Lath and plaster is not dangerous when it’s intact and undisturbed, but it can pose several serious health risks the moment you cut into it, sand it, or let it deteriorate. The main concerns are asbestos fibers mixed into the plaster, lead paint on the surface, and fine silica dust released during demolition. Whether your lath and plaster is a problem depends largely on when your home was built, what condition the walls and ceilings are in, and whether you’re planning any renovation work.
Asbestos in the Plaster Itself
Homes built before the 1980s commonly contain asbestos in their plaster. Manufacturers mixed asbestos fibers directly into the plaster compound or used them as reinforcement within the plaster layers, primarily for fire resistance and insulation. When the plaster is solid and painted over, those fibers stay locked in place and don’t pose an inhalation risk. The danger begins when you drill, scrape, break, or sand the plaster, releasing microscopic asbestos fibers into the air.
You cannot identify asbestos by looking at plaster. The fibers are too small to see, and they were blended into the mix at the factory. If your home was built before 1980 and you’re planning any renovation that disturbs the walls or ceilings, getting a sample tested by a certified lab is the only reliable way to know. Testing typically costs between $25 and $75 per sample, and it can save you from an exposure that’s linked to lung cancer and mesothelioma decades later.
Lead Paint on Plaster Surfaces
Lead-based paint was commonly used on interior surfaces until the 1950s and wasn’t banned from residential use until 1978. Plaster walls are frequently covered in multiple layers of paint accumulated over decades, and in older homes, the bottom layers almost certainly contain lead. HUD documentation notes that lead-based paint is especially common on glossy painted wall surfaces like kitchens and bathrooms, as well as on wooden trim and metal fixtures.
When that paint is in good condition, the risk is minimal for adults. The problem starts when the paint chips, flakes, or turns to dust, which happens naturally as plaster cracks and deteriorates. Water-damaged plaster is particularly concerning because moisture causes paint to peel and crumble, creating lead-contaminated dust that settles on floors and windowsills. For young children, who put their hands in their mouths frequently, even small amounts of lead dust can cause developmental problems. If you’re sanding or scraping old plaster walls, you can generate concentrated lead dust very quickly.
Silica Dust During Demolition
Plaster is largely made of calcium, sand, and sometimes Portland cement. When you tear it apart, the resulting dust contains crystalline silica, which the International Agency for Research on Cancer classifies as a known human lung carcinogen. Construction dust from demolition sites also carries significant levels of lead and other toxic compounds.
The health consequences of heavy silica exposure are severe. Silicosis, a permanent scarring of the lungs, is the primary risk for workers who regularly demolish plaster without protection. Research published in Safety and Health at Work found that workers with high silica exposure had a silicosis-related mortality risk more than 22 times greater than those with the lowest exposure. The same research estimated that the excess lifetime risk of dying from lung cancer ranged from 32 to 60 per 1,000 exposed workers. Chronic obstructive pulmonary disease is another documented outcome.
For a homeowner doing a single renovation project, the cumulative risk is far lower than for a career demolition worker. But a weekend of ripping out plaster in a closed room without a respirator still delivers a concentrated dose of harmful dust. OSHA sets the permissible exposure limit for respirable crystalline silica at 50 micrograms per cubic meter over an eight-hour shift, a threshold that’s easy to exceed during active plaster demolition.
Ceiling Collapse Risk
The structural danger of lath and plaster is most acute overhead. Plaster ceilings are held in place by a simple mechanical system: wet plaster was pushed through gaps between thin wooden laths (roughly 32mm wide by 6mm thick) nailed to the ceiling joists. The plaster oozed over the top edges of the laths and hardened into small hooks called “keys” or “nibs.” Those nibs are the only thing holding the full weight of the ceiling in place.
Plaster is brittle, and over time, vibration from foot traffic on the floor above causes keys to snap off one by one. Water leaks accelerate the process because moisture soaks into the porous plaster and weakens the nibs. Once enough keys fail in one area, the ceiling lets go suddenly. A section of plaster an inch thick falling from ceiling height can cause serious injury.
Warning signs that a plaster ceiling is failing include visible sagging or drooping, new cracks that seem to be widening, cracking sounds from above, and small circular blisters in a line where the plaster is pulling away from the laths. If you press gently on a suspect area and feel it move or hear a hollow, drum-like sound, the keys behind that section have likely already broken. Any ceiling showing these signs should be addressed promptly, either by having a professional re-secure the plaster to the joists using screws and washers, or by replacing it entirely.
Horsehair Plaster and Anthrax
This one comes up often in older homes where you can see animal hair fibers mixed into the plaster. Horsehair was added to lime plaster as a binding agent, and because anthrax is a disease of herbivores, there’s a theoretical possibility that spores could survive in the hair. The UK government lists horse-hair plaster as a potential source of anthrax contamination alongside animal hides and contaminated bone meal.
In practice, the risk is extremely low. The alkaline chemistry of lime plaster is hostile to most biological organisms, and documented cases of anthrax from old plaster are essentially nonexistent in the medical literature. If you’re concerned during a renovation, having a small sample tested (roughly the size of a credit card) is an option, but this ranks well below asbestos, lead, and silica on the list of realistic hazards.
Protecting Yourself During Renovation
If you’re removing or disturbing lath and plaster, the precautions are straightforward but non-negotiable. Wear a respirator rated for fine particulates (P100 filters provide the highest level of protection against asbestos, lead, and silica dust). Regular dust masks are not sufficient. Wear sealed goggles rather than safety glasses, because fine plaster dust gets around open frames easily. Use gloves to protect against the nails embedded in the laths and splinters from the wood. Close-toed shoes and dedicated work clothes round out the basics.
Seal the work area from the rest of the house with plastic sheeting over doorways and HVAC vents. Plaster dust is incredibly fine and will travel through an entire home if given the chance. Misting the plaster with water before demolition cuts down on airborne dust significantly. If you’re working in a pre-1980 home and haven’t tested for asbestos, treat the material as if it contains asbestos until you know otherwise, which means wetting it thoroughly, avoiding power tools that create dust clouds, and bagging debris in sealed containers rather than tossing it loose into a dumpster.
For homes built before 1978, assume lead paint is present on the plaster surface. The same wet methods that reduce silica dust also help control lead dust. If you have children in the home, keep them well away from the work area and clean all surfaces with damp cloths afterward, since sweeping and vacuuming (unless you’re using a HEPA-filtered vacuum) can redistribute lead particles into the air.