Interior Painting right here in Milton, Massachusetts.

The Census Bureau puts the median construction year of Milton's housing at 1945, and 4,278 of the town's 9,335 housing units, or 45.8%, were built in 1939 or earlier. Inside a house that old, the surfaces under the current paint may have been coated many times by different hands, with different products, over several decades.

That history is what an interior estimate has to read. A wall can look fine from across the room and still have hairline cracks, old patch ridges, flaking at the ceiling line or a glossy layer that new paint will not grip. Those spots need to be found and fixed before the first coat, because paint applied over them tends to crack or lift where the old problem was.

Plaster walls and ceilings

A house built before the Second World War may still have its original plaster on wood or metal lath. Plaster is hard and quiet, but it moves with the framing over the years, which shows up as diagonal cracks above door openings, map-like crazing on ceilings and, in worse cases, areas where the plaster has let go of the lath and bulges when pressed.

Hairline cracks can be opened slightly, filled with a setting-type compound and sealed with primer so they do not telegraph through the finish. A ceiling that sags or sounds hollow is a repair item, not a painting item: it needs to be re-attached or patched before any color goes on, because paint adds weight and moisture to plaster that is already loose.

Ceilings deserve their own line on the estimate. Old calcimine or distemper coatings, which some early houses still have under later paint, can soften when wet and lift off in sheets, so a small test patch tells you whether the ceiling needs sealing first.

Lead dust is the main indoor hazard

By Census count, 7,606 Milton housing units, 81.5% of the total, were built before 1980. The bracket for the 1970s straddles the 1978 federal ban on lead-based residential paint, so a few of those homes postdate it, but the share of houses where older layers could contain lead is large either way.

Indoors, the risk comes from dust rather than chips. Sanding a window stool, scraping a door edge or opening up a cracked baseboard can release fine particles that settle on floors where children crawl. The EPA's Renovation, Repair and Painting rule requires certified firms and lead-safe practices for paid work that disturbs paint in pre-1978 homes: plastic containment, no power sanding or planing without HEPA-shrouded tools, HEPA vacuuming and a cleaning verification before the room is reopened. Our lead-safe painting page describes each step.

Trim from more than one era

Milton's housing did not all go up at once. The Census counts 795 units built in the 1940s and 1,347 in the 1950s, then 881 more since 2000. Woodwork from those periods was finished with different products, and older doors and casings may carry oil-based enamel somewhere in their layers.

Water-based paint brushed directly onto old oil enamel can look fine for a week and then scratch off with a fingernail. A quick adhesion test and, where needed, a bonding primer prevent that. Our comparison of latex and oil-based paint explains why the primer step is not optional on glossy old trim.

• Plaster crack repair and skim patching
• Ceilings, including sealing chalky older coatings
• Window casings, stools and sashes
• Doors, baseboards and stair balusters
• Built-in bookcases and paneled walls

Painting an occupied home

The town's housing also includes 1,070 units in two-family buildings, where an owner may be painting one floor while tenants live on the other. Whether it is a two-family or a single house, interior work goes better when rooms are done in a set order, furniture is grouped and covered rather than moved out, and shared hallways and stairs are scheduled so nobody is cut off from their own door.

Interior painting is not tied to the outdoor season, so the colder months are a practical time for it. Our notes on winter interior painting and on painting with kids and pets at home cover ventilation, drying times and keeping wet surfaces out of reach.