When plastered walls and ceilings need repairs that cover more than a fourth of the total plastered area, complete replacement may be more practical. When working on older buildings you will find different types of plaster systems were used. Each type requires different preparation for replastering. Early Wood Lath First remove the plaster down to the wood lath. A flat-edged shovel or heavy ice scraper can make this work go quicker than hammers and crow bars. Check the condition of the lath by looking for rusted out nails and decayed or broken lath. If the lath is in good condition you can just leave it in place. Brush off the lath and seal it with oil-base primer or bonding agent. This