Building Homes or Extensions/horsehair plaster


Moonwildflower wrote at 2013-08-01 16:00:15
I have currently researched and tried a couple solutions to this. I have found that the solutions given by professionals are wide ranging and very contradictory. First, be sure the answer is for OLD HORSEHAIR plaster. Many solutions are for plaster, which is different. It is smoother.  The options and contradictions given:

1.   Use premixed joint compound. My friend did this totally successfully in her home - giving a skim coat of about 1/16" and sanding it smooth.  And serveral professionals (at stores and on line) have said this is the way to go. BUT, many contractors say NOT to do this because the plaster, if it is lime based, will resist the gypsum in the premixed drywall plaster and it will cause it to prematurely (within weeks or years) fail. I used it on one wall, and it dried nicely, but was not as solid as the plaster or spackling compound. It primed and painted well, though, and the paint adhered well. So I am not convinced this is not a good solution. But time has not tested its permanence.

2.   Use setting joint compound.  I used this after talking to the people at USG about their products, and they said NOT to use the premixed, but to use this. I scraped it on thin onto one wall, as the person here suggested, but I saw that it dried quickly. One person had said to be careful as it could dry before it actually set. Then it would not be hard.. just a dried powder. Went back to USG and he said it needed to be at least 3/32” (who can measure that??) thick to insure it has time to set. I did the rest of the walls thicker.  The next day, the walls were very patchy of darker and lighter grey. I went to wet sand, but the stuff just washed off. It seemed dry, and just a little softer than the premixed, so I let it go.. but was concerned.  The next day I primed it with 123 Zinsser primer. Two days later, put the gentlest tape on it to hold up a paint chip… and the paint peeled right off.  Went back to the bag of compound, and noted that it said the product would get HOT when setting. My walls never got hot… or even warm . So I do not think it ever set.  So I have primer over a layer of dust in a very difficult-to -paint stairwell.

3.   Use Veneer plaster or plaster of paris. This I have not done. When I first started out a contractor said I should not use any joint compound, but this would be a harder, better surface.    I bought the bag and was about to start, but then read that I would need to let it set for nearly 30 days before I could paint. Also, many sites say you need to use a plaster bonder between the two plasters. I found that the plaster bonder was not sold by anyone locally (I would think if it was so necessary, it would be carried), and it was going to be 2 weeks for me to get it. I suspect the idea solution is to use the plaster bonder, and then the veneer plaster. And go for the long time period.  But I went the above routes. In retrospect, 5 weeks later, I should probably have done this.

4.   Durabond. I did not use this, but it is supposed to adhere to the horsehair plaster well. Only it is super hard to sand afterwards. My neighbor used it once in his house, then took the remainder of the bag to the dump as it was impossible to sand. He went with plaster of paris.

5.   Spackling compound.   This has not been suggested by anyone, but, after having gone through all the above, I think I will use spackling compound. It adheres to everything. Hardens well, Paints well.  Is compatible with all surfaces. And since I am only scraping on the thinnest layer, although it is pricier, it is worth it in the long run. Does anyone find a problem with this?  

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Bruce E. Johnson


I can answer any construction related question in regards to carpentry, concrete, drywall, masonry, structural elements of any type of building, residential or commercial. Interior or exterior.


Custom Commercial and residential buildings. Churches, theaters, schools and auditoriums. Most recently I am working with the Catholic Church on several design build committees. I have a website related to scheduling and project supervision. Although my expertise is more related to multimillion dollar commercial, educational and theatrical projects my generous credentials in residential and remodelling construction make me a viable source of information regarding all forms of building questions.

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