If you’ve just applied a smooth, thick layer of paint over a wall, you may be happy with the results. You’ve done such a good job, however, that you don’t want any damage or harm to come to the paint.
After all your work, you wouldn’t want the wall and its paint to end up peeling or chipped! So, how can you protect your paint? How can you make it last longer?
Well, polyurethane is the answer to your problems! Polyurethane is an extremely useful material that can add longevity and protection to your paint, as well as giving it a unique appearance.
However, you must be careful putting polyurethane over your paint – you must know exactly how and when it is safe to do it.
We’ve got the answers for you! In the guide below, you’ll find out all about polyurethane and its effects on different paints, as well as comprehensive breakdowns of how to apply it safely. Read on!
What Is Polyurethane?
Firstly, let’s start with the basics, and have a look at just what polyurethane is.
Polyurethane is a plastic material in liquid form. That may sound off, because you may think of plastics as solids, but this is a liquid form – which is how you can apply it over your paint. The material is a polymer that is derived from petroleum products.
What’s a polymer? Well, it’s a substance that’s made up of very large molecules.
Polyurethane can be made from a variety of different materials, such as ethylene, propylene, and butyl methacrylate. Ethylene is the most commonly used of all materials, but it can only be used sometimes because of its heavy molecular weight.
The ultimate purpose of a polyurethane coating on your paint is to make the paint last longer. It acts as a barrier, stopping outer conditions from getting to your paint and causing it to fall apart or fade.
Whether it’s fungus and molds, or rain and mud, the polyurethane should stop the paint from getting too affected by them. On top of that, it stops scratches happening to the paint, and won’t absorb water or let heat damage occur.
Not all heat damage, though, because extreme temperatures will break through – as with nasty chemicals.
You can get polyurethanes in either of these two forms:
This takes a longer time to dry when applied over paint. Once it is hard, though, it gives off an odor and an amber color. It’s more durable than water-based polyurethane, putting up with worse conditions and weather.
This polyurethane type dries and hardens quickly, much quicker than the oil-based. Also, it doesn’t have an amber shade to it. However, it isn’t as good at putting up with extreme conditions.
Can You Put Polyurethane Over Paint?
As you can probably tell by now, the answer is yes! However, there are a few things you’ll need to look out for a few things, especially the fact that using an oil-based one could cause amber discoloration. You’ll also need to keep in mind the following:
Waiting For Your Paint To Dry Before Applying Polyurethane
You must wait for your paint to dry before applying whichever form of polyurethane you’ve chosen to use. You can’t apply it on wet paint! You must leave at least 24 hours for the paint to dry, but ideally longer.
If you wait 72 hours, any type of paint should have dried by then, with both the top and bottom layers being fully dry.
Waiting For Your Paint To Cure
On top of drying, you need your paint to cure too. This is the term for when your paint becomes fully hard, which is a step beyond just drying from its liquid form. Sadly, paint shouldn’t properly cure until a few days after it’s dried.
So, if you waited 3 days for drying, you may have to wait for another couple on top of that.
Curing isn’t just a case of leaving it, either. The conditions need to be right! Make sure that you don’t leave any windows open, leaving the paint subjected to rain, wind, or cold.
It’s also a good idea to abrade the paint once it’s cured, as well as cleaning it.
This will remove any impurities in the paint, making it look a lot better and smoother. If you don’t do this, then the visible impurities will be trapped under the polyurethane, and then it’ll be even harder to get rid of them!
How Can You Tell When It’s Dried And Cured?
To check if your paint is dry, touch a section of it. If it’s sticky still, then it hasn’t dried yet.
On the other hand, to check if your paint has cured yet, touch a bit of it with your fingernail. If your fingernail leaves a little mark, then you must continue waiting – because it hasn’t cured yet. If there isn’t an indentation, though, then it should be done!
You must wait for your paint to dry AND cure before you even attempt applying polyurethane on top of it. If you don’t, it could ruin the paint – as well the wood itself.
If you want to know what might affect the drying and curing time of your paint, have a look near the bottom of our guide – we’ve got a whole breakdown of the things that might make it take longer!
Which Paints Can You Apply Polyurethane Over?
You may be wondering which types of paint you can successfully apply polyurethane over, including high gloss paints. These types are the toughest paints available, and have a reflective sheen to them.
Well, the answer is yes – as long as the high gloss paint is dried and cured beforehand.
Which other types of paint can you apply polyurethane over?
Loads! You can also use: semi gloss paint, latex paint, acrylic paint, chalk paint, water-based paint, and oil-based paint. Just to make sure that you let them all dry and cure before you even try to apply polyurethane over them.
Drying Times For Different Types Of Polyurethane
You can use either oil-based polyurethane or water-based polyurethane to apply over paint, the choice is completely up to you. Both work and both have their own benefits. However, they do take different lengths of time to dry properly.
If you choose to use water-based polyurethane, then your first coat can dry in about 2 hours, allowing you to go over it again with another coat. After about 24 hours, the polyurethane should be ready for simple uses.
After 3 days, it should be cured too.
With that being said, though, weather and temperature can also affect how quickly it will dry and cure. For that reason, you may want to leave it even longer – some suggest 21 days is a good amount to wait for a full cure. It’ll be worth the wait, because it ends up looking really crisp and clear.
On the other hand, you might choose to use an oil-based polyurethane. These notoriously take longer, and can be dry anywhere from 6 to 24 hours after applying it.
A regular one will take at least 12 hours, so it’s really only the ones that are branded as “fast-drying” that could be done in as little as 6 hours. After about a week, the painted wood should be ready for simple uses.
However, like with the water-based, you’ll want to wait 21 more days for it to become fully cured.
Make sure to remember that oil-based polyurethanes will give your painted surface an amber looking tint. If you don’t want this, and want the polyurethane to dry looking clear, then you’ll want to go for water-based polyurethane.
How To Apply Polyurethane Over Paint – A Step By Step Guide
Now you know all about polyurethane and how it works, it’s time to look at the application process.
Remember to take everything we’ve said so far on board – including making sure that your paint is fully dried and cured, as well as being free of impurities.
You’ll need a handful of materials and tools to properly apply polyurethane over your painted surface. They are:
- Oil-based polyurethane or water-based polyurethane
- Applicator – spray, paint brush, roller, or pad
- Detergent or trisodium phosphate
- Lint-free cloth & tack cloth
- 120-grit sandpaper for the deeper scratches
- 220-grit sandpaper
- Vacuum cleaner
And you’ll need to be wearing proper apparatus to keep your skin and eyes safe! You must wear:
- Safety goggles
- Rubber gloves
Once you’ve got all that, and you’re wearing the proper equipment, it’s time to start.
Step 1: Cleaning The Surface
Just like polyurethane cannot be applied to wet paint, you also need to make sure that your painted surface is not greasy or sticky. It’s not going to stick to any surfaces that are. Therefore, you must clean the painted surface.
How should you do this? Well, use trisodium phosphate if your painted surface was done a while ago. On the other hand, if your painted surface was only completed, dried, and cured recently then you can just use some detergent to clean away any grease or stickiness.
Since you’re dealing with cleaning materials, you’ll need to protect yourself from the harmful stuff that’s within them: make sure to wear rubber gloves and goggles.
Step 2: Sanding The Surface
Now take your 120-grit sandpaper and rub it repeatedly across the surface of the painted wood. This should get rid of any deep scratches that are on the surface, smoothing it out. If it isn’t working, try using a palm sander instead, for extra thoroughness.
Step 3: Tacking And Dusting The Wood
You’ll now have residue from the sandpaper all over your painted wood. Take a tack cloth, or a vacuum cleaner, and clean away the residue. A vacuum will especially get rid of all the dust, which you absolutely must get rid of!
A lint-free cloth dampened in water will also be an effective remover. However, you’ll need to let the wood dry after using that.
Step 4: Applying Your First Coat Of Polyurethane
Whether you’ve picked a water-based polyurethane or an oil-based polyurethane, it’s now time to apply the first coat of it. Whichever tool you use is up to you, be it a brush or a roller, a spray or a pad.
Simply dip your tool in the polyurethane and apply! As you’re doing it, make sure to follow the grain of the wood.
When you’ve done the first coat, leave it to dry.
Step 5: Sanding After The First Coat
When you’ve let the first coat dry, you’ll want to sandpaper it again. Use 220-grit sandpaper, getting rid of any marks or dust that have now got onto it from you applying the polyurethane. There may even be scratches! Make sure to sandpaper them down.
Step 6: Cleaning The Painted Surface Again
Your sandpaper work will have left dust and residue again, just like it did before. Use a tack cloth or a vacuum cleaner again, or a damp lint-free cloth.
Step 7: Applying Your Second Coat Of Polyurethane
For added polyurethane protection, you’ll want to be applying at least two coats of the stuff. Using the tools you did before, apply another thin coat of polyurethane, going against the grain again.
Once more, wait for it to dry.
You’ll then have to repeat the previous two steps again, because it’ll need sandpapering again after the second coat! And, of course, after the sandpaper comes more residue – so you must get rid of that, and the dust, too.
If you choose to apply any more coats of your chosen polyurethane, make sure to do all those cleaning steps with each one. Try not to apply too many coats though!
Using Acrylic Paints
Your wooden surface may be painted with acrylic paints, in which case you’ll need to know some differences regarding the use of polyurethane over this type of paint.
What Is Acrylic Paint?
Firstly, let’s have a look at what makes acrylic paint different from other types of paint. The key thing that makes acrylic paint stand out from other paints is that it’s very quick to dry, which others aren’t.
This terrific physical property makes acrylic a great choice for painting surfaces, on top of the fact that it also looks really good when wet – vibrant and smooth. Although, it will dry in quite a dull manner, which you’ll talk about later.
With that being said, you must be selective. If you’re going to use acrylic paint on your own surfaces, you must make sure that you use high-quality oil-based latex paint, as well as latex primer.
If you don’t use both of these, the paint will end up coming off in flakes. On top of this, acrylic paints dry very softly, which means that they collect a lot of dust.
For this reason, you’ll definitely want to apply some polyurethane on top of it, because it will help keep the dirt and the dust away from the surface!
Why Should You Apply Polyurethane Over Acrylic Paints?
As we’ve just mentioned, applying polyurethane on top of some acrylic paint will help to keep dust and dirt away from it – which it would usually collect loads of. On top of that, there are many other reasons to apply a polyurethane.
For one, they brighten acrylic paints up. While the paint may look vibrant when it’s wet, they take on a dark and dull appearance when they get dry. This isn’t ideal, since you can’t have wet paint over your surfaces forever!
Thankfully, adding some coats of polyurethane on top of your acrylic paint will help recapture some of its beauty and color.
Additionally, the polyurethane will also make the dried acrylic paint look much shinier. This is a positive, because it means that your surfaces will really pop, attracting the attention of any guests.
A few coatings of polyurethane will also change the texture of your dried acrylic paint. It makes the surface a lot smoother! Not entirely smooth, it has to be said, but a lot smoother than the acrylic would be naturally.
When Can You Apply Polyurethane Over Acrylic Paint?
As we’ve spoken about before, you can’t just apply polyurethane over your painted surfaces at any point. It won’t stick to wet paint, and on top of that there’s a few other things you’ll need to make sure you do first.
On the whole, you are going to need to wait anywhere between 24 and 72 hours for the acrylic to properly dry. Only then will you be able to apply whichever type of polyurethane you choose.
We understand that it can be frustrating having to wait, but it’s always worth it. Additionally, you can spend the waiting time making other repairs to it. The longer you wait, the better it will dry, so wait even longer than 72 hours if you have the chance to.
If you don’t allow it to dry fully before you apply the coats of polyurethane, it can create problems. The acrylic and the polyurethane will mix to make a rough, un-smooth finish that won’t endure as well.
It’s worth noting that the type of surface that you’re painting can affect the drying time of the acrylic paint too. Some surfaces will allow it to dry quicker than others will.
How To Apply Polyurethane Over Acrylic Paint – A Step By Step Guide
Now we’ve looked at all that, it’s time to apply polyurethane over your acrylic paint. Polyurethane will be a great way to protect your paint, as well as make it look a lot better, rather than dull and dark.
With that being said, however, you may not want to use an oil-based polyurethane. Remember, they will color your surface an amber shade. Water-based polyurethanes, on the other hand, won’t do that and will instead dry clean and see-through. They’ll also dry a lot quicker!
As for the tools that you will need, it’s largely the same as the previous step by step guide. Remember to wear safety clothing, like goggles and rubber gloves!
Step 1: Washing The Painted Surface
Firstly, you must get rid of any dirt that’s on your acrylic painted surface. You should do this gently, with warm water. Under no circumstances use soap! You may assume that it’s a thorough and great way to clean, but the soap could actually ruin the gloss that the polyurethane is supposed to bring.
On top of that, don’t use a latex remover either, because it could also ruin the texture of your painted surface.
Don’t just stop with removing dirt, either. If there’s any wax on the surface, use some mineral spirits to get rid of it. On top of that, if there are any drips of paint, you can use paint stripper (or even sandpaper) to carefully remove them.
Remember, you want the surface to be spotless before you apply the polyurethane.
Step 2: Scuffing The Surface
Grab your 120-grit sandpaper and sand down the surface. Don’t be too rough, but be thorough enough that you get rid of any bumps and scratches, creating a smooth surface.
If it’s a painted floor that you’re going to be applying to polyurethane, you can use a floor buffer to get out the scratches.
Once you’ve done your sandpapering, get rid of the residue and the dust that’s come from it by using a tack cloth or a damp lint-free cloth.
Step 3: Applying The First Coat Of Polyurethane
First, pick your type of polyurethane. Remember that oil-based polyurethanes will leave your surface looking more amber colored than it was before, so it may be wise using a water-based polyurethane.
Whichever you choose, you won’t need to thin it out, because it’s already the right amount of thinness. If you think it isn’t, pour out a small bit on some old material, and see for yourself!
You’re going to be using a brush or a spray gun to apply the polyurethane. Unlike with other paints, you cannot use a roller to do this, because it might leave bubbles that then solidify into the final product.
So, use your tool to apply a thin first coat on your wooden surface. Then wait for it to dry.
After it’s dried, wipe it lightly with some 120-grit sandpaper. This will get rid of any dust or bubbles, making the surface smooth and empty again.
Step 4: Applying The Second Polyurethane Coat
Once that’s all dried and cleaned up, you can apply a second coat of your chosen polyurethane. Follow the same instructions as the previous step, making sure to use sandpaper only when the coat has dried.
However, make sure not to apply more than 2 coats of polyurethane, because it can get too dense and thick.
Sealing Acrylic Paint By Using Minwax Polycrylic Finish
Minwax polycrylic is a material that’s used to protect wood, stopping it from getting damaged from threats such as water. On top of that, it makes the wood look a lot nicer too! In these senses, it’s very similar in its effects and uses to polyurethane, only it’s especially for acrylics.
Applying it takes just as much preparation and thought as applying polyurethane does, too. When you’ve painted your wooden surface with acrylic paint, you must make sure that it’s free of bumps and scratches, before allowing it to completely dry.
You can’t use Minwax Polycrylic on wet acrylic.
So, follow the following steps!
Pour your polyurethane into the corner area of the surface that you’re painting. With your foam brush, work the polyurethane outwards, spreading it wide. Be very gentle, though, because you don’t want to break the surface tension. Do it until the entire acrylic paint is covered.
Wait for a few hours, allowing the polyurethane to dry.
Wash your brush thoroughly and apply your second coat in the same way.
Wait a few more hours, clean your brush, and apply a third coat.
Will Polyurethane Stick To All Surfaces?
You may be wondering if you can apply polyurethane to any surface you want, or whether it won’t hold onto some. Well, you’re in luck! Polyurethane will indeed stick to most surfaces.
However, it will obviously only stick to surfaces that have been properly prepared – through every method that we’ve spoken about so far in this guide. That means letting the paint dry and cure, removing grease and wax, as well as getting rid of dust, dirt, and scratches.
What Will Affect The Drying And Curing Time Of The Paint?
There are a few factors that will affect the amount of time it takes for your paint to dry or cure.
Type Of Paint
The drying and curing time can change depending on the type of paint that you’ve used. Some will dry quicker than other types. Interestingly, a general rule is that lighter shades of paint will dry quicker than darker ones.
Milk paints will dry in just 30 minutes, but will take 30 days to properly cure. Similarly, if you use a chalk paint, then it will also take half an hour to dry – and 30 days for the curing to be done.
If you use an oil-based paint, then it could take anywhere from 6-8 hours to dry. As for curing, it’ll be another 30 days. Water-based, or latex, paints are quite different, though. They will dry in 4 hours, but will take 21 days to fully cure.
If you use a finish, things can be slightly different. Using a velvet finish will take about 8 hours to dry.
Type Of Wood
The type of wood that you’re painting will also affect how long it takes for the paint to dry. Unfortunately, a handful of wood types have large amounts of chemicals within them.
These stop paint from properly gripping and evaporating to the wood. One of these types of wood is Rosewood, which we would recommend you avoid painting – just for your ease!
The time it takes for paint to dry also depends on the temperature that it’s in. Wood finishes and paints will evaporate more quickly if they’re in heat, so the best temperature for a paint to dry on wood is anywhere between 70 and 77 degrees Fahrenheit.
If things drop below 50 degrees Fahrenheit, then the paint may begin to be not just dry, but be negatively affected. If this is happening, you can make the environment hotter by using a HVAC or a heat fan, or turning your own indoor heating up.
Humidity can also affect the drying time. If your environment is too humid, then it can cause extra moisture, and this can soak into your wood.
Annoyingly, this moisture would create bubbles, ruining the smoothness of your wooden surface, as well as possibly leading to the paint to begin peeling off. On top of that, this extra moisture will stop the paint from being able to evaporate as quickly.
To make sure that your humidity is the right amount, not too high and not too low, you can use a hygrometer to measure it. Looking at its readings, anywhere between 50% and 70% will be perfect for your paint.
How can you change the humidity? Well, if it’s too low then you can use a humidifier. On the other hand, if it’s too high then you can use a dehumidifier.
Having plenty of air will help your paint to dry faster, too. Having too little ventilation in your environment will cause the paint to dry much more slowly, so go and plug in a fan to add some wind to the wood.
Cleaning Up After You’ve Applied The Polyurethane
Once you’ve done the hard part of applying all your different coats of polyurethane, you’ll need to clean up after yourself. Thankfully, there shouldn’t be too much mess.
If there’s any excess polyurethane or other messes on the floor, then you can just clean it away with some soap and warm water. Make sure to not get it anywhere near your painted surface though! On top of that, you’ll want to clean your brushes in the same way.
You may find that the water and soap doesn’t get rid of it all, and this may be because you used an oil-based polyurethane rather than a water-based one. Not to worry! Just use some mineral spirit to clean your brushes and mess away.
And there you have it! You now know all the benefits of using polyurethane on top of your painted wood. When you follow our various steps, make sure to be careful and wear protective clothing!