Old paint removal and surface preparation

Surface preparation determines the outcome of any paint job — and removing old paint is the most demanding part. Up to 60–70% of paint failures trace back to inadequate surface prep. Proper paint removal and preparation ensure the new finish lasts 10–15 years.

This guide covers when old paint must be fully stripped versus when light sanding suffices. We compare methods — scraping, sanding, heat gun, chemical strippers, and infrared — and explain what tools and protective equipment you need.

When is sanding enough, when do you need full removal?

Not all old paint needs to come off. The key question is: is the old paint still firmly bonded to the wood?

Light sanding is enough when:

• Old paint is intact and well-adhered — no peeling, bubbling, or flaking
• The paint type stays the same (water-based over water-based, oil over oil)
• The surface is dirty or dull but structurally sound

Sand the surface with 80–120 grit, wash off the dust, and paint directly.

Full removal is needed when:

• Paint is peeling, bubbling, or flaking over large areas
• So many coats have built up that the surface is thick and uneven
• The old paint is oil-based and you want to switch to water-based (or vice versa)
• Wood has greyed or rotted beneath the old paint
• You suspect lead paint (houses built before 1970)

Identifying the old paint type

Before removing paint, it's important to know what type you're dealing with. This affects both the removal method and the choice of new paint.

Bend test

Peel off a chip of flaking paint and bend it between your fingers:

• Flexes and bends → water-based paint (acrylic or latex)
• Snaps and breaks → oil-based paint (alkyd or linseed oil)

If the old paint is oil-based, the new paint should be the same type or a transition product like alkyd-acrylic. Water-based paint can generally be applied over oil-based if the surface is thoroughly sanded and an adhesion-promoting primer is used.

Solvent test

Dampen a cotton swab with acetone and rub the surface. If the paint softens or sticks to the swab, it's water-based. Oil-based paint does not react to acetone.

Comparing removal methods

1. Scraping

The most traditional and affordable method. A steel scraper removes peeling and loose paint from the wood surface.

• Pros: inexpensive, no power needed, dust-free, doesn't heat the wood
• Cons: slow on large areas, physically demanding, won't remove firmly adhered paint
• Best for: spot removal of peeling areas and small sections

2. Sanding

Machine sanding with a belt sander or random orbital sander removes paint efficiently and levels the surface.

• Pros: fast on large areas, levels the surface simultaneously, suitable for both removal and scuffing
• Cons: creates heavy dust (requires respirator), uses a lot of sandpaper, can remove too much wood
• Best for: flat wall surfaces where paint has partially come loose

Use 40–60 grit for removal and 80–120 grit for finishing. Always sand in the direction of the wood grain.

3. Heat gun

A heat gun softens paint at 300–600 °C, after which it lifts off easily with a scraper.

• Pros: effective for thick paint layers, less dust than sanding
• Cons: fire risk (especially near insulation in old houses), can release toxic fumes from lead paint, slow on large areas
• Best for: thick, multi-layer paint on small areas

Warning: do not use a heat gun on lead paint — high temperatures release lead vapour. Do not aim at window glass — it may crack.

4. Chemical paint strippers

Chemical strippers soften paint, which is then scraped off after the dwell time. Modern products are typically solvent-free and low-odour.

• Pros: no heat, no dust, ideal for profiled surfaces (mouldings, ornamental trim)
• Cons: slow (dwell time 2–24 hours), expensive on large areas, requires thorough neutralising, waste is hazardous
• Best for: detail work, profiled trim, and small areas

5. Infrared paint removal

An infrared device heats paint to 80–150 °C — enough to soften it, but not as hot as a heat gun. The paint lifts off in large sheets with a scraper.

• Pros: most efficient method for large areas, low temperature reduces fire risk, doesn't release lead vapour, no dust, warms the wood, improving primer oil absorption
• Cons: the device is expensive (€400–2,000, rental available), requires power, doesn't suit tight spots
• Best for: whole-house paint stripping, safer alternative for lead paint, thick paint layers

Infrared paint removal has become increasingly popular in the Nordic countries and is often the best choice for stripping an entire house. The device uses radiant heat that penetrates the paint evenly. The wood surface warms at the same time, opening the pores and improving primer oil absorption.

Lead paint — identification and safe removal

Houses built before 1970 may have exterior paint containing lead. Lead paint was commonly used in Finland until the 1950s and is found particularly on windows, doors, and facades. Lead is toxic and requires special precautions.

Identification

• Lead test: a lead test kit from a pharmacy or hardware store can confirm. The test strip changes colour if the paint contains lead.
• Age: if the house was built before 1970 and the exterior paint has never been fully stripped, lead layers may exist beneath newer coats.
• Appearance: lead paint often peels in a characteristic "alligator" pattern — a fine grid of cracking.

Safe removal

• Use infrared or chemical stripper — do not sand or use a heat gun, as they spread lead dust or vapour
• PPE: P3 respirator, disposable coverall, protective gloves, and safety goggles
• Protect the ground: lay plastic sheeting along the wall and collect all paint waste
• Waste is hazardous: take lead-containing paint waste to the municipal hazardous waste collection point — not general waste
• Children and pets: keep the work area cordoned off throughout the project

If in doubt, do a lead test before starting. Professional lead paint removal costs more but is the safest option.

Mould and rot under old paint

Removing old paint can reveal problems the paint surface was hiding:

• Greying: UV-damaged surface greying is normal and not a structural defect. Sand off the grey layer and prime.
• Mould and algae: dark or green patches must be treated with mould wash before continuing. Let dry for 1–2 days.
• Rot: soft, crumbling wood is rotten. Small rot spots can be repaired with wood filler and hardener. Extensive damage requires board replacement — don't paint over rot.
• Blue stain: bluish discolouration in wood is caused by blue stain fungus. It doesn't weaken the wood structurally but indicates a moisture problem. Identify the moisture source before painting.

Choosing primer after paint removal

Bare wood always needs primer. Primer evens out absorption, improves adhesion, and protects the wood from moisture.

• Water-based alkyd primer (e.g. Tikkurila Vinha or Cello Wintex) — good all-round choice, fast drying, low odour
• Oil-based primer — excellent adhesion and moisture protection, slow drying (12–24 h), strong odour
• Linseed oil primer (e.g. Uula Pellavaöljymaali (linseed oil paint) or Teknos WOODEX EKO) — traditional choice for old houses, penetrates deep into the wood, requires long drying time (1–3 days)

Always use primer and topcoat from the same manufacturer's product line to ensure compatibility. If you used infrared removal, primer oil absorbs especially well into the warm wood.

Tools and protective equipment

Basic tools

• Steel scrapers (straight and hook scraper)
• Sander (random orbital for wall surfaces, detail sander for corners)
• Sandpaper: 40–60 grit for removal, 80–120 grit for finishing
• Wire brush, hand and machine-operated
• Painter's tape and protective sheeting

Additional tools

• Heat gun (300–600 °C)
• Infrared paint removal device (rental available)
• Moisture meter to check wood moisture content
• Wood filler and wood hardener for rot repair

Personal protective equipment (PPE)

• Respirator: P2 for sanding, P3 for lead paint
• Safety goggles: prevent paint dust and chips from reaching your eyes
• Ear protection: during machine sanding
• Gloves: nitrile gloves when handling chemical strippers
• Long-sleeved workwear: protects skin from dust and chemicals

Step-by-step workflow

1. Do a lead test if the house was built before 1970
1. Protect the surroundings — plastic on the ground, tape over windows and doors
1. Remove peeling paint — scraping, sanding, heat gun, or infrared
1. Check the wood condition — repair rot, treat mould
1. Sand the surface smooth — 80–120 grit, following the wood grain
1. Wash and let dry — at least 1–2 days, wood moisture below 15%
1. Apply primer — to all bare wood surfaces with a brush
1. Check conditions for topcoating — temperature, humidity, wind, and rain

Also read the guide House painting step by step — topcoating, cost estimates, and scheduling are covered in detail. Surface prep and weather planning are covered in the guide Outdoor painting fundamentals.