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Best Practices for Saving Historic Plaster

Plaster in old houses needn't be torn out. With the right tools and some understanding of the materials, a good repair will make the plaster look like new

<p>By affixing this loose ceiling with an acrylic adhesive injected through 3/16-inch holes throughout the damaged area, repairs can be made without adding permanent hardware to the plaster surface.</p>

By affixing this loose ceiling with an acrylic adhesive injected through 3/16-inch holes throughout the damaged area, repairs can be made without adding permanent hardware to the plaster surface.

Photo by Kolin Smith

Lime plasters have been used in construction for thousands of years

everywhere from Japan to Europe. When the TOH TV project house in Charlestown was

built in 1865, plasterers used lime plaster. Lime plasters are ideal candidates for repairs, because they crystallize over a long period of time, are flexible, and resist water damage. In short, with maintenance, lime plaster will not only last forever but will actually get better with age.

While old house plaster problems are unique to each historic building,

with a few basic tools and materials and an appreciation of history,

solutions easily present themselves. The Charlestown House had different

basic problems: a steady increase in car and truck vibration on nearby

streets, peeling paint, and water damage.

The second-floor living room suffered from its proximity to a main

street and modern traffic. Cracks radiated from the corners of the

ceiling toward the center medallion, thanks to the movement of the

outside wall.

To determine if the plaster was still attached to the lath, I drilled

several holes and judged the distance between the two. In this case,

although cattle hair kept the plaster from falling, it no longer adhered

to the lath. So the first step of my repair was reattaching the

plaster. To do this, I injected an adhesive under pressure through the

holes I drilled for evaluation, and clamped the area with screws and

washers. This adhesive established a wide, flexible bond between the

plaster and the lath that allowed movement, vibration absorption and

preservation of the historic plaster. When the adhesive was set, I

removed the clamping washers, raked out all cracks and holes and filled

them with a soft mixture of lime and gypsum so they were flush with the

surrounding plaster.

Away from the main street, the dining room's plaster ceiling suffered

less from vibration than from peeling paint. Originally covered in

calcimine, a water-soluble paint that was frequently reapplied, the

ceiling was eventually covered with modern paint. Over the years, the

different paints began to expand and contract at different rates,

opening up cracks in the paint that allowed water vapor to re-hydrate

the calcimine and release its bond with the plaster, causing the paint

to peel. The good news was that a few passes with a wallpaper steamer

removed the rest of the paint without harming the plaster below. The

plaster was then washed, allowed to dry and painted. The main rooms'

ceilings suffered from this malady and benefited from this simple cure.

The house's medallions suffered from the same problem as its ceilings. The

medallion in the second-floor living room, marked by a fruit-and-vegetable motif, was moved to the dining room and a new medallion,

suitably Second Empire in style, was installed there. To duplicate the

original medallion, I removed the paint, made repairs, made a mold and

cast a new medallion. On the first floor I used this same treatment on

the three medallions to uncover detail lost to paint buildup and damage

incurred when the house switched from gas to electric light. Once

repaired, the ornaments were reattached with adhesive plaster as they

had been originally.

The house's cornice work was sound but suffered from water damage and

holes left behind by old steam heating pipes. In addition, layout

changes required new cornices to match the old. For these repairs,

in-kind replacements were the order of the day. Holes and cracks were raked

out and filled using a mixture of lime putty and gypsum with a higher

level of gypsum than in general plaster repairs. As the plaster started

to set, I developed the cornice profile with a mitre rod.

The number one at-risk historic material in this country is interior

plaster. Historic plasters can be fixed and preserved to be part of a

cost-effective restoration process. Modern alternatives do not measure

up in the long run to maintaining historic plasters. Sadly in the 20th

century, maintenance was often considered an unfortunate side effect of

house custodianship. In this new century people are now reaching back to

preserve our collective architectural history.