Some technical stuff about paint

Updated: May 15, 2019

#paint #paintcolor #paintdisposal #painttechnical #technical

I've been getting some enquiries as DIY clients are feeling a bit overwhelmed by the technical side of painting. So I'm going to address this in 2 parts.

Part One will answer the more technical questions around health, what type of paint to use where, storage and how to dispose of paint.

Part Two will address How to Paint


Health Issues & Paint


It helps to understand there are 2 main categories of paint.

1. Latex/Emulsion/Acrylic. The name varies according to where you live. However the basics are these are water based and used mainly on walls and in various finishes eg. matt, flat, eggshell, satin etc

2. Oil Based. Solvent based and used where durability and movement occurs eg windows, doors, skirting boards. These produce a glossy finish. Some brands produce water based oils also - easier to wash up.


Next you need to understand what paint is made of.

1. Pigment - provides colour, hides imperfections, control gloss

2. Resin - the binder that holds pigments together and provides adhesion

3. Solvent - the carrier - either organic (eg turps) or water

4. Additives - enhancing properties eg ease of cleaning, mould/mold resistance, scuff resistance

So in terms of health, the risks are in paint with solvents and VOCs (Volatile Oil Compounds). These get released into the air as paint dries. As you paint this is the odor or smell. The VOCs evaporate into the air. Where's the chance you breathe them in. VOCs are also found in most consumer products such as cigarettes, dry cleaning products, cleansers, building furnishes, adhesives and more.

Common complaints if too much solvent or VOC is absorbed into the lungs are asthma, sinusitis, headaches, dizziness or fainting, nose or throat irritations. In great amounts, studies have shown these chemical substances (solvents & VOCs) can cause cancers, birth complications, and damage to the brain. However, if you're doing a one-off job or painting outside, the risks are very low. You just need to take the following precautions:

In general, always use:

Personal Protective Clothing (PPC) Always cover your hands with gloves, use masks and goggles. Cover skin with old clothing/overalls/apron.

Ventilation. Always work in a well ventilated space with windows/doors open. If possible work outside eg. if painting furniture

Don't use the room until paint is completely dry and use dust sheets on floor - to cover furnishings. Some recommendations to reduce the odor in a room include placing containers of crushed charcoal around room, baking soda (sprinkled on carpet and in containers with water). onions or vinegar. Dispose of after use.

Water-based paint pose fewer risks as they can be toxin free and have reduced odour.

Use Eco Paints or Natural Paints where possible. Or, look for paint with as low VOC as possible. The thing is VOC is used to solidify paint, make a wet wall become dry and it evaporates as you paint - giving the odor. Paint manufacturers are using technology to reduce the levels as much as possible. You'll just need to do a bit of homework according to how important this is to you. The safe level of VOC should be fifty grams per liter and below. Ask the painting manufacturers to display their technical data sheet to check the details how safe and environmentally friendly their paint really is. There can be a difference of between 20-80% in cost with various brands low or no VOC paint.

Paint Stripping & Sanding

Be aware old paint layers may contain lead (now illegal in paint). Lead was used as a pigment and to speed up drying. The age of house is an indicator. Anything in the past 40 years will be fine. If older than 40 years, either paint over the top if possible. This will apply if the old paint is in reasonable condition. If not, use a professional painter who will know how to remove and dispose of lead based paint.

Stripping and sanding may expose mould and spores that are breathed in. Use PPC.


See if water based options or low VOC options available from your supplier. Take frequent breaks and work in a well ventilated room.

Carpet Laying

Use PPC when laying. Buy wool, cotton, rattan or jute carpets. Vacuum regularly



Tackling Mould/Mold

This usually involves the use of bleaches so wear PPC and have good ventilation.

Installing Insulation

The materials often are made of glass fibre/shards. PPC is imperative with all skin covered.


In general, new environmental regulations & consumer demand has led to development of low-VOC & zero-VOCs and finishes. They are durable and less harmful to human & environmental health.

Health: reduced toxins, allergies and sensitivities

Environment: reduced landfill waste, groundwater & ozone depleting contaminants

Effective: good coverage, scrubbability, covers flaws

Reduced hazardous fumes: reduced odor while applying, no odor once cured, no off-gassing, can occupy room sooner

Not deemed hazardous waste: clean-up and disposal simplified


The easiest thing to do is talk with your paint supplier to ensure you're getting the right product on the right surface. For example there's some really good brands out now with a primer/topcoat in one - which eliminates the need for purchasing a primer. But this does depend on the surface you're covering. Some can be applied straight on to gib board ( but not if its in a bathroom/kitchen). See - that's why you should check.

It's all about the preparation and surface you're painting on. In general you should always clean down the surface (sometimes a sanding is required so the paint has something to adhere to). There are so many different types of surfaces, I can't cover it all here so check with your supplier - tell them what you're type of surface you're painting over (wood, plastic, metal, etc, where (interior/exterior), in what room (kitchen/bathroom or living/bedroom etc) and what you're trying to achieve - then use their experience and advice.

But here's some broad guidelines.


Windows, doors, trims, cupboards, furniture - anything that may get knocks or needs to handle movement - use an oil based paint. Having said that, with the good technology that goes into paint manufacturing now, there are some great water-based enamels on the market so check in with your supplier. Primers as recomended by supplier. These paints have a gloss or semi-gloss finish.

Decks, outdoor furniture etc. on wood. Use a stain or paint. There are water based stains on the market but the experts tell me an oil-based product gives a more true colour and lasts longer. Meaning you have to do the job less often !


Everything else use a water based product. These paints come in a variety of finishes - it depends on the brand what name they give it - but it ranges from flat or matt, satin, eggshell through to low or high sheen. The higher the sheen - the easier to wipe down/clean so consider that in kitchens or bathrooms especially.

Exteriors including roofs. Use specialised paint formulated to handle the sun and atmospheric conditions. These can be water based.


In general, well sealed paint in cans will last up to 10 years if stored well and kept from freezing. Used paint can be stored for up to 2 years if sealed well and stored in a cool, dry space.

As paint manufacturers face tighter restrictions on what preservatives they can use, and solvents are reduced or eliminated altogether in paint, in can make them more susceptible to bacterial growth. The bacteria grow in the can and release hydrogen sulphide gas which is like a bad egg small, and ammonia which is a urine like smell.

If you come across this in new cans, return to your supplier. If you've already painted and still get the strong smells, still talk to the supplier. They will know how to solve the issue - eg an alkaline based sealer - which should be at no cost to you.


Yes, some more than others. If you find mould in the can - take it back and talk to the supplier.

If however, you find mould in other areas such as your bathroom walls or a bedroom or kitchen it needs different consideration. How do you know its mould? It will have a must odor, discolouration and unidentified blackish clumps or colonies across the wall or ceiling. Mould usually occurs in warm, humid environments or where there is a leak or has veen. First ensure any leaks or lack of ventilation are taken care of. Secondly, clean down the walls/ceiling - there are specific products on the market to clean off mould depending on the surface. Thirdly, repaint with a paint specially designed for kitchens or bathrooms. These paints have mould inhibitors in the mix.

It pays to discuss this with your supplier again. Some paints on the market now have this built in all paints and you can use the same paint throughout the entire house - regardless if its a kitchen, bathroom, lounge or bedroom etc. This can be cost-effective but it depends on the size of your project.




In general

  1. Solvent based paints need to be treated as household hazardous waste - refer to your local council guidelines

  2. Steel paint cans are recyclable. Refer to local council as above

  3. Aerosols - don't puncture or throw in incinerator. Empty by spraying leftover paint into cardboard box and dispose of as household waste


  • work out quantities before purchasing. Measure the space and remember to x2 for two coats. Your supplier often can help with calculations or there are paint calculators on brand websites. Just google it ! A guestimate works fine (eg coverage/spreading rate is 11 square metres per litre of paint)

  • use it all up - apply an extra coat if that works

  • find another project - if you look around the home there are plenty of things that could be painted - google it for inspiration

  • give it to someone who can use it - eg a local school, charity, neighbour

  • store (for approx 2 years) with a well-sealed lid in cool, dry space. Use it as a base paint for a future project. As long as you don't mix water and oil based on the same wall you'll be good to go.

  • avoid dangerous practice of storing in other containers & ensure its out of reach of children

  • leave water-based paints to dry in can - then dispose according to local council guidelines

  • oil-based paints can be soaked up with kitty litter, newspaper other absorbent materials

  • avoid pouring paint, thinners, turps, mineral spirits, or any solvents down drains, storm sewers or on the ground. These have an unlimited shelf life if stored properly. Keep and use


Yes - at 32 degrees F (O degrees C) for water based paints - the same as water. Oil based paint freezes at lower temperatures.

How do I know if it's been frozen at some point? It will have a strange consistency, be ropey, stringey, clumpy or gritty.

What can I do? Thaw it out! Stir & assess. Take it to be shaken at a paint store. Discard if it doesn't return to usual consistency.


In general, no lower than 10 degrees C (50F) or higher than 32 degrees C (90F). Best drying times are within humidity range of 40 - 70%.

If you want to be a bit more technical:

Oil based - 5 - 32 C (40 - 90 F)

Water based - 10 - 29 C (50 - 85 F)


Storage best practice

  • Try basement or attic or storage area inside home - within a temperature controlled environment

  • Cool, dark, dry space

  • Try and avoid outdoor shed as temperatures vary a lot - there may be moisture problems

  • Avoid storing in other containers, especially unmarked

  • For further protection - plastic wrap over top of can & pound lid with mallet to seal well

And thats a wrap.

Next blog, we'll talk more about how to prepare the surface and apply the paint.

If you want some more advice, as suggested always talk with your local hardware or paint supplier. These guys usually have a wealth of knowledge you can tap into.

If you would like some help from me on how to get the right look and feel - along with a suggested colour palette click here



Wellington | New Zealand

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