Quarry foundations and the problems that come with them

A quarry foundation? What the heck is that?

That’s exactly what I asked myself.  Then the old timer building inspector told me the old failing foundation he was inspecting was a “Quarry Foundation”.

To make a long story short. After pulling off the basement wall finishes (Drywall etc.) we were looking at a crumbling foundation with horizontal cracks running around the mid height of the concrete walls. Which is a major warning sign of big foundation problems. Of course, we showed the homeowners, building inspector and brought in the engineers. After a brief site visit the foundation was condemned by the engineer. To prove conclusively that it was un-savable we had the foundation core tested. The engineering process is to drill into the wall, remove a concrete sample. Then apply a force to the sample till it breaks and that is the strength of the foundation concrete. We ordered 6 samples for testing. After 6 attempts to get the needed core sample, only one didn’t crumble in the core barrel. 6 more core holes were drilled and only ½ a sample was able to be rescued from the core bit. The foundation was truly condemned at that point.

Now to go back in history to the last ice age and Lake Iroquois shoreline reseed to the now Lake Ontario. The old beaches were left high and dry by the reseeding lake and became a great and easy location to mine aggregates for many things. This beach sand can be found in the concrete of many foundations in certain pockets around Toronto.

At the time the concrete technology was not perfected. It was found later that the tumbled beach sand from the wave action of the lake, rounded and smoothed the aggregates (sand and gravel). The rounded polished smoothed surface of the sand and stones made it difficult for the cement to bond to these materials. Over time they separated from each other causing the failure of the concrete.

The foundation fix was interesting. We removed as much of the home as possible, to reduce the weight. Then lifted the home and replaced the foundation. After, the home was placed back onto the new foundation and we continued with the addition and renovations. The picture below is of the house lifted over the new foundation.