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60VIDEO Sanding Between Coats
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Jan 24, 2024
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View Video Transcript
0:00
In this video, I want to explain to you the single most important step in successful interior wood finishing
0:08
Lots of the steps are important, of course, but if you miss this, you will never achieve an excellent finish
0:15
Now, this is a piece of cherry that I showed you in a previous video
0:19
We coated this with water-based urethane. Both sides were sanded. This side is uncoated
0:27
It's very, very smooth. feels great, very inviting to the touch. This side used to feel that way
0:33
but it definitely does not feel that way now. And that really doesn't come across too much in the video
0:38
but I wonder if you take a close look, maybe we can get in with the camera, take a close look
0:44
You can see some light shining off here. You can see that this is no longer smooth
0:50
That's no surprise to you. I told you it wouldn't be smooth because the wood fibers that were laying down
0:55
soaked up some of the urethane and they stood up and then they hardened in the upright position
1:01
All microscopically, of course. But that's why it doesn't feel so smooth. And that's why we need to do this vital step of sanding between coats
1:11
The most important time you sand between coats is after the first coat has dried thoroughly
1:16
But you still should do it after every coat except the last coat
1:21
And even in that case, if you're going to go on to buff the surface
1:25
then you're going to want to sand that last coat too. But normally, if you're not buffing
1:30
and you're going to get to all that later, if you're just going to apply a urethane finish
1:34
you're going to brush a coat on, you're going to sand between coats, you're going to brush another coat on
1:39
you're going to sand after that coat is dry, and then probably put on a third coat and then just call it a day
1:44
That's a very serviceable finish, nothing to be ashamed of there. It's not as good as it can get, but it's very good
1:51
So the sanding between coats is a very, light sanding and its job is definitely not to go through the finish that you've
2:01
applied but just to knock over knock off those bumps and if you've chosen your
2:07
urethane well and if you've allowed that urethane to dry fully then it's a very
2:13
quick job just one or two quick passes over any given spot and you're done and
2:19
you know you're doing a good job when this sanding creates a kind of a white
2:24
powder which I'll show you in a second. As far as sandpaper goes, it's got to be fine
2:31
So this is P220 so that's 220 grit sandpaper which means on any given square
2:40
inch on here there should be about 220 particles. So the bigger the number the smaller
2:47
of the particles because it all fitting into one square inch So that what that means and 220 is as coarse as you want to use Sometimes you see 240 pretty much the same as 220 you can really tell the difference
3:02
You'll also find 320, which works pretty well. It gets a little bit, it wears out a little bit too fast for my liking
3:10
So I go with 220 or 240 and there's two ways you can actually sand the wood
3:17
First of all, you can take a quarter sheet of sandpaper like this and you can fold it in thirds along its length and that makes for a really nice
3:29
handy piece of sandpaper to sand with because we've got the surface here that we're going to sand
3:34
with the other surface is also rough so my hand's not going to slip on the paper like it might
3:40
if I was trying to sand this way with my hand against the actual paper so I get I get traction
3:46
I get a nice shape and I can flip it I can
3:51
refold it to expose fresh surfaces. So I'm going to use this whole quarter sheet of sandpaper
3:58
before I throw it out. It's going to be completely used up. This is a small piece of wood
4:04
so there's really no need to use a power tool. But a finishing sander like this is very useful
4:10
for most real world projects. I mean, this is just a sample. But if you're building a cabinet
4:15
or a table or anything like that, then a quarter sheet finishing sander is going to save you
4:23
a lot of time and it's going to help you to do a better job. Do not use a random orbit sander
4:28
or anything like that, way, way too aggressive. You're going to go right through your finish
4:32
and you're basically going to go back to square one again because you would have removed pretty much all the earth thing you put on. This is much gentler. It just vibrates a little bit
4:40
That's all it does. So it is one of the mildest power sand
4:45
you can use. In both cases though, so whether I'm sanding by hand with a quarter of a sheet
4:53
of paper or I take this quarter sheet and I put it on this sander, in both cases I need to have
5:00
a quarter sheet. This is a full sheet of sandpaper. This is the way it comes when you buy it
5:05
eight and a half by 11 in size, just like a regular sheet of paper. But you know, you shouldn't
5:10
use scissors to cut this into quarters. I mean, it's on now
5:15
You've got to find the scissors, you've got to use the scissors, and it also dulls the scissors
5:21
But if you just fold it in half, like I've shown you here, and then you take a sharp edge, any kind of a sharp edge, it doesn't matter a table or machine or just a scrap of wood like this, and you just put it over
5:32
That sharp edge is going to do a really nice job, tearing that for you
5:39
It's good, and you can double up. And when you have the two halves, you can..
5:45
There you go. They all set for a while The actual sanding it not difficult to do this well but there are a few pitfalls that I want to warn you about So unlike when I was coating this where I really benefited from
6:01
light coming in at a shallow angle so I could see where I coated and where I hadn't coated
6:06
that's not so important for sanding between coats because, well, as you see, you can really see
6:13
where you stand it. That's it. All of a sudden, that's gone from quite rough
6:24
to amazingly smooth. Really, really smooth. And look at how that's powdered up
6:29
That's exactly what you want to see. Bad quality erythane never gets dry enough
6:36
so that it will form powder like this. It'll get kind of gummy
6:40
and it'll leave little streaks of gumminess on the sandpaper. You don't want to see that
6:47
That can be caused if urethane hasn't been allowed to dry long enough. But more often than not, it's because the urethane isn't that
6:54
it isn't that good quality. The urethanes that I'm recommending here never do that
6:58
so you don't have to worry. I'm going to use this next
7:03
and really there's no need for me to use it here, but I'm just going to show you how it works
7:08
and just to mention again how useful it is on larger surfaces
7:27
Oh, that's it. If this was a piece of furniture and say I had finished an edge somewhere
7:34
I wouldn't use the quarter sheet finishing center on the edge. edge, even if I had a lot of edges to do, just because it's so easy for the sander to tip to one side, maybe, go right through the finish, round over the corner that shouldn't be rounded, for instance
7:50
So whenever I have edges or any narrow surfaces, I'm going to do it by hand. Now, this is not a sanded surface, it's not a finished surface, but this is the way I would do it
8:01
Just holding it like this, with my thumb applying some pressure, and that's just about all it's going to take
8:08
Now the next major step here is to put on another coat of your thing and I'll show you about that later
8:14
but before we do that I think you can imagine that we need to make this perfectly clean
8:20
I could go at this with a tack rag a tack rag is just kind of a sticky rag that's sold for
8:27
preparing surfaces before finishing it's often used in the auto industry I don't really like tack
8:32
rags though when I have vacuum at my disposal so here my workshop I have a central
8:38
vac use it mostly for preparing for finishes actually but you can use a regular household vac a shop vac it doesn matter You just want to put a bristle brush on it And watch what happens here when I suck up all this dust
9:10
Now that is ready to go. It's ready to go for our second coat, beautifully smooth and inviting to the touch
9:18
And that's going to get even better once we get the second coat on, and we start to work that down a little bit too
9:24
But sanding between coats, absolutely vital for any kind of a film-forming urethane finish
9:31
I also happen to use it on wipe-on poly finishes, which don't really form a film to the same extent
9:38
but they do cause the surface fibers to rise up and get kind of fuzzy and hardened
9:43
So sanding between coats, it's the wood finisher's best friend. I almost forgot one thing
9:50
When you're sanding small things like this between coats, it's always a good idea to do it on some sort of a resilient surface
9:59
So that's why I have this piece of foam here. I mean, you can see it's kind of high mileage foam
10:03
I've used it for a lot of jobs where I don't want this
10:08
surface I'm working on to mar my wood. Now if we were working on a freestanding
10:13
cabinet or something like that, sanding between coats there, well this wouldn't
10:17
make any sense because the thing is standing in mid-air and we're working it
10:21
that way but it's not unusual if you're making a shelf, finishing a shelf, say, or
10:26
some smaller wooden item, but both sides of something need to be smooth and
10:30
presentable. And if I had just the sanding I had done just now, if I had done it
10:36
on this wood surface here, well I could guarantee you that the underside of the wood would have been marred because there's
10:42
just glue bumps here and all kinds of things but the foam sidesteps all that
10:48
because it's got a little bit of give to it you don't necessarily need to use a
10:52
piece of foam three or four layers of a blanket you know fold it on itself and
10:57
a chop blanket something that you don't mind getting dirty and dusty that works
11:00
too but just remember that when you're sanding and this applies to sanding
11:05
between coats or or even sanding wood for the first time before you even get to the finishing process you want some sort of resilient
11:12
surface that's it's clean and smooth with no bumps on it it's not going to
11:16
cause any damage to the wood because especially when I'm sanding with an
11:22
electric sander that's imparting a kind of a vibration to the wood and if that
11:27
vibration is coupled with something hard underneath a little bump or an
11:32
oven or something then that's definitely going to mar the wood an old piece of
11:37
carpet. That's another great idea. Just anything soft to keep this protected, especially if you're using
11:43
electric sands
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