Saddled with a foundation problem

Q: My question regards the best way to stabilize the perimeter foundation on my 1872 farmhouse. The "concrete" surface is turning to dust in places where the harder finish coat has been chipped or broken away. I know the core of the continuous perimeter foundation is good and hard, because I've drilled into it when I bolted the house down and shear-paneled the cripples.

Small gaps are appearing between the mudsill and the concrete and my thought is to stuff in some oakum strands before applying the concrete finish.

What product might stop further spalling? What kind of concrete finish coat do you recommend?

A: Simply stuffing some oakum in the gaps and covering it up with a cement topcoat isn't enough and will only be a cosmetic fix.

Oakum is an oiled ropelike material used back in the day for joining "hubbed" cast iron drainpipe. It worked because lead is soft, oakum is flexible and the water pressure in drain, water and vent pipes is very low. But the flexibility of oakum makes it unsuitable for foundation repair.

Concrete spalling occurs when moisture is wicked into the foundation from the ground and the lime in the concrete mix leeches out. Spalling looks like powdery pockmarks on the finish of the concrete.

Depending when the foundation was placed under your 1872 house, it may not be structurally sound, never mind meeting current building codes. We doubt that the foundation is of 1872 vintage. But if it is, the concrete was almost certainly hand mixed in a wheelbarrow and does not contain any steel reinforcing bar (rebar). If it's a retrofit, no telling how it was done. The fact that you had to bolt it suggests that reinforcing steel wasn't an option when the foundation was placed. ...CONTINUED

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