Bulging Concrete Block Basement Wall 18

jcali,

Have you evaluated strapping the wall with steel angle iron and anchor bolts held in place via epoxy? We have used and proposed the above in a few situations were laterial soil pressure on house basement walls (cast concrete and block) became a concern.

regards,

This is a common problem here in Wisconsin, and there are contractors who do nothing but repair residential basements. I think the state of the art involves something like soil nailing, where anchors are drilled through the wall into the soil.

DaveAtkins

I ran into a very neat detail for reinforcing masonry basement walls. The installation I saw used S3x5.7 vertical columns @ 4' centers (you have to figure the size and spacing for your specific case) set tight to the masonry wall. The bottom of the columns had a "angle shoe" with two drill-in bolts into the concrete floor. The top of the column had an angle bracket bolted to the wood floor joist with a cap screw through the angle that could be used to adjust the force on the top of the column. Very neat detail, not too expensive and didn't require excavation of the backfill. Also, the 3" columns would fit within a 2x4 stud wall if you wanted to firr out the wall.

I'm not sure where the detail came from so I can't give credit for it or take credit for it.

There are a few styles of franchised remedy.

One is to use deadmen plates in the surrounding soil and plates on the interior wall. They are tied together with threaded rod. Check the Yellow Pages, most likely you can get a quote over the phone.
Another technique uses helical piers applied horzontally.

If you get a 'handyman' involved, most likely the remedy will be to stabilize the wall using channel columns grouted into the floor and bolted to the floor above. If the bow isn't more than 3 inches this remedy can be successful.
If you are budgeting around 10 grand for the remedy, you are in the ballpark.

jcali,

If you plan to use tie backs through the wall you will have to ensure the anchors are installed past the soil wedge behind the wall. I am not to sure if the use of plates or screw anchors are the best since you will have to remove or drill out large holes in blocks (depending on size of plate/screw anchor). Also, you will have to check to see what the forces will be if you plan on anchoring to the floor joists. The top of the blocks should have been filled in with mortar and using them to anchor to is what I like rather than the floor joists.

My opinion is best not to tie to floor joists or concrete slab. Best to reinforce wall, and a connection detail to the footing would be better than the concrete floor, because the strapping would be independent of floor movements.

Another option is to strap wall and pour a concrete wall adjacent the existing block wall. This is more expensive but should be cheaper then removing and replacing blocks.

regards,

cdh61,

I respectfully disagree! There is nothing wrong with using drill-in anchors to the floor slab and lag bolts to the floor joist for connections of the vertical columns that are used to reinforce a basement block wall. As long as the allowable loads on the bolts and the lags are not exceeded.

They bolted I beams every 5 ft (or so) at my parents house (was not block but poured concrete) and then put a drain under the floor to collect seepage. Work was done about 3-4 years ago and is working fine. The cost was $17,000.

So, to follow-up, if any of you were looking to buy a house, and you found a crack and bulge in the basement wall, would this be a "deal-breaker" for you? -Jcali

Not necessarily. Find out how much it is going to cost to fix and knock that off of the asking price.

Personally, I would be reluctant to buy ANY house with a CMU basement wall, even if no problems were evident. They tend to have more problems than cast-in-place basement walls.

DaveAtkins

To follow-up again. Yesterday, I inspected a bulging concrete block basement wall in a house that a friend was interested in buying. That was only part of the problem. The mortar in the joints was like powder. I could dig away at the mortar with my finger. Needless to say, I told my friend to walk away. I don't know how to fix such a masonry problem, except for shoring the house and building whole new foundation walls. Have any of you had experience with masonry repair work for this condition? Is there a structural fix?

jcali,

How about grouting the blocks' interior cells if they are now holllow?

The only reason I could claim to know anything about this is the crash course I took upon myself when interested in a house with a buckled basement wall (block).

In theory, you would need to straighten the wall, and place #5 rebar in the cells (closer to inside wall) and then grout it. Or rely upon the many commercially available remedies such as columns or tiebacks.

Who knows what the cells currently have in them, or the alignment of cells? Each cell would need access and a grout pump would need to be on-site for some time. Access would most likely be a large diameter hole from a hollow-core bit near the top of the wall and a weep hole (or two) further down.


I have a hard time seeing this as a sweat-equity project due to the equipment involved (vibrator, grout pump, rotary hammer) over an extended period.

I also doubt a contractor would have at it unless the building was jacked-up and the wall was rebuilt. Great opportunity to make a taller basement, for sure. The experience is out there. This sort of work is done not just for money, but also for the sake of saving something "worth saving". Those folks are out there both as owner and contractor, they just need to get together.

Getting a vibrator into the cells would be problematic.

Would I get involved? Only if the numbers looked good for all parties concerned.

If on a large lot, you might be better served by moving the building to a new foundation. Usually that's not the situation, though.

g7mann [geotechnical]

Dear jcali:

This siutation is NOT a deal breaker if the house price is right. It does provide a negotiating point regarding the selling price.

In my opinion, based on my experience, you have two practical options here. Thge best method is to raise the house [temporarily], demolish the existing block basement walls and then replace them with a poured or sprayed-in-place concrete wall. This alos provides you an opportunity to install a basement level wall drain system too.

The second option, which avoids such a dramatic process, is to install a series of drilled-in-place tie back anchors through the existing block wall and then install a new reinforced concrete or shotcrete wall over the face of the existing blocks. With this option you will lose about six to eight inches of interior space around the basement perimeter, but will have gained a stable basement structure. We do this sort of repair all the time and it is not particularly difficult.

hope this helps.

gzman,

Thanks for your post! I'm interested in knowing more about shotcreting to help in repair of this condition. Could you direct me?

-jcali

g7mann [geotechnical]

Hi jcali:

You should be able to find a local shotcrete contractor in the yellow pages. Alternatively, you might call one of my local shotcreters, a guy who does very high quality work. He can probably put you in touch with a local specialist. Call John Fulford at 206-634-1521 or FAX to him at 206-634-1570.

Good luck.

I recently designed a repair for a residential foundation that had horizontal cracks in a concrete basement wall. The house is less than 10 years old. Part of the repair consisted of designing steel channels that were fit tight to the masonry, and bolted to the floor slab and the floor joists. I think this method is preferable to just bolting an angle to the wall for reinforcement because just bolting an angle to the wall does nothing to help transfer the wall reaction into the floor framing. In this case, the anchor bolts between the foundation and the sill plate didn't even meet code. Also, if you do the calculations for 1/2" dia anchor bolts at 6' spacing you will see that this does not work on paper, even for a good granular backfill. By designing these steel "strongbacks", you end up providing a more complete load path.

I must disagree with the idea that grouting the cells of an existing CMU wall would be prohibitive.

1. If the cells of the wall don't align enough to allow grouting, the wall is so poorly built it should be demo'd anyway. The only difficulty I could imagine is if the block were laid on a 1/4 bond, but that basement doesn't exist.

2. Using a vibrator shouldn't even be a consideration. Using a high slump mix or a plasticizer with 3/8" coarse aggregate eliminates the need for vibrating. If vibrating is something that you feel strongly about, touching it against the outside of the wall will acheive similar results.

3. If the holes at the top course are prepared ahead of time, the pump should only have to be on site for one day.

4. The holes in the block only need to be made with a hammer. There is no need to worry about the inside web of the block, since the sill plate bears on the outside of the block. (yes, I would perform this task from inside the basement)

5. Trying to install a lenght of rebar would be prohibitive, but is not necessarily needed. No poured basement walls around here have re-bar mats.

On the topic of re-bar in the cells of a block foundation wall, does any one have an opinion for a new installation?

I have clay-ey soil and specified #4 bars vertical every 4th cell. The local code official feels that they should be every other cell, but he cannot back this up.

Any thoughts?