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How to Stain the Exterior of a Therma-Tru Fiberglass Door

Therma-Tru fiberglass Classic-Craft and Fiber-Classic doors come from the factory coated with a special primer. To create a stain wood appearance, use the Therma-Tru stain over the primed surface. The company offers a range of pre-mixed stain colors, which you can inter-mix to create a custom stain. It also sells a stain kit which includes everything you need for both the interior and exterior of the door, including stain, applicators, clear protective finish and mineral spirits for cleaning up. Purchase the stain and stain kits online through Therma-Tru or at a Therma-Tru dealer.

Step 1

Clean the door with a rag soaked in mineral spirits to remove surface dirt and very fine surface scratches and scuffs. 

Step 2

Mask door glass, hardware and hinges with blue painter's tape.  Either mask the weatherstripping, or remove it. Push the weather-stripping back into place after the door is finished and dry. 

Step 3

Stir the stain thoroughly with a stir stick (provided in the Therma-Tru stain kit) Mix all the pigment from the bottom of the can by scraping it up with the end of the stir stick and stirring until you have achieved a uniform consistency, without lumps. 

Step 4

Wipe some of the stain onto the provided sample piece of fiberglass if you are using the stain kit on a new door.  Use one of the rags provided in the stain kit, and remove the excess with a clean rag. Wait a few minutes before wiping off the excess; apply a second coat if you want a darker effect. 

Step 5

Apply the stain using the sponge and rag applicators provided.  Use the sponge to brush the stain into the edges and panel grooves and the rag for the flat areas. Work it into the grain with a circular motion, making sure all the grain and edges are saturated.  Wait 10 to 15 minutes for the stain to dry. Wipe away the excess with the rag. 

Step 6

Brush the wiped stain in the direction of the grain with the natural bristle brush provided, which blends and softens the stain.  Let the stain dry for at least 6 hours. Test for dryness by pressing a piece of masking tape to your sample.  If the tape doesn't pull stain away when you remove it, you can proceed with the top coat. If any stain lifts with the tape, allow more drying time. 

Step 7

Stir (don't shake) the clear top coat. 

Step 8

Apply at least two thin, even coats of top coat, waiting 2 to 4 hours between coats.  Use the 2-inch synthetic brush provided. The top coat will have a milky appearance at first but becomes clear as it dries. 

Things You Will Need

  • Therma-Tru stain kit
  • Mineral spirits
  • Rags
  • Blue painter's tape
  • Stir sticks
  • Fiberglass sample
  • Sponge applicator
  • Stain
  • Natural bristle brush
  • Top coat
  • Synthetic brush

Tips

  • You do not have to take the door down to finish it. It's fine to stain and varnish the door in place.
  • Don't sand the door before staining it because you'll create small scratches that will show up in the stain.

Warnings

  • Open windows or use fans if working indoors to dissipate solvent fumes and speed drying time.
  • Don't apply stain or top coat if the temperature is below 50 degrees F or if it's very humid or threatening to rain.

About the Author

Stevie Donald has been an online writer since 2004, producing articles for numerous websites and magazines. Her writing chops include three books on dog care and training, one of which won a prestigious national award in 2003. Donald has also been a painting contractor since 1979, painting interiors and exteriors.