Stripping Wood Stains and Oils: When to Sand vs. When to Scrub

You look at your garden decking or your wooden cladding. It looks terrible. Maybe it is black and sticky because you applied too many coats of oil over the years. Maybe it is peeling and flaking because the old stain has failed.

You know you need to get it back to bare wood before you can treat it again. But how? Do you rent a heavy industrial floor sander and grind the surface down? Or do you buy a chemical stripper and scrub the mess off?

Make the wrong choice, and you will either ruin the profile of your wood or create a chemical sludge that never dries. Here is the professional rulebook on Mechanical (Sanding) vs. Chemical (Scrubbing) stripping.

1. The Diagnosis: What is currently on the wood?

Before you choose a weapon, identify the enemy. Rub your hand over the surface.

• Scenario A: It is Flaking / Peeling.

• If you can pick plastic-like chips off with your fingernail, this is a Film-Forming Coating (Varnish, Paint, or High-Build Stain).

• The Verdict: Sand it. Chemicals struggle to eat through thick plastic skins.

• Scenario B: It is Black / Sticky / Faded.

• If the wood looks dark or greasy but nothing is peeling off, this is a Penetrating Oil or dirt accumulation.

• The Verdict: Scrub it. You can dissolve this chemically.

2. When to Scrub (Chemical Stripping)

This is the preferred method for Decking. Why? Because decking has grooves (castellations). If you sand decking, you sand the ridges off, leaving you with a weird, uneven, semi-flat plank.

The Product: You need a Decking Stripper.

• Note: Do not confuse this with "Decking Cleaner." Cleaners (Bleach) just remove algae. Strippers (usually Sodium Hydroxide) remove old coatings.

The Process:

1. Apply: Brush the gel onto the dry wood.

2. Dwell: Leave it for 20–30 minutes. It will start to dissolve the old oil, turning it into a brown goo.

3. Agitate: Use a stiff nylon brush to scrub the goo out of the grooves.

4. Blast: Pressure wash it off. The old oil washes away, leaving bare wood.

5. Neutralise: Strippers are Alkaline. You must rinse thoroughly (sometimes using a brightener) to restore the pH before recoating.

3. When to Sand (Mechanical Stripping)

This is the preferred method for Flat Surfaces (Handrails, Tabletops, Benches). If the coating is a hard varnish or a paint that is sitting on top of the wood, chemical strippers often turn it into a sticky mess that is a nightmare to clean up. Sanding is cleaner and faster for hard coatings.

The Tools:

• Belt Sander: For large flat areas (table tops). Always sand with the grain.

• Detail Sander: For corners and edges.

• The Grit Progression: Start with 40 grit (to rip the coating off), then 80 grit (to smooth scratches), then 120 grit (to finish).

Warning: Do not use a high-powered belt sander on Decking Boards. You will hit the screw heads, tear the sandpaper, and potentially spark a fire (or just ruin the screw drive so you can never remove the board).

4. The "Hybrid" Problem: Acrylic Stains

The hardest product to remove is a water-based Acrylic Decking Stain. These are often sold in supermarkets as "One Coat" colours. They act like paint (film-forming) but soak in like oil.

• Strippers often fail to melt the acrylic resin.

• Sanding is difficult because the stain is deep in the grooves.

The Solution: You often need a two-stage attack.

1. Use a Stripper and a pressure washer to blast 80% of the loose coating out of the grooves.

2. Let it dry, then lightly Sand the raised ridges to remove the stubborn patches.

5. Cleaning vs. Stripping: Don't Confuse Them

Many people think a "Pressure Wash" is enough to strip wood. It isn't. A pressure washer removes dirt and grey UV cells. It does not remove oil. If you pressure wash an oiled deck and then try to apply a different type of stain (e.g., changing from a solvent oil to a water-based stain), the new stain will fail. The invisible remnants of the old oil will repel the new coating. You must use a chemical stripping agent to emulsify the old oil.

Conclusion

The choice comes down to the profile of the wood.

• Grooved Decking? Chemical Strip. Do not sand the grooves away

• Flat Wood (Furniture/Handrails)? Sand. It gives a smoother finish

• Peeling Varnish? Sand

• Sticky Oil? Scrub