Why Do Window Screens Turn Black?

These are the usual causes, from the most common:

• Dirt, dust and pollen caught in the weave, which leave the mesh dark and hazy
• Soot and exhaust on homes near busy roads, a gray-black film over the mesh
• Mildew, which grows on that dirt in Florida's humidity and shows as black or dark green spots
• Corrosion on aluminum mesh near salt water, which turns it dull, dark and brittle
• Old spline, the rubber cord that holds the mesh in, breaking down into black crumbs along the frame

Dirt and soot sit on the surface. Mildew that has set in, corrosion and crumbling spline are in the window screen itself.

It helps to know what color the mesh started. Most fiberglass window screen mesh is charcoal, a dark gray that looks almost black from outside, more so in front of a dark room. That is the normal color, chosen because it is easier to see through than lighter mesh. If your window screens have always looked dark from the street and the view from inside is still clear, nothing has gone wrong.

The sun does the opposite of turning mesh black. Years of strong sun fade charcoal fiberglass to a lighter, chalky gray before it turns brittle.

Mildew needs damp and something to feed on, and window screens in Florida have both. It tends to be worst on the shady side of the house, along the bottom of the frame where rain sits, and on window screens that sprinklers reach. Early on it is a surface stain. Left for years, it sets into the weave and stains the mesh for good, and by then the mesh around it is usually worn as well.

Near the Gulf and the bay, salt air corrodes aluminum. On aluminum mesh it shows as dark, dull patches, and the wire turns brittle and starts to break. On the frame it shows as white powder and pitting, most often at the corners. Fiberglass mesh does not corrode, which is one reason it is the usual choice near salt water.

Black crumbs or marks along the edge of the mesh usually come from the spline. Old spline dries out in the heat, cracks and breaks into pieces, and the mesh starts to pull loose soon after. Black streaks on the sill or the wall below a window can also be dirt that rain has washed out of the mesh.

A dark window screen needs new mesh when:

• Dark spots or stains have set into the weave
• The mesh feels stiff or crackles when it is pressed lightly
• Aluminum mesh has dark, brittle patches or is breaking
• The spline is cracked or crumbling and the mesh is pulling away from the frame
• The view out stays hazy even when the mesh is clean

That is a window rescreening job: the old mesh and spline come out, and new mesh and spline go into the frame you already have. If the frame itself is corroded or bent, it needs window screen replacement instead. Our post on whether to repair, rescreen or replace a window screen goes through each case.

New mesh can be the same as before or a different kind. Standard fiberglass is the usual choice and does not corrode near salt water. No-see-um mesh suits the windows near the water, solar mesh the sunny side, and pet-resistant mesh anywhere a dog or cat can reach. Our post on the best window screens for Florida homes explains which suits which window.

Call us if:

• Your window screens have turned dark, blotchy or hazy and you want to know if they can be saved
• The mesh is stained, brittle or breaking
• There are black crumbs along the frame, or the mesh is pulling loose at the edges
• Aluminum mesh or frames are corroding near the water