Your deck,
restored.

Depends on current finish life: Clear sealer 1-3 yrs (Thompson's 2, Olympic 3). Semi-transparent stain 3-5 yrs. Solid stain 5-7 yrs. Deck paint 5-10 yrs. Tropical hardwood oil (Penofin Marine) yearly. Signs to refinish: water no longer beads on surface (drop test), color faded/grayed, wood feels rough/dry, finish peeling or cracking. Skip cycles = wood lifespan drops 30-40%. Most decks need full refinish (vs maintenance coat) every 5-10 years.

DIY if: light condition + small deck (<300 sqft) + you have a weekend + power-washer access. Pro if: heavy condition + large deck (>500 sqft) + paint-to-stain transition + you value warranty. Hybrid usually wins for most homeowners: DIY power-wash + apply finish (easy, low-risk), hire pro for strip + sand + brighten (skill + equipment dependent). Hybrid saves 25-40% vs full pro. Time investment: DIY full refinish = 6-24 hours active work over 2-4 weekends; pro = 1-3 weekends start-to-finish (you don't lift a finger).

Sometimes yes, sometimes no. Strip required: current finish is paint or solid stain (opaque finishes can't be over-coated cleanly); converting to lighter finish (e.g., solid → semi-trans); finish is peeling/flaking. Strip NOT required: same finish refresh (sealer→sealer, semi-trans→semi-trans), and current finish is intact + clean. When in doubt, do a small test patch — apply new finish to a 1-sq-ft area; if it absorbs unevenly or beads on top, strip first. Stripping adds $0.45/sqft DIY or $2.20/sqft pro plus 1 day of work.

Yes, in 60% of cases. Skip sanding if: same finish refresh, light condition, wood surface is smooth + not splintering. Sand mandatory if: stripping old finish (always need to remove softened residue), heavy weathering (silvered wood), paint → stain transition (paint residue must be sanded away), or any board feels rough/raised-grain underfoot. Sanding adds $0.18/sqft DIY rental + ~0.025 hr/sqft labor; pro $1.85/sqft. Worth it for heavy decks — extends finish life ~30%.

Application costs are similar; product + prep differ. DIY material per sqft: sealer $0.45, semi-trans stain $0.85, solid stain $1.20, paint $1.55. Pro full-service: sealer $1.85, semi-trans $2.40, solid stain $2.90, paint $3.20. Paint is most expensive AND most demanding prep (full strip + prime if going from raw wood or stain). Paint lifespan 5-10 yrs (longest); semi-trans 3-5 yrs (shortest besides clear sealer); solid stain 5-7 yrs. Cost per year of protection: solid stain wins, paint close second.

Small deck (<300 sqft) light condition: 1 weekend DIY (6-10 hrs spread over 2 days for drying), or 1 day pro. Medium deck (300-500 sqft) moderate condition: 2 weekends DIY (10-20 hrs), 2 days pro. Large deck (>500 sqft) heavy condition: 3-4 weekends DIY (18-30+ hrs), 3-5 days pro. Drying time between phases is the limiting factor: power-wash needs 48 hrs dry before strip; strip needs 24 hrs; sand can happen same day; brighten needs 24 hrs; apply-finish needs 24-72 hrs cure before furniture goes back.

No — composite (Trex/TimberTech/Fiberon) and PVC (AZEK/Zuri/Wolf) decks should NEVER be refinished. Their factory-applied caps cannot be sanded or stained. Maintenance: soap + soft brush + water rinse. Mildew spots: mild oxalic acid cleaner. Stains (wine, oil, sunscreen): clean within 24 hrs with same soap-wash. If a composite cap is damaged (deep scratch through to wood-fiber core, gouge from dropped tool), the only fix is board replacement — typically $80-150 per board including labor. This calc is exclusively for wood decks (PT, cedar, redwood, tropical hardwoods).

Almost never. Refinishing = cosmetic work, no structural changes. Permits required only if: replacing structural members (joists, beams, posts) — that's not refinishing, that's repair; expanding the deck footprint; significantly altering railing per current code; >50% of boards being replaced (some jurisdictions count this as 'rebuilding'). For typical strip + sand + refinish: no permit. Verify with your municipality if doing extensive board replacement (>10 boards).

Active ingredients: sodium hydroxide (lye) in alkaline strippers (Cabot Problem Solver, Behr Multi-Surface Stripper); oxalic acid in brighteners (neutralizers); methylene chloride was common pre-2019 but is now restricted by EPA — modern strippers use safer NMP, DBE, or proprietary blends. DIY safety: wear chemical-resistant gloves (nitrile), safety goggles, long sleeves + pants, P95 respirator if indoor / windy outdoor application. Avoid skin contact (burns), mucous membrane (eye damage). Dispose of spent chemicals at hazmat-rated facility per local code, never down storm drain. Generally safe DIY if you follow product instructions; pros handle it daily with better equipment.