1942 Concrete foundation wall deterioration & new lintel.

[CELinOttawa]

Hello All,

So we're being asked to prepare a design for a pair of existing windows to be cut wider, from 12"x14" and 24"x33" to 24"x48" each. I've done this type of work a number of times before, but what is bothering me this time is that The interior surface of the wall is heavily salt stained, and the concrete is crumble in your hands weak immediately around the existing windows and for 6 to 8" up the wall to a depth of 1 to 1.5". The wall is 12" thick, and everything else appears to be in good shape. The constructor called immediately upon finding the interior of the foundation wall to be deteriorated, and I have recommended to the client that they undertake to remove and restore all soft areas and follow this by taking steps to waterproof the basement, but this would have to wait for spring.

I'm specifying that the contractor chip down to sound concrete and come back up with Sika 623 as a repair material. The new lintel is being made from jacketing steel, and the compressive strength of the wall is not of significant concern as I am through bolting and having threaded rods epoxied at 450mm centres. In order to allow the wall to now span horizontally, I will have 15M bars at 300mm centres run horizontally across the wall in the Sika 623 and add an outer layer of WWM 6x6-9/9 to control the cracking as the vertical reinforcing. Finally I'll run timber columns at the two ends to not have to rely on the shear capacity of the existing concrete.

The owner wants to press ahead with the work, and says they will correct the deterioration throughout and waterproof or otherwise mitigate the possibility of further deterioration due to water ingress in the spring.

Two questions:

1) I am worried that this current work will get done, everything will be closed up, and the owner will simply not investigate further nor waterproof the foundation. I feel I have a duty of care to see that this is corrected, but at what point does one flag the job to the local authority having jurisdiction? I am certain that water has been involved in the deterioration, but we still don't know what actually caused the deterioration. It almost looks like a freeze thaw damage on a bridge, but goes deeper while being classically moist. Besides, freeze-thaw is not at all likely at the bottom of a heated basement wall! The age of the building does mean that the basement could have been finished laterand the deterioration could have started long ago and been concealed; the fit-up which was demoed in this job was from the 80s and that may have been the first time the basement became occupied space. The contractor advised that the bottom foot of the drywall lining he removed was wet and had mould on the face towards the concrete. The concrete had been covered in a series of 1/4" lath strips to which they fastened the GIB. I'm certain that if we stop the water ingress, we will stop the deterioration, whatever the cause. How far do you push *knowing* the cause of the deterioration, particularly when the damage is still in the cosmetic/poor durability range?

2) Should I insist the whole of the foundation's interior be exposed and subject to repair wherever soft concrete is found? I have already made this recommendation in a field report, but nothing I have seen to date looked to be a structurally compromising situation... It is just heading that way if not addressed.

Your thoughts are appreciated...

 

[bridgebuster]

Two things;

First; the management frowns upon posting the same question in multiple forums.

Second: Is your wall cast in place concrete or block? If it's a block wall are they actual CMU or more likely "cinder" block? Some will argue that there's no real difference between the two. Where I lived in NY for most of my life, most of the houses were pre-WWII with basement walls constructed from cinder block. water seepage wasn't uncommon. Generally, these blocks didn't contain much stone. I've seen quite a few crumbling blocks, some was probably due to freeze thaw but I think most of the damage was due to erosion from the seepage. Not all houses experienced these problems.

You didn't describe the drainage characteristics around the property. If you have cinder block keeping the water away from the house is vital. Is the water table above basement? I think you need to look into this as part of coming to a solution. Repairing the concrete IS important but as a consequence you might be moving the seepage problem to another part of the foundation.

 

[CELinOttawa]

Hi Bridgebuster,

Thanks for the reply. Noted regarding the double threads; I'll not do it again.

- The foundation is concrete, but an obvious case of site mixed (some variation, but overall a good consistency) concrete with some very large aggregate thrown in (in one area the contractor has uncovered a stone ~9"x11" on the face.
- The contractor has removed the deteriorated (actually disintegrating) concrete to a depth which varies between 1/2" at most down to 1-1/2". The concrete beneath is quite sound.
- The grade is at the level of the window sill, and it appears that water has penetrated between the untreated pine frames and the existing concrete.
- Note that when the brick above was repointed a few years ago they did a horrific job, appear to have not cleaned down to 1/3 depth of the bed (more like 3/8" total depth) and filled the weep holes in the bottom course.

Note that my first field report (issued after the first site visit) contained the following recommendations:

- An investigation should be undertaken in the spring regarding the weeping tile or lack thereof around the foundation.
- The grade should be dropped away from the windows and varied as necessary to ensure water drains away from the structure.
- The foundation walls which have been exposed must be repaired. Plans for this purpose may be included in the structural drawings for the new lintel installations.
- We recommend that the Owner have further test locations opened to determine if similar deterioration is present throughout. While this adds to the cost of the current construction, it is likely to save a great deal of expense later on.
- The foundation wall below the existing 33 inch window in the south-west corner should be repaired, strengthened or otherwise have the loads transferred to reliable founding and structure.
- Weep holes in brickwork should be restored at a maximum spacing of every fourth brick. Once restored they may be covered with a purpose-made weep hole cover should the client so desire.

I have made it very clear to the owner and contractor that the water ingress must be stopped. My concerns in my original post were regarding both how far to push the determination of the specific cause of deterioration and how far to go in insisting the foundation be made free of water ingress.

At this point it seems the owner is committed to doing this right, and we expect to be back on site in the spring to see if there is a modern big-O, and otherwise to install at an elevation 6" below the basement floor level.