Fiberglass bathtubs are popular for one big reason: they’re affordable, lightweight, and easier to repair than cast iron or porcelain tubs. That said, DIY fiberglass bathtub repairs often go wrong, not because repairs are impossible, but because homeowners don’t use the best products or have proper instruction.
If you’re planning to fix cracks, chips, soft spots, or holes yourself, this guide will save you time, money, and frustration. Below, we’ll break down the most common fiberglass bathtub repair mistakes DIYers make and how to avoid them using the right materials, techniques, and repair kits.
Mistake #1: Ignoring the Root Cause of the Damage
One of the biggest DIY repair mistakes is fixing the surface without addressing what caused the damage in the first place.
Common underlying causes include:
- No support under the floor
- Flexing from years of use
- Improper installation
- Water intrusion beneath the tub
For example, if your tub floor feels soft or spongy, simply patching the crack won’t last. The repair will fail again probably after a few uses.
Pro tip: If the damage is on the tub floor, you must stabilize and reinforce the area before applying any surface repair. Otherwise, cracks will reappear no matter how good your patch looks.
Mistake #2: Skipping Surface Preparation
Surface prep is where most DIY repairs fail—even when the right kit is used.
Common prep mistakes:
- Not sanding enough
- Leaving soap residue, oils, or wax behind
Fiberglass repair compounds will not bond properly unless the surface is clean, dry, and mechanically roughened.
Proper prep steps:
- Clean the area thoroughly with a degreaser or thinner product such as acetone
- Sand beyond the damaged area to create a strong bonding surface
- Remove all dust and moisture before applying the repair material
This step may feel tedious, but it’s the difference between a repair that lasts months vs. years.
Mistake #3: Underestimating Large Wall Damage
Hairline cracks and small chips are relatively easy to fix. But larger wall damage, such as large holes and cracks, requires a completely different approach.
Many DIYers make the mistake of:
- Try to make shift a backing that is not firm
- Sacrificing strength for looks and making the repair too thin
- Not making the patch overlap wide enough
This leads to sagging, weak repairs that eventually cave in.
The correct solution
For significant wall damage, a reinforced kit like the Large Wall Damage Tub Repair Kit is designed specifically for:
- Holes up to the size of a baseball (with a single kit.) Larger holes can be tackled by adding more Fiberglass Filler
- Structural reinforcement
- Vertical surface repairs that won’t slump or crack
Trying to “wing it” on major wall damage usually ends in redoing the repair or replacing the tub altogether.
Mistake #4: Treating Floor Cracks Like Cosmetic Damage
Floor cracks are not cosmetic issues—they’re structural.
A very common DIY mistake is applying a simple surface patch over a tub floor crack without reinforcing the area underneath. Because the tub floor bears body weight, these repairs fail quickly.
Why floor repairs are different:
- Constant flexing under load
- High stress concentration
- Water exposure beneath the tub
What actually works
A system specifically designed for Floor Crack Repair provides:
- Structural reinforcement
- Load-bearing strength
- Long-term durability under daily use
Ignoring this difference is one of the fastest ways to turn a small crack into a full tub replacement.
Mistake #5: Rushing the Curing Process
DIYers often assume that once the repair looks dry, it’s ready to use. That’s a costly assumption.
Common curing mistakes:
- Using the tub too soon
- Applying the topcoat without cleaning the repair first
- Exposing repairs to moisture prematurely
Always follow the manufacturer’s recommended cure times—even if the surface feels hard to the touch.
Mistake #6: Expecting Professional Results Without the Right Finish
Even a structurally sound repair can look terrible if the finishing steps are rushed.
DIYers often skip:
- Feathering the sanding
- Color matching
- Proper polishing
This results in visible patches, uneven texture, or discoloration.
A properly repaired tub will not only fix the damage but also pass visual inspection, truly saving your tub and your home’s equity.
Final Thoughts: DIY Fiberglass Tub Repair Done Right
Fiberglass bathtub repair can absolutely be a successful DIY project—but only if you avoid the most common mistakes:
✔ Fix the cause, not just the damage
✔ Use the right repair and coating materials
✔ Prep the surface properly
✔ Clean the repair before applying paint
✔ Respect curing times
✔ Don’t underestimate floor or large wall damageWhen done correctly with the right Tub repair kit, DIY repairs can save you $1,000s compared to other professional services.