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Cracking Concrete Block Basement Walls

Cracking Concrete Block Basement Walls

Cracking Concrete Block Basement Walls

Have a very bad situation.  Home built about 6 years ago, with full basement.  Basement walls are block and about 16' high.  I'm told contractor placed rebar in the blocks while building, but can't confirm.  Basement imediately began serious leaking.  Toe drain and exterior waterproofing has already been replaced once, but leaking continues.  Basement wall(s) are now showing vertical to 45% cracking.  Floor slab (no cracks) is between 4-8" (not sure in all areas).

Before proceeding with new drainage work, I'm concerned about the "free" standing and cracking walls.  One expert consulted recommended cuting through the slab, placing a foundation and building up a block pilaster over rebar and tieing the pilaster to the block wall.  Sounds practical to me, but would like another opinion.  Also would welcome any suggestions on best method to accomplish.

RE: Cracking Concrete Block Basement Walls

We see again in your case a mix of deficient design or at least construction for strength and/or stability and damp-proofing. Making a cellar means simply make a damp-proof vessel. Those that have suffered your problems know it is just that. On the one hand, much customary must be the masonry construction in your area to be considered technically correct for a 16 ft tall retaining wall, even concrete ones can have joint or crack related water penetration problems only solved by careful detail. It looks as if the deformations your basement wall is undergoing are ripping what repaired, or otherwise not all the penetration ways were when the reparation was made obstructed. If the wall is strong enough for your vertical loads (weight of the house at least...is there as well some foundation strength problem?) and you have certainty on the water not having ever penetrated through the bottom slab at the cellar, my best advice is make a reinforced concrete surrounding wall that can keep away any movement and serve as basis of new impermeabilization, and bring this to the bottom of the slab...and use whichever special products are required to seal any junctions you doubt are damp-proof can appear. No cheap and you will have to add something to the bottom slab one way or another.

You want to impermeabilize from the inside? Call one Sika or so damp-proofing specialist, and after ensuring that mechanical strength is enough, let them damp-proof your whole inner vessel with their special products. If they don't see complete salvage, maybe you can accept some water input behind some new walls hiding channels to a pump.

Also: Give ventilation as much as possible to your cellar, it helps to dry...this can mean add new thermal insulation at level ground floor.

RE: Cracking Concrete Block Basement Walls

First some questions,

Are you describing vertical cracks in your walls?  If so, are they wider at the top or bottom?  I would have expected horizontal cracking to have occurred if the walls were not reinforced adequately for the lateral pressure.  Vertical cracking implies block shrinkage or foundation movement.  Diagonal cracking usually occurs near wall corners where the wall is warping in two axes.

The re-waterproofing you referred to .... is it truly waterproofing or dampproofing.  Most residential builders use a paint-type product that has no capacity for bridging cracks.  

You might want to consider having a structural engineer investigate the wall.  You can check on the reinforcing spacing using non-destructive devices.  Locally breaking into a grouted-reinforced cell can also get you the bar size.  With this, the engineer can check on the wall capacity versus the lateral earth pressure.  16' sounds pretty high for an 8" block wall with earth against it.  Is it 8" thick?

A true waterproofing product can be used (vs. dampproofing).  Elastomeric products and protection boards can provide good seal-off of your walls.  The joint at your footing/wall interface is more difficult but can also be dealt with by using a self-sealing product such as SynkoFlex (713)671-9502.  

While the water leakage can be dealt with, the cracks are your real concern and your engineer can provide good recommendations ... the pilaster concept sounds feasible.  If the wall isn't properly reinforced, it is difficult to improve within the wall so external elements usually must be added.

RE: Cracking Concrete Block Basement Walls

The wall is 8x8x16 CMU.  Cracks are diagonal, following joints for the most part, however, some extend through the middle of a CMU into the joint above.  Believe the cracks are a realitively small problem compared to other issues.
Dampproofing was alphastic paste.  Structural engineer did look at the walls and recommended pilasters to "strengthen" the walls prior to doing any outside excavation.  He did not do any testing (destructive or otherwise) on the integrity of the wall(s).

I personnaly concur with his recommendation concerning pilasters.  Plan to cut throught the slab, excavate to a depth of about 2', and place a solid, reinforced fountation for each pilaster.  Set rebar into the foundation and construct the pilaster with CMU, tieing it into the existing wall with rebar (grouted into existing wall), and filling each CMU with concrete during construction.

Drainage/water problem is another issue altogether.  He is recommending retention ponds to capture surface water and does not recommend toe drains (I nonconcur).

Again, you'd have to see a sketch to really understand the complete problem.

RE: Cracking Concrete Block Basement Walls

I recently looked at a very similar basement with a similar water problem (but not the cracking problem). I agree with JAE that if the wall did not have enough capacity for the earth pressure then you would expect horizontal cracks rather than diagonal or vertical. Also it is very likely that it has been dampproofed rather than waterproofed. Now waterproofing a basement after construction is very difficult to do. It should form a complete seal around the basement but you cannot get under the slab any more to seal it right down the walls and under the slab. The option we went for was to put a sump in the basement and an automatic pump. Because it was a wine cellar the client could live with a bit of dampness on the walls. I did gie him the option of building another wall inside to form a damp cavity with the sump. This would give dry walls inside.

Carl Bauer

RE: Cracking Concrete Block Basement Walls

Cracks are more on the line of 45 degrees following the joints for the most part.  However, some of the cracks begin at the joint and as they progress at a 45 suddenly extend vertically through the middle of a block then pick up again along the joint.

Tried a pump.  Didn't really work.  Too much water from too many places.

The wall(s) are approximetly 16 ft. high, 8x8x16" block.  Again, can't really tell about reinforcement.  In fact, I'm not even sure what type of foundation the blocks rest upon.

I did have a structural guy take a look at it.  He recommended placing pilasters along the wall at about 8' centers and tied into the wall with Hilte connections (?)  He has not provided fountation or reinforcing details.

No doubt in my mind I must reinforce the walls prior to working the water issue.

Plan to get better structural info from my consultant (including footings, reinforcement etc) then tackle the water issue.

I also believe there are subsurface issues concering a "missing" foundation along one area of the wall.  Apparently the original contractor encountered rock and rather than go through it, went over it with the wall (depending on the rock for a foundation).

I was told the first time someone entered the basement one section of the wall was simply fractured rock.  THe original owner had the contactor "wall it up" to ensure visual astetics.

Simply put, I have no idea where the water is actually entering the basement.  It has appeared from all the "underground" basement walls at one time or another.

Once the pilasters are in place, I plan to excavate down to and just below footing level, clean the exterior walls and damp-proof again.  I'll install a adequate toe drain and  line and an area extending out about about 24" from the wall.  As I backfill, I'll fill with gravel protected by goetex to within 12" of the surface.  I'll also ensure the ground slopes away from the structure and that a swell or other feature directs the surface runoff away from the structure.

I'd welcome any other suggestions.

RE: Cracking Concrete Block Basement Walls

Your external drainage idea sounds good. On your foundation issue however you do need to get your consultant to look at that. Basement slabs often provide their own foundation with a thickened edge strip because they are already down into a suitable founding strata. If there is rock you may have a headache with external drainage because of the rock. You may then be forced to use internal drainage. To do this you would build a 'dry' basement within the wet basement and pump out the outer basement.

Carl Bauer

RE: Cracking Concrete Block Basement Walls

My condolances. Sounds like you are on the right track. Check out www.jlconline.com or webx.taunton.com/WebX?for other suggestions.
Good Luck

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