Deck Sandpaper: CCA Check, Grits, Strip-or-Sand

For pressure-treated pine decks: 60 → 80 → 120 grit. For cedar or redwood: 80 → 120 → 150 grit. Always use open-coat paper to prevent clogging from soft resinous wood. Check CCA status before any sanding on pre-2004 decks — arsenic-treated wood should never be sanded. P100 respirator outdoors for any pressure-treated lumber. This guide covers the safety checks the other deck-sanding articles skip, the strip-vs-sand decision rule, and brand picks by deck type.

Three checks before you sand any deck

1. Is the wood CCA-treated (pre-2004)?

Decks built before December 2003 may be CCA-treated lumber — chromated copper arsenate. The “treated” green tint contains arsenic, chromium, and copper compounds pressed into the wood fiber. Do not sand CCA wood. Sanding aerosolizes arsenic into your face.

The EPA phased out CCA for residential use in 2004, but the wood doesn’t expire — a 20-year-old deck is almost certainly CCA. Identify it:

• Greenish tint (sometimes faded with age)
• Building age pre-2004 (check permit records or ask the builder)
• Sometimes stamped “CCA” or “Wolmanized” on the underside of boards

If CCA: power-wash, brighten, re-stain. Don’t sand. If you must remove material, hire a hazmat abatement contractor.

2. Is the wood ACQ or MCA-treated (post-2004)?

Current pressure-treated lumber uses copper-based preservatives (ACQ, MCA, Copper Azole). Less acutely toxic than CCA but the copper dust is still a respiratory irritant and a known sensitizer.

Sanding ACQ/MCA wood requires:

• Outdoor work only. Never sand pressure-treated lumber in an enclosed porch or screened-in area.
• P100 respirator, not a paper mask. The fine copper-saturated dust gets past N95 seals.
• No food or drink in the work area; copper dust contaminates surfaces.
• Wash work clothes separately from family laundry afterward.

3. Is the deck pre-1978 and painted?

Lead paint on old decks is more common than people expect — porch decks, balconies, exterior stair treads were routinely painted with lead-bearing paint pre-1978. Same $15 lead test kit as the indoor floor articles. Positive = chemical strip with containment, or hire RRP-certified contractor. Negative = proceed with PT-lumber precautions above.

Picks by deck type

Your situation	Best sandpaper	Where to buy
Post-2004 PT pine deck, weathered gray, no coating	5” or 6” open-coat aluminum-oxide hook-and-loop discs, 60/80/120 (belt sander + open-coat belts as the aggressive option on big flat decks)	VA Amazon search
Cedar or redwood deck, light weathering	Diablo SandNet 80/120 on a random orbital	Amazon search Diablo SandNet — better feel on softwood, same commission either way
Heavily weathered or coated deck	Strip first (deck stripper), then 80-grit cleanup pass	Hardware store deck stripper + 80-grit open-coat disc
CCA-treated wood (pre-2004)	None — do not sand	n/a
Pre-1978 painted deck	Test for lead first	$15 lead test kit at any hardware store

Strip or sand? The 60-second decision test

Sanding makes sense when: boards are sound, coating is light or absent, surface is gray weathering. Sanding fails on: cupped boards, board ends turning up, thick layers of solid-color stain.

The decision test:

1. Look at the boards from the side, at deck height. Boards bowing up at the edges (cupping) won’t sand flat — the orbital or belt sander rides the high spots.
2. Push a screwdriver into the board face. Sinks easily = wood fiber is rotted, sanding won’t help, board needs replacement.
3. Scratch the coating with a key. Bare wood underneath = stripper-then-sand. Multiple paint layers = stripper-only.

If 1 or 2 fail: stop. The job is board replacement, not refinishing. If 3 shows multiple coatings: deck stripper (sodium hydroxide based works on solid stain; benzyl alcohol on semi-transparent), then light 80-grit cleanup pass after stripper dries 24+ hours.

Why deck sanding is different from indoor floor sanding

• Soft, resinous wood. Pressure-treated pine and cedar load sandpaper fast.
• Outdoor weathering. Gray patina, mill scale, UV oxidation require aggressive starting grits.
• Grain raising from moisture. Wood fibers swell after rain or wash; a final pass flattens them before stain.
• Treatment chemicals. PT lumber dust is hazardous. Cedar is safe; PT is not.
• Coatings vary wildly. Solid stains, semi-transparent stains, sealers, paint — each strips differently.

Grit sequences by deck wood

Pressure-treated pine (most common)

Pressure-treated lumber is chemically softened and splinters easily. Start coarser than for hardwood, but never below 60 grit (60 grit gouges PT in soft spots).

1. 60 grit — opens the surface, removes weathering and light mill scale. One pass with random orbital or belt sander.
2. 80 grit — removes 60-grit scratches. Second pass.
3. 120 grit — final pass before stain or sealant. Can drop to 100 if budget-constrained.

Total: 3 passes. Timeline: 4–6 hours for 400 sq ft.

Don’t go past 120 on PT pine — the soft fiber burnishes easily and blocks stain absorption.

Cedar or redwood

Cedar is harder than PT pine but still softer than hardwood. Beautiful when freshly sanded; dense grain takes a slightly different approach:

1. 80 grit — first pass. Cedar responds well to 80; no need to start at 60.
2. 100 grit — removes 80-grit scratches.
3. 120 grit — final pass before stain. Cedar takes stain better at 120 than 100.

Total: 3 passes. Cedar often requires less total sanding than PT.

Old painted decks (lead negative)

1. 36 grit — initial paint removal pass.
2. 60 grit — second pass; removes 36-grit scratches and paint residue.
3. 80 grit — third pass; smooths the bare wood.
4. 120 grit — final pass for stain prep.

See our paint removal guide for the full process — same logic applies outdoors, plus the fire-risk callout (paint dust + oil-based deck stains).

Open coat is non-negotiable for decks

Open coat (50–70% grit coverage, 30–50% air space) lets soft resinous dust fall away instead of building up on the paper. Closed coat (90–100% coverage) loads with PT or cedar resin in minutes.

For deck work, specify open-coat sheets in all grits. You’ll change sheets 3× less often than with closed-coat.

Belt sander vs. random orbital

Random orbital (recommended for most decks)

• Portable, lightweight, easy to control
• Lower pressure than belt sander = safer on softwood
• Works around railings, posts, and irregular shapes
• Standard 5-inch or 6-inch discs
• Cost: own one for $80–150 or rent for $15–25/day

Belt sander

• Faster on open flat areas
• More aggressive — can gouge PT in seconds
• Better for severely weathered or heavily coated boards
• Standard 4×24” belts
• Cost: $30–50/day rental

Drum sander (skip it)

Drum sanders are designed for hardwood flooring with heavy poly. On softwood deck boards, the drum gouges in seconds and the rental cost ($60–100/day) isn’t justified.

Sandpaper quantity by deck size

For a 400 sq ft deck:

Grit	Random orbital discs	4×24” belt sander belts
60 (if starting there)	4–6	2–3
80	5–7	3–4
100	4–5	2–3
120	3–4	1–2

Overestimate slightly; unused open-coat sheets keep for years.

Deck sanding technique

• Always sand with the grain. Softwoods splinter easily; cross-grain creates permanent damage.
• Light pressure. Press hard and you’ll gouge PT or burn cedar.
• Overlap passes 2–3 inches.
• Sand the edges separately by hand or with a small detail sander. Don’t bullnose the deck edges.
• Don’t power-sand vertical posts or rails — hand sand for control.
• Do a final grain-raiser pass. After sanding, wet the deck lightly, let dry 24 hours, then very-light 120 grit pass to lay down grain whiskers before staining.

Dust safety — even outdoors

Yes, outdoors. The dust still ends up in your lungs if you’re leaning over the work.

• P100 respirator (not N95) for any PT lumber sanding
• Safety glasses — orbital sanders throw debris at face height
• Hearing protection — orbital sanders run 80–90 dB; belt sanders louder
• Long sleeves and pants even in summer heat (copper dust skin sensitizer)
• Wash work clothes separately from family laundry
• Vacuum the deck with HEPA before re-staining; sweep aerosolizes the dust

After sanding

• Vacuum thoroughly with HEPA filter.
• Wait 24 hours before staining — moisture from cleaning raises grain.
• Optional final 120/150 grit pass to flatten raised whiskers from the moisture cycle.
• Test stain on a hidden board before committing to the full deck.

Apply stain or sealer per manufacturer instructions. Most deck stains don’t require sanding between coats. If the first coat feels rough after drying, a light 150-grit scuff removes dust nibs.

When to replace boards instead of sand

• Boards cupping severely (>1/8” rise)
• Screwdriver sinks into board face (rot)
• Multiple boards with end-grain checking or splits
• Joist contact points are rotting through

Replacing 2–3 bad boards before sanding the rest costs $50 and saves you from a redo. Not all old decks justify refinishing — some justify replacement.

Test for treatment chemistry, test for lead if it’s old, and don’t sand what should be replaced. The deck rewards the careful prep more than any indoor floor.

Matt.