Do old weatherboards need stripping back before repainting?

When does a weatherboard house need a full strip?

Stripping every board back to bare timber is slow, messy and expensive, and on most houses it isn't necessary. It starts to make sense when:

• Paint is peeling or failing an adhesion test across large areas, not just in patches.
• There are so many old layers that the paint is cracking in a crazed, alligator-skin pattern.
• Earlier coats were put over dirt, chalk or failed paint, so everything above them keeps letting go.
• The paint contains lead and is deteriorating, and the owner has decided to remove it rather than cover it.

How can you tell if the old paint is sound?

Look closely, then test. Run a hand over a sunny wall: if it comes away chalky, the surface needs a thorough wash. Push a scraper along a lap joint: if paint lifts easily in long pieces, it's not holding.

Dulux's Weathershield datasheet describes a tape test for adhesion. Cut an X through a clean area of paint with a sharp knife, press sticky tape firmly over it, and rip it off. If old paint comes away with the tape, it should be removed before repainting. The same datasheet notes that apparently sound paint can lose adhesion when recoated, particularly under a darker colour, so it's worth testing before a colour change.

Try it on a few walls. The side that cops the afternoon sun often looks very different from a sheltered side of the same house.

What does good weatherboard prep involve?

For previously painted surfaces, Dulux's datasheet says to test the surface, scrape off all loose and flaking paint, fill cracks and holes with a suitable exterior filler, sand to a flat finish and remove greyed timber, then dust off. In practice on a weatherboard house that usually means:

• Washing the walls to remove dirt, chalk, cobwebs and any salt build-up.
• Scraping loose paint, especially along the bottom edges of boards and around windows where water sits.
• Sanding the edges of scraped areas so they don't show through as ridges.
• Replacing or repairing rotten boards, and punching and filling popped nails.
• Sealing gaps at joints and around frames with a flexible exterior filler or sealant.
• Priming bare timber, then applying the topcoats.

Why does grey, weathered timber have to be sanded off?

Where paint has been gone for a while, the surface of the timber breaks down into a grey, soft layer. Paint applied over it sticks to that weak layer rather than the sound wood underneath, and it can peel off with the grey fibres attached. That's why Dulux's instructions say to remove greyed timber before painting, on bare boards as well as previously painted ones. Dulux's datasheet also specifies three coats of Weathershield on bare unpainted timber, which is more than a recoat over sound paint needs.

Could my weatherboards have lead paint?

If the house was built before 1970, there's a real chance. The Australian Government's Lead Alert guide says paints with as much as 50 per cent lead were used inside and outside homes built before 1950, that paint with more than 1 per cent lead was still used until the late 1960s, and that newer homes can also have it if old or industrial paints were used. The limit for house paint has been 0.1 per cent since December 1997.

WorkSafe Victoria advises that paint on buildings from before 1970 should be tested before it's disturbed. Lead dust from sanding and scraping is harmful, and young children and pregnant women are most at risk. Lead test kits from hardware and paint stores can screen for it, but the Lead Alert guide warns they can give false results, so if in doubt treat the paint as containing lead or get it tested professionally.

How is lead paint on weatherboards handled safely?

The Lead Alert guide is clear about what not to do: don't dry sand, don't use a power sander, and don't use abrasive blasting. Dry scraping, burning and power-tool cleaning create the most serious dangers because the dust is fine enough to breathe in and settles into soil, carpets and furnishings.

Safer approaches it describes include wet scraping and wet sanding over plastic drop sheets, chemical strippers, and electric heat guns kept below 370°C. If lead paint is in good condition and not flaking or chalking, it can be covered by painting over it, though the guide notes that's a temporary solution that needs keeping up.

For businesses, WorkSafe Victoria treats machine sanding and abrasive blasting of lead paint as lead processes with their own duties. If you're getting quotes on an older weatherboard house, ask each painter how they'll deal with possible lead paint. A clear answer is a good sign.

Aussie Painting doesn't take on lead paint removal. If a house looks like it may have lead paint, we'll say so at the quote and point you to someone set up for it, rather than sanding it and spreading the dust through your yard.

Does living near the coast change the prep?

The steps are the same, but washing matters more. Salt and grime settle on walls facing the water and can stop new paint bonding properly, so a thorough wash and rinse before prep is essential. Our guide to how long exterior paint lasts near the beach covers the maintenance side.

If your weatherboards are peeling in places and you're not sure how far back they need to go, we can look at them when we quote an exterior repaint. The written quote spells out the prep for each part of the house, so you can see exactly what you're paying for.

Quick questions

Sources

What this guide relies on. Product advice changes, so check the maker's current instructions for the exact paint you're using.

1. Lead Alert: the six step guide to painting your home (5th edition) — Commonwealth of Australia
2. Managing lead-based paint removal — WorkSafe Victoria
3. Lead exposure and your health — Better Health Channel, Victorian Department of Health
4. Weathershield Low Sheen technical datasheet (surface preparation) — Dulux