Costing a DIY borer job before you buy
The shelf price of one bottle tells you very little. The real DIY cost depends on how much timber you have and how many coats it takes.
Facts and prices checked 5 November 2026
A DIY borer treatment costs the product for two coats over every bare surface, plus protective gear and a sprayer. As a rough guide, one retailer lists a 500 ml concentrate (about $70 to $90) as making 5 litres of mix, enough for about 50 square metres, which works out at around 10 square metres per litre of mixed product per coat. Measure your timber, double it for two coats, and you have a fair estimate. This page walks through that sum for typical jobs. For professional prices, see the borer treatment cost page.
How do you measure the timber to treat?
Measure the timber by surface area, not floor area, because you're coating every face of every board, joist and rafter you can reach. A subfloor's treated surface is several times its floor area once you add the sides of joists and bearers, the pile tops and the underside of the boards. Roof spaces are similar. Small items are easier: measure each face.
Quick ways to estimate:
- Floorboards from above, sanded bare: room length × width
- Subfloor: floor area × about 2.5 to 3, to allow for joist and bearer faces (an estimate, not a rule)
- Roof space: ceiling area × about 2, plus rafters and sarking
- Shed or garage framing: count studs and rafters, multiply by their length and the faces you can reach
- Furniture: bare faces only; finished faces are injected instead
How far does a litre of borer treatment go?
Going by one retailer's listing, a litre of mixed product covers about 10 square metres per coat on bare timber. Rough, dry, old timber drinks more; planed timber takes less. The manufacturer's directions say to apply liberally and to put on a second coat once the first has soaked in (usually two to six hours), so plan on two coats. That makes about 5 square metres per litre for the finished job.
| Job | Rough surface area | Mixed product for two coats | What to buy |
|---|---|---|---|
| Small piece of furniture, bare back | 1 to 2 m² | Under 0.5 L | 680 ml ready-to-use spray, about $36 |
| Room of sanded floorboards (15 m²) | 15 m² | About 3 L | 500 ml concentrate, about $70 to $90 |
| Garden shed framing | 20 to 30 m² | 4 to 6 L | One or two 500 ml concentrates |
| Roof space, 100 m² house | 200 m² or more | 40 L or more | 5 L concentrate, about $475 |
| Subfloor, 100 m² house | 250 to 300 m² | 50 to 60 L | 5 L concentrate plus extra |
These are working estimates built from the published coverage and dilution, not measurements of any particular house. Mix only what you'll use: one manufacturer says to use diluted product within 48 hours.
What else does a DIY job cost?
Beyond product, a DIY job needs a pump sprayer or brushes, a respirator suited to the product, eye protection, gloves and disposable coveralls, plus a good torch and crawl boards for the roof space. Check current hardware-store prices for each, because they add up. If you're injecting finished timber as well, add injector cans: they go quickly on a floor or hallway with many holes.
What people often forget:
- Replacement filters for a reusable respirator
- A drop sheet and rags for spills
- Filler, sandpaper and paint for making good afterwards
- A second session, because two coats need a gap of a few hours
Borer under the floor or in the roof space? Get a written quote
Where does DIY stop saving money?
DIY stops saving money somewhere around a whole roof space or subfloor. Product for two coats over 200 or 300 square metres of framing approaches $475 to $600 on its own, before gear, and published Auckland price lists put a professional roof space treatment at roughly $350 to $600 and a subfloor at about $450 to $750. At that point the gap is mostly your own labour, in an uncomfortable space.
That's why the common split is: do the furniture, shed, sanded floors and easy patches yourself, and get the roof space and subfloor treated. Our products or a specialist answer helps you decide which parts are which.
How long does a DIY treatment take?
A DIY treatment takes longer than people expect. A shed might be a morning. A roof space can take most of a day once you include moving insulation, working from crawl boards, two coats and breaks from the heat. A low subfloor is slower still. Injecting a hallway's skirtings and architraves hole by hole can take hours on its own.
The DIY mistakes answer lists the shortcuts that cost people a second job.
Questions people ask
How much borer treatment do I need for a subfloor?
Work out the timber surface area (roughly two and a half to three times the floor area, for joists and bearers), then allow about one litre of mixed product per 5 square metres for two coats. For a 100 square metre house that's around 50 litres of mix, or a 5 litre concentrate and more.
Is ready-to-use or concentrate better value?
Concentrate is much better value for anything bigger than a small item. A 500 ml concentrate makes 5 litres of mix, while a 680 ml ready-to-use bottle is just that. Ready-to-use suits furniture and quick patches.
Can I use leftover mixed product later?
Not for long. One manufacturer says to use diluted mix within 48 hours. Mix only what you need, and see our answer on disposing of borer treatment.
Where this fits in the bigger picture is laid out on our main page for borer treatment across Auckland.