Furniture and antiques

Borer in furniture and antiques

An old chest of drawers or a second-hand table can bring borer into a house that would otherwise be low risk. Most affected pieces can be kept. The questions are how to stop the beetle without spoiling the finish, and how to stop it reaching the house's own timber. A borer inspection can include any pieces you are worried about.

Borer in furniture is usually the common house borer in native or pine pieces, or the powderpost beetle in hardwoods such as oak. Live borer in a piece worth keeping is usually dealt with by injecting a borer product into the exit holes and treating bare, unfinished timber such as backs, drawer sides and undersides. Polished faces are left alone, because a finish stops surface products soaking in.

Check second-hand and antique pieces before they are carried into the house, and keep a piece with fresh dust apart from the house until it has been dealt with.

How do you check furniture for borer before bringing it home?

Turn the piece over and look where the timber is bare: backs, drawer bottoms and sides, feet, rails and the underside of tops. Fresh borer shows as clean, pale-edged holes and small heaps of powder under the piece or in the drawers. Old holes dark with wax or polish suggest historic damage. Tap the piece over a sheet of paper and see whether fine dust falls out.

Round holes of about 1–2 mm in native or pine timber point to the common house borer.
Pinholes of 0.8–1.6 mm with talc-like powder in oak, ash or other hardwood point to the powderpost beetle.
Soft corners, crumbling feet or legs that flex mean structural damage that needs a restorer, not only treatment.

If a piece shows fresh signs, keep it away from untreated timber, ideally outside the house, until it has been treated. That matters most from late spring through summer, when adult beetles are emerging.

How is borer in furniture treated?

Furniture treatment works around the finish. Holes in polished or painted surfaces are injected with a borer product so it reaches the tunnels behind them, and bare timber on backs, undersides and inside drawers is brushed or sprayed with a residual product that can soak in. Follow the product label at every step, and try it on a out-of-sight corner first, since solvents can mark some finishes.

Aerosol foggers do nothing useful for a piece of furniture. Consumer NZ points out that airborne treatments only reach adult beetles in flight, not larvae inside the wood. The borer bombs and sprays guide compares what each retail product type reaches.

Consumer NZ notes that fumigation is used for furniture, since a single piece can be fully enclosed in a way a house cannot. Fumigants are controlled substances that WorkSafe limits to holders of a controlled substance licence, so fumigation is a specialist service, not a home method.

Does borer treatment damage antique finishes?

It can, if done carelessly. Surface sprays and brush-on products are designed for bare timber and can stain, lift or cloud shellac, French polish, wax and some lacquers. Injection keeps the product inside the holes and off the polished surface, which is why it is the usual approach for finished pieces. Wipe away anything that runs out, and leave repair of the surface itself to a restorer.

Filling the holes afterwards is a finishing job, not part of the treatment. Leave it until the piece has been through a summer without fresh dust, so you know the treatment has worked before the evidence is covered.

When should a furniture restorer be involved?

Bring in a furniture restorer when a piece has value beyond its use, when borer has weakened a joint, leg or rail, or when the finish needs repair after treatment. A restorer can replace or consolidate damaged parts, fill holes in a way that suits the finish, and judge what an antique can take. The borer inspection identifies the beetle and whether it is live; the restorer looks after the piece.

For an heirloom or a collectable piece, ask the restorer before any product goes on, because some surfaces are difficult to put right afterwards.

Will borer move from a piece of furniture into the house?

It can. Adult beetles that emerge from an infested piece fly, and can reach untreated sapwood in floorboards, skirtings, and framing in the roof space or subfloor. Furniture is one way borer turns up in a newer house built with treated framing, usually in its untreated parts. The risk is highest when a piece with fresh activity sits indoors through the November to January emergence of the common house borer.

Treating a piece before early summer, and keeping new arrivals apart until they have been checked, protects the house. If borer has already appeared in a floor near where a piece stood, borer in floorboards covers what to look for next.

Which furniture timbers are most at risk from borer?

Untreated native and pine pieces are the common house borer's territory, especially where sapwood was used for backs, drawer parts and frames; rimu, kahikatea and radiata pine are all recorded hosts. Hardwood pieces in oak, ash or elm, and New Zealand tawa, can carry the powderpost beetle, which attacks only the sapwood of hardwoods with large pores and plenty of starch. Solid heartwood pieces are at lower risk.

The life cycles differ too: the common house borer spends about three to four years as a larva, the powderpost beetle usually one. The powderpost beetle guide covers hardwood pieces in more detail.

Questions people ask

Can you treat borer in furniture yourself?

Often, yes. Retail borer products need no licence, and injecting holes and treating bare timber on the back and underside is within reach of a careful owner who follows the label. Get advice first if the piece is valuable, the finish is delicate, or the timber is soft, and remember that a product does not tell you whether the borer was live in the first place.

How long do borer live in furniture?

The larvae of the common house borer spend roughly three to four years feeding in the wood before emerging, so a piece can carry live borer for years before the first hole appears. Powderpost beetle larvae usually take about a year. One generation can be followed by another in the same piece if nothing is done.

Should I throw out furniture with borer?

Rarely. Most pieces with borer can be treated and kept, and old inactive holes need no treatment at all. A piece is worth giving up on when the timber has lost so much strength that it cannot be repaired sensibly, or when it has little value and is sitting next to untreated house timber with fresh dust coming out of it.

If one piece of furniture has borer, does the house need treating?

Not automatically. If the borer is confined to the piece and the house timber shows no fresh holes or dust, treating the piece may be all that is needed. If floors, skirtings or the subfloor show activity too, the house needs its own assessment, and the options are set out under treating live borer.