Plastering & Rendering

Strange small damp patches on plastered walls

Anonymous user 23/02/2024 - 2.55 PM

I'm not sure if this is a Plastering problem or a Damp problem. I've got a mid terraced, 2 bed house built around 1900. Down stairs in the lounge there are quite a number of small damp patches on the walls. They are small, ranging from only 1cm across to some about 10cm across. They are scattered randomly on some of the walls mainly the walls between the two houses on either side. Strangely enough, none on the outside wall. I have tried painting over them with Damp Seal (more than once) but they keep coming back (admittedly getting fewer each time I do it but not totally cured). They are causing the plaster walls to 'blister' in places like the external corners on the chimney breast. But the are mainly on the adjoining wall where there is no chimney breast so its not a 'damp getting down the chimney' problem. I've had a couple of people round to look at it but they didn't get back to me - maybe because it isn't standard rising damp or something straight forward. My brother also has the same problem but he has more of them and his house is also a mid terrace round about the same age but he has some damp patches upstairs too. Has anyone come across this before? What is the most likely cause, and what is the best way to cure the problem?