CMU Foundation Walls
CMU Foundation Walls
(OP)
I have a slab on grade building with masonry foundation walls bearing on concrete footing. The masonry walls have #4 dowels at 48" o.c.. The masonry walls will be below grade 36" for frost protection and not subject to lateral forces. The rebar is in there to just tie the masonry to the concrete footing.
My question is: Do the masonry walls have to be grouted solid or is it ok to only fill the cores that have the rebar?
My question is: Do the masonry walls have to be grouted solid or is it ok to only fill the cores that have the rebar?






RE: CMU Foundation Walls
RE: CMU Foundation Walls
There is no structural reason, but it is a good place to dump the excess if you used grout and not concrete.
If you are really worried about uplift it is a plus, but with verticals at 48" you still have the footing and associated loads.
RE: CMU Foundation Walls
RE: CMU Foundation Walls
RE: CMU Foundation Walls
RE: CMU Foundation Walls
RE: CMU Foundation Walls
For controlled, specified grouting, smart engineers will use blocks with cores that align to facilitate proper, complete filling with 8" - 11" slump grout. Normal three core or two core block (even with flush ends) do not align well enough. Engineers/inspectors make a big deal out of mortar projections into the core space when grouting, but permit units that cause the same or worse situations. Conventional 2 core block with open ends (half cores) will leak leak grout, creating a semi-solid pyramid around the rebar if it ends up having good bond. In any case the rare problem of water accululation still existes. If concrete is used instesd of grout, you are just permitting a location to dump unconsolidated left over concrete.
You can do it, but it is not professional or correct.
In 40 years I have not seen too many problems (except for remodeling/alterations) and later utility access.
Forgive the tiraid, but I have seen too many good uses of masonry internationally and hate to see U.S. engineers habitually misuse it.
Dick
RE: CMU Foundation Walls
RE: CMU Foundation Walls
RE: CMU Foundation Walls
RE: CMU Foundation Walls
Also I think type S (maybe M) mortar should be used when CMU is below grade. I'm at the house can't remember which.
I'm not sure but in Florida it might be code that CMU must be solidly grouted.
RE: CMU Foundation Walls
An additional consideration is that sometimes CMU walls have to be grouted solid full height for fire separation resons, i.e., too close to another building, an interior fire wall, etc.
Mike McCann
MMC Engineering
RE: CMU Foundation Walls
You say the walls extend 36' below grade for frost protection?? I am not sure I understand how this helps you. Can you elaborate on the logic behind this? I guess we don't have to worry about this in the South.
RE: CMU Foundation Walls
It has nothing to do with whether the walls are brick block or concrete.
From a practical point, once a building is constructed and becomes part of a "heat island" frost to the design is quite rare unless this is a north wall with less sun exposure.
there are other ways to minimize the possibility of frost heaves, but they often rely on keeping the moisture in the soil below at a low point, which is always a challenge,
RE: CMU Foundation Walls
It seems the general consensus is to fill the cmu walls below grade solid regardless is there is rebar or not. Can anyone tell me if this is a code requirement. If so, what code and where is it.
RE: CMU Foundation Walls
It is not a code requirement. Many 20 story loadbearing high rise masonry structures are built using partially grouted walls. Many codes (IBC, IRC, etc.) permit the use of hollow CMU construction, since there are cases where it is preferred. - It is just a "if does not work use a bigger hammer" or belt and supenders easy approach without looking further.
If the cores are filled, it should be required and filled according to code specification, not just dumping concrete since there are different specifications for grout and concrete.
A good deceased engineer friend and author always said "Do not count on what your are not sure about, able to observe or specify" - He said this in regard to his books on CMU structural seismic design and general masonry construction, but also applies to engineers attempting to do additions and modifications. We ran into this both above grade and below grade after the Northridge quake.
If the CMUs are filled as an afterthought or plan omissions, there should be a revision to the drawings or as-builts. Nothing is worse than an owner not having proper drawings and contracting with someone (GC, utility contractor, etc.) for revisions and run into sloppy drawings that do not reflect what was built.
RE: CMU Foundation Walls
Don Phillips
http://worthingtonengineering.com