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Bulging Concrete Block Basement Wall

Bulging Concrete Block Basement Wall

(OP)
This seems to be a common problem in residential construction.  A concrete block basement wall that is cracked horizontally (mid height) and bulging inward, obviously due to lateral earth pressure with inadequate or no wall reinforcement.  What is the state-of-the art way of repairing this?  I'm looking for a solution that spares the home buyer (or seller) from an extensive and costly wall reconstruction project.  Any ideas or success stories would be appreciated.

-JCali  

RE: Bulging Concrete Block Basement Wall

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,

RE: Bulging Concrete Block Basement Wall

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

RE: Bulging Concrete Block Basement Wall

3
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.

RE: Bulging Concrete Block Basement Wall

2
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.  http://www.anchoredwalls.com/basement_stabilization.html

Another technique uses helical piers applied horzontally.
http://www.helitechonline.com/

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.   http://www.durdydave.com/basement/wallstabalization.htm

If you are budgeting around 10 grand for the remedy, you are in the ballpark.

RE: Bulging Concrete Block Basement Wall

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,  

RE: Bulging Concrete Block Basement Wall

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.

RE: Bulging Concrete Block Basement Wall

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.

RE: Bulging Concrete Block Basement Wall

(OP)
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  

RE: Bulging Concrete Block Basement Wall

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

RE: Bulging Concrete Block Basement Wall

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

RE: Bulging Concrete Block Basement Wall

(OP)
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?   

RE: Bulging Concrete Block Basement Wall

jcali,

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

RE: Bulging Concrete Block Basement Wall

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.

RE: Bulging Concrete Block Basement Wall

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.

RE: Bulging Concrete Block Basement Wall

(OP)
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  

RE: Bulging Concrete Block Basement Wall

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.

RE: Bulging Concrete Block Basement Wall

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.

RE: Bulging Concrete Block Basement Wall

2
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.

RE: Bulging Concrete Block Basement Wall

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?  

RE: Bulging Concrete Block Basement Wall

Just a note - we see these problems often in the SE.  One of the more common repairs is the installation of soldier beams consisting of two back to back sections of C5x9 channel separated by a 2"x4"stud.  The top of the channels are cross-bolted through the joists while the bases are connected to the floor slab with 3 inch angles. We have found that the beams should be set on maximum 5 to 6 foot intervals to prevent bulging between soldier beams.  This method works well when horizontal wall deflections are less than 2 to 3 inches.  In situations of greater deflections, helical tie-back anchors are run through the soldier beam.

This much said, the repairs are generally band-aids that don't address the actual problem.  In most of these cases, the backfill against the foundation wall was improperly compacted and has settled over a period of years.  This results in negative drainage toward the foundations and a build-up of hydrostatic pressure against the walls (note that the bowing walls often coincide with damp or wet basements).  In order to fully correct the problem, exterior drainage must be controlled and re-directed away from the foundations.  By the way, recent codes have addressed some of the foundation problems by requiring reinforced foundations for unbalanced fill foundation walls.

RE: Bulging Concrete Block Basement Wall

WHEngineer,

Since the wall is bulging inward, it will probably be bearing on your double channels in only one location.  Do you require that the gap between the wall and the double channels be filled with shims or grout in order to provide continuous bearing and support?

RE: Bulging Concrete Block Basement Wall

I think it could be worth while to investigate the use of a fiber reinforced polymer (frp) bonded with epoxy.  The frp comes in cloth like sheets and is applied similar to wall paper with epoxy.  This method is used to retrofit concrete columns and bridges but I don't think it would be too difficult to adapt for your needs.  I don't have any experience with this, it's just an idea so I can't say how well it will perform or even if its a good way to go.  If it were my house I would at least check it ou tthough.  It would be easy to apply, you wouldn't need to demo anything major and it wouldn't add a signifcant amount of depth to the wall.  Fyfe Co, LLC is a company out of California that manufactures these product and may be able to give you technical advice on the feasibility of using it in your basement.  Here's a link to their website:  http://www.fyfeco.com/

Good Luck!

RE: Bulging Concrete Block Basement Wall

(OP)
Following up -

How do you install a vertically reinforced masonry basement wall under an existing wood frame superstructure wall? How do you get the rebars in and build the blocks around them?  Or, how do you build the blocks and then insert the vertical bars?

JCali

RE: Bulging Concrete Block Basement Wall

Here in town an existing two house was moved onto a new lot.  The house was set on cribbing and the basement footings, slab and block foundation wall built under it.  Once the reinforced block wall reached it's full strength the house was lowered on to it. It is actually not as difficult as you might think, however it was an experianced house moving contractor that did it.  This is not for the "weekend mason" to try.

RE: Bulging Concrete Block Basement Wall

One way to get the rebar in the wall:

Place the full height vert. rebar in its location complete with hook at top if required.  Cut the head out of some units so that the cell to be grouted can fit around the rebar.  This is not the same as cutting the end out of the unit which would make it 2" short.  Do this all the way up, just at each bar location and cut the face out of the bottom unit for a clean-out.  For the lintel, lay several block along the course and slide the reinforcement in from the end of the last unit.  Keep going down the wall.  Before you get to the last few slide the remaining rebar into the lintel course and as each of the last units are placed keep bringing the rebar forward.  At the last one slide the rebar into its final position which should lap a bar grouted into the existing masonry or concrete if it's there.  Cut the final lintel block deeper and work it under the rebar and into place, or cut it in half and bring the 2 halves together around the rebar from each side.  This may or may not be necessary at the first one or two lintel block.  The block at the top will need some cuts to allow a pump hose to fit along with some cuts in the lintels as necessary so that the wall can be pumped.

This can be done easily by regular crews with no special lifting of the house.  Saws are very common on masonry crews.  In fact, if the crew doesn't have a saw, that's a hint that there is something wrong whether they are too cheap or not as skilled in their work.  Saw cut units reflect crews that take the time to do a good job and care about the final product of their work plus it saves the integrity of the block from being compromised by hammer-cuts.  Years ago special saw cutting was considered too expensive and still shoul dbe avoided if possible.  Today's houses are however much more complex then those that used to be built and saws and saw-cuts are an everyday occurance.  

RE: Bulging Concrete Block Basement Wall

this months Journal of Light Construction has an article on this subject.

RE: Bulging Concrete Block Basement Wall

We have built several dry fit block walls using a structural skin product to bond the outsides of the blocks.  This may be suitable in some cases to apply on the inside surface of a failing wall to prevent further movement.

RE: Bulging Concrete Block Basement Wall

I recently bought my first project/venture house about 6 months ago. It had a 6 foot daylight with a 6 inches thick, non-reinforced wall. The ACI has about three really good publications on Shot Crete or Gunnite (both correct and interchangeably used). I had the house lifted 3 feet in the air for $10,000, finding a good house mover was not really easy but not terribly hard either. To get a recommendation on a Gunnite contractor, I called a local ready mix plant that I have frequently worked with to give me a recommendation.
My wife and I bent and tied a mat of reinforcement to the inside face, about 2" off the old concrete wall, hooked and epoxied into the base of the wall and terminating in the upper portion. Plywood was nailed to the rim of the raised house and the sill plate with anchor bolts already in it was screwed to the inside. The Gunnite was shot in about 4 inches thick over the old concrete wall and of course about 10 inches thick at the two foot void created by lifting the house. The Gunnite cost me $3000 for material and labor. An important point about Gunnite, I used #3@6"o/c vertically to give the Gunnite something to hold on to vs. a large bar with a bigger spacing. My contractor didn't like the idea of Welded Wire fabric but I'm not convinced that it couldn't be used in this application. The bonding of Gunnite to existing block or concrete can be surprisingly strong however a good attachment at the top and bottom would still be prudent. I think this idea could be adapted to a failing block wall; the prices were for 2004 in the Seattle area if that helps.

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