Best methods of Damp Proofing a building depending on construction

Published: 25th May 2010
Views: N/A

Damp proofing of both domestic and commercial structures, although not the most glamorous aspect of a construction project, is still a vital part of the build process to get right.  New build properties will, unless there has been a negligent moment by a contractor or architect, will have a physical isolation membrane around 150mm above external ground level ( a damp proof course or dpc). This acts to prevent capillary movement of moisture rising higher than the barrier and effectively damp proofs the property above this barrier.  So if the building has no earth bridging above the dpc and no leaking pipes, gutters or flashing, then you should have no problems in terms of damp proofing. It's all relatively straight forward.
Physical membranes as a vertical separation layer or dpc construction has been a standard in all brick and blockwork construction for well over 50 years.  Older properties or properties built out of stone or rubble have significant challenges when it comes to damp proofing and there are limitations in terms of what can be achieved when looking at insertion of a dpc. 
Let's first look at how we can damp proof a stone or random rubble wall property.   This form of construction will not have a dpc so one possibility is to have a chemical dpc inserted into the build to isolate the internal property from the affects of rising dampness.   This insertion into stone or non uniform walls is extremely difficult to apply and even more difficult to guarantee that you're getting it right.  For these kind of chemical products to be effective damp proofing, they need to form a uniform layer of cream or liquid which will stop the passage of water vapour moving into the wall above.  There are companies out there that will "guarantee" a chemical dpc in a stone or random wall construction but be wary! I would be asking the question "How can you test that the system installed is going to work?"  It just isn't possible! The principle of putting in a membrane is still the best way forward.   The advantages of using a physical membrane such as the Newlath 2000 type dimpled sheet product which you can mechanically fix to the damp stone and then apply a finish over like render or plaster is a fail safe way of dealing with dampness no matter where it is coming from.  These sheet dimpled membranes create an air gap and allow the walls to "dry out" over time which they will do if there is a heating system in the property.  Any staining from salts which will be coming out of the structure will be isolated as well and will not be able to affect internal finishes.  There really is no comparison with these products in stone structures. The membrane requires no surface preparation so if the building is listed it is "reversible". Therefore you will have no problems there and it just takes all the guess work out of the damp proofing process.
When you're dealing with brick built properties a chemical dpc is more likely to work in the way it was designed to.  As you have a mortar bed in a uniform formation the cream products or liquids can form a barrier across the mortar bed just like a physical dpc and stop the capillary movement of water "wicking" up the walls damaging internal finishes.  This form of damp proofing still has its challenges. Once you have drilled and injected the cream a re-rendering process needs to occur with a salt retardant additive to stop any salts coming through the render and damaging finishes.  This can cause problems by moving salts and contaminants higher than the level of the treated damp proofing .   Once again the simplicity of the mechanically fixed dimpled membrane covers all bases here.  Once the membrane is installed the contractor can even dot and dab and skim on top, which means no lengthy drying out times so you can get in and decorate within a couple of days.  The other approach can take weeks and weeks.  
To conclude, the main benefit of having damp proof membranes that are physically applied is that they deal with all aspects of damp in structures by creating an air gap separating the internal finish from the damp wall.  This separation does of course cover up the damp wall but the membrane is only 3mm or 5mm thick so it can still give the contoured effect of a wall.  Injection is an alternative when dealing with brick/block but not with random rubble or stone walls. So with the options laid out above it's a matter of personal preference which is going to suit your purposes the best. 

Report this article Ask About This Article

More to Explore