Friday, October 7, 2016
Historic Masonry Restoration
MASONRY AND BRICK VENEER
Section 1--The Basics
Brick and masonry might be among the longest-lasting, most weatherproof building elements, but masonry buildings still require maintenance and repair. This section of the Old House Web Exterior Walls guide focuses on ways to clean old brick and masonry buildings and also how to repair minor weatherization and age damage to these structures. These suggestions also apply to stone and concrete block.
Typically, masonry structures have problems and damage associated with one or more of the following:
Photo: HearthMasters, Inc.
Foundation displacement--also known as settling--over time
Water penetrating into structural walls
Stresses on the masonry walls due to fluctuations in temperature
Aging of mortar in masonry joints
Section 2--How to Clean Masonry Walls
Before undertaking any cleaning task, examine the wall carefully. Will your cleaning further degrade the mortar and masonry? Although dirt and airborne pollutants can significantly diminish the beauty of brick, a cosmetic makeover may actually do more harm than good, especially in very old houses or structures.
In any preservation work with old masonry buildings, you'll want to tackle cleaning with the least invasive process possible. If the structure has historical significance, you also should consult with a rehabilitation professional. Resist the temptation to blast the building with a high-pressure power washer! Although you'll remove decades of built-up dirt, you'll also remove mortar and most likely a thin layer of the brick itself.
If you use any chemical cleaners, you should clean a small test area first to see how the cleaner interacts with the existing masonry.
2.1: Cleaning Masonry With a Brush
You can clean old masonry walls during a home restoration with dish-washing detergent, cleaners such as Simple Green, or laundry detergent mixed with water. Oftentimes, deep stains can be removed with grease-removing cleaners such as Formula 409. Certain stains, such as water marks or leaching of coloring agents from within the brick itself, can be cleaned with acid-based cleaners. However, acid can discolor masonry, as well as damage glass and metal surfaces such as flashing around windows. Acid should be a last resort, and it must be thoroughly washed off after cleaning.
2.2: Cleaning With a Pressure Washer
If faced with a huge amount of wall space in a home renovation project, you can use a pressure washer if it's set on low or medium power. High-pressure spray should never be used to clean old masonry. Although you can clean a large surface volume quickly with a power or steam washer, you might be better off to tackle the chore with a brush to avoid blasting decaying mortar from aging joints.
2.3: Using Abrasive Blasting to Clean Masonry
Most abrasive blasting is done with sand, but the problems that can occur with sand blasting are similar to using high-pressure water. Softer materials, such as glass beads, finely ground nutshells, or peach or cherry pits, can be used to clean old masonry or brick. If you plan on using one of these softer blasting materials, test a small portion of wall and examine the brick and mortar before continuing.
Section 3--Applying Protecting Coatings to Masonry Walls
Clear coatings help repel water and graffiti. Coatings are either a protective film on top of the brick, or they actually penetrate the brick. The effectiveness of clear coating masonry walls is debatable, however.
3.1: Film Coatings
Film coatings include:
Pros: Film coatings can help fill cracks in brick and keep graffiti from penetrating the brick's surface.
Cons: The film may darken bricks, and it can prevent water from evaporating from the brick face.
3.2: Penetrating Coatings
These coatings usually permeate the brick to a depth of 3/8 of an inch.
Pros: The coating can last up to 10 years.
Cons: Penetrating coatings can't be applied over film coatings, and they don't work to seal cracks in mortar joints.
Section 4--Fixing Decaying Mortar
A brick wall is only as strong as the mortar that holds it together. Brick can last for several hundred years in the right conditions, but mortar is estimated to have a 25-year life. If the mortar has eroded more than 1/4 of an inch, it must be replaced or re-pointed.
4.1: Concerns and Cautions When Re-pointing
The mortars used today are stronger than their predecessors, so the stress loads and weight transfers that any structure undergoes may be transferred from the mortar joints and into the brick itself. Consult with a professional mason to ensure you mix the proper mortar for repointing.
Serious structural flaws in brick or masonry walls, such as large cracks or displaced or deteriorated bricks should be handled by a professional mason. A professional can assess the problem--and most importantly, the underlying factors that led to the degradation of the wall.