Damp issues worsening over time, DPC injection and external render made it worse.

am sorry but so far all the advice you have received so far are wrong for this type & age of property the three things you should not do to this property render it with modern render re point with modern cement paint the external walls with modern masonry paint you live in a solid brick built house built with lime mortar, it would have had a slate damp proof course installed at the time of building this will never fail, lime mortar allows your building to breathe,there are no additives or cement in lime mortar anybody that tells you different run a mile from you have rendered it with a cement render this seals the wall and stops it being able to breathe creating dampness, the problem is today's tradesmen are schooled in modern construction methods /materials and so don't really understand how all the materials used in the construction of your property worked together to keep it water tight, you have injected an injected damp proof course, this is only effective against rising damp this will create a barrier at the level it has been installed allowing a build up of dampness behind the render at this level , the render needs to be removed and the wall re pointed with N.H.L. mortar to allow the building to breathe properly old buildings and modern materials do not work as they are trying to achieve different things, latest which findings rising damp is misdiagnosed in over 75% of property's rising to 95 % in older property's firstly read the rising damp myth on the net, then find some one who specalises in older propetys and understands how the materials used in there construction help to stop dampness and keep them water tight

Good Morning. As this was done by a cowboy builder it is extremely hard to tell what they have done and what damages have been caused to the wall. The issues you are experiencing sound like a non-porous cement render was used on your building. This would lead to moisture being unable to leave the wall. Also if the render was done badly cracks can appear which would allow further water ingress over time. Unfortunately, there isn't an easy answer as there are too many unknowns. Ideally, get a repeatable builder to survey the affected area and repair the wall.

No easy, quick fix solution so I would knock all outside render off and whatever affected plaster inside to investigate. Damp may only rise 1.5m or 2m in extreme cases. Also check there is a clear run off for any water around the building.

Could be a possibility that the damp isn’t rising and coming down the walls due to water ingress from guttering or no adequate ventilation or cavity trays insufficient weep holes a number of possibilities to rule out however making assessments of all possible problems and then making judgement where problems could arise or can be resolved