When you make repairs or do a rehabilitation project on your historic house or commercial building, you want the best return on your investment. You might be tempted to choose the “quick, cheap and easy” approach to a project. However, this decision will nearly always be a mistake that will cost you more money and frustration. Here are 10 of the most common mistakes by the owners of historic houses and buildings — and tips on how to avoid making them.

Mistake #1: Poor Paint Selection and Surface Preparation

Painting is part of your regular maintenance and upkeep of your historic house or building. If you skimp on poor-quality paint and do not prepare the surface properly, paint failure will result. By investing in a high-quality, durable, long-lasting paint, you will get a much better payback on your paint purchase. Also, make sure that you properly prepare the surface to be painted. If your wood or masonry exterior is not thoroughly prepared, the paint will not stick to the surface as long as it should. Completely clean the surface of dirt, mildew and dust, and scrape off as much loose paint as possible and add an underlying primer coat before your finish coats.

Mistake #2: Applying Waterproof Coatings

Keeping water out of your historic house or buildings should be at the top of your historic preservation and maintenance list. This goal is best accomplished by keeping your roof surfaces, gutters and downspouts in good condition. You should not apply the exterior waterproof coatings that are sold as a means to prevent water penetration in a building. These waterproof coatings create a vapor barrier that prevents the wood and masonry walls in your older building from being able to breathe. The heating and cooling system in your older building generates moisture due to varying inside and outside temperatures. If this moisture cannot be released due to the vapor barrier created by a waterproof coating, your plaster walls will peel, your drywall will be damaged and your exterior paint will blister and peel.

Mistake #3: Using Abrasive Cleaning Techniques and Materials on Masonry

Sandblasting of masonry buildings was a popular practice in the 1970s and 1980s, but it has fallen out of favor due to the damage and long-term maintenance issues it causes. You should avoid using other abrasive cleaning materials, such as walnut shells, dry ice, baking soda or glass beads. Most 19^th and early 20^th century masonry buildings were built with low-temperature fired bricks, which made the bricks softer in the middle. Abrasive cleaning materials and methods remove the hard crust on brick surfaces, exposing the softer brick material underneath it. The soft brick core was not designed to withstand the elements and can erode over time. Abrasive cleaning also eats away the mortar joints, which often makes repointing necessary. You can remove dirt or paint on masonry surfaces by using mild detergent or chemical cleaning agents, which are just as effective and do not cause the same damage.

CAUTION: If your masonry building is listed on the National Register of Historic Places, it is against the law to abrasively clean it. Wisconsin State Statute 101.1215 makes it a crime to use any type of abrasive blasting on the exterior of a National Register-listed property. This crime is punishable by a fine.

Mistake #4: Using the Wrong Mortar for Repointing

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Dane County. This is an example of poor repointing - the mortar joints are not only wider than the original mortar joints, but the new mortar is also a different color. Poor repointing will adversely affect the overall appearance of the historic building. Source: WHS - State Historic Preservation Office.

If your mortar joints need to be repointed, you should not introduce a hard mortar to brick that originally had soft mortar. The harder mortar can produce long-term maintenance problems. Most 19^th and early 20^th century masonry buildings were built with soft lime mortar. The Portland cement mortar that was widely used later is much harder than lime mortar. When soft bricks are repointed with Portland cement, they can no longer expand and contract and may start to crumble. You can use Portland cement with high-temperature fired brick and hard stone, but it will cause soft brick and stone to deteriorate rapidly. If you have soft brick or stone, always use a compatible mortar that can expand and contract.

Mistake #5: Overlooking Attic Insulation

You should not overlook the long-term economic benefits of increasing the amount of attic insulation in your historic house or building. According to the Department of Energy, almost one-third of energy loss in the average house is through floors, walls and especially ceilings. By adding batt or blown insulation in your attic or crawl spaces, you will reduce your heating and cooling bills and recover your expenses over time. Insulation is rated in terms of thermal resistance, called the R-value, which indicates the level of resistance to heat flow: The higher the R-value of an insulation product, the greater its insulating effectiveness. The R-value of thermal insulation depends on the type of material and its thickness and density. The R-value of a multi-layered installation is calculated by adding the R-values of the individual layers. You should insulate your attic and crawl spaces with glass fiber, mineral fiber or cellulose insulation in the R-30 to R-38 range.  

Mistake #6: Removing Interior Plaster

Most commercial buildings and dwellings built before World War II have interior walls of wood lath and two or three coats of plaster. Plastering takes both time and skill, but it produces a smooth finish and offers good insulation values. New building techniques were introduced during the housing boom of the mid-20^th century, including the use of an interior wall surface called gypsum board. Today, gypsum board is widely known as “drywall.” Some house and building owners removed the plaster down to the studs and applied drywall instead. If your house has original plaster walls, you should repair and maintain them. Repairing plaster can be expensive, but your plaster walls are part of the historic character of your house or building. Plaster also provides much better insulation value than drywall. Most plaster walls are at least one inch thick, while drywall is only one-half inch thick. Keeping your plaster walls is also a more sustainable approach than replacement because you will not be dumping this material in a landfill.

Mistake #7: Applying Synthetic Siding

Some house and building owners avoid the expense of maintaining their original wood siding by covering it with synthetic vinyl or aluminum siding. If you apply one of these synthetic siding materials to your historic house or building, you will drastically alter its original appearance. However, this is not the only reason you should avoid synthetic sidings. Synthetic siding materials will not allow your original wood siding to breathe. Vinyl siding traps water vapor in the walls of an old building, which can cause deterioration of the original siding and structural damage. Aluminum siding also traps moisture and is easily dented. Neither type of siding is maintenance-free, because over time they will lose their finish and require painting — vinyl breaks down under the sun’s ultraviolet rays, and aluminum oxidizes.

Mistake #8: Using Pressure-Treated Wood

Much of the wood sold in lumberyards today is yellow pine that has been pressure-treated with chemical compounds. If you need to replace deteriorated wood frame elements or wood siding in your historic house or building, consider using cypress, cedar or Douglas fir instead of pressure-treated pine. Even after pressure-treated wood is cleaned and dried, the chemicals leach out and cause premature paint failure. In addition, pressure-treated lumber often contains 30% or more moisture, and you need the moisture content to be 15% or less for painting. Even if you allow the wood to dry for a month or two to reach the critical 15% or less moisture content, the wood will have warped, bowed and twisted from the drying process.

Mistake #9: Replacing Original Windows

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Brown County. A sliding vinyl window is not an appropriate replacement for a historic roof dormer. Source: WHS - State Historic Preservation Office.

If you replace your original wood windows, the replacement windows will detract from the historic architectural character of your house or building. Replacing windows is often not cost effective as well. Windows in buildings built before World War II are generally made of old-growth wood and can last indefinitely with proper maintenance and repair. Replacement vinyl windows do not have the same appearance as historic wood windows and have seals and springs that are prone to failure. You can rebuild your original windows and add appropriate storm windows to improve the energy efficiency of your windows. Although repairing and rebuilding original wood windows takes some expense and time, you will get a better payback for your investment than wholesale window replacement.

Mistake #10: Blowing Insulation in Plastered Exterior Walls

When you add insulation to your attic and crawl space, you may be tempted to blow additional insulation into the wall cavity between your exterior walls and the plaster and lath interior walls. However, you should leave your plaster walls alone so your house or building can breathe the way it was designed to do. Blown-in insulation materials like loose-fill fiberglass and mineral wool, and especially cellulose, have a tendency to deteriorate and settle at the bottom of the cavity wall. The degree of settling can be up to 20% for cellulose. Older houses and buildings with plaster walls have no vapor barrier under the plaster, so water vapor produced inside the structure will condensate on the settled insulation. As a result, the plaster on the inside wall will be damp and cause paint failure on the exterior wall.