Sealing Split Faced Concrete Block does not solve the problem, but this does.
By William Decker, CMI. Decker Inspection Services
Since the mid 1990s, especially during the building boom of the early to mid 2000’s, there were many new construction buildings in the Chicago area made with a material called split faced concrete block. Some of these buildings are condominiums and apartments, but there are also single family houses and mixed use properties. Most are now experiencing problems, expensive repair bills and a reluctance by the public to purchase condominiums or houses made with this material. The common misconception is that this problem can be fixed by just sealing the exterior block of the building, but now these homeowners are finding out, the hard way, that this is not a permanent solution. Now there is a program, the “Split Block Certified” program, which brings together architects, contractors, inspectors, banks and insurance companies so as to provide clear and obtainable solution. It is our hope that this article will help to inform the public on how to deal with this growing problem.
Problems and Causes:
The symptoms that people notice with these type of buildings; water damage, buckling hardwood floors, musty smells, mold growth and in extreme cases, structural collapse of roof and floors, are just that, symptoms.
The real problem, the root cause of these symptoms, is very simple. You simply do not build a single wythe masonry building in wet and cold areas as we have here in the Chicago / Milwaukee area.
Masonry walls are, usually, not one wall but a series of walls, with each layer called a wythe. In newer construction, typically, a masonry wall is built with an interior wythe of concrete block (CMU – concrete masonry unit, commonly known as a “cinder block”) and an outer wythe which can be brick, stone or some other type of decorative masonry. The inner wythe provides structural support, actually holding the building up, while the outer wythe provides the pleasing appearance.
Most of the classic, 1910-1920 Chicago brick buildings that I have evaluated actually have 3 or 4 wythes of brick with two or three of the inner wythes being structural. These different wythes are tied together; in the older buildings with brick bull headers and in the newer buildings with metal straps. These ties not only hold the wall assembly together but also serve to maintain the air gap, sometime referred to as wall cavity, between the different masonry wythes. It is the existence of this wall cavity that is important to our current problem.
Obviously, building a single wythe masonry wall takes less time and is less expensive than building a double or triple wythe wall. Each wythe requires more time and material and money to build. This brings us to the problem with these buildings with water problems. They were built with only one wythe, usually 8″ thick concrete block with either a rough split face or a smooth face which we know as cinder block. There is no air gap in the wall. This means that water can easily migrate directly through the wall because all masonry is porous.
To deal with this situation, many people (including many masonry companies) have come up with the “solution” – sealing the block. They apply either a penetrating type sealer or coat the block with a rubberized, “plugger” type paint believing that this will keep water from entering the block and therefore, from going through the wall. While having the block sealed is better than nothing, sealing creates its own problems:
- The cost to properly “seal” a typical 3 story, duplex down condominium building in the Chicago area, with the work being done by licensed and insured, professional contractors and according to the sealer manufacturer’s instructions, will run between $16,000 and $19,000. Much of this cost is the expense of putting up and taking down the required scaffolding. It is a simple fact that professional, licensed and qualified contractors cost more money. Avoid purchasing a cheap, $4,000 special job done by some guy in a white panel van that you will never see again. This winds up costing more in the long run anyway.
- Penetrating sealers usually last between 3 and 5 years, but only if properly and professionally applied. Elastomeric “plugger” type paints last about 10 – 15 years. So, you are talking about spending about $17,000 every few years for maintenance. Recently, a large Chicago area sealing contractor went bankrupt because they were advertising 20 year warranty sealing and the buildings that he treated started to leak again after 3 – 4 years.
- Years of research have show that only 8 – 12% of the water enters through the walls. So, even if the product application is done correctly, sealing the block only stops 8 – 12% of the water intrusion. Is that enough to allow the building to dry faster than it gets wet? Will the sealer wind up sealing old water inside the block as well as keeping new water out? What if you spend a large sum sealing the block and you still get water coming in. What are the most cost effective fixes?
So, what is the solution? How do we repair these buildings so that they don’t require expensive repairs every few years? The answer is fairly easy. Let’s do some fairly minor modifications to the wall and convert the single wythe wall into a double wythe one. To do this, we must first look at how the wall was constructed.
As you can see from the picture on the left, CMU blocks have inner cells. These cells were added to lower the cost and weight of the block, and can be used for reinforcing steel bars to add strength to the walls, but they also wind up holding water trapped in the wall. The diagram (below) shows that while some water does enter through the exterior of the wall, most of the intrusion is through the unflashed parapet wall coping, So seal the exterior of the block and flash over the parapet and all is fixed, right?
What if we used these block cells as an air cavity, just like we see in a double wythe wall?
If the parapet wall coping is flashed, and ventilated, this will allow the air within the block cells to “breath” and promote evaporation and convection of the air cavity. If weep vents are added at the through-wall joist pocket flashing, this air flow is better and allows air drying of the block cells.
By ventilating the block cells, we have effectively converted a single wythe wall into a double wythe wall with an air cavity. Because the exterior web of the block has free flowing “outside” air on both sides, it dries naturally. Because the air on both sides of the outer web has the same temperature, humidity and vapor pressure, there are very little hydro- or thermo-dynamic forces acting on the masonry. At this point, it makes no difference if the exterior of the block is sealed or not. Furthermore, there is no moisture accumulation on the inner web of the block and therefore no water intrusion into the interior of the building.
The first step is to hire a professional, licensed and qualified building inspector, preferably one who is also experienced with thermal imaging and building science. The inspector can completely evaluate the property and recommend the necessary fixes. Our firm prepares reports listing the needed repairs in cost / benefit order. There are masonry and flashing contractors out there who now specialize in these type of repairs, in fact one (Wick Right) has been at the forefront of this problem for years, but each building is different and must be evaluated in its own right. Not all contractors, even experienced masons, can properly do these repairs. With newer construction comes newer materials but these materials are not always the best choices. Professional home inspectors can bridge this gap between the tradesman and the home buyer, many times also informing the Architect and General Contractor.