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Identifying Problems with Your Historic Stone Foundation

Identifying Problems with Your Historic Stone Foundation | Wisconsin Historical Society
EnlargeCut stone foundation

Waukesha County. A cut stone foundation in good condition. Source: WHS - Historic Preservation - Public History.

If your historic house or building is over 100 years old, it might have a stone foundation. Your stone foundation will consist of limestone, sandstone or a variety of field or river stones. The problems you might face with your stone foundation will depend on the type of stone foundation you have in your historic structure.

Limestone and Sandstone Foundations

Limestone and sandstone foundations are constructed with cut blocks or rubble stones that can be small or large. Each block or stone is a different size and usually consists of broken pieces interlocked together. The color of these stones ranges from off-white to red, with shades of beige being the most typical colors.

Limestone and sandstone are a softer type of rock. To determine whether your stone is limestone or sandstone, use a screwdriver to scratch a stone in an inconspicuous interior location. Limestone will scratch with a bit of effort, while the even softer sandstone will scratch with little effort.

EnlargeRubble stone foundation

Green Lake County. Field stone foundations were typically used for barns as seen in this photo. Source: WHS - Historic Preservation - Public History.

Field and River Stone Foundations

Field and river stone foundations are made up of many types of stones and rock that vary in color. The stones tend to be more rounded in shape. These stones are much harder than limestone or sandstone and will not scratch as easily.

Rubble Stone Foundations

EnlargeFoundation wall

Typical rubble stone foundation as seen from the building's exterior. Source: Bob Yapp

Rubble stone foundations are the oldest type of construction technique used for stone foundations. This method dates back thousands of years, and was used in the earliest pyramids of Mexico, Central America and South America. Your Wisconsin house might have a rubble stone foundation if it dates from around 1850 to as late as 1890.

The footings of a rubble stone foundation wall consist of large, flat stones, usually made of limestone, laid at the bottom of the foundation trench. These stones are generally at least one-third wider than the stone wall placed above them. The foundation walls are constructed of random sized, uncut stones that are carefully fit into rows in an interlocking fashion. Lime-based mortar is installed between the stones.

The exterior of some rubble stone foundations is parged—covered with a lime-based, stucco-like coating. The parging is applied from the top of the foundation wall down to the stone footing. In many cases, lines were tooled into the above-ground parging while it was still wet to simulate the appearance of block stone.

If you have a rubble stone foundation, you have one of the most trouble-free and easily repaired foundations. Even if massive quantities of mortar have failed, the interlocked stones tend to stay in place.   

Block-Faced Rubble Stone Foundations

If your foundation has one layer of uniform, cut stone blocks on the exterior, it could be a block-faced rubble stone foundation. This type of foundation is essentially the same as a rubble stone foundation except it has a more finished, uniform look on the exterior.

Cut-Stone Block Foundations

EnlargeStone basement wall

Iron Block Building, 1899

Milwaukee, Wisconsin. Here is a rubble stone foundation wall with an inverted brick arch detail. Source: WHS - Historic Preservation - Public History.

A cut-stone block foundation is constructed of stones cut into uniform blocks at the stone quarry. The stones were laid with lime-based mortar in early houses. The stones were laid with mortar and a small amount of Portland cement in later houses.

Typical Stone Foundation Problems

You may want to hire a preservation masonry professional to identify the cause of any problems you are having with your stone foundation.

The most common problems you are likely to encounter with your stone foundation are discussed below. Click the link on each subject to learn how to solve the problem.

Common ProblemLearn More
  • Mortar is missing or crumbling between your stones.
Repairing Mortar on Your Historic Masonry Building
  • Your stones always seem wet and are deteriorating from excessive moisture. To solve this problem, you need to get the water to move away from your foundation. Grade the ground around your foundation so it is angled away from your foundation and add ground extenders to your gutter downspouts.
Maintaining the Gutters on Your Historic House
  • Your interior foundation walls are parged or painted and appear to be trapping water because the parging or paint is flaking off.
Remove all the loose cement or paint and allow the rest to flake off over time. Any coating on the inside of a stone wall will prevent the normal migration of moisture. The trapped moisture freezes inside the wall, causing mortar deterioration and spalling of the stones.
  • One or more sections of your foundation wall are bowing inward or collapsing from exterior forces such as water and tree roots.
  • Your foundation wall has cracks that look like stair steps.
  • Your foundation shows efflorescence, a white powdery substance leaching in between the bricks.
  • Your cut-stone blocks are cracked or broken.
  • Your foundation wall has sunk (settled) or heaved upwards.
  • Your stones are dirty or have moss or mold growing on them.
  • Your stones are cracking or pieces are flaking off the face of the bricks, known as spalling.
  • The cement coating (parging) on the exterior of your stone foundation wall is deteriorating.  You should hire a professional mason to dig around the exterior of the foundation and coat the exterior surface with a waterproofing material. Have the mason verify the condition of the mortar when the foundation is exposed, because excessive moisture for an extended period of time can leave mineral deposits that break down the mortar. If this is the case, the foundation may need to be repointed while the foundation is exposed. The mason should also install tiling around the foundation to channel water away from your foundation.
  • The mortar between your stones is showing excessive deterioration, and water is entering your basement. This problem occurs because no exterior waterproofing was ever installed below ground. You should hire a professional mason to dig around the exterior of your foundation and coat the exterior surface with a waterproofing material. Have the mason verify the condition of the mortar while your foundation is exposed, because excessive moisture for an extended period of time can leave mineral deposits that break down the mortar. If this is the case, your foundation may need to be repointed while it is still exposed. The mason should also install tiling around the foundation to channel water away from your foundation.
Identifying Problems with Your Historic Stone Building
  • Your stones show deterioration and excessive wear. This happens because the stone used on your house is soft sandstone. 
  • The surface of your stones is coarse and shedding sand particles excessively.
Exposed sandstone naturally erodes over time; however, rarely does this result in the foundation wall being structurally compromised