If you own a home built before the 1940s, you likely have a foundation made of fieldstone, limestone, or brick. You may also be familiar with the "dust" on the basement floor, the damp smell, or the chunks of mortar falling out of the joints.
Your first instinct might be to grab a bag of standard mortar mix from the hardware store to patch it up. Stop right there.
Using modern Portland cement on an historic stone foundation is one of the most common—and damaging—mistakes a homeowner can make. To save your foundation, you need to look to the past. You need Lime Mortar.
The Problem: Why Portland Cement Destroys Old Walls
Modern homes are built with concrete and steel—rigid materials designed to be unmoving and waterproof. Old homes, however, were built to move and breathe.
When you pack the joints of a soft stone foundation with hard, dense Portland cement, you create two major problems:
- The Moisture Trap: Cement is non-porous. It traps ground moisture inside the wall. Since the water cannot evaporate through the hard cement mortar, it forces its way through the stones themselves. This causes the stone faces to flake off (spalling) and eventually crumble.
- The Stress Fracture: Old foundations shift slightly with the seasons. Portland cement is too rigid to flex with this movement. Instead of the mortar hairline cracking (which is fine), the tension builds up until the stones crack.
The Golden Rule of Masonry: The mortar must always be softer than the stone it holds together.
The Solution: Breathable PHL Lime Mortar
For centuries, builders used lime—not cement—to bind stone. Lime mortar acts as a "sacrificial" layer. It is softer than the stone and highly breathable. It acts like a wick, drawing moisture out of the wall and allowing it to evaporate harmlessly into the air.
At Pro Mason Supply, we specialize in PHL (Pozzolanic Hydraulic Lime) Mortars that are specifically engineered for these historic restorations.
Why Choose Pro Mason Supply PHL Mortars?
Our PHL mortars are formulated to match the strength and flexibility of historic masonry while providing the durability needed for basements.
- 100% Breathable: Allows trapped moisture to escape, keeping your basement drier and your stones intact.
- Flexible: Accommodates the natural settling and shifting of old houses without damaging the stone.
- Self-Healing: Unlike cement, lime possesses "autogenous healing" properties. When fine cracks form, rainwater dissolves free lime in the mortar and redeposits it in the crack, effectively sealing it back up over time.
- No Portland Cement: Our mixes are free from the harsh salts and rigid binders found in modern cement.
For most residential stone foundations, we recommend our PHL 3.5, which offers the perfect balance of moderate strength and high breathability.
Taking It a Step Further: Lime Pro Plaster
Once you have repointed the joints with PHL mortar, many homeowners want to brighten up their dark, rubble-stone basement walls. Painting them with standard latex or waterproofing paint is a disaster waiting to happen (it traps moisture just like cement does).
The answer is Lime Pro Plaster.
Lime Pro Plaster is our breathable, lime-based coating designed to go directly over your masonry. Think of it as a "skin" for your foundation that allows it to sweat.
- Beautiful Finish: Transforms a jagged, dusty stone wall into a clean, uniform surface.
- Moisture Management: Acts as a continuous wicking surface to help regulate basement humidity.
- Mold Resistant: The high pH of lime is naturally antifungal, discouraging mold growth on your walls.
How to Restore Your Foundation
- Remove the Old: Gently rake out the loose, crumbling mortar (and any hard cement patches) to a depth of about twice the joint width.
- Repoint: Fill the joints with Pro Mason Supply PHL 3.5 Mortar. Pack it in tight to support the stones.
- Finish (Optional): For a clean look, apply a coat of Lime Pro Plaster over the wall.
Save Your Stone Today
Don’t let modern materials ruin your historic home. Restore your foundation with the materials it was built to love.
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