deteriorated CMU wall options

[SLTA]

Earlier today, I was investigating a crack in a CMU basement wall from approx 1920 or so. The wall is retaining and has been in direct contact with soil for its life. There was no appearance of waterproofing, but no real way to tell. I looked hard at the CMU because it just looked weird, then took my awl and poked it. The CMU was complete mush. Turns out I was able to pry off the entire face on one block, and the entire back wall and retaining part of the side wall is soft like that. The poor realtor looked shocked as I just started laughing - CMU isn't supposed to do that!

So, to the question. Is there any possible way to repair mushy CMU? The current plan is to recommend replacement of the two damaged walls, including appropriate waterproofing details. This is a residential garage with a small apartment above it, in a posh part of town, so repair is worth it. I thought about recommending that a new wall be built just inside the existing walls, with separation to keep from deterioration, and to take the load from the small apartment above, but that would remove a lot of the interior space. Any thoughts?

I've attached a picture of my awl, deep in the CMU...

 

[concretemasonry]

I would provide support for the vertical loads and remove the existing wall and built a replacement wall in the same area to preserve the original support for the structure.

This would require some scheduling and if excavation of a portion of the soil retained is required, a properly installed drain tile systems could be installed to decrease the actual soil loading in the future.

Dick



Engineer and international traveler interested in construction techniques, problems and proper design.

 

[MiketheEngineer]

No choice - replace it

 

[bgatto]

I agree with concretemasonry or else I would use something like this:

 

[csd72]

Looks to me like they may have used cinder block rather than CMU. Agree that the only proper repair is replacement though standard methods may not be appropriate due to the already compromised state of the wall.

 

[bridgebuster]

I agree it definitely looks like cinder block. All the houses in my old neighborhood were built with them.

Can you cut slots in the wall and build columns/pilasters, then underpin the apartment and waterproof the wall? Roofing tar works very well as a waterproofing system on those blocks.

 

[jhenry]

I agree with cutting in columns down to the foundation and placing new column reinf. Consider 8" x 12" columns with 4 #5 vert. and #3 ties at 8" o/c. The colummns can be at 4' o/c, with the #5 bars drilled and epoxied into the foundation and cap beam, (if they exist.)
Otherwise a new sister wall can be considered.

 

[dik]

Just a caution... with old structures, changing the loading/support regime may cause minor cracking elsewhere.

Dik

 

[csd72]

dik makes a good point. I always notify this in writing to the client prior to carrying out the design.

You just cannot completely prevent cracks in masonry building when you redistribute the load path.

 

[dik]

and once one is located (old or otherwise), 'new' ones are found...

Dik