Bumps in a refinished bathtub are usually one of three things: trapped air bubbles, debris in the coating, or roller texture that wasn’t smoothed out. All of them are fixable with sandpaper and patience. Here’s how.

What Causes Bumps?

Bubbles / blistering — Air was trapped in the coating. Usually caused by applying too thick a coat, shaking the product before applying (introduces air), or rolling too fast. The bubbles may show immediately or appear as the coating cures.

Debris / nibs — Dust, lint, or pet hair settled into the wet coating before it cured. Common in dusty bathrooms. Shows up as small hard bumps, often with a visible particle at the center.

Roller texture — A coarser foam roller leaves an orange-peel texture. Not bubbles, but a surface roughness that feels bumpy. Very common with thicker coatings applied with the wrong roller.

Fish eyes — Circular depressions surrounded by a raised ring. Caused by silicone contamination on the surface before coating. If your bathroom had silicone caulk or spray that didn’t get removed in prep, this shows up in the finish. Removing old caulk completely before refinishing is critical — see how to remove bathtub caulk if that step was skipped.

How to Fix Bumps After Curing

The approach is the same for all of the above: wet sand, then polish or recoat.

What You’ll Need

  • 400-grit wet/dry sandpaper — for initial leveling
  • 600-grit wet/dry sandpaper — for smoothing
  • 800–1000-grit wet/dry sandpaper — for final smoothing before polish
  • Spray bottle with water — wet sanding requires water
  • Automotive polishing compound — to restore gloss after sanding
  • Soft cloth or foam pad — for buffing
  • Optionally: additional refinishing coating if you sand through to bare surface

Step 1: Wait for Full Cure

Do not try to fix bumps in fresh coating. Wait until the coating is fully cured — typically 5–7 days. Fresh coating will gum up on sandpaper and you’ll make it worse.

If the coating is still within 24 hours of application and you see debris, you can sometimes pick debris out carefully with tweezers and let the surface level itself. But once it’s set, wait for full cure.

Step 2: Wet Sand the Bumps

Wet sanding is critical — dry sanding scratches too aggressively.

Dip the 400-grit sandpaper in water or use a spray bottle to keep the surface wet. Sand the bumpy area with light circular motions. You’re leveling — removing the high spots. Don’t press hard.

Wipe clean and check. Bumps should be flattening. Continue until the surface is level.

Step 3: Step Up Grits

Once level, switch to 600-grit and sand the entire repaired area uniformly. This removes the 400-grit scratches.

Then 800-grit, then 1000-grit if you want a very smooth result. Each grit removes the scratches from the previous one.

After 1000-grit wet sand, the surface will look dull and scratched — that’s normal. The polish step restores the gloss.

Step 4: Polish

Apply automotive polishing compound (Meguiar’s Ultimate Compound or similar) to the sanded area with a soft cloth or foam applicator. Work in circles with moderate pressure. The compound cuts away the fine sanding scratches and restores the gloss.

Wipe off residue with a clean damp cloth. The area should now match the surrounding finish. For a more extensive dullness problem across the whole tub, the process of polishing a refinished bathtub to restore overall shine is covered in detail separately.

Step 5: Recoat If Needed

If you sanded through the coating in places — you’ll see the original tub surface or primer showing through — you need to apply a new thin coat over the repaired area.

Clean with isopropyl alcohol, let dry, then apply one thin coat of the same coating you used originally. Let cure fully before sanding and polishing as above.

Preventing Bumps on Future Applications

Use the right roller. A fine-cell foam roller (like a 4” foam trim roller) leaves much less texture than a standard paint roller.

Don’t shake the product. Stir slowly with a stick. Shaking introduces air bubbles that show up in the finish.

Apply thin coats. Most bumps from DIY applications come from applying too much product at once. Two thin coats will give a smoother result than one thick coat every time.

Remove dust before applying. Wipe the surface with a tack cloth right before coating. In dusty bathrooms, close off vents and let dust settle for an hour before applying.

Work in a cooler temperature. Very warm surfaces cause the coating to skin over too fast, trapping bubbles.

What About Bumps Under the Refinishing (Not From the Coating)?

If the bumps were there before you refinished — mineral deposits, old calcium buildup, existing texture — the coating just conforms to whatever is underneath it. No amount of coating will smooth a rough underlying surface.

Solution: sand or strip the existing coating, prep the bare surface more thoroughly, and recoat. This is more work but the only real fix.

How to refinish a bathtub start to finish →