The furniture and the woodworking projects we build are bound and determined to be used and worn over time. This means a durable top coat is a critical part of building quality projects. So you’re wondering how to apply polyurethane, and that’s what I want to share with you today.
Why I Use Polyurethane
Whether it be brush on or wipe on, I really love a good polyurethane finish. It creates a very durable top coat that can withstand years of heat, cold, and abuse.
I tend to use brush-on polyurethane for table tops, and surfaces I want to build up a thicker finish. I’ll use wipe-on-poly most of the time, but even after seven or eight coats it still doesn’t build up quite the same durable finish of three or four coats of brush on poly.
I’m not really set up for a spray-on finish in my wood shop. While I would really enjoy the expedited process of using lacquer, I’m not so fond of dealing with the the flammability factor and the overspray. How long does it take polyurethane to cure? More on that in a minute.
But in the end, because of my preferences and limitations, that leaves me mostly with boiled linseed oil and polyurethane. Yes, an oil finish looks amazing and is so easy to apply I wish I could do it to all of my projects. But the problem is that it just does not create the hard surface and extreme protection that polyurethane creates.
How To Apply Polyurethane – Here’s What You Need Before Starting
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.
The exception may be if you were trying to pinch pennies, you might be able to clean the brush out with paint thinner to get some more use out of it.
When using a foam brush, I don’t use gloves as I just haven’t had the need for them, like when using the wipe on method. If you do want to avoid getting any drips of polyurethane on your skin, go ahead and use nitrile gloves. I advise against using regular old latex gloves because the poly will eat right through it.
As far as the poly goes, I always apply my first several coats with a clear gloss. Even though I prefer the satin finish, you should never begin with a satin polyurethane. After applying several coats of satin poly, the finish becomes cloudy and can’t even look dingy.
So apply several layers of clear gloss, then the final two coats can be satin, and that’s plenty to give it a beautiful satin sheen. This is exactly what I just did on this desk project, and I think it turned out great.
Prepping The Material And Work Area
I prefer getting my projects sanded to a 220 grit sandpaper. This is smooth enough to leave a nice, soft touch, but not such a fine grit that the sanding process takes much longer then I want to spend on this step.
Just a quick rundown – my sanding process to this point: 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 create so much sawdust that the shop vac can’t catch, I don’t use it for the following step.
I switch to my regular electric quarter-sheet finishing sander, and I’ll use that for 120 grit, 180 grit, and 220 Grit. 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.
How to apply polyurethane in a dusty environment
During any project, I’m creating a lot of sawdust in my 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 before I begin applying poly, I use compressed air to clean off the material I’m working on, and the work surfaces I’ll be using in this process. Most of this dust ends up on the floor, but some will settle right back where it started. So give it a few hours, or even a day, before moving on from here.
After that I just take some tack cloth and wipe down the material to pull off any remaining dust. At this point the wood is prepped for an oil-based polyurethane finish.
In addition to clean up and prepping the wood surface, 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 existing dry material surface. This only applies on the second coat and after, because the first coat changes the color of the wood so it’s easy to see where the poly has been applied.
Gloss? Satin? What’s The Difference?
A clear gloss polyurethane creates a very reflective, shiny, glossy finish. 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. This 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 cloudy finish. If this is settled on the bottom and not mixed well before use, it will be a high gloss finish after it dries.
How To Apply Polyurethane – The Procedure
So now you’re ready to apply the finish, and if you’re like me you get the urge to brush it on just like you would have 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 base paint. At least not the way I was taught to apply it.
First I’ll take my poly foam brush, and dip it at least three-quarters the way into the poly. I’ll hold it there for a few seconds so it really soaks in and fills up the brush.
I let some excess drip off back into the can, I turn it both ways until that is mostly done, and then I bring it to the wood surface. I continue rotating it from side to side to avoid any more dripping. This is because the poly will tend to run out of the foam brush at the lowest point, if the brush is not turned.
Then I 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 on a large 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 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 maybe too long and can result in these two rows not blending well.
Let’s Wrap This Up
In conclusion I’d like to summarize how to apply polyurethane the exact way I typically do on my wood projects.
- Sand the material up to 220 grit sandpaper
- Remove all dust and clean the work area
- Bust out the gloos and the satin polyurethane, and stir the satin one really well
- Fill my foam brush at least three quarters the way full of polyurethane
- Apply coat row by row, each row having a single touchdown and lift off point
- Final 2 coats are satin, before that I use the gloss.
How many coats, and how long does it take polyurethane to dry?
When brushing on polyurethane, the coats go on pretty thick. For this reason I would suggest doing 3 coats, and no more than five. This is just my own personal preference, as I’ve noticed when it gets too thick it starts to look like plastic.
Remember if you’re wanting a satin finish, everything up until the final two coats should be a clear gloss coat, so the finish doesn’t become murky looking.
On thick coats like this I wait a full day between each. When I believe I’ve applied enough, I inspect the project after 2 days to make sure the finished looks even and perfect. If it doesn’t ,I will apply another coat.
Minimum I wait is 7 days before I bring it in the house, but to fully cure you’ll want to give it 30 days. That just means don’t put it under heavy use or high temperatures for that period, but it can be brought in and used with care prior to that.