1920's lime and gravel foundation

[Banks]

I recently inspected an old foundation that has a cement stucco on the interior. There are a couple locations where the stucco has broken off, and the foundation wall has been exposed. At these locations (and I'm assuming along the entire wall) the wall has deteriorated and just brushes off. The wall is composed of a gravel and what I'm thinking is a lime mix and I'm wondering about the best way of repairing the foundation walls. If I try and put concrete against the existing wall am I going to run into future problems with having a portland cement product in direct contact with a lime and gravel product? I know it's an issue for brick walls, but I'm not sure if that's the same with this foundation wall. I was thinking of shoring, removing the stucco and brushing off the loose portion of wall and placing a new finish - 6" or more on the inside of the wall.

 

[youngstructural]

You will have future problems if your motar is too stiff. I am not aware of any fundamental chemical reaction occuring to cause deterioration between cement and lime mixes... That doesn't mean there aren't any!

Okay, so you need your new mortar to creep. I would suggest looking into a mix design that uses lime as well as cement, and also you're going to need to be very careful about how you do your pointing. I hope you have access to an experienced contractor who has handled lime mortar masonry restoration before.

One other detail: Are you dealing with stone or is this brick? Since you're at the foundation, I would presume stone, however well-fired dark red brick laid directly on the ground in a step-out pattern is not unheard of for an old foundation. If you have brick, I would suggest not removing broken units; At the foundation it is simply too dangerous an undertaking.

Hopefully some of our other friends out there will chime in with useful contributions. Good luck!

Cheers,

YS

B.Eng (Carleton), P.Eng (Ontario), MIPENZ (Structural-New Zealand)
Working in Canada, and missing my adoptive New Zealand family... at least I brought the little Kiwi with me!

 

[Banks]

There's no stone or brick. At first I was expecting to look at a stone and mortar foundation and when I got out there it was just gravel and lime (an assumption - no chemical tests have been done).

Worst case scenario is they replace it, but I was hoping to avoid it if anything safe could be done.

Thanks for your thoughts - I'm trying to brainstorm with as many people as I can.

 

[BAretired]

If the concern is the wall pushing inward due to soil pressure, you could provide new wood studs on the inside face and fasten them to the floor above and below, blocking between the studs and the existing wall to provide lateral support. It might be best to leave the stucco in place as it may serve to contain the lime and gravel.

If the concern is the axial capacity of the existing walls, a new wall on the inside won't help much as it will not be under the load and will not be resting on a footing.



BA

 

[dik]

Early foundations were sometimes constructed using non-hydraulic limes for the mortar/cement mix. Durable masonry required that the lime used had hydraulic materials that would not 'wash' away over the years. It might be that the early cement/mortar used for this foundation didn't have this property.

It is also possible that you may have soluble sulphates in the soil and that the early cement wasn't sulphate resistant.

It may be that the only option is to underpin and remove the existing foundation wall.

Dik

 

[youngstructural]

Sorry about that, I didn't catch that the whole foundation was thought to be this early agg/lime mix... I have seen thin base layers (failing similarly to your's) of say 150 to 300 cement-like material below a spread brick foundation. These are notoriously (in my own mind) difficult to remediate as the underpinning suggested by Dik and alluded to by BAretired nearly always results in brick falls.

I agree with our estimed colleagues; You are most likely going to have to replace this foundation. I've provided new foundations adjacent to existing (insufficient, failing, etc) foundations, needled the wall above and carried the existing wall in this manner. It is difficult, expensive, and requires access to both sides. Otherwise you can repair/remediate the wall by needling the existing onto temporary founds (again, normally requiring two sides of access) and remove/replace/repair the existing foundation in-situ.

Now just in case I'll point out that Needling is the process of removing some bricks (often in multi-whythe walls) and passing a beam perpendicularly through the hole to carry the bricks above while you work on/replace/remove the bricks below.

Okay, so there is still yet another possible solution: Replace the existing load carrying system with a new wall and foundation; This is not cheap, but is sometimes quite practical... I've seen this done (in a magazine), though never attempted it myself. Essentially you are being wholly unsympathetic to the existing (and possibly historic) structure, but it is on occasion the right way to go as it can permit full change of use/expansion/replacement of the structure.

Good luck and let us know how it goes,
Cheers,

YS

B.Eng (Carleton), P.Eng (Ontario), MIPENZ (Structural-New Zealand)
Working in Canada, and missing my adoptive New Zealand family... at least I brought the little Kiwi with me!