Last year I visited a property with several issues contributing to dampness in the third floor attic room chimney. The client who had instructed a roofing contractor to undertake repairs had been monitoring the problem themselves by drawing around the visible damp stains with a pencil to evaluate whether or not this was a developing issue.
I surveyed the roof, chimney and gable with the drone during my assessment and also removed several samples for moisture analyses using gravimetrics, which revealed that the repairs undertaken by the clients contractor hadn’t been successful. The contractor had removed all the chimney pots, sealing the flues absent from ventilation. There were several missing / damaged slates which had been missed and a few minor issues with the flashing. The contractor returned to site and as a last resort installed a liquid applied waterproof membrane to the flaunching hoping that would solve the problem.
The results from our gravimetric analyses highlighted that the dampness remained in the chimney, irrespective of the repairs undertaken.
Judging by the quality of repairs and the illogical approach to the situation, I recommended a series of repairs to the client using our own nominated and trusted roofing contractor followed by a period of monitoring.
Just over a year later, I’ve been back to revisit the situation. The client was a little concerned as after implementing our recommendations the condition of the finish internally hadn’t improved. I followed the same procedure as before, surveying the roof and chimney with the drone and removed some more samples for comparative purposes. I could use the samples taken in 2023 to compare against those taken now in 2024.
The results showed a significant improvement irrespective of appearance. The chimney is now dry towards the apex in both locations sampled and is drying down nicely beneath the stack. The reason the condition of the plasterwork hasn’t improved is simply due to the effects of hygroscopicity from salt contamination.
Hygroscopic salts are mineral salts that have a natural affinity for water vapour in the surrounding environment. Unlike efflorescent salts, which crystallise at the point of evaporation, hygroscopic salts remain in a damp or dissolved state within the material. When hygroscopic salts encounter moisture in the form of humidity or dampness, they absorb water vapour from the air, thus leading to an increase in dampness of the contaminated material. Hygroscopic salts are commonly found in and around chimneys due to the combustion of fossil fuels over many years and can be very problematic.
Here’s one thing to remember, you CANNOT distinguish between free water (active dampness) and hygroscopic salt contamination using an electronic moisture meter.
Dryfix, There’s a reason we’re Yorkshire’s Leading Damp & Timber Specialists!
This article was written by Russell Rafton
Russell is founder of Dryfix, an award-winning preservation and restoration specialist with over 20 years of experience. His PCA-accredited firm in North England provides expert diagnosis and repair of damp, timber, and water damage issues. Russell’s innovative approach and commitment to using the most suitable products set Dryfix apart. You can read more of Russell’s insights into the industry on his Linkedin profile  or by visiting his companies website https://www.dryfix.net/