Masonry Below & At Grade
Masonry Below & At Grade
(OP)
I review Structural Drawings for a design/construction firm. Architects & Structural Engineers, often detail CMU/Brick being used below grade, without being waterproofed.(not talking about basements) This is especially disturbing when CMU stem walls are supported on spread footings extending to finish floor grade, when reinforced concrete would seem a better choice. The Brick Industry Association in their Technical Notes 28B – Brick Veneer does state, “If the soil immediately adjacent to the brickwork is not free-draining the brick wythe exterior should be waterproofed below grade.” However; I have found nothing in the National Concrete Masonry TEKs concerning this and their details use CMU extensively below grade without waterproofing. To me this does not seem to be good engineering practice and I would like to see waterproofing masonry below grade be addressed better by the Masonry Societies, due to the Environmental problems of algae, mildew, mold, staining, and efflorescence.
Another problem I do not see addressed is CMU Walls being placed at Floor Grade without Masonry/Brick Ledges.
This joint often becomes unbonded from the foundation, losing the shear strength, and creating a crack which often causes water penetration in blowing rains. Therefore, masonry/brick ledge should be installed, which is more accepted for brick than CMU.
Please provide your recommendations and thought on these two subjects, as I often feel I am the only one concerned about these two problems. Known Code or Technical references would be helpful. I posted a similar Thread and received no replies.
Another problem I do not see addressed is CMU Walls being placed at Floor Grade without Masonry/Brick Ledges.
This joint often becomes unbonded from the foundation, losing the shear strength, and creating a crack which often causes water penetration in blowing rains. Therefore, masonry/brick ledge should be installed, which is more accepted for brick than CMU.
Please provide your recommendations and thought on these two subjects, as I often feel I am the only one concerned about these two problems. Known Code or Technical references would be helpful. I posted a similar Thread and received no replies.






RE: Masonry Below & At Grade
As for the second problem, I only see this being a problem if the CMU is the exterior cladding. The joint between the bottom CMU and the slab on grade would have the potential to leak. If their is a brick veneer in front of the CMU, I don't see how blowing rain can be a problem to the CMU. The brick would stop it. Although, if the brick veneer doesn't drain properly, water could collect between the two wythes and potentially seep under the CMU.
RE: Masonry Below & At Grade
RE: Masonry Below & At Grade
Usually the details I am referring to the below grade reinforced CMU Stem Wall extends up to grade and the exterior CMU wall extends from there (often single wythe) which I tried to cover in my last post. Therefore, I am concerned with the wicking you noted & environmental problems noted in Thread. It seems architects also like to extend masonry(brick & CMU) below grade as they do not want the foundation exposed.
Yes, CMU is the exterior clading mostly single wythe. I have personally investigated carpet getting wet and tile becoming unbonded from the floor due to leaks at perimeter walls caused by blowing or rain wetting the walls where the joint between the reinforced concrete foundation and first course of CMU had become unbonded, which often does occur. Has anyone else experienced this?
It is my further opinion that Single Wythe CMU walls should only be used in austere facilities like pump houses, warehouses etc. where no interior finises are provided as they are prone to leak as there is no way to effectively flash them.
RE: Masonry Below & At Grade
RE: Masonry Below & At Grade
RE: Masonry Below & At Grade
Just like concrete isn't waterproof, a CMU wall, even fully grouted, isn't waterproof. The architect should specify a waterproofing on the outside of the wall. Don't stick you head in the sand if he doesn't show it. Tell him he needs it.
Also, check the IBC for the exact requirements, but in the CMU empirical design section, you aren't required to grout solid if the wall height is less than something like 5'. As almost all basement walls are higher than 5', they need to be grouted.
RE: Masonry Below & At Grade
RE: Masonry Below & At Grade
RE: Masonry Below & At Grade