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Ask the Carpenter: Making a faded fiberglass door look like new

Ask the Expert Home Improvement
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Q. Ten years ago we had a new fiberglass entry door installed. The door is in the front of the house and gets a lot of sun in the afternoon. About two years ago, I noticed that the exterior finish on a few sections had started to fade. I contacted the manufacturer, who was no help, and discovered that the warranty had expired. The door has a wood look to it, so should I apply a clear marine varnish or a different product? When I apply a product, should I just do the areas that have faded or the entire door? The surface seems smooth, so do I need to do any other preparation besides cleaning it?

R.S.

A. Fiberglass doors have a much higher resistance to weathering than wood and steel, but exposure to sunlight can fade them, as you have discovered. Depending on the fading, you may be able to patch the stain.

Before you paint or stain the surface, clean your door properly. Use a non-sudsing cleaner like TSP and water and a sponge. Dry off the door with a clean rag.

Patching in the stain

You can use gel stain to touch up faded areas. Use a color that matches your fiberglass as closely as possible. Typically one thin layer will accomplish what you need. Apply it with a natural-bristle paintbrush. Gel stain will protect the door from fading. When the door is dry, look to see whether you need to apply another coat or change the color. Finish up with at least two layers of fiberglass topcoat, waiting for it to dry between applications.

Refinishing the whole door

To remove the old, faded finish, apply a thin layer of water-based stripper and wait at least an hour.

Therma-Tru, which makes fiberglass doors, recommends using a methylene chloride stripper, because you need something that will cut through the topcoat as well as the stain layers.

When stripping a finish, you may need to apply subsequent layers, repeating this process until the finish begins to loosen and you can scrape it off with a putty knife.

Once you’ve removed the layers, sand the door a bit with 120-grit paper. Clean the entire surface with a rag soaked in denatured alcohol.

Apply a gel stain. Once it dries and you’re happy with the color, apply at least two layers of fiberglass topcoat, waiting for it to dry between applications.

Painting over it all

If you choose to go this route, use an exterior acrylic. Acrylics are more resistant to ultraviolet light than many other paints and are designed to withstand weathering, making them perfect for fiberglass doors. You can apply exterior acrylics over gel stain; however, you must prime the surface first. Use a roller to apply at least two coats of exterior acrylic primer to the door. Use a natural-bristle brush to apply the acrylic paint over the primer. One note: Dark colors will absorb more heat, which could cause warping.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.