The Brownstone Guide cover

The Brownstone Guide, published by the New York Landmarks Conservancy Technical Services Center, is an eight page PDF that is more a consumer’s brownstone maintenance and restoration handbook than a technical manual. Rather than a source of step-by-step instructions for repair materials and techniques, the Guide is designed to help owners of historic properties understand the character of sandstone and the basic causes of its decay.

In addition, it provides an introduction to the various methods and materials for sandstone repair and restoration. With this background, building owners can make more informed choices about maintaining and repairing historic brownstone. You can find the complete Brownstone Guide PDF here.

The following are excerpts to help familiarize you with the contents of the guide:

Brownstone as a Building Material

“Brownstone” is the common name for a variety of brown, red, and pink sandstone widely used as building materials from the mid-1800s until the early-1900s. In fact, it was so common that the word became synonymous with “row house.”


Need a professional opinion? Try Brownstoner Services, where you can talk to a concierge (it’s free) or browse our community of pros. >>


Inspecting the Condition of Brownstone

Brownstone has two basic characteristics that determine its appearance and performance in buildings:

– Composition: Sandstone is made up of grains of sand and other minerals held together by natural cementing agents.

– Structure: The minerals that form the stone were deposited into layers, or strata, by water and wind over many centuries. Within the stone, natural areas of weakness, called bedding planes, occur where each layer comes into contact with the next.

Brownstone Maintenance Strategies

Building owners and stewards can avoid many problems commonly associated with brownstone through proper maintenance. A regular maintenance program can remedy water infiltration and slow the rate of decay. Deteriorating stone often can be protected, and repair and replacement costs can be reduced.

Causes of Brownstone Deterioration

Brownstone, like other sandstones, consists essentially of grains of sand that have been consolidated by the pressure of overlying sediments and the presence of a cementing matrix, or binder, between the grains. Many of the brownstones used in New York are composed mainly of quartz and feldspar, bound by clays and iron oxides. In some cases, silica or calcite are also present in the binder.

Most brownstone deterioration is caused by the failure of its cementing matrix. As the mortar joints between the stones deteriorate, water finds its way into the interior bedding planes of the stones. Hard freezes cause expansion of the trapped water within the tiny crevices of the stone, destroying the stone’s solidity from within. The recrystallization of salts from deicing compounds or mortars also plays a role in deterioration.

Brownstone Composite Repairs

Composite repair, the application of a tinted mortar-like patch to the surface of a deteriorated stone or portion of a stone, is one of the most common techniques utilized to repair deteriorated brownstone surfaces. Composite repairs are appropriate where small areas of mechanical damage have occurred or where the entire face of a unit has exfoliated. Composite repairs last longer in locations that do not have heavy exposure to rain. Composites applied to windowsills and wall copings often fail prematurely, due to water infiltration and disaggregation of the stone beneath the repair. In areas where direct wetting of the patch is not a problem, such as sheltered vertical wall surfaces, composites may be very durable. Satisfactory adhesion of a composite repair requires removal of all deteriorated stone down to solid material. The sound stone is then scarified or roughened to provide some mechanical anchorage for the composite patch. For large repairs, rods and wire armatures are sometimes added to provide additional support and to assure that the patch does not separate from the substrate. The rods can be made of fiberglass, nylon, or stainless steel. A durable composite repair must be at least 3/4” thick.

Due to the difficulty of exact color matching, composites applied to the full face of a deteriorated stone unit are the most successful visually. Usually, it is preferable to apply composite repairs separately to individual stone units, stopping the edge of the repair at the mortar joint that separates the unit from adjacent stones.

Since the 1930s, many brownstone contractors have completely covered the façades of small buildings with tinted stuccos. When an entire façade is heavily deteriorated or when a façade has been refaced once before, this approach may be appropriate. Refacing is most successful when they faithfully replicate window hoods, door surrounds, and other trim elements. Complete refacing should be avoided, however, when significant sections of original brownstone are intact and may be retained.

Related Stories
Get Advice on Home Renovation and All Things Brooklyn in the Brownstoner Forum
Backyard and Roof Decks — Everything You Ever Wanted to Know
Need Help? Try the Brownstoner Concierge

Email tips@brownstoner.com with further comments, questions or tips. Follow Brownstoner on Twitter and Instagram, and like us on Facebook.

Brooklyn in Your Inbox

* indicates required
 
Subscribe

 


What's Your Take? Leave a Comment