How to investigate for damp behind dry lining?

My house is single leaf cavity block which was dry lined.
I want to get it externally insulated for obvious reasons.
At the same time I have concerns about there being possible damp behind the dry lining. At the time of survey the surveyor said there was minimal insulation behind the dry lining - so cold walls meeting warm rooms - surely a recipe for mould.

Without ripping the plaster off the walls is there any way to test for this - any company that provides such a service that doesn't cost the earth? (like externally insulating is costing us!!)
Once the walls are externally insulated presumably the concrete will dry out and any mould will die away anyhow and with it any health concerns, or is that incorrect to assume?
We have a baby on the way and i want to get the house "healthy" before they come into the world. Thanks.

RiceCakes said:

1. Without ripping the plaster off the walls is there any way to test for this - any company that provides such a service that doesn't cost the earth? (like externally insulating is costing us!!)
2. Once the walls are externally insulated presumably the concrete will dry out and any mould will die away anyhow and with it any health concerns, or is that incorrect to assume?
3. We have a baby on the way and i want to get the house "healthy" before they come into the world. Thanks.

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1. I would suggest you take away a piece of skirting and cut a hole in the dry-lining and take a look/cope a feel. pick a number of places where perhaps there is moisture in the air normally, also behind a wardrobe, under the bath etc (areas that are easily patched up or covered over) not ideal but the next alternative is to get in someone with a borescope and pretty much do the same thing only making smaller holes.
2. not necessarily mould spores last a long time, if there is a problem I would be inclined to get to both the cause and remove the symptoms of it. it could be as you've suggested mould caused by cold surfaces, but it could also be a lack of proper ventilation or even a hidden leak/damp hidden by the Dry-lining.
3. a health house is well worth attaining, the natural_house_book is a good starting place. think natural paint, natural insulation, fewer plastics/adhesives/synthetic materials(VOC's), dump the microwave, many plasterboards contain formaldehyde, if the house is old - asbestos, good ventilation, , maintenance of heating system and NOx, Radon, RH & fire sensors etc... I don't mean scaremonger

Some damp meter put a radio frequency into the wall and so check inside the wall for damp rather than the surface, I used to have one. Contact one of the specialist companies and see if they have one of these meters, and do a survey.

If you have mould growth then it needs to be removed first. Installing external insulation can be expensive, and although it will make your house warmer and airtight, the existing mould growth still needs to be removed.
I would look at repairing the internal dry lining first, especially where you are having mould problems. Mould killer needs to be applied to the infected areas behind the plasterboard. Sufficient insulation, vapour barrier, plasterboard and final skim should then be fitted.

You also need to confirm if there is a DPM (Damp Proof Membrane) in the blockwork. This is normally 6 inches above finished floor level. This prevents rising damp.

Dampness where cold and warm surfaces meet is a seperate issue. When you say the wall is drylined on the inside. What is it dry lined with? When was it done? When was the house built and what sqm footage is it? Is it a rear extension issue only?

Is there an alternative to add an additional external leaf with cavity insulation? Would this be cheaper than the external insulation option.

Protim et al or an engineer would check using a damp meter. Are there any signs of dampness? and in what locations (ie. bathrooms etc) and where on the walls is the dampness ( floor level, ceiling level etc)