How to Stain a Therma-Tru Fiberglass Door

How to Stain a Therma-Tru Fiberglass Door

Guide to Staining a Therma-Tru Fiberglass Door

Therma-Tru fiberglass doors are known for their durability, energy efficiency, and aesthetic appeal. While these doors come in various finishes, you may want to customize the look of your Therma-Tru fiberglass door by staining it.

Staining a Therma-Tru fiberglass door can elevate its appearance and change the look to your home’s entryway. This guide will delve into staining a Therma-Tru fiberglass door, addressing common questions and providing step-by-step instructions.

Can You Stain a Therma-Tru Fiberglass Door?

Yes, you can stain a Therma-Tru fiberglass door. Despite the misconception that fiberglass doors cannot be stained, Therma-Tru doors are specifically designed to accommodate staining. However, following the correct procedure is vital to ensure optimal results and preserve the door’s integrity.

Before Beginning, Know the Do’s and Don’ts


  • For optimal staining conditions, ensure temperatures range between 50°F and 90°F, with relative humidity below 80%.
  • Stain all exposed edges and ends of your fiberglass door and approved Therma-Tru composite materials.
  • Finish all weather-exposed wood surfaces within two weeks of exposure.


  • Stain or apply topcoat when dew is present.
  • Stain in direct sunlight.
  • Sand stainable polyurethane door surrounds.

What Is the Best Way to Stain a Therma-Tru Fiberglass Door?

Staining a Therma-Tru fiberglass door involves several steps to achieve a professional-looking finish. Here’s a breakdown of the best way to stain your door.


Start by removing existing hardware from the door, such as handles and locks. The weatherstrip may be removed from the jambs by gently pulling it out. Re-insert the weatherstrip by pushing it in after the door is finished and dry.

Next, thoroughly clean the door surface using mild detergent and water. You must remove dirt, grime, and other contaminants. The door must dry completely before proceeding to the next step.

Steps for Cleaning Excess Sealant on Glass

  • Spray the area with a standard glass cleaner.
  • Scrape off the excess sealant with a new razor scraper, holding it at a 45° angle. Be careful not to scratch the glass.
  • Wipe the area with a dry, clean rag.
  • Check for gaps between the glass frame and the glass and fill before staining. 

Color Test and Stain

Before starting the staining process, you must choose a high-quality exterior stain suitable for Therma-Tru Door surfaces. 

Once selected and before applying, stir the stain well with a stir stick. Improperly mixed stain will not dry correctly.

Practice staining before applying stain directly to your Therma-Tru composite materials. If staining a previously stained door, choose a stain test sample that best matches your door to practice applying the stain. Set the remaining fiberglass test sample aside to be used later to test for dryness.

Practice applying stain on a scrap piece. If this cannot be done, practice using stain on a hidden product area.

Should you want to start over, the test stain can be removed with mineral spirits and reapplied until you reach your desired color.

Test The Sample Area For Dryness

To ascertain if the stain has dried adequately for the topcoat application, follow these steps in the area where you did the test.

  1. Allow the test area to dry for at least 6 hours before assessing its dryness and proceeding with the topcoat application.
  2. Place a masking tape on the test sample, ensuring it adheres firmly.
  3. Press down on the tape firmly, then remove it.
  4. The stain is completely dry when the tape can be removed without lifting any of the stain from the sample.

If the stain is not dry, repeat the testing process every hour until dryness is achieved.

how to stain a therma-tru fiberglass door

Apply Stain

Use a brush or a staining clean rag to apply the stain evenly to the door’s surface, following the direction of the grain or circular or cross-grain motion.

To achieve optimal results, follow these steps for applying stain to your door section by section.

  • Begin with the glass frame, if applicable.
  • Address deep grooves in door panels using the tip of the foam brush.
  • Proceed to interior panels.
  • Apply stain to interior flat sections.
  • Address exterior flat sections.
  • Finish with the door frame, wood door edges, brick mold, mullions, and astragals if applicable.

Remember to use the staining rag or foam brush to ensure even color distribution, wiping the stain toward the grain. Allow the stain to dry for 10–15 minutes.

Wipe Off

Next, use a cleaning rag to achieve your desired shade, wiping in the direction of the grain. Wait a few minutes for lighter shades, then rub off the excess stain. Allow the stain to dry for 2–4 hours before adding coats for darker applications.

Allow to Dry

Allow the stained door to dry completely according to the manufacturer’s instructions. This typically takes several hours, depending on the weather conditions and the type of stain used. Avoid touching the door during this time to prevent smudges or fingerprints.

Apply a Sealant Protectant Top Coat

Consider applying a clear sealant or topcoat over the stained surface for added protection and longevity. This helps seal the stain and provides an extra defense against the elements.

Stir the topcoat thoroughly using a stir stick, avoiding shaking, as it can introduce bubbles and lead to improper application. Although initially milky, the topcoat will dry clear.

To prevent bristle loss during application, periodically tug on the bristles with a rag to remove any loose strands.

To begin applying the topcoat, dampen the tips of a 2″ synthetic brush and apply a thin initial layer of topcoat. Apply the topcoat smoothly and evenly, avoiding excessive brush strokes to prevent bubbling or loosening of the stain. If such issues occur, promptly remove the flawed topcoat before it dries by gently wiping it with a clean rag and touch up with a fresh layer of topcoat.

After application, clean the brush with water. Allow the first layer to dry for 2–3 hours before applying a second thin layer. Surfaces should appear wet but not milky. Clean the brush again after each application,

Reattach Hardware

Once the door is fully dry and the sealant, if used, has cured, reattach the hardware, such as handles and locks, to the door according to the manufacturer’s instructions.

Do You Need to Strip Before Restaining a Therma-Tru Fiberglass Door?

In most cases, stripping the old finish is unnecessary when restaining a Therma-Tru fiberglass door. However, stripping may be required to achieve satisfactory results if the door has previously been painted or stained with a thick or uneven layer or if the existing finish is chipping or peeling. Use a paint stripper designed explicitly for fiberglass surfaces and follow the manufacturer’s instructions carefully.

Stripping For Refinishing

Select a standard paint stripper from the approved list below for use with Therma-Tru Door Systems.

  • CitriStrip® Multi-Surface Paint Remover*
  • Multi-Strip® Advanced Paint Stripper
  • Jasco® Premium Paint and Epoxy Remover
  • Klean-Strip® Kwik Paint and Varnish Remover
  • Savogran® SuperStrip

  1. Follow the manufacturer’s directions and cautions for proper use. Consult the manufacturer of your fiberglass doors or composite materials for specific details.
  2. Apply the stripper to small areas at a time.
  3. Start by applying the stripper to the (A) glass frame first and then (B) the raised panels (see illustration) before proceeding to the rest of the door.
  4. Remove the stripper according to the manufacturer’s instructions. Prolonged exposure to paint strippers may remove factory-applied primer from fiberglass doors or approved Therma-Tru composite materials.
  5. Use a brass wire brush or nylon bristle brush for easier paint and stain removal from wood-grain textures. Grade 000 steel wool can also be used for fiberglass doors.
  6. Rinse off any remaining stripper. After removing the stain or paint, clean the surface with mild soap and water to remove all residue. Rinse thoroughly and wipe dry. the surface must be entirely clean and dry before proceeding with refinishing.

(please note all of these instructions may not work on all surfaces and for everyone. Therefore, it is highly recommended to consult a professional before staining a Therma-Tru fiberglass door)

Sand the Surface

Lightly sand the surface of the door with fine-grit sandpaper. This helps to roughen the surface slightly, allowing the stain to adhere better. Sand in the direction of the grain to avoid damaging the fiberglass.

Are You Ready To Get Started?

Staining a Therma-Tru fiberglass door is a rewarding DIY project that can enhance your home’s beauty and curb appeal.

Whether you’re looking to refresh the look of your existing door or customize a new one, staining is a versatile and effective way to achieve your desired aesthetic. With proper care and maintenance, your stained Therma-Tru fiberglass door will continue to impress for years.

If you would rather a professional stain your Therma-Tru door, contact Carolina Blue Painting. As staining any project can be quite a challenging task, to ensure the results of your door is the absolute best, contact us here.