Learn how damp proof courses stop moisture in its tracks!
In masonry construction, damp proof courses (also commonly referred to as DPC’s) are added to prevent rising damp from continuing above or significantly above the building footing and foundation. Ground water at or near a building footing will permeate into the building footing when left or built unprotected. Modern foundations are required to have damp proofing or waterproofing systems built around the footing and / or foundation, but this was not the case in the decades of the construction of the majority of the historic buildings in Washington, DC.
This type of installation is commonly found, even in historic masonry. Brick masonry buildings constructed over a 100 years ago will often include damp proof courses made by historic means. At the time of the original construction modern low permeability roll type flexible materials were not available but builders of the time understood the principles and threat that rising damp poses on brick masonry construction.
By stopping or limiting rising damp, through the use of a damp proof course, interior portions of the building are protected. Through capillary action, water has the natural tendency to wick upwards through permeable or semi permeable materials. Historic brick masonry appears largely impermeable; however it is actually semi-permeable and in saturated subgrade conditions, susceptible to the ingress of moisture, also known as hydrostatic pressure.
The image below shows an example of a historic brick building with a Del Carmen slate tile laid into a brick wall at approximately five courses above the adjacent the adjacent grade.
In this case, the damp roof course is positioned at least five courses above the adjacent grade. That positioning is strategic and intentional. If, for example, as an alternative, the damp roof course was installed adjacent or in closer proximity to the adjacent paving, the wall would also be susceptible to hydration through splash back in typical precipitation cycles. The article at the following link takes a closer look at deterioration of brick masonry mortar joints, related to splash back conditions.
The following picture below shows in another example of a mortar joint area with a Del Carmen slate used as a damp proof course.
In historic times, the flexible impermeable flashings used today were not yet invented and therefore not available. Historic builders were still aware of the conditions and problems associated with rising damp, in historic brick masonry walls. In this case, it was understood that slate had low permeability and this type of applicaction was one of the best ways to deter the proliferation, propagation, or spread of moisture.
The picture below shows another example of a close up view of a historic brick mortar joint. The original mortar is deteriorated at the face of the brick facade. In this example, this building is over 100 years old, and in need of proper pointing. You can see an example in the left side of the picture below where the damp proof course is still hidden from view, at that area, pointing has been applied to the wall, but this application was just scam pointing and not true historic masonry restoration tuckpointing or repointing. Our company, Infinity Design Solutions, recommends against this type of improper pointing because it does not address or repair the actual cause deterioration or susceptibility. In many cases scam pointing can significantly accelerate deterioration and actualy worsened the condition of a brick facade. Instead of improving conditions, scam pointing can actually exacerbate the problems associated with natural existing deterioration.
Signs of rising damp can often be identified through visual observation of deterioration in the form of efflorescence and through instrumentation such as moisture meters.
The article at the following link discusses some of the top risks and threats to historic brick masonry, click the following link. In this article we talked about the top threats and potential sources of deterioration and damage to historic brick building facades.
