How to tell whether your house has lead paint before you sand it

You cannot tell by looking, so go by the age of the building and then test the paint. Health New Zealand says lead-based paint cannot be identified by its appearance, and that a building built in the 1980s or earlier is best presumed to have been painted with lead-based paint, so have it tested before anyone sands or strips it.

A test takes days. Cleaning lead dust out of a garden, a carpet or a child's blood takes far longer, which is why the test comes before the sander, not after.

Why does the age of the house matter so much?

Because the lead is in the old layers, not the new ones. Health New Zealand's guidance says that until 1965 many paints on the New Zealand market had high lead levels, particularly paints made before 1945. A 1920s villa that was last painted with a modern acrylic still has decades of older coatings underneath, and those older layers are what a sander reaches first when it cuts through a flaking patch.

So a fresh-looking topcoat tells you nothing. Neither does a renovation history you were told when you bought the house. What matters is the oldest paint on the surface you are about to disturb.

Different parts of the same house can also have different histories. Weatherboards may have been stripped and repainted at some point while the window joinery, soffits, doors and interior skirtings still carry original paint. Treat each surface as its own question.

What are the ways to test for lead paint?

There are three realistic options, and they answer slightly different questions.

Option	What it tells you	Good for	Limits
Home test kit	whether lead shows up at the spot you tested	a quick first check on a small DIY job	a result from one spot says nothing about other surfaces; follow the kit's instructions exactly
Laboratory analysis of paint chips	a measured result, classified as lead paint or lead-free	a definite answer before a large preparation job	slower; the result is only as good as the sample you send
Professional assessment	sampling across the house plus advice on what it means	a whole-house repaint, a purchase, or a rental	costs more than doing it yourself

The National Public Health Service's guide to safely removing lead-based paint says test kits are sold at hardware and paint stores, that you should assume a home painted before 1980 may have lead paint if you cannot get one, and that your local National Public Health Service office can advise on testing.

For a lab result, Hill Laboratories offers accredited testing of dried paint chips and classifies each sample as lead paint or lead-free paint against AS/NZS 4361.2:2017, which defines lead paint as paint containing more than 0.1% lead by mass in the dry film. That definition is useful to know: it is the line a lab result is measured against, not a colour-change on a swab.

How do you take a sample that actually means something?

• Take the sample through every layer down to the timber or plaster. A chip of the top two coats tests the top two coats.
• Sample each type of surface separately: weatherboards, window frames and sills, doors, and interior trims.
• Choose spots where the paint is already failing if you can, so you are not creating new damage.
• Mist the area with water first, cut the chip out with a sharp blade, and catch it on a sheet or in a bag. Do not sand to get a sample.
• Label each sample with where it came from, so a positive result points at a specific part of the house.

What changes if the test is positive?

The painting is still possible. What changes is how the old paint comes off and how the mess is contained.

The National Public Health Service guide lists wet sanding with water-dampened sandpaper and wet scraping as the preferred methods, because they keep dust down. It lists dry sanding, chemical strippers, water-blasting, abrasive blasting and heat-based removal as not recommended, heat because it produces lead fumes. It also calls for properly fitted dust respirators, disposable overalls and head covering, cleaning with wet cloths and HEPA-filter vacuums only, never burning lead-painted material, washing work clothes separately and showering after work. Health New Zealand adds that children and pets should be kept away from the work area and away from paint debris.

In practice, on an exterior, that means:

• ground sheeted under every wall being prepared, and debris collected daily, so flakes do not end up in the vegetable garden or the lawn;
• windows and doors on that side closed while work is under way;
• scraping and wet-sanding only the failed paint, and leaving sound paint alone rather than taking the whole house back to timber;
• no water-blaster on the loose paint.

Indoors, the containment is tighter still: plastic over doorways, soft furnishings out of the room, and a proper clean-down at the end of each day rather than at the end of the job.

What if the test comes back negative?

Then you prepare the surface normally. Just be clear about what was tested. A negative result on a weatherboard that was stripped in the 1990s says nothing about the original sashes. If the house has visible layers of different ages, test the ones you are about to disturb.

Can you do the testing and preparation yourself?

Testing, yes. Taking a paint chip properly and sending it to a lab is well within any homeowner's reach, and a test kit on an interior skirting before you repaint a bedroom is a sensible habit.

Preparation on a positive result depends on scale. Wet-scraping a flaking window sill with the ground sheeted is a manageable DIY job. Preparing the whole exterior of a two-storey villa lead-safe is not, mainly because the containment, the clean-up and the access take longer than the scraping. That is where a painter who already works this way is worth it. Our lead paint removal guide covers how the work is planned in more detail.

Lead-safe preparation belongs in the written quote for any exterior repaint on an older house, not as an extra discovered halfway through.

If you are pregnant or have young children in the house, have the testing done and the plan agreed before any preparation starts, and keep them away from the work until the clean-up is finished.

If you are not sure your house needs testing, or what a positive result means for a repaint you are planning, get in touch and we will talk it through before anything gets sanded.