Clean a glass skylight as you would a window. Use only a mild soap or detergent solution on a polycarbonate plastic skylight; acrylic plastics can stand a weak ammonia solution. Avoid window-cleaning preparations and strong solvents such as acetone, alcohol, or gasoline; they can cause the surface to craze.
Remove grease or tar from acrylic with a soft cloth and kerosene, methanol, or high-grade naphtha; use either naphtha or isopropyl alcohol on polycarbonate. Never use abrasive cleaners or pads on any kind of plastic, or scrape off stubborn spots with a putty knife or razor blade. Minor scratches can often be obscured with a light buffing of automobile wax – it also protects a skylight’s luster.
If water stains develop on the ceiling around the frame, or if water drips from the edges of a skylight after a heavy rain, look first at the flashing above the skylight. Then check the outside joint where the skylight and the roofing meet. If you see any cracks or gaps, plug them with roofing cement and smooth the surface to get rid of pockets in which water can collect. If you can’t see a gap, line the entire joint with cement anyway to seal any invisible pinholes. If this doesn’t help, the leak’s true origin may be elsewhere on the roof. If water leaks through the skylight itself, the problem maybe that the watertight seal, or gasket, has deteriorated or come loose. Pry out the old seal with a chisel or screw-driver, clean the surfaces, and install a new seal with the adhesive recommended by the manufacturer.
A persistent leak in a new skylight may indicate a faulty product or improper installation. Check the guarantee; contact the supplier to have the skylight reinstalled or replaced.