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A Look At Bad Joint Practices

On our travels around the world, inspecting construction jobsite after construction jobsite, we have repeatedly found two major problems in existing concrete decks. The first and more destructive problem is the lack of an adequate number of expansion/control joints in concrete slabs. The second, and only marginally less important problem, is the lack of an adequate number of strategically placed deck drains. In some cases, it’s the combination of both that creates the hazardous and costly conditions that property owners are confronted with time and time again.

Since our business growth and development has been based in large part upon the repair and resurfacing of these failed concrete surfaces, we have become acutely aware of such defects that are designed and built into concrete decks. We bring a special insight to the projects, because of our unique experience. What seems so obvious and simple to us, is quite often overlooked by others. It’s possible that the professionals who design, engineer, specify, or pour concrete slabs aren’t directly involved in the retrofit business to the extent that we are. Things that practically jump up and bite us, are simply invisible to many professionals. The way we see it, expansion/control joints and deck drains are critical to the long term success of any project.

Although many concrete contractors can quote chapter and verse on the quality of the concrete pour, tensile strength, reinforcing admix formula, etc., they seem oblivious to the importance of control joints and deck drains. If queried about it, the usual answers are, "that’s the way we’ve always done it", "that’s what the spec’s called for", or "I’m just following orders". Not surprisingly, our response is, maybe that’s why the concrete always cracks!

I recall attending a seminar many years ago, where the speaker explained why his company could guarantee the concrete they poured to be crack free for ten years. His solution to this long standing dilemma was to put expansion joints every 10 feet in both directions. They made the joints at least 1 inch wide and a minimum of 1 inch deep. He explained that his method created a series of floating concrete panels that allowed for extensive movement of the concrete as it expanded and contracted with temperature changes, settling, and ground movement. If cracks developed, they would be in the joint, not the slab.

We were exhilarated, instantly recognizing the simplicity of his solution, while understanding the effectiveness of the concept. It was our kind of solution, simple, straightforward, direct and reasonable; something that anybody could understand. We immediately incorporated the information into our company’s construction specifications. It works wherever it is utilized.

We believe that diagonal joints should be built in at major stress points, as well. These stress points usually take place at the corners of buildings, walls, planters, or pillars where the vertical and horizontal surfaces meet. If diagonal control joints are put in when the concrete is poured, the stress will be relieved. If any cracks develop, they will be in the diagonal joint. They will not develop into unsightly, dangerous moving cracks that radiate out from the corners of the deck.

Adding to the joint problem is the almost equally destructive problem of a lack of deck drains. If there are no drains where is the water supposed to go? Merely sloping the original pour 1/8 inch or 1/4 inch isn’t enough. As the surface cures and settles, low spots develop. The low spots allow water to pond, sometimes for months at a time, all the while promoting the growth of algae or fungus. Not to mention that people will be tracking the dirt and gunk from the puddles inside, as they walk through them. If the project is subject to health department jurisdiction there may be added problems to overcome.

When you think about it logically, the construction sequence is reversed with regard to the placement of the deck drains. How can anyone predict in advance where the water will settle. Therefore, unless the concrete is sloped dramatically to the drains, it’s inevitable. The water will stand where it’s not supposed to stand. The slab should be designed with numerous, properly placed, deck drains. They shouldn’t be placed exclusively along the outer or inner edge of the concrete, but scattered systematically throughout the entire area.

Furthermore, the drains must be installed below the level of the deck. The grates used on top of the drains need to be installed lower than the concrete as well. The grates are meant to prevent debris from clogging the drain. Water runoff is supposed to flow to a predetermined location, presumably a drain. But, how can it, if the water can't even reach the drain?

We recently walked a 12,000 sq. ft. rooftop deck over subterranean parking that had five deck drains. Not one drain was anywhere near the spots where the puddles formed. This particular project, a major ski resort, was located in Colorado. In this case, ponding water was freezing on the deck. The ice that formed on the deck created a very serious safety hazard. Yet, the maintenance engineer never considered the lack of deck drains as a contributing factor. Naturally, our specifications included the installation of additional deck drains. For this project, we recommended the installation of channel drains, since there weren’t enough expansion joints either.

We prefer channel drains because they fulfill two necessary functions. They act as a drainage system as well as an expansion joint system. However, for some renovation projects, channel drains may not be financially feasible. In new construction, it is much easier and far less expensive to install such a system.

It is a well known fact of life that people naturally resist change; fearing the unknown keeps people stuck with the same old habits year after year. It is also a well know fact that technology is advancing rapidly. How do we reconcile the two? In the construction industry it is a very slow difficult process. Education however, is the first step in changing the status quo!


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