Question: What Can I Do About Congestion?
What can I do about congestion? The short answer is take an anti-histamine and call your doctor. Oh, not that type of congestion! That’s a sinus problem and all in your head anyway!
Congestion in a concrete masonry unit (CMU) wall creates frustration and aggravation for the mason. This leads to lower productivity and the possibility of mistakes by actions or omissions. Add it all together and you have created the potential for a less than expected quality product.
“Congested” is defined as something being too full or overcrowded. There are several ways that CMU wall can suffer from congestion. The main contributors to the clutter in the CMU wall are the mechanical, electrical, and plumbing trades. Masonry is the only one of the three major wall types that is expected to accommodate their “stuff” as we build the wall. Wood and stud walls are built and then the MEP folks do their rough install. On the other hand, we (masonry) are expected to install piping, boxes, conduit, holes for duct work, etc. the accumulation of these things created congestion.
One of the worst I ever saw was a section of an 8” CMU wall over 48” long with two rows of ¾” conduits side by side. There was no room for a web of the CMU. The wall was going to contain the electrical panels. The thing that was funny to everyone, except the Architect, was the fact that the wall was supposed to be a two hour fire assembly! To add to the misery, was a 4” x 4” electrical outlet in each side of the wall. So there was no way this wall was going to be a two-hour single wythe wall. It eventually became a double wythe wall.
Another point of congestion is the first masonry cell adjacent to a door. This is a typical location for a light switch. The cell could have a rebar lap, a switch box, joint reinforcing and a door anchor, all gathered in the same area.
The 90 degree corner of the top of a CMU wall can also get congested within the bond beam. If the structural design has a vertical rebar in the corner and two adjacent cells, it could almost be solid rebar in the bond beam. You could have two bars in each direction along with two corner bars lapping the bars in the bond beam. When you add hook bars for the vertical bars, you could have five and maybe six bars at the top of the vertical cell. If you are using a shallow (2 ¾”) depth bond beam block, you are unable to stack the laps. What can you do? Do your homework and “Just Say No!”
One of the main considerations of reinforced masonry is solidity of the grout. Solidly grouted spaces are always our goal. There are a couple of places in TMS 402/602 that you can get some help. In TMS 402-16 Chapter 6 is a chapter you should get to know intimately. Section 6.1 gives you the maximum amount of rebar in bond beams and vertical cells. The vertical cell reinforcement is maxed out at 6% of the area of the grout space. Chapter 3 Section 3.2 addresses conduits, pipes, and sleeves built into the wall.
Remember that the engineers design the reinforcing and a supplier’s detailer locates the laps. The MEP engineer locates their built-ins for the benefit of those trades. NO ONE considers the mason. Be a forward thinker. Check the rebar shop drawings and MEP shop drawings for your own benefit. No one else will. Most of the time I am of the opinion that the structural engineer and MEP engineer have not been introduced to each other. Use the structural engineer to your benefit. Write a Request for Information (RFI) regarding clarifications or changes. Always “Get It In Writing!” When “anything” besides grout and reinforcing is n a reinforced cell, get the engineer to have it removed or do away with the reinforced cell. If he allows the impediment to remain, he must not need it anyway.
Two other ways to insure solidity of the grout is to use a “fine” grout, which is allowed by code, and vibration/consolidation, which is required by code. Just remember, any time congestion appears to be a problem, use the code and project engineer to your advantage. And, “Get It In Writing!” Otherwise, take two pills and call me in the morning!
Till next month, “Raise the line and come on around the corner!”