, use the extractor fan, use pot lids. In the bathroom, use the extractor fan and where possible open the window to allow moisture to escape.

Cause – lifestyle change due to arrival of baby, unusually cold weather and lack of ventilation.

Solution – reduce sources of moisture and vent where possible, especially during cold weather spells.

Cost – none, just the cost to redecorate a few walls after the issue was resolved.

Case Study 2 – Jake From Guildford in Surrey

We were contacted by Jake from Surrey, his property was suffering from an isolated damp patch on the ceiling which had spread onto the upper part of the wall.

Jake had used the services of a separate roofing company to solve the problem by replacing the roof valley located directly above the damp patch. This was done at a cost of £650.00.

Unfortunately, this didn’t solve the damp issue.

We were asked to look at the damp patch and provide a second opinion.

An inspection of the roof and gutters didn’t show any problems and the roof repairs were done to a high standard.

We went into the loft and quickly discovered the cause of the isolated damp.

An extractor fan was in the bathroom but unfortunately, the ducting had deteriorated and had also come loose from the external wall vent. Every time the bathroom fan was switched on, moisture was being discharged directly onto the ceiling and only a few inches from the wall.

The new ducting only cost a few pounds and took 15 minutes to replace.

Cause – extractor fan ducting had come loose.

Solution – replace ducting.

Cost – minimal.

Case Study 3 – Michelle from Basingstoke in Hampshire

Michelle contacted us during April and had an issue with damp on both the internal and external wall at the front of her terraced property.

She had been supplied with a quote to inject damp proofing chemicals into the wall and replace the plastering at a cost of £4000 but she was suspicious so asked us for a second opinion.

On arrival at the property, we immediately noticed that the property had concrete roof gutters.

These are prone to leaks so we put a ladder up and inspected them.

Both neighbours either side had new lining fitted to the gutters but Michelle’s concrete gutters were unlined and showing the telltale signs of leaks; movement cracks and moss/mould growing on the outside of the concrete, also peeling paint was evident.

While we didn’t offer a gutter relining service, we advised Michelle to have the gutters lined by another company. We also suggested that the damp proofing work might be unnecessary and that either way, the gutters needed to sealed first.

Michelle sent us a thank you email about a month later; the gutters were relined at a cost of £900 and the damp immediately began to recede. She had booked in a plasterer to repair the walls the following week at a cost of several hundred pounds. The total cost of the work was less than half that quoted by a specialist damp proofing firm, who had incorrectly diagnosed the cause of the damp.

Cause – concrete gutter movement and leaks into cavity void

Solution – re-line gutters with a flexible rubber membrane, replaster walls and redecorate.

Cost – £1300

Case Study 4 – Steve From Portsmouth in Hampshire

Our friend Steve works as a builder and like us, he has experience of renovating houses. In March 2015 he purchased a 3-bed house at auction with the intention of renovating it for re-sale at a profit.

Being an experienced builder, Steve chose not to have a professional inspection of the house done beforehand, although he was aware of some damp issues along the rear wall which appeared to be caused by a patio being laid too high and breaching the damp course.

Steve removed the old patio and installed a new one 150mm lower, this gave a clear 100mm gap between the wall damp course and the top of the patio. He also installed a drainage channel between the wall and the patio and connected this to the existing soakaway.

After plastering and making good of the internal walls, Steve noticed that the damp had started to return albeit in only one patch.

As the damp appeared along the wall and not the flooring, Steve removed the plasterboard along the entire affected wall and injected a damp proofing chemical into two horizontal lines. He also did the same to the outside wall. New plasterboard was fixed into place and the wall plastered and redecorated.

The damp issues didn’t return, even though it was a very wet month with plenty of rain.

Cause – underground damp underneath wall.

Solution – multiple; minimise rainwater pooling adjacent and beneath wall by lowering patio and installing drainage channel. Also, chemical injections to prevent any water that does collect from rising up the wall.

Cost – as Steve did the work himself and the house as vacant, the costs were kept to a minimum. Read our price guide below for this type of damp proofing, it can get expensive.

Case Study 5 – Jason in Farnham, Surrey

Jason contacted us in January with what he thought was a substantial roof leak above his gable wall.

Upon inspection, we could clearly see damp patches on the external walls and also mould and black spots on the internal walls.

The area affected was from about 1 metre below the top of the gable down to ground level. In total, about 6 metres of wall appeared to be damp.

An inspection of the roof didn’t reveal any problems with the roof covering and as the property was located on the top of a hill with the ground sloping away from the building in all directions, we couldn’t see how ground water could rise 6 metres up just one wall. Drainage was clearly not an issue.

After asking a few probing questions and taking a closer look at the wall we discovered the cause of the damp.

Jason had new cavity wall insulation inserted into the wall the previous year and this was the first clue to the problem.

As previously stated, the house was located on a hill and the affected wall was in a very exposed windswept location. Several decades of driving rain had taken its toll on the brickwork and cement work to the wall. Most of the cement was washed out and what remained was very soft and absorbent.

This in itself isn’t enough to cause damp to an internal wall as bricks and cement dry out very quickly after rainfall. Our investigation did reveal, however, that the cavity wall insulation was soaked and was holding water and passing it onto the inside wall.

We removed one external brick and pulled out a handful of soaked wall insulation.

We suggested the following course of action to Jason:

  • remove several bricks and suck out the wet insulation (it takes months to dry if left in place)
  • allow the wall to breath for a few days and on a dry day:
  • re-cement bricks into place
  • re-point the entire wall
  • after the pointing has fully dried, apply two coats of a breathable waterproof sealer to the external wall (suggested as it really was an exposed wall)
  • hire a dehumidifier and leave in the house for a couple of weeks to dry out internal walls

Cause – rain onto a windswept wall that wasn’t well maintained, moisture then transferred to an internal wall by the poor choice of insulation material.

Solution – scaffold erected, damp insulation removed, wall repointed and then sealed.

Cost – Scaffold: £600. Pointing £950. Sealing: £600. Dehumidifier £60 per week.

Rising damp to wall

Steps You Should Not Take

We have provided details and solutions to several common causes of damp but here are two steps we think you should avoid, or at least defer:

1 – Internal Paints and Sealers

When damp is first spotted on a wall or ceiling, you might be tempted to paint over the internal wall with a waterproof sealer.

In fact, this is the worst step you could take.

By taking this step you are sealing the moisture in the wall rather than solving the underlying cause.

Internal wall sealers and paints are very good at masking the problem but the damp is still there and will almost certainly spread along the plaster.

Solve the problem first, then redecorate the wall.

2 – Going Directly to a Damp Proofing Company

As you have learnt from our case studies, in the vast majority of scenarios, damp issues are not caused by rising damp and can be solved without expensive chemical wall injections.

We will provide more information about damp proofing companies further down this page. But it’s sufficient for us to say that if you contact a damp proofing company, they will most likely result in them recommending a damp proof product and that may not be the best or cheapest course of action.

Keep reading to discover what we think about damp proofing companies and why an independent surveyor should be consulted before you get a quote from a specialist.

The Damp Proofing Industry – Is the Bad Reputation Deserved?

There is very little profit in replacing a gutter joint or repairing a single cracked roof tile but there is plenty of profit in damp proofing a wall with chemical injections as this involves removing the plaster, injecting the walls, waiting for the walls to dry and then replastering and redecorating. The work is very disruptive and cannot be completed quickly.

As previously stated; if you contact a damp proofing specialist, chances are they will sell you their most expensive product.

While we don’t want to tar every business with the same brush, the industry is well known for mis-selling. There is, however, one step you can take to protect yourself.

Get an independent surveyor to inspect the damp.

We have already provided details about the most common causes of damp and also some case studies but if none of them applies to your situation, the next step isn’t to go directly to a damp specialist, instead you should contact an independent surveyor who can:

  • conduct an independent investigation into the damp
  • inform you of the cause
  • supply you with a course of action
  • give you a guide price for the work

Wall Damp Proof Prices – A Guide

Damp proofing a wall involves the following steps:

  • remove carpet and flooring near the wall
  • cut back the plaster and remove plasterboard from the ground up (how high depends)
  • inject chemical waterproof sealants into both the internal and external walls
  • wait for the wall to dry, use dehumidifiers for severe cases of damp
  • seal internal wall with sealer
  • wait for wall sealer to dry and then fix new plasterboards to wall
  • plaster over boards and redecorate

Expect to pay around £350-500 per linear metre of wall with a minimum charge of £1500 depending on where you live. This figure includes replastering.

Try Our Checklist

If you are trying to diagnose a damp issue, try our checklist which can be used to isolate the damp problem:

PDF damp proof checklist

Get a Quote

As with all our prices guides on this site, we have tried to explain in detail all the options open to you, along with a realistic cost.

However, as damp can be caused by a multitude of issues, we recommend sourcing a custom quote for the work.

To see how we can help you with that, just hit the link below:

Get a Quote Online

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Job Prices is a work-in-progress project created by a group of home improvement specialists who have experience in almost all aspects of construction and building work.

The site was created so homeowners can get an idea of how much popular home improvement projects will cost so they can budget accordingly.

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The prices on this page were last checked in April 2017.
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