Polyurethane is a fantastic water-resistant wood finish.
Just a few coats of any oil-based or water-based sealant can work wonders. And it not only protects wood from water damage, it also safeguards it from scratches and scrapes as well.
So, if you want a truly durable Polycrylic finish, should you top coat it with polyurethane?
Well, in this post, you’ll learn the difference between a dry Polycrylic finish and a cured one — and why it matters when it comes to applying polyurethane over it.
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Is Polycrylic The Same Thing As Polyurethane?
Well, Polycrylic is a water-based acrylic urethane blended product made by Minwax. It is an interior wood sealer that’s incredibly easy to apply, leaving behind a clear finish.
What’s more, just like a water-based polyurethane, it is water-resistant, scratch proof, and even food safe.
And Which Is More Durable? Oil-Based Polyurethane Or Water-Based Polyurethane?
Generally, oil-based polyurethanes are more durable. They penetrate deeper into wood than water-based polys, and they’re a touch more heat resistant.
In fact, oil-based polyurethanes can handle temperatures as high as 200°F (93°C).
But the difference between oil-based and water-based polys isn’t that wide. What’s more likely to effect polyurethane durability are the additional chemicals and ingredients added to a specific brand.
For example, some polyurethanes have added antibacterial agents and/or UV-resistant additives to make them more weatherproof.
What About Polycrylic? Is Polycrylic Waterproof And Weatherproof Too?
It is certainly water-resistant, more so than many natural oil finishes such as Linseed oil or Tung oil.
However, it is not wholly waterproof. And if enough water gets on it, it’ll soak past the Polycrylic film, damaging the wood underneath.
That’s why Polycrylic should only be used on interior wooden surfaces. If you used it on exterior wood, then rain, humidity, and even morning dew, will sink past this finish.
OK. So Can You Put Polyurethane Over A Water Based Polyurethane?
First off, you don’t need to added a separate poly top coat over a urethane-based sealant.
In fact, you’re much better off simply applying another coat of the self-same finish. Especially as Polycrylic is designed to be a top coat.
Having said that — if you’ve allowed the Polycrylic coat to dry AND cure — you can apply a separate polyurethane over it.
But, take note…drying and curing are not the same thing.
Drying often takes 2-3 hours for Polycrylic to complete. Drying means that, through evaporation, this water-based finish will turn from a liquid into a soft film.
On the other hand, curing often takes longer, (much longer in cooler and/or more humid climates). And curing is a 24-72 hours long chemical process that changes Polycrylic into its final durable form.
Now, you only need to wait for Polycrylic to dry before you add a 2nd (or 3rd) coat of the same finish. However, if you want to coat a completely different polyurethane finish over it, you must wait for Polycrylic to completely cure.
And Why Must I Wait For It To Cure First?
Waiting for curing to complete is important. Especially if you plan on coating an oil-based polyurethane over a water-based finish.
And this is because of adhesion.
Polyurethane won’t stick and stay atop a ‘contaminated’ wooden surface. So, if there are any oils or chemicals on a surface, polyurethane will end up peeling right off of it.
Worse still, if polyurethane is still drying/curing, it will release VOCs (Volatile Organic Compounds).
Those VOC’s are the fumes you can smell as it dries. And VOC’s can cause tiny air bubbles to appear in that top coating polyurethane.
But, once polyurethane has cured, it is no longer leeching oils/chemicals or releasing fumes.
And How Do You Finish The Final Top Coat Of Polycrylic?
Always apply that final top coat using a quality bristle brush. A foam brush will leave lots of tiny air bubbles on the surface.
But, as long as you apply Polycrylic with the grain, you needn’t worry about brush streaks standing out markedly.
To Wrap Up, Here Are The 3 Key Takeaways From This Post…
- 1). Polycrylic is a water-based acrylic + urethane blended finish that is ideal for interior wood, such as furniture and cabinets.
- 2). Polycrylic is water-resistant, but not wholly waterproof. So, it is not suitable for exterior wooden surfaces.
- 3). You can apply a separate polyurethane finish over Polycrylic if you so choose. But, always wait for the Polycrylic finish to dry and cure first, before you apply anything else over it.