If our damp problem is identified as condensation, what would be the best method of removing the black spots?
The first thing is to cure the condensation by reducing internal humidity.
Ventilation, avoiding drying washing on radiators or indoor clothes lines, using an extract fan when showering or bathing will all help.
The black spots are collections of fungal spores. Wiping with an household surface cleaner may erase the black spots but will not eradicate the spores.
Use a proprietary spray such as ‘Polycell Mould Killer’. If you need to redecorate choose a paint containing a fungicide>
Our garage and kitchen extension were built up to the boundary with our neighbour who has now built a raised concrete patio which has buried the damp proof course of our garage and extension.
I have always understood that damp proof courses should not be covered, but my neighbour says covering damp proof courses with concrete is acceptable because concrete is waterproof.
I am not convinced and should be grateful for your advice.
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You are correct. Concrete is not waterproof; if it were, one would not need to incorporate a damp proof membrane in solid floors.
Covering a damp proof course creates a bridge for both rising and lateral damp.
My house, built around 1870 had a damp proof course installed about 50 years ago but now we have damp along the side wall.
Do you have any suggestions?
50 years ago the damp proof course was probably a ‘pressure injection’ type.
The chemical compound then used slowly becomes diluted by the moisture it is repelling. I suspect that you need a new damp proof course.
Modern nano particle technology has created damp proofing creams that are injected into holes drilled into the mortar surrounding the bricks using a simple hand held cartridge dispenser.
It is an easy job and does not require specialist skill or equipment.