Damp returning in house which had rising damp injection and specialist plastering done

You do not say how old the property is and if it is solid wall construction, Hi Andrew, injected damp proof courses do not work in this type of property, 99% chance it is not rising damp in which case the damp proof course installed will be making the problem worse. Without looking at the house it is not really possible to be 100% sure of the exact cause, but is more than likely either penetrating damp or from above. This type of property will have been built using lime mortar this allows your walls to breathe, if the walls have been repointed using any type of cement based pointing this will not allow your walls to breathe and will hold in water causing dampness, as will rendering, there is no cement or additives in lime mortar, you have to find the source of the water ingress before you can cure your issues, could be a faulty gutter, gutter felt, splayed brickwork, bad pointing, broken roof tiles, etc Most modern damp proofing methods seal the water in the walls, rather than find and stop the water ingress. Older building materials and new building materials do not work together very well, most older buildings are built with materials that today's tradesmen do not understand either how they work or how to apply them. Although these materials are still available from specialist suppliers, they cost a lot more than modern materials. Finding someone capable of using them might be harder to find, you really want someone who specializes in older properties and how the materials used work. Drilling your brickwork from the outside and applying another injection course is a total waste of time. Rising damp is diagnosed wrongly in approx 70% of cases Good luck Alex

I would check the flooring should be wood. Not Concrete air vent clean or replace as required this should solve the problem

Cement based rendering and silicon injection remedies do not work on older buildings ,rendering in cement just pushes water up the walls to a height of around a meter.So you'll get some sort of guarantee from the builder who'll be happy to render your walls,but this just covers up the problem. Use Lime on Old Buildings and avoid cement based remedies ,they'll fail every time.