My house had a chemical DPC 25 years ago. It has solid walls and built 200yrs ago. On some sections of the interior walls a damp meter reading shows red at skirting level and up to 1ft in some places and 1 metre in others. About 6 months ago we dug out the soil to about 6inches below DPC holes as this was bridged and also a few small areas below skirting were bridged so we hacked this plaster off. The walls are still reading red and I wondered how long the walls take to dry out and read green? or do they never dry out and read green unless I re do the plaster as you have said in other replies with the salt retardent/sand and cement mix? Also the fact it was bridged, has this broken down the chemical DPC? or will it start working again now that I have un bridged these areas,or will it need injected again? Note the rest of the room is still working and showing green on meter reading.