Timber stump replacement

Why timber stumps fail

Hardwood stumps were the standard for Queensland houses for a very long time, and they were a sensible choice. Dense local hardwood, set in the ground, carrying a light timber framed building. Plenty of them have done eighty years of service.

They fail for three reasons, usually working together.

Rot. The critical zone is right at ground level and just below it, where the timber is alternately wet and dry and oxygen is still available. That combination is ideal for fungal decay. This is why a stump can look completely sound from a metre away and be soft as cork at the base. The failure is almost always at the bottom.

Termites. South East Queensland has among the heaviest termite pressure in the country. A timber post in damp soil, in direct contact with the ground, is the easiest possible entry point into a house. Termites hollow the stump from the inside while leaving a thin outer shell, so a stump can look intact and have almost nothing left in it.

Load and shrinkage. Timber shrinks across the grain as it seasons and it crushes slowly under sustained load. Over decades, a stack of hardwood stumps loses a small amount of height. Where that loss is uneven, the floor above records it.

Checking them yourself

If you can get under the house safely, you can learn a great deal in twenty minutes with a torch and a screwdriver. Do not crawl into a space you are not confident about, and stop immediately if you find live termite activity rather than disturbing it.

• Probe the base of each stump. Push firmly at ground level and just above. Resistance is good. Give is not.
• Look for splitting. Deep vertical splits mean the stump is losing its ability to carry load evenly.
• Check plumb. Sight along the row. Leaners are doing less than they should.
• Look at the ant caps. Missing, corroded or bridged caps are a problem in their own right.
• Look for mud tracks. Thin mud tunnels running up a stump or over an ant cap are termite workings. Stop, and call a licensed pest inspector before anyone touches anything.
• Feel the ground. Persistently damp soil under the house tells you why the stumps are going, and it needs addressing regardless of what you do about the stumps.

Replace all or replace some

Almost every quote you get will have to answer this and the answer should come from evidence rather than policy.

The case for partial replacement is that it costs less now and that failure genuinely can be localised, particularly where one specific water problem has been attacking one part of the house.

The case for doing the lot is that the remaining stumps are the same timber, the same age, and in the same ground. If a third of them are gone, most of the rest are on the way. Because supporting and jacking the house is a large fixed part of the cost, doing it twice is substantially more expensive than doing it once.

A middle position that often makes sense is replacing everything in the affected zone plus a margin, and leaving a genuinely sound section that is separated by a clear structural or drainage boundary.

What replaces them

Almost nobody replaces timber with timber, and for good reason. The two standard options are precast concrete and galvanised steel.

Concrete is the traditional Queensland replacement. Cheaper, extremely durable in the ground, immune to termites and rot. Fixed height once it is set, so future adjustment means jacking and packing.

Galvanised steel costs more and has an adjustable threaded head, so future levelling is a matter of turning a collar. Very useful on reactive clay. The galvanising has to stay intact, which is a real consideration near the coast and in salt affected areas.

Both need a proper footing at the base and a galvanised ant cap at the top, and both need to be founded deep enough for the soil they are in. Depth is not a detail. A support founded in the zone where clay is still swelling and shrinking will move with the clay.

Sequence when termites are involved

If there is any evidence of termite activity, the order of operations matters and getting it wrong is expensive.

1. A licensed pest inspector assesses the property and identifies whether activity is live and how far it extends. Disturbing workings before this can scatter a colony and make the inspection less useful.
2. Treatment or management is carried out as recommended.
3. The structural extent of the damage is established, which frequently reaches beyond the stumps into bearers and joists.
4. The structural repair or replacement happens.
5. Ongoing management is put in place, because treating once does not make a property permanently immune.

The pest side and the structural side are two different licensed disciplines. A restumping contractor is not a pest inspector and should not be treated as one.