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Damaged plaster crown molding

I have a 1927 tudor style home that has plaster crown molding in several rooms. One area has some damage from a previous water leak. (see attached photos)

The plaster is large and most likely made with a form. Is there a way to repair this plaster, or do I need to remove the plaster crown for the entire room, and install new crown molding?

I took measurements and have started to create a profile, so I can make a form (possibly out of wood) that matches the crown molding. The thought was to chip away all the loose plaster and use the form to mold some new plaster in place. My concern is - will the new plaster adhere to the old, or will the weight of it make it fall to the floor over time?

Hank Bauer
Re: Damaged plaster crown molding

Yes you can repair the plaster cornice in place it should be fine.
First use a section of the cornice that has a good profile scribe a straight line square from either the top or bottom than saw cut this about one inch deep cut a piece of poster paper or card board insert in saw cut scribe profile from cornice to paper.
Use this profile to copy on to peel and stick paper like lable paper for the printer.
Stick this to a sheet of 18 guage sheet steel ( by it at Lowes )use a scroll saw and cut to the lines tihs will be an exact match to existing.
I use the blades that have 15 / 18 teeth per inch they are for mild steel you will get about 3 inches of cut per blade.
Than file and sand paper smooth.
Mount to a piece of plywood with one end thatb has a foot to ride on the ceiling and one foot to ride on the wall.
Temp nail a straight edge to wall use as a guide. ( like a railroad track )
For repair material I would use a mixture of Lime puddy ( lime mixed with water )you can mix all this you think will be required ahead of time just keep cover with a little water.
When you are ready to start the repairs mix moulding plaster ( Plaster of Paris )with the lime.
Mix at a ratio of 8 parts of lime to 1 part moulding if this sets to fast for you use 1/2 part moulding.Or adjust set time by adding /subtracting plaster.
Also you may want to do the cornice in half sections.
To do this use the ceiling and the flat area in the cornice and due the top first than the bottom using the flat area as a intersecting point this may make it easy for someone not used to working with plaster.Also this will let you remove the template with out any problems.

Re: Damaged plaster crown molding


I use 26 ga sheet metal and cut it out with tin snips. There is a plastering book called "Plastering Skills" by Van Den Branden / Hartsell. Covers cornice work very well.

Hope this helps

Hank Bauer
Re: Damaged plaster crown molding

Plastering Skills is a very good reference for plastering.
If you need other plastering books for templates try the following Building With Lime by Stafford Holmes and Michael Wingate.
And for the very best book on plastering get hold of Plastering Plain & Decorative by William Millar ( Donhead Publishing Ltd )This book will give the best details.
Building with Lime will be the easyest to follow for a DIYer.
As for the gauge of metal 26 Ga. will work but will bend if the material sets to fast for the worker.
I find 18 ga. better for cornice due to the fact it will cut the material after it has started to set with out bending.
And yes wood can be used but will not product as fine detail like metal.
I have also used plastic sheet material but this must be 3/16 to 1/4 inch thickness and will wear and change the profile for long runs.
You can also restore the cornice using mitering rods this has to be done in small sections at a time and you must start with a good section in the existing cornice and work away form that point.

Re: Damaged plaster crown molding

I have patched damaged plaster crown moldings by forming a profile from wood. I traced the profile in a similar manner to the posts above. I scraped and sanded the loose plaster down to firm plaster. After dampening the damaged plaster, I used "hot mud" drywall compound as the patching medium. I prefer Durabond Easy Sand 20 as it can be sanded and shaped easily after applic- ation. Easy Sand also has very good adhesion. Products such as plaster of paris do not like to feather out. Plasterers use a bonding agent around the edges of a patch where the plaster becomes very thin. If the bottom edge of the crown is not straight, I fasten a straight board to the wall upon which I can drag the profile.

My meathod might be somewhat unorthodox, but it does the trick. Also, good plasterers are somewhat hard to come by, especially when you need them. In many areas of the country, plastering is seldom used on new construction. The plasterers who are still to be found, exist by patching old construction from years gone by.

I remember about 25 years ago when the Auditorium Theater in Chicago (circa 1883) was re-habbed, they had difficulty finding tradesmen skilled in plaster molding. As I recall, they tapped into foreign tradesmen from Europe who were trained in that craft.

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