Ten Reasons for Damp Around the Chimney Breast

Ten Reasons for Damp Around the Chimney Breast

10th February, 2023

Many homes with chimneys have unexpected problems with chimney damp. Dampness in a house will worsen over time and lead to further deterioration. We briefly examine the signs of chimney damp. Thereafter, we look at ten possible causes for chimney damp.

Signs of Chimney Damp

Damp has the same symptoms, regardless of where it is. Chimney damp is no exception, except that the signs will be focussed on the chimney breast and around the fireplace itself. Look out for the following indications of chimney damp:

  • Damp patches that arise and disappear with changes in the weather
  • A damp tidemark that keeps rising
  • Brown or yellow discoloration to the walls
  • Paintwork flaking off

Causes of Chimney Damp

It is essential to identify the cause(s) of chimney damp. Take note that there can be multiple causes and all need to be addressed and repaired. In this way, you can resolve the dampness issues affecting other parts of your property too. Dampness in a house can be avoided by asking for a pre purchase survey. Some of these causes only apply to chimneys. We look at the possible culprits next.

Broken and/or Open Chimney Pots

Chimney pots can be either capped, open-topped, or have a chimney cap missing. Open, unused chimney pots are vulnerable to the elements and moisture can find its way inside. If the chimney is capped, there could be damage to the structure that is allowing rain to seep in. Keep in mind that a chimney provides air flow and should not be sealed at the top. A chimney needs ventilation to avoid rising damp. This is the case even if the chimney is not actively in use.

Chimney Stacks with Insufficient Air Circulation

Damp caused by a blocked chimney occurs when the ventilation is insufficient. Condensation treatment is utilised to deal with a build-up of moisture in a blocked chimney. A chimney cowl is fitted to keep condensation from forming but the moisture must still be allowed to dry out, which is not possible with a closed chimney. It could also be as a result of a blockage. This can be prevented by regular sweeping of chimneys.

Chimney Stack Masonry Crack

If you have eliminated the causes already listed, visually look for cracks in the mortar. Perhaps lightweight plaster was used. This is an easy fix. The crumbling substances are removed and refilled with a tough substance that will endure for years. The process is called tuckpointing. Brickwork may need to be replaced.

When Neighbours Share a Chimney

When you share a chimney with your neighbour, actions taken by one party may affect the other. Problems can also follow a sequence, such as insufficient air flow or a badly installed flue leading to damp when one party puts in a wood burner. Both homes are affected.

Chimney Damp Due to Poor Construction

Building faults, such as absorbent masonry, roof tiles missing, water leaks, and insufficient guttering, can contribute towards damp on the chimney breast. Stains (yellow/brown) on ceilings and walls are warnings of chimney damp.

Damp Caused by Continuous Exposure to Weather Elements

Weather elements tend to degrade substances exposed to the open air permanently. This is the reason that chimney surveys should be carried out before buying an older property. These chimneys have been open to the elements for decades. This includes the sun, rain, sleep, fog, snow, and wind.

Brickwork can start to crumble. The mortar joints decay, making them penetrable and able to hold water. Cracks occur. This is how water enters the chimney, creating chimney damp. Sometimes, this spreads to the rest of the house.

The first step towards resolving this problem is to start repairs on the chimney structures. The entire surface of the chimney must be painted with a masonry water repellent. A good product will provide your chimney with protection from the elements for another quarter of a century.

Weak Lead Flashing

A lead-based waterproof tape is utilised to increase protection against wet weather. Sometimes, this has not been correctly positioned to cover intersections, such as between the wall and the flat roof, leaving gaps where rain can get in. Secondly, the lead must be to a certain depth, or it can come loose during very windy conditions, thus allowing water to seep in below the flashing.

To check the chimney flashing, observe it from inside the roof space or the attic. No daylight should penetrate. You may also find evidence of water leaks. If you see hygroscopic salts (they absorb water), this is a sure indicator of problems with your flashing.

Once the flashing has been restored, the chimney must be damp proofed.

Condition of Roof Tiles

Perform an examination of your roof. Cover the entire surface and identify where tiles are missing or cracked. Replace these tiles to protect your entire home from the elements.

Gutters that are Blocked or Broken

Blocked or broken gutters are responsible for some instances of damp chimneys. They permit water to get in via gaps in the mortar as the designed waterflow off the roof should be through the channelling gutters. Guttering should ideally flow off away from the house. Do regular upkeep to ensure that gutters are free of debris and repair any damage.

Rising Damp Responsible for Chimney Damp

Dampness in a house can come from above, such as from the elements, or below as rising damp which presents as a tidemark made of salt. The cause of rising damp is either that there is no damp-proof course (DPC) or the DPC is bridged.

Look for structures that could be providing this bridging capacity and remove them. Not having DPC is common in older houses. This allows wet soil to rise, causing rising damp. The most suitable rising damp treatment is to inject a damp proofing cream into the chimney’s base.

Most of these issues can be avoided by having a survey done before taking ownership of a property, checking for quality if you have the house constructed, and routine checks and maintenance. If you are unsure of how to deal with damp, get hold of a damp specialist London.