Form tie holes, tie bolts and penetrations

A straight pipe through the wall

On a basement or tank wall, the holes usually announce themselves: a regular pattern of small round wet spots or drips across the face, often more active at the bottom of the wall where the head of water behind is greatest. On a dry day they may show only as rust-coloured tears running down from each hole, or as a bloom of white efflorescence around them, which is salt left behind by water that has been moving through and evaporating.

Because the path is straight and short, a tie hole leaks under very little head. A crack has to be connected, has to be wide enough, and has to run somewhere useful before it will pass water. A tie hole is already all three. This is why a wall can be perfectly sound, uncracked and correctly poured and still be wet across its whole face.

It is also why tie holes are worth doing properly the first time. They are individually small, individually cheap, and there are usually a great many of them, so the cost of doing them twice is the cost of doing them all again.

Why a mortar plug always weeps again

The standard treatment, on site and in most previous repairs you will find, is to push a mortar plug into each end of the hole and trowel it flush. It looks finished. It usually is not.

Cement-based materials shrink as they cure. A plug pressed into a round hole shrinks away from the wall of that hole, and what opens up is an annulus - a thin ring-shaped gap around the outside of the plug, following the original hole all the way through the wall. The plug is still there. The water simply goes around it. That is why so many of these holes weep around the edge of an existing repair rather than through the middle of it, and it is the visual signature you are looking for when assessing a previously plugged wall.

The fix is not a better mortar. It is a different order of operations: drill the failed plug out back to clean concrete, install a mechanical packer in the hole, and inject hydrophobic polyurethane so the resin fills the full through-wall path including the annulus, then plug both faces with a non-shrink hydraulic plug or repair mortar and finish flush. The resin does the waterproofing. The mortar does the finishing. Reversing those two roles is the entire failure.

The steel tie that may still be in there

Some formwork systems use ties that are broken back or removed after the pour. Others leave part of the steel permanently in the wall. If a steel tie is still in place, you have two problems in one hole rather than one: a water path, and a continuous piece of unprotected steel running through the wall from wet face to dry face.

That steel corrodes, and corroding steel expands. It is the same mechanism as concrete cancer, in miniature, at every hole in the grid. The tell is rust staining at the hole, or a rust-coloured tear running down the face below it.

So the sequence includes cutting any residual steel tie back at least 25 to 40 mm from each face before the hole is filled, so that the cut end sits inside the wall with cover over it rather than being exposed at the surface. This step costs minutes per hole and it is the difference between a repair that lasts and a grid of rust stains reappearing through your new paint in two years.

How a hole is actually sealed

1. Drill out the old plugBack to clean, sound concrete for the full depth of the previous repair. This is the step that gets skipped, and skipping it means injecting into a partly blocked hole, which gives a false refusal at the pump and a wall that is still wet next week. Drilling in an enclosed basement means on-tool dust extraction or wet drilling - the workplace exposure standard for respirable crystalline silica is 0.05 mg per cubic metre, and a car park with no cross ventilation is where that number bites.
2. Cut back any residual steel tieAt least 25 to 40 mm from each face, both sides where both are accessible, so the fill can provide cover over the cut end.
3. Clean and flush the holeFlush the path with clean water to clear drilling dust, laitance, salt deposits and any rust scale, and to confirm the hole is actually open through the wall. Flushing also pre-wets the path, which matters because hydrophobic polyurethane is water-reactive and needs water present to cure.
4. Set a mechanical packer and injectA mechanical packer seals within the hole and takes pressure, so the resin is driven through the wall rather than smeared on the face. Hydrophobic polyurethane is the workhorse here because the path is usually wet and often flowing, and because the cured foam is dimensionally stable through wet and dry cycling rather than shrinking when the wall dries out in a Queensland winter.
5. Fill the full through-wall path, not just the mouthThe objective is a continuous plug of cured resin from one face to the other, including the shrinkage annulus around any earlier repair. Watch for resin appearing at the far face where the far face is visible - that is the direct confirmation the path is full.
6. Plug both faces and finish flushNon-shrink hydraulic plug or polymer-modified repair mortar at each face, finished flush. Tell us up front what the final finish will be, because a hole that will be left as bare concrete in a plant room is finished differently from one that will be rendered and painted in a lobby.
7. Observe before signing it offA minimum of 24 to 48 hours, and where the program allows it, across a rain event. On a tank wall, refill and hold. Record which holes were treated, on a marked-up elevation, so that if a hole weeps later everybody can tell in minutes whether it was one of ours or one that was missed.

Count the holes before anyone quotes

This is the whole commercial risk of the job. Tie holes come in a grid, and a grid on a basement wall means the count is rarely twelve. It is routinely one hundred and fifty, and on a full basement perimeter it can be several hundred. The phrase a few tie holes has turned into a fortnight's work more times than anyone in this trade would like to admit.

The arithmetic below is simply the published production rate of 20 to 50 holes per crew per day and the $45 to $120 per hole band, applied to a counted quantity. It is not an estimate of your building. It is a demonstration of why the count, and not the rate, is what determines the price.

What moves the per-hole rate

Within the $45 to $120 band, the variation is not arbitrary. Five things move it, and all five are visible before the work starts.

Volume genuinely reduces the rate. Above roughly 50 holes on one visit, set-up, mobilisation and pump priming are spread thin enough that the per-hole price should drop toward the bottom of the band. Below that, the site attendance minimum of $450 to $900 dominates, which is why the minimum job sits at $600 to $1,200 no matter how few holes there are. Two holes and eight holes cost close to the same, and any contractor who tells you otherwise is either not attending or not telling you what attendance costs.

Pipe penetrations and box-outs, which look the same and are not

The same wall almost always carries service penetrations: conduits, pipes, sleeves and box-outs that were cast in or cored later. They present the same way as a tie hole - a round leak in a concrete wall - and they take a different approach.

A penetration leaks in one of two places, and which one it is decides the scope. If water is coming through the gap between the pipe and the concrete, that is an annulus, and it is grouted: microfine cement grout is the natural material for annulus grouting around a pipe, because it is a permanent, non-degrading, chemically and thermally compatible fill that will not creep or embrittle the way a resin can. If water is coming through the concrete around the penetration, you are usually looking at honeycombing where the concrete failed to consolidate around a congested detail, and that is a void network, not a hole.

The distinction matters commercially, because a void network has no knowable volume. Honeycombing is priced by day rate or by grout volume with a provisional sum, never by the item, and if any reinforcement is exposed inside the honeycomb it has to be cleaned and treated rather than sealed over. A per-hole rate applied to honeycombing is a variation waiting to happen.

When the tie holes are not your problem

The holes are the most visible defect on a wall like this, which makes them the easiest thing to sell and the easiest thing to blame. Three situations where sealing them will not deliver a dry wall, and we will say so before quoting.

• The kicker joint is the real path. If there is a wet band along the base of the wall as well as active tie holes, the joint between the wall and the slab is very likely carrying most of the water. Sealing 200 tie holes and leaving the kicker joint is an expensive way to change very little. Price the joint and the holes together, and be clear about which one is doing the work.
• The whole face is damp, not just the holes. Broad-area seepage through the body of the wall is porosity or hydrostatic transmission, and there is nothing for a per-hole repair to grip. That is a negative-side tanking, drained cavity or curtain injection conversation.
• It is condensation, not ingress. A cold below-ground wall in a still, humid, poorly ventilated basement will run with water in a Brisbane summer with no rain involved at all. If the dampness has no correlation with rainfall and the space has no ventilation, sealing holes achieves nothing and the client is worse off by the cost of it. The test is cheap: tape a sheet of plastic tightly to a dry patch of the wall and look at it 48 hours later. Water on the room side of the plastic is condensation. Water on the wall side is ingress.

What it costs

Indicative only, and excluding GST. Build a line-by-line estimate for your own job with the price book, or read the working behind the rates in the 2026 cost guide.

Questions we actually get asked

Can we just render over the tie holes instead?

No. Render is a finish, not a water barrier, and a tie hole is a through-wall path under pressure. Rendering over an active hole gives you a few weeks of looking finished, then a damp patch, then the render debonding around it as salts crystallise behind the coating. If the wall is going to be rendered as part of the works, the holes have to be injected and plugged first, and the render goes on afterwards as a separate item.

Do all the holes need doing, or only the ones that are actually wet?

It depends on what changes behind the wall. A hole that is dry today is dry because the water behind it is not currently high enough or the path is partly blocked with debris and rust scale. On a wall where the water table or the surface drainage varies seasonally, the dry holes are simply the ones that have not started yet, and doing half a grid means mobilising twice. Where the wall backs onto a stable condition and only a defined band is active, treating that band and monitoring the rest is a legitimate, cheaper call. We will tell you which situation we think you are in and price both ways if it is close.

There is rust weeping out of the holes. Does that change the job?

Usually it means a steel tie is still in place and corroding, and yes, it changes the job. Those holes need the residual steel cut back at least 25 to 40 mm from each face before they are filled, so the repair provides cover over the cut end. If instead the rust staining is running along cracks rather than out of the holes, and there is spalling or hollow-sounding concrete nearby, you are looking at corrosion of the main reinforcement, which is a concrete repair scope rather than a hole sealing scope, and we would say so before quoting.

How do we count the holes if the wall is rendered or painted?

Sometimes you can read the grid through the coating, because the plugs and the render over them weather and stain differently to the surrounding face. Often you cannot, and then the honest answer is that the count is unknown until the finish comes off. In that case the right structure is a provisional quantity: a rate per hole, a counted quantity confirmed once the wall is exposed, and exposure priced as its own line. A lump sum over an uncounted grid is a gamble one of the two parties is going to lose.

The far face of the wall is against soil and we cannot reach it. Can you still do it?

Yes, and it needs to be said plainly what that changes. Working from one face only, we inject from the accessible side and drive resin through the full path, so the seal forms within the wall thickness rather than being closed off at both ends. That is a sound repair and it is what negative-side work is. What it means is that we cannot plug the buried face and we cannot see resin emerge there, so verification relies on pressure behaviour, take per hole and observation of the dry face afterwards. We will tell you which holes were done blind.

The wall is a potable water tank. Is anything different?

Yes. Every product that will touch the water - resin, plug mortar, any coating over the top - needs current AS/NZS 4020 test evidence, and the test report is valid for five years. Get the certificate for the specific product rather than a general assurance from a supplier or a rep. The tank also has to be drained, the repair fully cured and flushed, and in most cases the water authority will require chlorination and clearance before it goes back into service. That sequence needs to be in the program from the start, not discovered at handover.

Is 20 to 50 holes a day realistic on a car park soffit or a high wall?

No, and nobody should quote it that way. That band assumes holes you can reach standing on the floor, with reasonable light and no traffic around you. Above head height you are on an elevated work platform, which is $450 to $1,600 per day delivered, and every hole includes repositioning. In an operating car park, add certified traffic management at $900 to $2,500 per day and staged closures. The per-hole rate does not really change; the day rate around it does, and that is why access should be its own line on the quote.