A fiberglass shower can be one of the most convenient and cost-effective ways to have a fully waterproof and durable shower installed in your home. However, over time, fiberglass can become damaged from impacts, water exposure, or just regular wear and tear. When damage occurs, it is possible to repair a fiberglass shower and restore it to like-new condition again. With some basic tools, materials, and repair knowledge, you can fix chips, cracks, and other damage in a fiberglass shower surround. Here is a comprehensive guide on how to properly repair a fiberglass shower.

Assessing the Damage

Before starting any repairs, you need to fully assess the type and extent of damage to your fiberglass shower unit. Here are some of the most common issues to look for:

Chips and Cracks – Over time, dropped objects, bumps, and normal wear can cause small chips and cracks in the fiberglass. Check the tub floor, walls, and thresholds thoroughly for any cracks or fractured areas.

Delamination – Delamination occurs when the outer gelcoat layer separates from the underlying fiberglass. You may see bubbling or cracks appearing. Press gently on suspect areas to check for delamination.

Water Damage – Leaks, flooding, or chronic moisture exposure can cause the resin in fiberglass to swell and distort. Inspect for areas of white, softened fiberglass.

Mold/Mildew – Discoloration, soft spots, or musty odor can indicate mold or mildew growth. This is usually caused by chronic moisture.

Stains/Discoloration – Over time, hard water, dirt, soap residue and chemicals can stain the gelcoat surface. Assess the severity and cause of any stains.

Thoroughly inspect all surfaces of the fiberglass tub surround, including the walls, base, thresholds and any shells or fixtures. Make note of each area of damage, the size, and probable cause. This information will determine the necessary steps and materials for repair.

Gather the Right Repair Supplies

Fixing fiberglass shower damage requires using the proper materials and supplies specifically designed for fiberglass repair. Gather these supplies before starting your project:

  • Acetone – Used for cleaning and prepping the repair area. Ensure it is 100% pure acetone without any additives.
  • Fiberglass cloth – A cloth fabric made of fiberglass fibers soaked in resin. This adds strength to repaired areas.
  • Fiberglass mat – A compressed fiberglass sheet used for patches and replacements.
  • Resin – Polyester resin is used to soak and adhere fiberglass patches and cloths.
  • ** MEKP catalyst** – Methyl ethyl ketone peroxide that hardens and cures the resin.
  • Body filler or Bondo – Used for filling holes, chips, and cracks before painting.
  • Gelcoat – Pigmented polyester resin used for the outer finish layer.
  • Sandpaper – An assortment of grits like 80, 150, 220 for sanding.
  • Paint – Matched touch-up paint for refinishing repaired areas.
  • Paint brushes, rollers – For applying resin and paint. Disposable brushes recommended.
  • Mixing cups, sticks – For accurately measuring and mixing repair products.
  • Gloves, safety glasses – For protecting your hands and eyes.
  • Drop cloths – For protecting surrounding surfaces from drips.

Purchase fiberglass specific repair products from a hardware store, auto body shop, or marine supplier. Avoid cheaper, general purpose fillers and adhesives. Investing in the right materials will ensure much better results.

Repairing Chips and Cracks

Small chips, cracks, and voids are some of the most common fiberglass shower damage. Here are the steps for properly repairing them:

Step 1 – Thoroughly clean and sand the area with 80 grit sandpaper to remove any gloss and roughen the surface. This helps the repair adhere properly. Wipe away all dust with acetone.

Step 2 – Mix a small amount of resin with MEKP catalyst according to the product instructions. Stir thoroughly until fully blended.

Step 3 – Use a disposable chip brush to apply the resin mixture into the crack or void. Fill it slightly above the surface.

Step 4 – Before the resin cures, press fiberglass cloth or mat into the resin patch. Use a plastic spreader to smooth it out. Apply more resin over top.

Step 5 – Once cured, sand the area flush and smooth with 150 and then 220 grit sandpaper. Blow away dust.

Step 6 – Apply gelcoat with a small foam roller over the repair to restore the glossy finish. Allow to fully cure.

Step 7 – Blend and touch up surrounding areas with matching paint if needed. Be sure paint is formulated for fiberglass.

The fiberglass cloth layers reinforce the repair and bond it to the tub surface. Take care to smooth the edges so the patch blends in seamlessly. With this method, you can easily fill chips under 1 inch wide.

Using Body Filler for Larger Holes and Gouges

For larger holes, gouges, and cracks wider than 1 inch, using a fiberglass body filler like Bondo is recommended before applying the fiberglass cloth. Here is the repair process:

Step 1 – Enlarge the damaged area slightly and sand with 80 grit to remove loose, chipped gelcoat. Acetone wash.

Step 2 – Mix a small batch of body filler and use a plastic spreader to fill the hole or gouge, leaving it slightly higher than the surface.

Step 3 – Allow filler to fully cure. Then sand smooth and level with the surrounding surface using 150 followed by 220 grit.

Step 4 – Mix resin and soak fiberglass cloth in it. Apply over the filler patch. Add more resin over top. Smooth with a spreader. Allow to harden.

Step 5 – Sand smooth with 220 grit when cured. Apply gelcoat and paint to finish.

The filler provides bulk and structure, while the fiberglass cloth integrates the patch with the tub surface. This technique is good for holes up to several inches wide or cracks longer than 12 inches.

Repairing Delaminated Areas

If you find areas where the gelcoat has delaminated or bubbled up from the underlying fiberglass, follow these steps:

Step 1 – Use an angle grinder or rotary tool to remove all of the loose, hollow gelcoat. Grind to solid, hard fiberglass.

Step 2 – Sand the area with 80 grit, taper the edges, and clean with acetone.

Step 3 – Mix resin and saturate strips of fiberglass cloth. Apply the cloth over the repair. Cover with more resin.

Step 4 – Once cured, use 220 grit to smooth and level the patch. Apply gelcoat. Sand and paint surrounding areas.

Delamination exposes moisture under the gelcoat, so it’s important to fully remove the damaged layer and rebuild with saturated fiberglass cloth. Grinding to solid fiberglass prevents the delamination from spreading.

Fixing Water-Damaged Areas

If you have water damage indicated by swelled or distorted areas, use the following repair process:

Step 1 – Dry the area thoroughly. Use a rotary tool, angle grinder, or chisel to remove all softened, swelled fiberglass.

Step 2 – Sand and acetone wash the area after removal. Inspect closely for any remaining moisture or soft spots.

Step 3 – Fill large voids with Bondo filler, allow to cure, then sand smooth.

Step 4 – Cut fiberglass mat to the size of the damaged section. Mix resin and saturate the mat. Apply resin first then the saturated mat. Cover with more resin.

Step 5 – Once fully hardened, use 220 grit sandpaper to blend and smooth the edges. Apply gelcoat and paint.

Thorough removal of water-damaged fiberglass is crucial. The mat patch will be much stronger than the water-degraded original fiberglass. Take your time building up thin layers for a seamless patch.

Mold and Mildew Removal

If you discover mold or mildew, here is how to safely remove and prevent regrowth:

Step 1 – Mix 1 cup bleach with 1 gallon of water. Scrub affected areas with the diluted bleach solution using gloves and a stiff nylon brush. Rinse thoroughly.

Step 2 – Spray straight 3% hydrogen peroxide on the area and allow it to bubble on the surface for 5 minutes before rinsing. Repeat if needed.

Step 3 – Allow the area to fully dry for 1-2 days. Check for any remaining discoloration or softness.

Step 4 – If any lingering signs of mildew, repeat the bleach and peroxide treatments.

Step 5 – Apply a mildew resistant paint formulated for bathrooms. Allow adequate ventilation post-showering.

Chemical removal combined with mildew resistant paint will remove stubborn fungal growth and help prevent it from returning quickly. Improve bathroom ventilation to keep moisture levels down.

Removing Stains and Discoloration

Here are some tips for removing common fiberglass stains and discoloration:

Hard water spots – Vinegar or diluted muriatic acid. Spot test first.

Soap scum – Dampen with vinegar water. Use a Magic Eraser scrub pad.

Dirt and grime – All purpose bathroom cleaner and non-abrasive scrub sponge.

Chemical staining – Lightly sand and use acetone. Spot test acetone first.

Dye transfer – Bleach gel applied sparingly to stain for 5 minutes. Rinse.

Permanent marker – Rubbing alcohol applied with cotton rag. Most markers will slightly stain.

Etch marks – From drain cleaner. Sand and buff. Gelcoat may permanently lose gloss.

For best results, address staining early before it has time to set and oxidize in the gelcoat. Avoid harsh chemical cleaners which can damage fiberglass. Test products first.

Professional Repairs for Extensive Damage

While many fiberglass shower repairs can be done as DIY projects, there are cases where professional help may be needed:

  • Cracks or holes wider than 4 inches
  • Entire walls or base need replacing
  • Significant delamination affecting over 30% of surfaces
  • Major buckling or wall detachment
  • Pre-existing repairs failing
  • Leaks originating from plumbing faults or seams

If damage is beyond a simple repair, call in a professional refinishing company. They have the expertise to fully rebuild fiberglass tub surrounds and properly address underlying issues.

For less than the cost of full shower replacement, professionals can often restore severely damaged fiberglass showers to like-new condition. Get an estimate before deciding on replacement.

Helpful Tips for Successful Repairs

Follow these tips to ensure your fiberglass shower repairs go smoothly and have long lasting results:

  • Clean and sand each area thoroughly before starting repairs. Deglossing is critical.
  • Avoid cheap general purpose adhesives like liquid nails. Use resins designed for fiberglass.
  • Always wear gloves when using resin, gelcoat, catalysts. Use proper ventilation.
  • Measure catalyst amounts carefully. Too much hardener makes resin cure too fast.
  • Apply resin and saturate fiberglass layers fully. Avoid dry spots.
  • For vertical repairs, apply thin coats allowing each to partially gel before adding more.
  • Let all repairs cure fully (up to 24 hours) before additional sanding or painting.
  • Finish repairs by matching surrounding paint or gelcoat colors. Blend edges.

Take the proper safety precautions when working with resins and paints. Allow sufficient cure times between steps. Rushing the job can result in weak repairs prone to failure down the road.

Frequently Asked Questions

Here are answers to some common questions about repairing fiberglass shower units:

Can I use auto body filler instead of Bondo?
Yes, polyester auto body filler works well for repairing fiberglass. Ensure any product is polyester based.

Do repairs need fiberglass cloth reinforcement?
It is highly recommended for structural integrity. However very small chips may only need resin and paint.

What grit sandpaper do I use between coats?
Use 180-220 grit to allow each layer to bond well. Finish with 220 grit.

Can I add another fiberglass layer over the existing walls?
Yes, to reinforce weak or delaminated areas. Rough up surface first.

Is gelcoat necessary for repairs?
Gelcoat restores glossy finish and protects from UV rays. Clear resin alone may discolor or yellow.

How long does fiberglass resin take to fully cure?
Cure time depends on type of resin used and amount of hardener. Most take 16-24 hours minimum.

Can I use a hair dryer to speed up cure time?
No, never attempt to accelerate curing. Doing so results in weaker repairs prone to failure.

What causes fiberglass to delaminate?
Age, sun exposure, underlying moisture damage. Prevent by re-sealing every few years.

How do I prep walls for painting after repairs?
Sand with 220 grit, then clean with acetone. Use adhesion promoting primer before painting.


Repairing common fiberglass shower damage like cracks, chips, and delamination is very achievable as a DIY project. With some basic tools and supplies, plus following fundamental repair steps, you can successfully restore your fiberglass surround to like-new condition again. Carefully assess and address each type of damage using the techniques above. Seek professional help for extensive repairs beyond cosmetic fixes. With proper maintenance and re-sealing, a fiberglass shower can provide many additional years of service life.