The new plasterboard on this wall can be finished up to the existing cornice. This will prevent damage to the cornice or other walls when removing the render. I suggest using a rip saw make a cut down the internal corners and along the ceiling line. If you only need to treat one wall this way and you have a decorative cornice you want to keep. In this case, I would consider stripping off all the remaining render and replace it with Plasterboard. If you get an area of fall out as large as area "A" I would seriously consider this wall to be irreparable. Area A, is what I would call a "falling out" of the render. I have noted 3 types of areas "A", "B", "C" and a typical crack. This Diagram, indicates several typical scenarios, that can occur when repairing lath and plaster wall. Replacing with Plasterboard, (required for area "a" type damage) If the render feels like it wants to lift away, then cut it out back to where it becomes solid again. It is important to remove ALL the loose material. With the trimming knife, I make a cut down each side of the crack in a v shape, (see diagram below). Or my preferred method is a trimming knife.
You can buy a triangular shaped scraping tool to do the job. I recommend that the crack is scraped out to 15mm to 20mm wide. Therefore you need to dig the crack out, all the way to the substrate. The biggest mistake I see being made, is people try to fill over cracks in lath and plaster, or just scrape the surface.Ī crack in lath and plaster or render, runs right through to the substrate behind it. If a lath and plaster wall is repaired properly, there is no reason the repairs won't last for years. If a lath and plaster wall can be repaired, it can save a lot of money in renovation cost. These are the areas like this in lath and plaster, need to be removed and replaced.
Areas that sound hollow, or loose, are what is termed, 'DRUMMY". You do this by tapping on the surface, if it sounds firm it is most likely ok.
The first thing you need to do when assessing lath and plaster for repair, is to see if the wall is "DRUMMY". If you re-block your home, cracks in lath and plaster can become, "slabs of plaster" missing, or falling out. Most old buildings with lath and plaster have some cracking. Where I consider an cracks in lath and plaster repairable, I have include the best methods of making the repairs below. I have provided below, examples of typical damage to lath and plaster, that I consider repairable, or not repairable. Ultimately the decision to repair or replace the lath and plaster, is up to you. Working out if a lath and plaster wall or ceiling is worth fixing, will depend largely on the nature of the project and the amount of money, or work, you are prepared to put in.