• Martin Young

Types of Damp: Penetrating Damp and Mould Growth in Your Home

Updated: May 18



What Causes Penetrating Damp?

There are different categories of damp. Some sources will tell you there are 3 categories, others 6 or more. Essentially, damp is classified by its cause. Penetrating damp is usually the result of defective or damaged building materials such as damaged roof tiles, cracks in the wall, faulty guttering, internal damage from leaking or burst pipes, cracked pointing, blocked weep holes or defective seals. There's an endless list of possible defects and damage that can allow moisture to penetrate from the exterior of a building to the interior. Moisture infiltrates materials or seals that should be impermeable due to damage or defect. The water will find its way in through the walls, roof, window or door surrounds at any level of a property. This is also sometimes referred to as water ingress.


Other causes of penetrating damp include:

  • Spalled bricks and defective masonry. External brickwork, if left to fall into disrepair over time, can become defective, allowing water to penetrate a property.

  • Porous walls. Some masonry is too porous, meaning it absorbs moisture to the extent that it's unable to keep rain from penetrating to the inside of the property. This typically occurs through degradation. When walls have degraded to the point where they become porous, they allow water ingress to pass through the external wall into the property.


How to Identify Penetrating Damp?

Typically the signs of penetrating damp are very similar to other types of damp which can make diagnosing damp problematic if you are not sure what to look out for. Regardless of size or scale, you should be able to spot the signs of penetrating damp from the following symptoms:


  • Staining - staining on external walls.

  • Damaged Decoration - deterioration and staining on internal walls.

  • Damaged Plaster - wet and crumbly plaster, blistering, salting and disintegration.

  • Rotting Skirting Boards or Floor Timberswet rot decay can develop as a result of moisture saturating timber.

  • Localised dampness – Random damp patches at a high and low level that grow in size when coming into contact with moisture.

  • Mould Growth – visible mould growth (black mould patch) and musty smell.

  • Drips and puddles. Pooled water.

  • Brick Damage - damage to the brickwork on external walls resulting in spalling and cracks in the structure of the wall can allow moisture to enter the property.


Does Building Insurance Cover Against Penetrating Damp?

Many building insurance policies do not cover damage caused by penetrating damp. as penetrating damp is caused by water ingress from building defects or deterioration. If you are planning on carrying out DIY solutions for the problem yourself, check with your insurance policy provider first as carrying the work out yourself could invalidate your insurance policy.


How Does Penetrating Damp Cause Mould?

Molds are very common in buildings and homes. Mold will grow in places with a lot of moisture, such as around leaks in roofs, windows, or pipes, or where there has been flooding. Mold grows well on paper products, cardboard, ceiling tiles, and wood products. Mold can also grow in dust, paints, wallpaper, insulation, drywall, carpet, fabric, and upholstery.

Center for Disease Control


Mould spores are abundant in outdoor air. They can float indoors through windows and doors as well as attaching themselves to clothing, shoes and even pets. Once indoors they will take root in your surfaces seeking out moisture. Mould spores thrive in homes with damp conditions such as those caused by penetrating damp. They feed on the moisture as well as the cellulose found in wallpaper, tiles and timber. Mould spores can also feed on biofilm, a nice name for the microscopic layer of detritus that builds up on most surfaces in human habitations.


Are Damp and Mould a Risk to Health?

The UK government have classified mould as a Category 1 Health Hazard - the same as asbestos. The World Health Organisation found links between toxic mould exposure and the illnesses below. In addition to the below, there's a number of other illnesses which have been linked to toxic mould exposure in clinical studies. The area is one that is still being explored and researched.


  • Allergic rhinitis

  • Exacerbation of asthma

  • Respiratory infections

  • Cough

  • Upper respiratory tract (nasal and throat) symptoms

  • Wheeze

  • Allergic alveolitis

  • Allergic fungal sinusitis

  • Chronic rhinosinusitis

  • Hypersensitivity pneumonitis


Can I Wipe Mould Away Myself?

It must be remembered that black mould, or any other type of household mould for that matter, is a living organism. It has defence mechanisms when under threat. If you simply wipe at a mould colony with a cloth or spray it with an over the counter cleaning product, it simply causes it to spore aggressively into your airspace as a means of survival. Doing so massively increases the concentration of toxic spores, mycotoxins, glucans, mould fragments and mVOCs in your airspace, and inevitably, in your own body. Mould must be treated in a way that destroys the mould first before it is physically disturbed.

Even bleach does not kill mould. This is a common misunderstanding found everywhere online. Bleach depigments the mould, rendering it invisible, so it looks like it is entirely gone. In actual fact you've probably just wiped away the top of the black mould growth, while it's now invisible roots remain very much alive, embedded in the surface of your home. Except your airspace is now saturated with toxic agents caused by the agitated mould, meaning both a greater risk to your health and a higher likelihood of the returning and worsening of the problem.


How Do I Get Rid of Mould?

When you pay a professional to come in and resolve a mould problem, you expect them to deliver a service that is beyond your own skillset and expertise. You could buy a fungicidal sterilant and wipe or spray it onto a mouldy surface relatively easily. However, professionals know that 95% of mould is invisible and at the point at which you can see mould on a surface, your property is likely saturated with invisible mould spores; on surfaces, in the air and hidden within and behind walls, floors and furnishings.


Our dry fog system removes all types of household mould - on surfaces, in the air and the hidden mould behind cavity walls, under floorboards and in soft furnishings. Our dry fog also decontaminates the building by eradicating all microorganisms in the treated area. What’s more, our anti-microbial film coats all surfaces, preventing the mould from coming back.


What makes the process innovative is the particle size into which the fogger forces our sterilant. This means three things. First, it is unable to condense on surfaces and dwells in the air; eradicating the abundance of mould spores and significantly reducing the harmful mycotoxins traditional methods can’t deal with. Second, our dry fog machine creates positive air pressure, meaning the dry fog is forced to fill the entire volume of a room or house, forcing the sterilant to dwell on every surface and object. Third, it can reach every conceivable space within your home including behind cavity walls, meaning we are able to comprehensively eradicate every last trace of mould.


Want a Quote For Professional Mould Remediation?

Our team of in-house experts will be happy to talk you through cost, process and availability.


GET A QUOTE