Rain on a fresh pour in Rockhampton: what to do in the first hour.

Six things to do before you call anyone

1. Cover it, but do not smother it. Builders plastic or curing blankets, held clear of the surface on battens, star pickets or empty buckets. Plastic lying flat on green concrete leaves permanent mottled blotches, and on coloured or oxide work that mottling is the damage.
2. Divert the water before it reaches the slab. Most of the real rain damage we see in Rockhampton is not the rain that falls on the pour, it is the sheet of runoff arriving from somewhere uphill. A shovel trench, a length of timber or a sandbag laid across the flow path is worth more than anything you can do to the concrete itself.
3. Protect the edges. Exposed slab edges and the top of a thickened edge beam are where running water cuts first. Once the mesh or the beam steel is showing you are into a rebuild at $80 to $160 per lineal metre rather than a wash and a reseal.
4. Do not add anything to the surface. No dry cement dusted on to soak up water, no sand, no hosing it clean, no leaf blower. Every one of those makes the surface weaker, not stronger.
5. Keep the load off. No foot traffic, no ladders, no propping the shed frame on it. A slab that is still plastic will take a permanent print, and a slab poured over deep fill that has just been saturated can have a void under it you cannot see.
6. Record everything. Time of pour, time of rain, the docket number and the concrete grade off the docket, plus wide photos and close ups. If this ends up as a warranty conversation or an insurance claim, that ten minutes of phone camera work is the whole case.

The reason the first hour matters is that concrete stops caring about rain once it has taken its initial set. In Rockhampton summer conditions, with the mix leaving the plant warm and a 34 degree afternoon on top of it, initial set is commonly 3 to 5 hours after placing. On a cool, still winter morning it can stretch to 8 hours. Before that window closes, rainwater mixes into the top few millimetres and raises the water to cement ratio exactly where you least want it, at the wearing surface. After that window, rain is a nuisance that spots the finish and delays the sealer.

What makes the damage worse in the next 24 hours

Nearly every expensive rain job we are called to was made expensive after the storm, not during it. These are the four things that do the damage.

Troweling water back into the surface. A finisher trying to save the job will work the pooled water into the top. That water becomes part of the paste, so the surface ends up with a far higher water to cement ratio than the concrete underneath, which is precisely why it dusts, scales and wears through in two summers. If the slab is firm enough to walk a board on, push the water off the edge with a squeegee. Otherwise leave it alone and let it evaporate.

Dusting cement powder onto the wet patches. It looks like it dries the surface. What it actually makes is a thin, unbonded, high shrinkage crust that will delaminate within a year.

Driving or loading it early. Concrete gains strength over 28 days. Foot traffic is generally fine at 24 to 48 hours, a light car at 7 days, and a loaded trailer, caravan, boat or delivery truck at 28 days. After a soaking, the subgrade underneath is as much of a weak point as the slab, particularly on the reactive black clay through Gracemere, the Fitzroy flats and parts of North Rockhampton. A slab that would have been fine can crack simply because the ground under it turned to porridge.

Sealing too early. A sealer applied over a damp slab traps moisture and goes cloudy or white, and it then has to be stripped at $15 to $35 per square metre before you can start again. Concrete needs to dry for at least 28 days before a topical seal, and after a wet week make that longer. There is more on timing and product choice in our guide to sealing and maintaining concrete in Rockhampton.

What you can safely do yourself, and what is genuinely dangerous

Safe for a homeowner

• Tenting plastic or hessian over the slab and weighting the edges down.
• Digging a diversion trench or laying a timber or sandbag barrier upstream of the pour.
• Clearing a blocked downpipe or spreader that is dumping roof water onto the slab.
• Squeegeeing standing water off a slab that is firm enough to walk a plank on, pushing it away from the pour rather than through it.
• Photographing everything and keeping the delivery dockets somewhere safe.

Leave this to a tradesperson

• Grinding or dry cutting. Cutting and grinding concrete releases respirable crystalline silica, and Queensland work health and safety law is strict about it for good reason. On tool water suppression or dust extraction plus a properly fitted P2 respirator is the minimum. A cheap angle grinder and a paper mask from the hardware aisle is not the same thing.
• Cutting control joints. Depth and timing decide whether the joint controls the crack or does nothing at all. Too shallow and the slab cracks somewhere else, too late and it has already cracked.
• Working on or beside an undermined slab. If water has washed fill out from under an edge there can be a void you cannot see. Do not put weight on it and do not dig alongside it.
• Anything involving standing water and electricity. Leads, pumps, saws and site power sitting in water is the one that actually kills people. Isolate at the switchboard, and if anyone is in contact with power, call emergency services on triple zero and do not touch them.
• Skin contact with wet concrete. Fresh concrete is strongly alkaline and causes chemical burns that can become serious before they even hurt. Gloves and boots, rinse skin immediately with clean water, and get medical advice for anything more than a mild sting.

An after hours call out against waiting until Monday

Here is the honest arithmetic. A quote or assessment visit during business hours across Rockhampton, North Rockhampton, Gracemere, Parkhurst and out to Yeppoon is free. An after hours or weekend attendance to make a site safe, cover a pour or cut a diversion typically costs $250 to $450 for the first hour and $120 to $180 an hour after that, plus materials. If plant has to come with it, a saw or a pump adds $400 to $900 on top.

When it is not an emergency at all, and waiting saves you real money

This is the part most people never get told. Concrete keeps changing for a month. It gains most of its strength in the first 7 days and reaches its design strength at 28 days, and the colour and surface appearance keep moving that whole time. A large share of the panicked calls we take on day 2 or day 3 turn out to be nothing at all by day 28.

Rain spotting on plain grey concrete usually weathers out within a few months. Efflorescence, the chalky white bloom that shows up after a wet week, is salt coming out of the slab: it is not damage, it is not mould, and it generally washes and wears away over one or two seasons. Uneven colour on an oxide or exposed aggregate finish almost always evens up as the slab dries, and judging it while the surface is still damp is how people talk themselves into a $3,000 recolour they never needed. Fine crazing is cosmetic and does not shorten the life of the slab by a single year.

So our standing advice is this: unless something on the urgent list above applies, cover it, keep the load off it, photograph it weekly and make the repair decision at day 28. Waiting a month costs you nothing and routinely saves between $500 and $2,500 in remediation that was never required. If the fault is real it will still be there at 28 days, and it will be easier to price accurately once the concrete has stopped moving.

If your problem is not a fresh pour but an older slab moving, cracking or dropping, that is a different diagnosis with different causes: start with when to worry about concrete cracks and slab prep on reactive soil. If storm or flood water caused the damage rather than the pour going wrong, our page on flood and storm damage insurance claims covers what a Queensland policy actually pays for.

How to stop it happening on the next pour

Rockhampton gets roughly 800mm of rain a year and most of it arrives between December and March, usually as afternoon and evening storms that build with very little warning. A crew that pours here properly plans around that rather than hoping.

• Start at first light. Trucks at 6am, screeded by mid morning, finished before the afternoon build up. That is the single biggest protection you can buy, and it costs nothing.
• Have the covers on site before the truck arrives. Plastic, battens and a squeegee sitting in the ute is the difference between a five minute response and a ruined surface.
• Stand the pour down if the radar says so. A cancelled truck costs a cancellation fee, commonly $150 to $400, plus a short load levy of $80 to $200 if part of the load is already batched. A ruined 60 square metre driveway costs $9,000 to $14,000 to replace. That decision is not close.
• Sort the stormwater first. Downpipes, spreaders and surface falls should be dealt with before the pour, not after. Ag line and a pit to take roof water away from a new slab runs about $80 to $150 per metre installed.
• Pour in the right season if you have the choice. Our guide to the best time of year to pour concrete in Rockhampton goes through the month by month trade offs, and new build concreting covers how a slab date fits a build program.

What we will not do

We will not grind and reseal a slab that is three days old to make a worried owner feel better, because at three days nobody can tell the difference between a surface that is genuinely weak and one that simply has not finished curing. We will not sell you a topping over a slab with a structural problem underneath, because the topping will crack in exactly the same place inside a year. And if the slab was poured by someone else and is still inside their statutory defects period, we will tell you to go back to them first rather than quote you for work their warranty should be covering.