More info for London damp proofing
All properties built within the last 50 years, at least in the UK, should have an actual barrier inserted in to the brick/block just work at 150mm above external ground levels. They are commonly called a damp proof course (dpc). This kind of London damp proofing membrane inserted in to the mortar course is a very effective barrier to cope with dampness from the floor moving up through capillary action to manifest internally within your property. So first it is essential to establish whether you have one.
It may not be an actual barrier because there are also chemical damp proof membranes which are used on properties which weren't built with an actual dpc or have already been retrofitted to the structure if the first was defective. Evidence of this can be seen in small holes that have been drilled in to the mortar course and later filled in, 150mm above ground level. This may have been done to cope with damp. These types of damp proof membranes are now utilising better technology from which used two decades previously. Take note these kind of products will still need skilled application and will need re-rendering as much as 1m internally with a salt retardant additive. The rendering process will require time and is likely to be introducing wet trades so you'll struggle to redecorate quickly - maybe as much as 6 weeks afterward. It is important to note that if your property does not have a uniform mortar course than the applying of a chemical damp proof membrane is likely to be extremely difficult. Be skeptical when someone offers you this damp proof membrane option.
Paint applied damp proof membranes will also be an option. This is not merely a matter of slapping a little black bitumen paint on the wall and hoping for the best. There are plenty of "miracle" cure, paint-on options. Surprisingly enough these may actually cause more problems than have there been in the beginning. Preparation may be the absolute key when applying this sort of product and would be the difference inside it working, not working or rendering it worse. So be very clear to have this right and understand the amount of time required to have the prep right. The most common problem with this sort of application may be the product. If it does cope with damp, it can develop a barrier and either move damp to where you haven't treated or push damp higher up the wall. The products will also not be very sympathetic to listed buildings and you might not have the ability to ever buy them off!
Look at cavity membrane systems as well as a damp proof membrane solution. The products are dimpled sheets which is often applied mechanically with special fixings internally or externally (stopping penetrating damp through poor pointing) and applying either an immediate plaster to the mesh on the membrane or dot and dab plasterboard to the product. The latter is popular now as once the damp proof membrane is applied to the wall you will not be looking forward to blow drying times and you are able to fix the membrane over stable existing plasterwork. There are choices with these kind of damp proof membranes from 3mm to 8mm comprehensive and are constructed with hdpp or hdpe. Your choices there are varied in order to marry these up with exiting plasterwork or if you prefer you are able to run them up the walls. These could also add thermal qualities to your wall. The air gap created behind allows for the walls to breath or dry and forms an actual barrier so internal finishes aren't contaminated with damp.
If you are in any doubt about which damp proof membrane is right for your project consult an established and reputable supplier or installation specialist. Always look for case studies and testimonials to verify quality. It never hurts!
