Salt Damp on chimney breast.

It is very common to find significant quantities of salt on chimney breasts which stem from the burning of fossil fuels and it is often mistaken for rainwater ingress.

[@paullynch277]

As you correctly stated Hydroscopic salts are coming through from the chimney - but the reason it is coming through the stone is because of the cement mortar which is impermeable and traps moisture in the wall. The stone appears a softer material than the Mortar, thus creating an easier path for the salts to travel through. The cement has cracked. Cement is harder than the stone in the wall. If the wall had a Lime Mortar then moisture would be able to be expelled through the joints. When jointing you always want to use a material that is less strong that the material you are jointing around. Correct way to fix is to remove all cement and replace with Hotlime/NHL2 Mortar. The salts in the stone (if surface is continually wiped to clean off salt buildup) will eventually exhaust and the problem will be resolved, but only if all the Cement/Gypsum is removed and replaced with Lime.

[@sallymorriss1682]

Thanks Neil. Your videos have really helped put my mind at ease over this problem/ not a problem. My house was fine until winter when I started using the log burner. Then damp and salts appeared which I thought had come from a problem in the roof. Now I know it is normal for my old house. I really appreciate you sharing your findings.

[@holtemporium]

It is important to note that salt is hygroscopic and not Hydroscopic

[@essentialhandyman]

What is the solution for getting rid of the dark staining?

[@zippy441]

Hi Neil, so I have a plastered chimney breast in 1890s building. No visual signs of damp but random isolated high readings with the Protimeter. I was assuming it was the salts either causing a false high reading or maybe there is a slightly more moisture there as the salts hydroscopic... Am I right in this thinking? Thanks again Neil, great video!

[@paullynch277]

Hi Zippy441. Check for the following - first assess the plaster, is it the original Lime plaster? If it is, then what is covering the plaster - is it covered in layers of wallpaper (this will be stopping the plaster from expelling any moisture, especially if you have any modern wallpapers which can have high latex/plastic content). Simply removing the layers of wallpaper will allow the wall to dry out and then redecorate with a breathable solution. Secondly, do you have any Gypsum Plaster or Cement anywhere? (Could be patch repairs over time or could be entirely in Gypsum/Cement). Both Cement and Gypsum are impermeable - so any moisture that gets into the wall has no way to get out, remains trapped and only spreads. If you have any Gypsum/Cement then you must remove it all, replace with Lime plaster and use a breathable finish (clay based paint / limewash / breathable wallpaper). If you have hydroscopic salts leaching through your Lime plaster you have two options - first if you are patient you can just expose the plaster and continually wipe off the salts and over time the salts will exhaust (as long as you continually wipe the residue off). Or more efficient is to remove the section of lime plaster affected by the salts and replaster in Lime. Also importantly - if you haven't already, add a chimney Bird cage that has Cap on it to prevent rain entering the chimney. Also, importantly - if your chimney is not in use (often the fireplace is closed/sealed up), you need to open it and clear out all the debris that will have fallen down the chimney over the years from bird nests, soot, etc. This material holds a lot of moisture and is often the source of damp issues in a disused chimney. After cleaning out, if you are leaving the chimney closed - you must have a vent at the bottom of the chimney and there are purpose made chimney caps for disused chimneys that allow for airflow.

[@Mr27363]

The slightly elevated readings on your moisture meter will be the result of hygroscopic salts within the building fabric stemming from the burning of fossil fuels. They will absorb atmospheric moisture and slightly elevate the M/C. If there is no visible damp staining I would not regard it as a problem. It is extremely common to record elevated meter readings on chimney breasts.👍

[@zippy441]

@@Mr27363 Thanks for the reply Neil, I thought it may be salts!

[@zippy441]

@@paullynch277 Just seen this Paul, thanks for the detailed reply... Some really useful info there!

[@Casualclips17]

if I treat the salt on the chimney inside of the bedroom, will the salt on the inside of the chimney be ok?

[@YouAreNotFree1]

Yep - I mistook for damp!