Painting Timber Sash Windows in a Period Home

Almost every original home through Toorak, Armadale, Hawksburn and Kooyong still has timber windows, and on the older houses those windows are double-hung sashes. They are the single most labour-intensive element of an exterior repaint, they are where most of the rot in a period home lives, and they are the part of the job most often quoted thin and then rushed.

If you have ever had a house painted and afterwards found a window that will not open, you have seen what rushing looks like.

Why sash windows are different

A sash window is not a fixed panel. It is two moving timber frames running in a boxed jamb, hung on cords over pulleys, with a parting bead between them. Paint has to protect the timber without building up in the running clearances. Get that balance wrong in either direction and you either seize the window or leave bare timber where water sits.

The other difference is exposure. Sills and the bottom rails of the lower sash take more weather than any other timber on the house. Water sits on a horizontal surface, works into the end grain at the joints, and stays there. That is why rot in a period home almost always starts in the same three places: the sill, the bottom rail, and the joint where the two meet.

What proper preparation actually involves

The window comes back to a sound, firm edge. On a house that has been painted a dozen times over a century that can mean a substantial amount of old coating has to go, particularly where it has built up in the corners and softened the profile.

Anything pre-1970 is treated as lead-painted until proven otherwise. That changes how the removal is done, meaning wet methods, controlled scraping, sheeting below to catch debris, and no dry power sanding. It is slower, and it is not optional. There is more detail on this in our piece on lead paint in older Melbourne homes.

Once the old coating is off, the timber gets assessed honestly. Soft sections are cut out and spliced with matching timber rather than packed with filler. Filler is for nail holes and small defects, not for structure. A bogged-up sill will fail again within two or three years, and it will take the new paint with it.

Bare timber is primed the same day it is exposed. An oil-based primer soaks into the end grain, and the end grain at the joints is where water gets in. Priming that properly is the difference between a repaint that lasts and one that starts bubbling at the joints in the second winter.

Keeping the window working

The moving faces of the sash and the parting bead get a thinner build than the exposed faces. The aim is protection without packing out the clearances. Windows are worked while the coating is still curing so it does not bond the sash to the jamb, and the cords are checked while everything is accessible.

If a sash cord has broken, that is the moment to replace it. The window is already apart, the boxing is already open, and doing it later means undoing the paintwork you just paid for. It is worth asking whether cord replacement is inside or outside a quote, because it frequently sits outside and then reappears as a variation.

Glazing putty

Old linseed putty goes hard, shrinks and lets go of the glass, and once it cracks water runs straight down inside the rebate. Failed putty is raked out and replaced, and new putty needs to cure before it is painted or the coating will wrinkle.

The paint line should run a couple of millimetres onto the glass. That is not sloppiness. It seals the junction between putty and glass, which is exactly where water would otherwise track in.

What it means for your quote

Sash windows are where quotes for the same house diverge most. One contractor allows for scraping back, splicing rot, replacing putty and freeing the sashes. Another allows for a scuff and two coats. The second number is lower, and it is lower because the work is not in it.

Worth asking directly: what happens if rot is found in the sills, is putty replacement included, and will the windows open when you are finished. Vague answers on those three tell you most of what you need to know.

Window work sits inside our Exterior House Repainting service, and on heritage properties it runs as part of Heritage and Period-Home Repaints, where profiles and colours have to suit the age of the house. Where sills and adjacent boards have gone too far, it overlaps with our Weatherboard and Render Restoration work.

The short version

Sash windows reward patience and punish shortcuts. Strip back properly, treat pre-1970 coatings as lead, splice rot rather than fill it, prime bare timber the day it is opened up, replace failed putty, and keep the running clearances clear. Do that and the windows will still be sliding in twenty years. Skip it and you will be back at them in three.