The wood furniture projects we build are bound and determined to be worn down over time. This means a durable top coat is a critical part of building quality projects. So you need to know how to apply polyurethane, and that’s what I want to help you with today.
I’ve built everything from toys, to outdoor patio tables, TV consoles, to my 6-seater dining room table. I’ve used several types of finishes and nothing protects quite like good ol’ polyurethane.
I’ve applied poly using several different techniques, and over the years I’ve fine-tuned my own technique, and it works fantastically! Plus, as I’m so limited on time in the wood shop, I ALWAYS focus on making things simpler and faster. I hope that sounds good to you, because that’s what you’re getting into here today.
So below I’ll explain my simple, fast, fantastic technique for applying polyurethane to your wood projects. With my 4 basic steps, you’ll get a long-lasting, beautiful finish, ready to impress.
Material List for Applying Polyurethane
- Oil Based Polyurethane in a can
- Sandpaper, up to 400 grit
- A couple lint-free rags
- Tack cloth or mineral spirits (for dust clean-up)
I use disposable cheap foam brushes. You know why? Because there’s no cleanup!
Seriously, how much do you enjoy getting done with a coat of oil-based-anything while using a $30 brush, then getting to spend the next 15 minutes cleaning that brush and making a mess?
I’m guessing you don’t enjoy that any more than I do. That’s why for the most part I try to avoid using nice brushes (if at all possible). If I’m putting on something oil-based, I’d rather just trash the paraphernalia.
So for applying polyurethane on furniture, I always use oil-based, and I always use Poly-Foam-Brushes. These are cheap foam brushes that lay on an even coat just right, and after each coat you can just throw it away.
Granted, investing in a decent brush and cleaning it after every use may save you money over the long term. But as for me, time is limited, so I prefer to save time.
When using a foam brush, you don’t really need gloves as you would when applying a wipe-on poly. But if you’re overly concerned about getting any poly finish on your skin, then use gloves (the blue nitrile kind). Otherwise, skip ‘em.
Why the blue nitrile gloves? Because the old fashioned standard latex gloves will get eaten up by chemicals and basically disintegrate right off your hand. Basically, the latex will start to shrivel and break apart, forming holes.
How To Apply Polyurethane To Your Wood Projects
Step 1 – Prep your project
You should sand the surface of your wood project up to a 180 or 220 grit sandpaper. The poly itself will create a new surface, as it is a film-building finish. So there’s no need to go beyond 220 on the bare wood itself. Doing so would just be a waste of time.
Quick outline of my sanding process:
For a tabletop surface I need to flatten I’ll use the belt sander. After that (or for non-table top surfaces), to get rid of all the machine and sanding marks I’ll use 80 grit on a random orbital sander. Because this creates so much sanding dust that the shop vac can’t catch, I don’t normally use it for the remaining sanding.
I switch to my regular electric quarter-sheet finishing sander, and I’ll use that for 120 grit, 180 grit, and 220 grit sandpapers. On edges and thin material, or just a quick sanding on a fairly small surface, I’ll just use 220 grit sandpaper with my velcro sanding block.
Once the sanding is complete, you need to remove all the sanding dust from the wood. This can be done with compressed air or a shop vac. Do a final wipe-down with some tack cloth or a rag made damp with mineral spirits. (I don’t always do this, but it is the best way to remove the final dust)
Note – If you’re going to stain your project first, do that now. After the stain has dried, you won’t want to continue sanding, you’ll instead move right into applying the polyurethane finish. If you need help learning how to stain wood, there’s a link for you at the end of this article.
Step 2 – Prep your work area
During any project, you will probably create a lot of sawdust in your shop, which settles on everything. This is not the type of environment you want to apply polyurethane in. Dust and poly don’t mix – well, they shouldn’t anyway. You can mix them if you want, but that’s probably a bad idea.
So as I mentioned above, you can use compressed air to clean off your project. You should do the same for your work area. Anything you may get against or work from while applying your finish should be dust free. That way you avoid stirring up dust while the poly is drying.
But cleaning up dust usually results in some of it (or all of it if you’re using compressed air) ending up airborne. This means it will settle again and you’ll need to do a final wipe down.
That’s why I like to prep my work area and my project at LEAST a few hours, or even a full day, before I intend on applying the polyurethane finish.
This gives the dust time to settle, allowing the air to clear out, and then I can do a final quick wipe down before starting.
In addition to the cleanup process, you need to consider your shop lighting. Because polyurethane is clear, you can only see where you’ve applied it by looking for the glare in the wet polyurethane, against the previous dried coat.
So it can be worthwhile to set up some additional lighting if your work area is poorly lit. I like having light in the backdrop of my work area, so I can easily find the glare as I look for the wet line.
And don’t forget about ventilation. The fumes from the oil-based polyurethane are toxic and you need fresh air. I personally don’t use a fan to force fresh air through, I just crack the doors and let it naturally ventilate.
If you do prefer to use a fan, clean the dust off, and also make sure it’s not blowing towards anything that has dust on it. This will stir up dust in the air and it will no doubt end up on your wet finish.
Step 3 – Apply the Polyurethane
So now you’re ready to apply the finish, and if you’re like I was, you’ll get the urge to brush it on just like you would have a coat of paint. This is what I did when I first started, and why I quickly moved over to wipe on poly as it was much easier.
What I learned was that brushing on poly is not at all like and oil based paint. At least not the way I was taught to apply it.
So here’s what you do:
First take your poly foam brush, and dip it at least half-way into the poly. Hold it there for a few seconds so it really soaks in and fills up the brush.
Let some excess drip off back into the can, turning it both ways until that is mostly done, and then bring it to the wood surface.
Then touch the brush at one corner of the surface, apply a little bit of pressure, and slowly brush one entire row without stopping or lifting. You quickly get a feel for how fast the poly is laid down, so don’t worry about your speed before you start. If you go too fast, it simply will not lay down evenly, and you can restart the row, just go slower.
Because you filled the entire foam brush up, it has a lot of polyurethane to lay down and this can last for 2 or 3 rows (or more) on a small or medium sized surface. You can see in the brush how full it still is, so as it gets close to emptying, you want to go refill it just like before.
The next row you want to overlap by a quarter inch, or really just enough to make sure you don’t accidentally leave a gap.
The foam brush has a nice straight edge tip, so when you get to the edge of the material, you’ll stop the brush right at the edge and lift off.
Because this is an oil-based finish, it’s slow to dry and tends to blend well into the preceding rows. This means when you’re done, if you did it correctly, you will not see any streaks or row-lines.
It’s best to make your touch down and lift off points at obvious seems or joints, or at the corner of the surface. For example, if you lift off in the middle of a flat board, it may be hard to blend that point into the next row or the same row if finished even immediately after.
What to avoid – If doing a larger surface, do not start in the middle row and go to one edge, with the intent of walking to the other side and doing the same thing. What this does is it creates a row that will get overlapped by another row possibly 10 or 15 minutes later. This is too long and can result in these two rows not blending well, and some pretty nasty streaking.
Here’s me in action using this exact process:
Step 4 – Sanding And Additional Coats
The first coat will really soak into the wood, so after it dries do not worry about sanding. The finish at that point will probably feel a bit rough. Let it dry at least 12 hours and check that it’s basically dry to the touch. If so, the second coat can be applied.
After the second coat, you’ll want to start giving it about 24 hours to dry (for each coat). So a full day after your second coat, make sure it’s dry to the touch before continuing.
Get some 400 grit sandpaper and sand the surface using a sanding block. It’s very important NOT to use the sandpaper in your hand. Your fingers are not flat, and the point here is to leave a smooth and FLAT finish.
Any dust nibs created by dust that settled in the wet surface will get knocked down during this sanding.
The finish will look horrible immediately after you sand, but that’s ok. You’ve essentially ‘scuffed’ up the surface to prep it for the next coat.
You do NOT need to sand very much or very hard. Just lightly sand and it should quickly feel smooth to the touch, especially after coat #3 and beyond.
Wipe off the poly dust from the surface with a dry, lint free rag. Then go ahead and repeat the process, laying on another coat.
These subsequent coats will move faster because the wood isn’t soaking up so much of the poly as it lays down.
Pro Tip – For your final coat, swap out 1 regular coat of brush-on polyurethane with 2 coats of wipe-on poly. You do this because the wipe on poly is thinned down. This means it dries much faster than regular poly. And the faster the finish dries, the less chance it has at picking up any additional dust particles.
I’ll link to my article on applying wipe-on poly below.
How Many Coats Of Polyurethane Are Needed?
Regular oil based polyurethane goes on much thicker than finishes like wipe-on poly, or lacquer. So these thick coats requires more dry time, but fewer coats overall.
I recommend applying 3 to 5 coats of polyurethane. Definitely 5 if it’s a surface that needs additional protection, like a table top.
After the final coat, do this:
- Wait 2 days to let it fully dry
- Inspect it in good lighting at different angles, and feel it with your hand. Do this to make sure it’s smooth and there were no detrimental dust nibs in that last coat.
- Give it 7 days before bringing it into the house.
- Wait until the 30 day mark (after that last coat) before stressing the finish with wear, heat, chemicals, etc…
At that point, the finish is fully cured and the protection is at 100%.
Why Put Polyurethane On The Bottom Of The Project?
This really applies to more than just the bottom. Basically, any part of the project that is not going to be seen, tends to get ignored in the finish process.
But when you’re applying a finish that seals the wood, you should apply that finish on all surfaces.
We do this because unsealed wood will soak up moisture from the environment’s humidity at a higher rate than sealed wood.
This variance can cause unneeded stress in the joinery, or even warping of a panel or large section of your project.
I personally have never seen it happen, but it does make sense. So I usually put 2 coats on the ‘unseen’ parts of my projects. That’s enough to really seal up the wood and reduce it’s moisture absorption rate.
When To Use Polyurethane On Wood
Whether it be brush-on or wipe-on, I really love a good polyurethane finish. It creates an incredibly durable top coat that can withstand years of heat, cold, cleaning chemicals, and abuse.
I tend to use brush-on polyurethane for table tops, and surfaces I want to build up a thicker finish. If you use wipe-on-poly instead, even after seven or eight coats it still doesn’t build up quite the same durable finish as three or four coats of regular poly.
If you’re not set up to spray, then you can’t get the full benefits of a Lacquer finish, so polyurethane is a great alternative, and it takes less setup and less equipment to apply.
The main benefit of a good polyurethane finish on wood is it’s superior protective qualities. It rates higher than other finishes for heat resistance, cold resistance, wear and tear, and chemical resistance.
It’s not quite the same as a spar varnish, which should be used when doing outdoor projects. Varnish is a bit more flexible (important with the changing humidity levels outside), and it has superior water resistant properties.
But for the best all-around finish for indoor furniture and shop projects, nothing beats a good polyurethane.
I’ve written a more detailed article comparing the major finishes, and when you would want to use each. I’ll link to that at the end of the article.
Gloss? Satin? What’s the Difference?
The difference is kind of like a foggy mirror vs a clean mirror.
A clear gloss polyurethane creates a very reflective, shiny finish. But depending on the type of wood you’re using, this can either look like a glass surface, a plastic coating, or wet wood.
I think gloss looks best on decorative projects, shelving, and anything that hangs on the wall with flat surfaces.
Usually I prefer a satin-finish, as it creates a nice sheen that reflects light, but not in the way a wet surface or a piece of glass would. It’s like the foggy mirror above, and it makes the finish seem deeper, and softer.
When applying a gloss finish, there’s really nothing you have to do to the polyurethane itself. But with a satin poly, you want to stir it really well before using it every time.
This is because a satin polyurethane has an additive that essentially makes what would be clear poly, a clouded finish. If this is settled on the bottom and not mixed well before use, you’ll basically be applying a high gloss finish.
What’s This Talk About A Dingy Satin Finish?
It’s discussed on many woodworking forums and videos, that applying too many coats of satin polyurethane can make the finish become dingy or mirky. So it’s perfectly OK to apply a few base coats of clear gloss, even if you want your final finish to be satin.
Whether or not this is true, I can’t be certain. While it’s commonly taught that you should start with clear gloss to avoid this issue, there has actually been scientific articles written on how the Satin poly works.
In these articles, the claim is that every coat eliminates the ‘Satin’ surface of the previous, meaning the cloudiness in fact does NOT build up and become mirky.
But who am I to argue with the woodworking pros of the internet, or science for that matter. I will keep my non-scientific opinions to myself, but I will share my methods with the world! (or at least with those of you who find my blog)
Either way you want to do it, you can still use my method above. If you want to start with gloss and end with satin, just make your final 2 coats satin. Everything up until that point can be the clear gloss.
How Long Is The Polyurethane Dry Time
In a nutshell, the “Dry Time” of polyurethane is about 24 hours. That’s when a coat basically becomes dry to the touch.
However, that’s different than its “Cure Time”, which is much longer. It could be anywhere from a week, to a full 30 days. It all depends on the environmental conditions (temp and humidity basically).
A good rule of thumb is to assume a curing finish is uncured until the 30 day mark, then it’s ready for full use or delivery.
With oil based polyurethane, I will typically bring my furniture project into the house after 7 days. I will not stress the finish (with things like heat or cleaning chemicals) until the 30 day mark from the final coat.
So in a nutshell, plan on 1 day to dry between coats, and plan on 30 days to fully cure. To expedite the curing, keep the project in a low humidity, warm environment.
If you have a good sniffer, then use it to gauge your curing finish. When it is no longer putting off a toxic smell, it’s cured!
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