Restoration Guide: Foundations Crack Repair
Editor's Note: This is article 9 of 9 in Chapter 1: Foundations of the Old House Web Restoration Guide. This guide was developed and edited for old homes from original materials in the U.S. Housing and Urban Development (HUD) Rehab Guide.
9. CRACK REPAIR, COATINGS, AND FINISHES
Basement wall and floor cracks have many sources:
- Drying shrinkage
- Thermal contraction
- Internal or external restraint
- Hydrostatic pressure
- Seismic activity
Cracks can also be due to inadequate reinforcement or poorly mixed concrete and mortar. Cracks of less than 1/16" in width are primarily cosmetic unless there is moisture coming through them. Wider cracks (1/8" or more) may indicate structural problems or at least significant settling. Do not repair cracks until the cause has been determined and corrected, or they will reoccur.
Section 2--Repairing Cracks in Walls and Slabs
2.1: Exterior Jacking
In the case of a foundation wall that has bowed or leaned out from the walls above, hydraulic ram jacks may be used to move it back into place. Distribute the load over a large enough area that the jacks do not penetrate the wall. Excavation is required on the side where the jacks will be placed. If any cracks occur while moving the wall, they must be repaired via patching or grouting. This repair also provides an opportunity to apply waterproofing to the wall.
2.2: Earth Anchors and Wall Plates
If a foundation wall has bowed inward, the use of an "earth anchor" is recommended to straighten it. Earth anchors are rods attached to the foundation wall via a wall plate and anchored in a second plate in a trench 7 to 8 feet from the exterior wall. A nut attached to the wall plate end can then be tightened with a torque wrench to gradually move the wall outward, a process that can take from one to three years.
2.3: Helical Screw Anchor
This technique is an alternative to the earth anchor, using helical screw anchors. Rather than digging a trench for anchor placement, the helical plate is part of the anchor rod. It is screwed into the soil to create resistance. This process uses a similar wall plate and nut as with the earth anchor, and as the nut is gradually tightened, the wall is moved outward.
This process can be less disruptive than earth anchors because it does not require excavations, but results may not be as noticeable.
2.4: Conventional Grouting Techniques
If cracks are not expanding or allowing water penetration, they may be repaired using grout. Thin cracks must be chipped open to allow the grout to penetrate. Conventional grout made of Portland cement and sand can be used, as can a variety of other grouting materials depending on conditions. This type of surface repair does not require specialized expertise, but remember that grout cannot repair structural cracks, only cosmetic ones.
2.5: Epoxy Injections
In the case of structural cracks, this is a proven technique. Holes are drilled along the crack, ports inserted, and epoxy injected under pressure by a trained and skilled contractor. This type of repair works better with concrete than with concrete block foundation walls.
Epoxy injections will not prevent further cracking and should be used after the foundations have been stabilized and the source of the cracking remedied. Epoxy should not be used in leaking cracks since water can loosen the bond.
2.6: Urethane Injections
Urethane is the preferred method of crack repair when water is present. Although they are not used for structural repair, urethane grouts do help bond materials. If water is present at the time of repair, a hydrophilic urethane grout should be used; otherwise, a hydrophobic grout is indicated. Application is similar to that of epoxy, pumped through injection ports under pressure by a skilled contractor.
Section 3--Coatings and Finishes
The primary purpose of surface treatments on foundation walls is to repel water. Exterior treatment material should allow water vapor to escape from the wall's interior. For the interior of a foundation wall, a latex paint with a polyvinyl acetate binder is most common. Use vinyl acrylic paint, which is weather-resistant, on exterior walls. If you prefer a natural, unpainted look in this critical preservation project, use a clear treatment formulated from silicone, silicate, or acrylic resins.
Section 4: Materials and Techniques
4.1: Cement-Based Coatings
These include parging, stucco, and cement-based products with latex binders and other performance-enhancing additives. They are water-resistant but may crack or delaminate under excessive expansion/contraction and weathering.
4.2: Elastomeric Coatings
Elastomeric polymer coatings can bridge small cracks and can be applied directly onto foundation walls of concrete or concrete block. They perform well where there is significant expansion and contraction, but these coatings are relatively expensive.
4.3: Paint Coatings
Latex paints with acrylic or polyvinyl binders perform well. Although they do not bridge cracks, paint manufacturers offer crack filling compounds for this purpose. Recently developed acrylic paints also work well. The downside to all paints is that they must be renewed periodically.