Preserving (horsehair) plaster in 1880 row home, advice please

amh2949December 28, 2009

Hello All,

I just recently bought my first home; an 1880 row house. It has many of the original features which is what I love about it, but the plaster situation has me in a bit of a pickle.

Until now, I have not been familiar with historic plaster. I have read some about it and I have reason to believe I am down to the rough layer of lime plaster (it appears to be comprised of a combo of sand, horsehair, and perhaps a lime mixture). The top half of the wall has areas with big holes, crumbling edges, old repair patches and cracks. The bottom portion unfortunately was literally disintegrated under the layers of old wall paper. I have removed as much of the wall paper as possible and now want to seal and harden the plaster, repair the holes and cracks, and properly finish it. I am at a loss for how to do this properly. Any help is appreciated.

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It was common in houses of this vintage to not have a finish plaster coat. The intention was that the walls would always be papered.

If you intend to undertake the restoration yourself, be prepared for a difficult and time consuming task. In places where sizable areas of plaster are missing right down to the wooden lath, pieces of sheet rock cut to fit and attached to the lathing with drywall screws is probably the easiest first step. Smaller holes can be filled with joint compound. Areas of crumbling plaster need to be removed back to sound areas,

Finishing the whole wall smoothly is not easy. Fiberglass mesh comes in 3 to 4 foot wide rolls. This has an adhesive on one side so it can be applied to the wall like wall paper. After that, it's layers of joint compound sanded and smoothed between coats, followed by primer and paint. The trouble with using joint compound is that it does not provide a hard surface like finish plaster, so it is prone to damage. Using actual plaster is not a DIY project. Plastering is a highly skilled trade that takes years to master.

There used to be a product called Nuwall - not sure if it's still on the market. This was a fiberglass cloth applied to the wall and then impregnated with resin. Left a hard, durable coat, but was never as easy to do as the manufacturer's directions implied.

    Bookmark   December 29, 2009 at 5:37AM
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Christopher Nelson Wallcovering and Painting

Nu wall is still out there but it is VERY difficult to work with.I hang paper for a living and found this product still hard to do. It does the job very well though.

Here is a link that might be useful: nu wall

    Bookmark   December 29, 2009 at 6:16AM
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If you wanted to, you could do the repairs with the original lime and horsehair plaster. It just has a rather long delay between when it is complete and when it can be painted. The time is measured in months. Before this summer, I was unacquainted with lime & horsehair, but the experiences I had with the material were mixed; it's kind of finicky and troublesome. There is a growing consensus in the preservation world that using gypsum-based repair products (Gypsolite/Structolite, Durabond, Easysand, gaging plaster, patching plaster, plaster of paris) are all doomed in the long run because they fail to chemically bond to the lime beneath. So, unless you choose to use old-fashioned lime, you need to assure a mechanical bond for the patching material. We have been using plaster bonding agent to get a bond between old and new for many years. Brands are Link and Plasterweld (among others).
It's brushed or sprayed on to cleaned plaster surfaces, or any kind of substrate like wood lath, brick, etc. Then the required patching material is troweled on. In cases where the plaster is entirely missing, a scratch coat is applied (Structolite type) followed by a brown coat (same material) and if a float finish is all that's needed, you may be done. If a white coat is called for, it can be done with typical lime & gaging, or for the less intrepid, Durabond 90 can be troweled on and worked smooth; uneven areas being worked smooth later with ordinary (green-label) drywall mud or a harder product such as Easysand.

    Bookmark   December 29, 2009 at 4:22PM
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Not much to add, but after repairs and before painting my 120 yo bare plaster walls, my painters gave them a coat of Farrow and Ball stabilising primer. It's a product we stumbled on and they were very impressed with it. At the time I did not appreciate the significance of the phrase "alkali resistance" on the product sheet, but since then I've heard about people running into trouble painting over old plaster. Apparently it is more alkali than modern base surfaces.

So, it might be useful for you.

from their advice sheet:
An acrylic copolymer resin, with excellent alkali resistance and adhesion to masonry surfaces.
Usage: For use on interior and exterior masonry and plaster surfaces which are porous, chalky or
lightly degraded but otherwise structurally sound. Provides a well-bound and durable base.

Disclaimer: I'm a huge farrow and ball fan, but I like Ellen Kennon too. Not affiliated with either co.

Here is a link that might be useful: stabilising primer

    Bookmark   December 29, 2009 at 5:36PM
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"If you wanted to, you could do the repairs with the original lime and horsehair plaster. It just has a rather long delay between when it is complete and when it can be painted. The time is measured in months. "

Straight lime putty was not commonly used in the US for plastering, mostly because of the very long cure times.
A mixture of lime putty and gauging plaster was a common mixture.

The base coat (brown coat) was lime putty, sand, horsehair, and gauging plaster.

The second coat (scratch coat) was lime putty, sand, and gauging plaster. The surface was textured when partly set to provide better mechanical bonding for the finish coat.

The finish coat was lime putty and gauging plaster.
Layers were added when the lower layer was set, but not necessarily dry, to facilitate binding.

If the surface dried (like over a weekend) it was dampened before the next layer was applied.

The curing time is around a week in a heated space, and after that it can be painted.

Bonding to old plaster with Easysand or Durabond often fails since the old material is very dry, and pulls moisture from the new preventing it from curing correctly (Easysand and Durabond cure by chemical reaction, not drying out like pre-mixed joint compound).

There are also binding agents. Many are polyvinyl acetate based the same as Elmer's Glue.
They are applied to the old edges and allowed to dry until tacky.

Old plaster walls intended to be papered may not have a finish coat, but a smooth scratch coat.
It is not hard to place a finish coat using bonding agents and modern setting joint compound.
A plasterer's trowel makes the job go much faster than trying to cover the large areas with a drywall knife even a wide one).

One thing often missed in plaster work is the use of retarders to slow the setting time of the plaster.
High temperatures and can result in very short setting times unless retarder is added to the plaster/lime mix.
Simply adding more lime usually extends the setting time excessively.

"Plastering" by Sawyer is a standard text.

    Bookmark   January 1, 2010 at 3:16PM
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