A brick foundation is a foundation built from red brick and mortar. Brick foundations were the most common way of building houses over 100 years ago. Because nobody builds brick foundations anymore, the brick you see on newer homes is merely a veneer. The home’s foundation under the brick veneer is not made from brick.
The bricks used to build brick foundations are made from clay and fired in a kiln to harden them. The bricks used in buildings constructed before 1900 are softer than those used in newer brick buildings because, over time, the kiln firing process improved.
If you own a house with a brick foundation and want to determine the hardness of the bricks, you can use a screwdriver to scratch one of the bricks. The bricks used to build your home are soft if the screwdriver can easily create a mark at least 1/16 inch deep. If the bricks seem impossible to scratch with a screwdriver, they’re hard-fired bricks.