Advertisement

Killing Mould

Mould is unsightly and can make you feel that visitors to your home will think you’re challenged in the cleaning department. But even worse, it can cause acute health problems for asthmatics and allergy sufferers. And it can also make people without allergies sick, too.

Many people are allergic to mould, and can become quite sick. The most effective remover of mould is bleach, but make sure you wear gloves, safety glasses and a respirator while using it.

The lowdown on mould
Mould is a fungus, and there are many types, including mildews. General mould is common where moisture from condensation settles on cool surfaces. Small localised areas of mould are more likely to be the result of leaks through the roof, through walls, under or around windows and flashings or near plumbing. If this occurs on timber, another form of fungal attack starts – wood rot.
Individual moulds are invisible to the naked eye, what you see on the wall as a dark stain is actually the mould colony. Other than being unattractive, mould won’t cause your home to collapse into a ruin, but surface finishes will be discoloured and permanently stained, and the air may smell musty.

For mould to occur you need mould spores – which are always in the air – a
surface to grow on, still air and moisture. There is little you can do about the spores, or surface for that matter. So that leaves the still air and the moisture.

You can’t just paint over mould, because it will come back. You need to get stuck in to eliminate it and deal with the reason it’s there in the first place.
Your challenge is to limit the amount of water available in the air in your home and to get the air moving. A bit like altering the weather, really.

Keep it dry, keep it clean
The amount of moisture or water vapour that air can carry (the relative humidity) is dependent on temperature. The warmer it is, the more water vapour the air can support. A point is reached where the air becomes saturated with moisture and the relative humidity is said to be 100 per cent. If the temperature goes up, the relative humidity drops – no problem. However, if the temperature drops, the air sheds water as dew.

In homes, problems occur when humid air migrates to cooler rooms or comes in contact with cool surfaces such as walls or ceilings. Water drops out as condensation. If this occurs day after day, mould has found its source of moisture. The favourite spots for mould growth are unheated bathrooms and bedrooms. And within them, corners and cornices – especially ornate ones, which are difficult to clean – where the air is still.

Winter is not the only time you can get mould. Pictures and furniture against solid masonry walls on the cool side of the house can also become mouldy as humid summer air condenses on the comparatively cool surfaces.


Your condensation and mould checklist

Put on your deerstalker hat and start detecting the obvious sources of moisture and still air around your home.
1. Older homes have vents in the top corners of rooms for natural airflow. If clogged with grime and paint or plastered over, open them up again.

2. Poorly designed extensions can block the original natural airflow in and under a home, especially in terrace homes. You may need a powered subfloor fan to get the air moving.

3. Maximise the sunshine your house gets each day. If it’s overshadowed by trees and shrubs, judicious pruning may improve things, and will also help your home make use of prevailing breezes.

4. Can you open windows on opposite sides of the house for cross-flow of air? When home, throw open the windows. Can they be locked partly open when the house is empty?

5. Are your old roof tiles porous, uncoated or unglazed? While they may not leak, they hold moisture, which can lift moisture levels in the home if there is no foil sarking under the tiles.

6. Check the sarking from the manhole. If it’s continuous over the ridge, moisture in the ceiling space can’t escape. Add a powered roof fan, wind turbine or vents high up in the gables if you have them.

7. Are the ceilings insulated? Insulation keeps your ceilings warmer and therefore less prone to condensation and mould.

8. Check the guttering and downpipes. If water just flows onto the ground around the base of the building, moisture will be plentiful.

9. Is the house damp underneath? Moisture will permeate up through timber floors into the house. Ponding water and moss growth indicate very wet conditions. Ensure surface water drains to the outside of the building.

10. Where the underside of your home is enclosed, are there sufficient vents for cross-flow of air? If you are in a damp area, you may need more than the regulations require – a minimum of two vents per room around the perimeter with breaks in internal underfloor walls. Brass mesh vents allow better airflow than older terracotta or pressed metal vents.

11. Do an audit of moisture generation inside the home. Check for a ducted rangehood over the cooktop and a working bathroom exhaust fan ducted to the outside – not the roof space. And, ideally, bathroom windows that open.

12. Duct clothes dryers to the outside. Most brands have ducting kits available.

13. Flueless gas heaters that plug into bayonet fittings generate huge amounts of moisture. Ventilate the room in which you are using the heater, to avoid damp in cooler rooms.

14. If you have rising damp with visible stains, bubbling paint or salt deposits on ground-floor walls, have it treated, to lower moisture levels.

15. Make sure exterior paint is sound, brick joints are pointed, and solid masonry walls without a cavity are weatherproofed or protected.


Dealing with a mould problem

A mouldy ceiling is caused by excessive moisture generation in the house and a humid roof space. The checklist on the previous page identifies things you can do inside, but if roof tiles are too porous, you have several choices. To sark the roof and install new tiles can cost thousands. Coatings for roof tiles aren’t cheap, have a limited life and only cover the exposed part of the tile.

The alternative used here is to install the low-profile Envirofan RF7 (about $399). This is a plug-in, 24V unit controlled by a $40 rechargeable timer to circulate air each day while switching off at night. You’ll need a power point installed in the roof space, but then you can fit the fan yourself. The fan moves nine cubic metres of air per minute, operates at 63db and is available in a range of popular roof colours.

Installing an Envirofan roof fan
Only get up on a roof if it is dry and rain isn’t pending. Wet roofs are treacherous. Make sure you wear a securely anchored safety harness before you start work.

Here’s how

Step 1 Remove a tile where the fan is to be installed, ideally fairly high up the roof but at least 2 tiles down from the ridge. To slip out a tile, slightly lift those above and overlapping at the sides and lift slightly so the lugs at the top can clear the batten. Also remove 2 tiles above the fan position.

Step 2 Where narrow tiles are used, adjacent tiles may need to be trimmed slightly so the fan can fit. This can be done by nibbling carefully with a pair of tile nippers or pliers. Fit fan with the straps pointing down into the opening.

Step 3 Push the upper flashing under the edges of the adjacent tiles. Bend the top of the flashing up a little to help protect against wind-driven rain blowing over the top in a violent storm.

Step 4 Reinsert the tiles above. You will need to partly lift the tiles above to get the lower tiles in.

Step 5 Dress the flashing down to match the tile profile, and, if necessary, cut to length at bottom so rainwater will run onto the tiles below.

Step 6 Back inside the roof space, screw straps to the battens, then plug the transformer, timer and fan into the power outlet.


Cleaning and painting

Step 1

Put on rubber gloves, goggles and a face mask and open the doors and
windows. Make up a solution of 1 part bleach in 3 parts water. The bleach contains hypochlorite which will nuke the mould or mildew and the spores. Be careful using some of the other popular solutions, as while they do wipe away the mould, they don’t kill the spores.

Step 2
Scrub all the walls and ceilings with bleach solution and a gentle scourer and wipe with a sponge. Just because you can’t see the mould colony doesn’t mean mould is not there. Let dry.

Step 3
Once dry, paint wall with a stain killer such as Dulux shellac-based Prep Lock, to cover any residual marks from the mould left after scrubbing. It dries quickly so you can put your final coats on within an hour or so. Cut in around the edges and corners with a brush, then use a roller to cover the rest. The stain killer is thin, so expect some of it to flick off the roller.

Step 4

Paint walls with a final coat of Dulux Wash-n-Wear (we used Stowe White) with 50ml of VC175 Mould Killer added to 10L of paint. This material is an irritant, so wear safety gear when mixing. Paint ceilings in ceiling white with the same mould killer added.