In a moment of questionable judgement, I recently invited that fine fellow and good friend of Traditional Painter Mr Charlie Budd to write an article, of his own choosing, to appear on my blog (I know, the madness of it!?!?!?)… Now, Mr B doesn’t shy away from “tough” subjects and hasn’t disappointed here – using the full breadth of his MSc brain (yes, he really does have a Masters Degree!!!) to address what every Painter & Decorator needs to know and understand…
Ladies and Gentlemen, for one night only, I give you Mr Charlie Budd, (at the end of the show he’ll be standing at the back of the hall signing copies of his forthcoming tome – “I know Science, me”… or catch him on his own website www.charlesbudddecorating.co.uk or on that Twitter thing as @charliebudd).
Take it away Mr Budd;
Whether you’re a professional or DIY decorator, you might want to watch how your paint dries. I don’t mean sitting there with a cup of tea staring at it meditatively for hours, but developing a bit of ‘knowing what it’s doing’.
Surely there are better things to be doing with your time? Peeling grapes. Folding fitted sheets. Working out the number of anagrams of ‘watching paint dry’, Watching Twilight Part 1, Part 2, Part zzzzz (angst-ridden mumbling teenage vampires don’t do it for me! Mind you, I do watch paint dry.)
Well that’s the point. You want to be doing other things. You want to get a good finish on your paintwork, and you want your paint to dry so you can clear up and do something else. Whether you’re a professional wanting to get onto the next job, or a DIYer wanting to have some down time at the weekend, this blog is for you.
I’m telling you now, there are two things you want:
1. To get a good finish with your paintwork.
2. To get it done quickly.
Unfortunately, these are sometimes not terribly compatible. Generally speaking, the longer the paint takes to dry, the more it levels out to a lovely flat finish. The quicker it dries, the greater the likelihood you’ll get brush marks or roller stipples. So how do you get the best of both worlds?
What are you painting?
With emulsions – on ceilings and walls, unless you’re going for a really top class smooth finish (in which case, you may be better off getting a specialist in to spray the paint) then minor brush marks and roller stipples won’t matter too much. Most emulsions are matt, which hides imperfections. So it doesn’t usually matter if your walls and ceilings dry really fast – the paint will level off enough unless your brushes, rollers and technique are somewhat ‘rustic’.
But if you’re painting woodwork – your skirting boards, doors and frames, shelving, furniture… you’re probably using a paint with a bit more sheen to it – as higher sheen paints are usually more durable – ideal for items which get a bit bashed about – like shelves, chairs and doors.
Oil and water
Until fairly recently, most woodwork was finished with oil-based paints. The oils take a long time to evaporate and the paint takes a long time to dry – so it has time to level off to a perfectly smooth finish. But new environmental and health regulations in the EU, USA and other countries are reducing (or even banning) the use of oil-based paints indoors – as they give off fumes (VOCs – Volatile Organic Compounds) which are harmful to health, contribute to air pollution and global warming.
Different paints have different amounts of VOCs in them.
So the trend is towards water-based (or sometimes hybrid water-oil) paints for woodwork. This is great as they give off less fumes, and dry a lot quicker. Typically, oil-based paints can be recoated after 16 hours (there are exceptions) but water-based can be recoated in a quarter of that time. Sorted! Yeah? Unless you’re after that perfectly smooth finish…
Water-based paints can dry so quickly that the brush marks and roller stipples don’t have time to level off.
Brush marks all over your doors and shelves? Your paint is drying TOO quickly! It’s convenient, but looks like a 5 year old did it (apologies to all 5 year old master decorators). What to do? Let’s get a little scientific, not too much, I promise.
Please explain, professor
Looking at it logically, paint drying means your solvent (usually water) is leaving the paint film and allowing the clever chemicals that the scientist wallahs put in it to knit together, forming a tough film to protect your surfaces.
So what makes your solvent leave the paint film? It can only go two ways – as the Vengaboys said in 1998, Up and Down… into the air, or into the substrate. So one factor is how absorbent your substrate is. Plaster or filler will suck water in like a thirsty warthog – whereas timber pre-primed with a shiny primer- undercoat will absorb a lot less. The main factor though is usually evaporation -how quickly can those pesky solvent particles escape to swan around in the atmosphere?
The factors include:
Humidity – air laden with water or oil molecules won’t accept more of those molecules as readily as dry air.
Temperature – the warmer it is, the more energetic your solvent particles will be, and the more readily they will escape from the paint.
Wind – a breeze can whisk your solvent particles away, leaving space in the air for more. Very still air can mean localised humidity (of water or oil molecules) above your paint.
Type of paint – some paints will just dry much more quickly – for reasons of complex chemistry. So let’s move on to become a…
Hmmm. So let’s say your paint is drying too quickly, and you’re getting lots of horrid brushmarks, and you can’t keep all your paint edges wet – they’re starting to dry and you’re dragging half-dry paint all over the place! What can you do?
1. If it’s a water-based paint, you can pre-moisten your substrate – either with a clean, damp microfibre cloth, or with a very fine garden mister. This radically reduces the absorption of water molecules into your substrate. This makes a huge practical difference – and some good decorators using this technique can get a finish similar to a spray finish, or an oil-based finish. The trick is not to moisten your substrate too much, or the paint will tend to slip and slide, and you’ll get drips and runs all over the place.
2. Secondly, you can put additives in your paint which increase the ‘wet edge time’, meaning you’re less likely to get paint dragging on your brush and more levelling. With water-based paints you can use a little water – and some experts insist this is the best, although others think this degrades the paint slightly and it’s better to add a paint conditioner like Floetrol. There are alternatives to Floetrol such as XIM Xtender (which is slightly blue so can colour your paint) or Fair Decor from Belgium – which seems more similar to Floetrol. If you’re using an oil-based paint, which I still do on exteriors, and it’s a hot, breezy day, sometimes your paint just dries too quickly to paint a panelled door for instance. The old technique was to add white spirit to make the paint thinner. This is all very well, but white spirit can increase paint drying in some cases, and it can also weaken the paint mixture. Many decorators now use Owatrol – which is a special oil blend which increases the wet edge time of oil paints, does not degrade them (in fact it has properties which can improve the paint!) and yet does not increase overall drying time. Clever stuff! More science. Let’s move on.
3. If you’re painting indoors, and you’ve got the central heating on and your paint is drying too quickly – you might want to switch the radiators off in the room you’re painting – at least while you’re painting the woodwork. Once the paint is touch dry, you can switch them on again to aid drying. If you’re painting outdoors in hot weather, you might want to consider applying critical coats of paint early in the morning, or (if you can) in the evening. But you have to be careful of being able to close doors and windows – and careful of dew/condensation in the evening, as this can dull a gloss finish.
Speed it up baby!
But how about getting the paint to dry quicker? This will only really apply if you’re painting emulsions or your trim/woodwork paint has already become touch dry. Now you know the reasons for paint drying, you’ll know what to do, won’t you? But just in case, this is what you can do:
1. Increase the temperature – in the winter I sometimes use a hair dryer mounted on a tripod to blow hot air into cold corners for instance. Or just turn on or turn up the heating temporarily in the rooms you’re decorating. Just be careful with the hair dryer. Mine switches off if it overheats. I’ve sometimes used a heat gun – but NEVER leave that running and unattended – not unless you’re trying to burn the house down (in which case I hope you enjoy prison food.) If you’re painting outside, then paint in the sun will dry quicker than paint in the shade.
2. Reduce the humidity – sometimes I have to use a dehumidifier in damp rooms, or houses which haven’t been lived in and heated properly for a few weeks (usually rental properties). You can also reduce localised humidity above painted surfaces using fans. But with fans and hair dryers, remember that they blow air around (Doh! That’s the point!), so make sure the rooms are as dust free as possible – unless you’re after a dust-textured finish! In the UK, few people have air conditioners in their homes, but they’ll do much the same job as a dehumidifier in this case. You can also open the window in dry weather! (One tends to forget this fact in Britain.)
3.Change the paint. As I’ve said, water-based paints will generally dry much quicker than oil-based ones. And there are some very good water-based paints (especially from Germany & Scandinavia) for exterior woodwork now. For some oil-based paints, professionals sometimes use metallic terebine dryers. These are particularly useful when using oil-based paints outdoors in cooler weather. I don’t use them as I don’t do exterior painting in the winter!
Don’t be thick
This may be obvious, but make sure you don’t put too much paint on! Slapping it on too thick will slow drying to the extent that you’re likely to get runs and drips, as well as possibly stopping the paint drying for… a… very… long… time.
Having said all of that. When is your paint actually totally ‘dry’? It may be dry to the touch, but always wait the recommended amount of time on the tin before recoating (professionals or experienced amateurs may know when they can break this ‘rule’). Having said that, it can take a week or more in normal conditions for a water-based paint to CURE, and much longer for many oil-based paints. Curing is not only when the solvents have evaporated, but when the chemical bonds between the molecules in the paint have fixed to their final positions and the paint film is at full strength. Although a ‘dry’ paint can be touched, it will still be pliable and easy to damage until it has totally ‘cured’.
If I was being completely honest, maybe I should have titled this blog ‘The Science of Watching Paint Dry’, but that doesn’t have the same ring to it. And besides, knowing the science just helps you to practice the art! And knowing when to use the techniques I’ve written about is an art – you can’t just apply them willy nilly!
And by the way, there are over 50,000 anagrams of ‘watching paint dry’.
Yes, I know, that’s about as interesting as watching paint dr….