Sawdust plugs the wood pores – Myth Debunked!

“Sanding at a very high grit will plug the pores of the wood, not allowing stain to be absorbed.”

If you never have heard this statement before then surely you have experienced it. You finish building your project and you are doing the sanding. You want that extra smooth touch and feel to be as if ice on glass. So you sand to the highest grit you have , 220, 400, 800, 1000! My god it’s smooth! Now it’s time to stain it.

After careful consideration, you choose the color that is going to completely transform it from a simple project into a work of art. You dip the rag into the stain and start to rub it on the wood. And then, disappointment sets in. It’s way too light in color. You pick up the can in disbelief, to make sure it’s the same color you thought it was. The color on the can looks much darker. So you read the directions. Maybe if you put it on thicker with a brush and let it sit longer. Well, all it did was make you wipe a bunch of stain off and waste it. Perhaps if you let it dry overnight and put a second layer on in the morning? And when morning arrives, disappointment is still there.

Now frustration sets in and you turn for the answers of all of man’s questions. Yes, I’m talking about the internet. At the simple click of a mouse, you find the answer and read, “Sanding at higher grits fills the pores with sawdust preventing the stain from absorbing.”  Well that’s got to be it. After all, it has been published on the internet.

And to this, my friends,  I reply, in the immortal words of Judge Judy, “Boloney!”

I always was troubled by that statement. Common sense tells me it can’t be possible. Even if i sand to 1000 grit, I can see the sawdust I am producing. But I am not able to see the pores of wood unless i use a microscope. How can I produce sawdust that I can see and it can fall into the pores of the wood that I can’t see? So i decided to do an experiment.

I took three blocks of pine wood.

The first block and started with 80 grit sandpaper and stopped sanding at 100 grit.

The second block I sanded with 80, 100, 150, and stopped at 220 grit sandpaper.

The third block I used no sandpaper at all. I just used my block plane and planed until I had paper thin shavings.

Then I selected the darkest stain I had, which was a walnut color.

When I applied the stain to my 100 grit block, the color was pretty close to the color on the can. When I applied the stain to the 220 grit block, it was much lighter in color. Hence, this is where the theory “the pores are filled with the fine sawdust not allowing the stain to be absorbed into the wood.” And if I stopped here with my experiment I would have to agree with that theory. However, the third block that was simply planed, and it had the least amount of absorption. How can the pores be filled when I didn’t even produce any sawdust at all?  There are two reasons why, so let me explain.

Left- 100 grit sandpaper. Middle- 220 grit sandpaper. Right- Hand planed

Reason 1- Too Smooth

The block that was sanded to 100 grit sandpaper produces deeper grooves in the wood. These deeper grooves allows the stain to fill the grooves and rest in it until it dries.

The 220 grit block has much shallower grooves resulting in less stain being able to fill them.

The planed block has even less. Thereby, less stain is actually sitting on the surface of the wood.

So it is clear, that sanding to a rougher grit can result in a darker stain color simply because it allows more stain to dry on the surface. But I have a second reason as well.

Reason 2- Raising the Grain

After staining but before putting a topcoat on the wood, a light sanding is required. Even though the wood is very smooth, when stain is applied, it “raises the grain” of the wood. What this means the stain causes the wood fibers to swell from absorbing the stain. (water based stain will raise the grain more that oil based stains) So the ultra smooth finish now feels slightly fuzzy or rough again. The easy solution is to, “knock it down”. Which is simply taking a very high grit sandpaper and going over the surface very lightly to sand off those swollen fillers that have stood up.

This is where my theory comes in. Sanding at a lower grit leaves behind bigger, rougher fibers. When the stain is applied, the fibers are able to absorb more and swell bigger. This then results in a more visible difference because the fibers are holding more of the color from the stain.

So sanding at lower grits results in a darker color, but what about it being smooth? This can be achieved through the layers of topcoats of finish.

On most projects, I stop sanding at 150 grit. However, in the case of this pine, I would stop at 100 grit. A sanding sealer would be applied to lock in the color, and after the sanding seal dries, it would be knocked down with a 220 grit sandpaper. From there, I would apply the first layer of topcoat. After drying, I would knock it down with 220. The second topcoat, I knock it down with 400. I do the same for the third coat. The fourth coat I’ll knock it down with and ultra smooth scotch bright pad, (or sometimes a brown paper bag) and then the final topcoat is applied giving me a beautiful dark and smooth finished project.

Doing this method gives me the best results for my furniture. This makes myself and my customers happy enough to dance!

Chad Stanton – Professional Furniture Maker