By Katie Townshend of 
Clean up in Wairoa following Cyclone Gabrielle. Photo: RNZ / Jonty Dine
The information in this story was first published following the Nelson and Marlborough floods in August.
Mud, silt and sewage have been left behind in Auckland, Northland, Bay of Plenty and Waikato homes after a deluge of rain brought flooding and slips to many parts of the North Island.
But, if you are allowed back home, how do you clean it up? Here is what you need to know.
Before you starting cleaning
While it is tempting to get stuck in, the first step is to stop, take photos, and document the damage for insurance purposes.
The Insurance Council of New Zealand (ICNZ) Te Kāhui Inihua o Aotearoa and Toka Tū Āke EQC urges people to contact their insurer before doing anything.
"They'll let you know what you need to do next, how to claim and what damage may be covered by your insurance or EQCover," ICNZ chief executive Tim Grafton says.
Insurance and Financial Services Ombudsman Karen Stevens warns that repairs should only be done after speaking to your insurer.
And throughout the process, make sure to document everything, she says.
"It's important to establish to your insurer what has been damaged and prove ownership. Your claims process will be easier with those documents to back up your claim."
Gear up
Floodwater is often contaminated with sewage and your house could be too, so you need to protect yourself.
"Floodwater can make the air in your home unhealthy. When things get wet for more than two days they usually get mouldy. There may also be germs and bugs in your home after a flood," the National Emergency Management Agency advises.
"Mould may make some people with asthma, allergies or other breathing problems sick. "
Make sure you wear long sleeves and pants - waterproof is even better - gloves, sturdy shoes and a mask or respirator.
Empty it out
Once you are allowed in, make sure the power is off and then clear the house out.
"Leave nothing inside the house that can trap moisture and slow the drying process," a BRANZ guide, Restoring a Home After Flooding, advises.
Anything wet needs to be thoroughly dried out - but if it is contaminated or cannot dry properly it may need to be thrown away.
Residents are also advised to throw away any wooden spoons, plastic utensils, and baby bottle teats and dummies if they have been covered by floodwater. There is no way to safely clean them.
Any contaminated food - including vegetables in gardens outside - will have to be thrown away.
Any appliances touched by water will need to be checked before being plugged back in.
Also, it is recommended you remove any valuables to protect against would-be thieves while you are getting the house habitable.
Along with clearing out all the visible muck, BRANZ advises you to search out any trapped water and debris. That involves removing skirting, kickboards and front panels to showers and baths, and clearing out any hidden mud and silt.
"Remove wall linings sufficiently to allow cleaning of the wall cavity and the removal of wet insulation materials."
If there is sufficient water available, and you are not still waiting for your supply to be reconnected, you can hose down walls and insert it into concealed spaces to flush out dirt.
Locals cleaning up around Gisborne Photo: RNZ/Nathan McKinnon
Get scrubbing
Once the debris is gone, it is time to employ the elbow grease - all surfaces need to be cleaned with disinfectant to ward off flood-carried infections, the BRANZ report advises.
"Hard linings such as wood panelling or wallboard can be scrubbed with a stiff bristle brush, water and detergent to remove dirt from cracks, corners and crevices. The surfaces should be well rinsed with clean cold water."
If plasterboard is used for bracing, it will have to be completely replaced. In other spots, it should be cut off 300mm above the flood line and just the affected part removed.
Other materials - such as those used for skirting and architraves - may have swollen and will need to be replaced.
Getting rid of mould
If mould has started growing on linings, it will need to be thrown away. Massey Univesrity school of Built Environment Massey University Dr Mikael Boulic says flooding provides perfect conditions for mould to grow.
"Mould is very tricky because you clean what you see, and don't clean what you don't see. Mould grows according to temperature and relative humidity, and often it is invisible. Your most effective weapon against it is to dry the house out as soon as possible.
"If you have power (and it's safe to use), turn on your air conditioner, a dehumidifier, and/or every fan you own. Keep the windows closed if you have a dehumidifier and an air conditioner to help the air circulate inside and get rid of excess moisture. Keep your windows open if you have only fans, and if there is no power and weather permits, open all your windows and doors to create airflow."
The Insurance Council says when things are wet, they usually get mouldy after two days. They also suggest opening cupboard doors and drawers to maximise air circulation.
BRANZ says any affected timber framing should be washed thoroughly, rinsed, treated and dried. If mould has been removed from the sides of a stud, it is likely to also be present on the back face of the stud, and this should be managed accordingly.
Floor coverings, such as vinyl and tiles, should be lifted to speed up the drying process.
Heaters and dehumidifiers can help speed the process along, but BRANZ advises against cranking the heater up to high, as too much heat can warp and split wood. Try and keep the temperature to about 20C, and keep the windows open so moist air can escape.
Throw it out
Once you have worked out what cannot be salvaged - and sorted it properly with your insurance company, you will need to dispose of the debris.
Auckland Council says if you have insurance, contact your insurance company in the first instance to confirm the process for disposing of storm-related waste, including building debris, soft furnishings and storm-damaged household items.
"A number of private waste companies can provide you with skip bin or flexi bag to collect your waste."
You can also take your debris and damaged items to a Waste Transfer station in Auckland. A list of these can be found here."
If you do not have insurance, Auckland Council has arranged for waste to be taken for free at participating transfer stations within the Auckland region. If you would like to take your waste to one of these stations, phone Auckland Council on 0800 22 22 00 to confirm your visit.
A list of participating facilities can be viewed here.
If you do not have transport to go to a transfer station, mention it to the council on the same number above so they can assess the best option for collecting your waste.
For other towns, contact your local council for further information.
- This story was first published on Stuff.
