I am finishing up a heater facing with 4″ solid concrete block. The client wants a smooth white plaster look finish that will compliment the rest of the walls in a mid 1850’s vintage house. I am considering a first coating of white thinset with a fiber mesh embedded, then using a setting type drywall compound as a final finish. I would be interested if any other heater builders have any other ideas or concerns about going this route ? Should I fire this thing up and get the moisture out first ?
My “plasteresque ” finish experiment was completed using an off the shelf setting type joint compound with a 60 minute working time. It was purchased from the “big orange ” box store for $12.25 /25lb. bag. I didn’t dry out the heater before finishing as I would have had to mount the doors, then remove them, then put them back on……..! I did gain some valuable experience. It is essential to have a round cornered pool float ( the more flexible the better ), and a sponge float to limit the trowel marks that are very hard to see on a white surface until they dry or the light changes or both. When this stuff sets it is virtually impossible to smooth out any imperfections with ordinary drywall finishing techniques. Sand paper and rub rocks are of little help. One would need to break out the diamond wheels and power tools! I think it makes a very durable heater finish, but not one I would like to repeat. I didn’t like the physical and emotional stress caused by the short working time.
I don’t like sweating a potential disaster by using the incorrect product for the job.
As a rule, I would avoid using anything like “hot mud” as a finish on a masonry heater, same with thinset, mortar, or grout as a finish plaster. You won’t be happy during the process and chances of disaster are really high.
I like real lime plaster, clay plaster, alis plaster, hemp plaster you won’t know until you have used them all.