Which primer to use on old plaster walls?


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I would like to use latex paint to on old plaster walls in a 1800's house. Some of the walls had to be patched with new plaster where the old plaster was removed down to the lathe. There appears they have been coated with calcimine before being wallpapered. I searched the internet on which primer to use before latex and now I'm totally confused. Should I use oil, water based, shellac or Zinsser Guardz?
 
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Hi there, the old plaster is probably lime based which ideally needs to breath. The purpose of priming is for the first coat to sink in to the substrate so the top coats can sit on top. If you use shellac it will peel off, water based is best. I would get a latex free contract Matt with a low sheen rating, diluted with maximum 20% water for the first coat. This will effectively sink in to the substrate providing a secure base. When the first coat is applied, the pigment in the contract Matt will highlight all of the imperfections which require filling. Use a portable site light to shine up the walls when filling. this will enable you not to miss any imperfections. The best filler to use is a pre mix plaster based filler such as toupret interior filler. Hope this helps
 
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I would recommend using a 150mm orbital sander to remove any of the original wallpaper adhesive. This can really ruin the top coats.
 
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Hi there, the old plaster is probably lime based which ideally needs to breath. The purpose of priming is for the first coat to sink in to the substrate so the top coats can sit on top. If you use shellac it will peel off, water based is best. I would get a latex free contract Matt with a low sheen rating, diluted with maximum 20% water for the first coat. This will effectively sink in to the substrate providing a secure base. When the first coat is applied, the pigment in the contract Matt will highlight all of the imperfections which require filling. Use a portable site light to shine up the walls when filling. this will enable you not to miss any imperfections. The best filler to use is a pre mix plaster based filler such as toupret interior filler. Hope this helps
Thank you for all the info. The only problem is finding a paint that will allow the room to breathe. Do you have any recommendations?
Also, I'm curious what would happen to the wall if you use a regular latex paint from a manufactuer such as Benajmin Moore?
 
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Hi. Most modern water based emulsion paints are latex Or vinyl based for durability. They’re only partially breathable but designed specifically for high traffic areas. Most reputable paint suppliers offer breathable or semi breathable paints tinted to a colour of your choice. The latter would be more suitable for lime plaster for longevity. Should you decide on a latex based topcoat, it will just sit on top of the wall without soaking in and breathing fully as required. My company usually fills and machine sands any imperfections and apply high grade, thick lining paper horizontally. This is the correct method however as we have pasting machines it’s a quick process for us, domestically however it’s hard work and time consuming. If your house is not high traffic in relation to kids and pets, I would use a breathable paint as stated above. Otherwise latex based should be fine for durability, but due to the high latex content the touch up capability is poor for highly lit areas. Any touch ups you carry out for marks on the walls will stand out heavily.
 
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Thank you for your clear explanation. I 'm not confused anymore. Can you give me an idea who makes breathable interior paint?
 
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No problem, I’ve just checked the website I’ve referred to again, however I think they only sell solutions for lime masonry. If you were to apply contract Matt in a tint of your choice to the wall after the primer coat this has never failed my company. Plus it’s cheaper and the finish is more contemporary. Hope this helps. Best of luck with the project.
 

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