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I recently bought a house and decided to remove the carpet from the stairs and install hardwood instead. To save money, I decided to buy unfinished stair treads and risers and to finish them myself. This is my first time with woodworking, so please bear with me here.

After researching on the web, I bought sanding paper, oil-based stains and polyurethane, and started working.

My first and perhaps only problem is that despite sanding for a long time with an ROS, the wood just does not seem smooth. The density of the wood seems unequal and I can see small gaps along the grain in some areas. Those areas are smooth to the touch when I run my hand along the grain, but not across the grain. See below:

Linear gaps along the grain.

Giving up on sanding, I decided to apply stain on the surface. The areas with gaps absorb more stain, and it actually creates a good-looking color effect. However, we can clearly see that the darker areas are "rougher":

Result after stain application

Applying 2 coats of oil-based poly over this does not really fix the problem. It looks like light reflects differently on the darker areas and it doesn't look very good when placed under the light.

Is all of this normal? Is it because of bad wood quality? Did I just not sand enough?

Thanks for your help.

Note: the wood used is a smaller piece just for testing purposes prior to finishing the actual stair treads.

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The density of the wood seems unequal and I can see small gaps along the grain in some areas.

The wood in your pictures appears to be oak and the texture in the grain is common in that wood. I assume that you began with a course sandpaper 80-100 grit +/- to remove an major dents or impressions in the wood and proceeded to finer grits such as 150 an finally 220. The root cause of the tiny gaps in the wood is due to the cellular structure of the wood. Annual growth of the tree adds less dense fiber in the spring and denser material later in the year. That is why the stain is expressed lighter and darker across the board. More stain is absorbed into the cellular structure in the less dense areas with much less absorption where the grain is tighter. This is common in oak and the variation in darkness with the stain is one of its appealing features. If you apply several coats of finish the varnish/poly will bridge the gaps and provide good finish appearance. If you take a close look at other installations you will probably find similar conditions. I suggest you finish a test piece first to satisfy yourself that the overall result is acceptable.

  • Yes, I started with 80 and gradually moved up to 220. Thanks for your answer. It's good to know that sanding is not the problem. I'll see what happens after several coats of polyurethane. – Kevin Jun 1 '17 at 6:29
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You haven't done anything wrong and there's no issue with the wood. Oak is just an open-grained or coarse-grained wood. It's quite normal for it to have a visible, and tactile, texture like this after finishing.

You can get rid of this if desired, but not by sanding alone because no matter how much sanding you do you'll continue to expose the natural grain structure of the wood. The application of a film finish such as varnish will diminish the texture somewhat by itself because it partially fills the grain and slightly rounds the edges of it. In order to completely remove it though the grain needs to be filled.

There are a number of ways to fill grain but generally it's done either using grain filler (followed by varnishing as normal) or by filling with the final finish (you apply it thickly enough that you can sand down to a flat surface), after which you complete the finishing with one or two last coats of finish. The second does tend to waste quite a bit of the varnish because so much is applied that will be sanded away.

Note: the wood used is a smaller piece just for testing purposes prior to finishing the actual stair treads.

Well done on doing a test before committing to finishing the stairs! You wouldn't believe the number of people with far more woodworking experience who omit this step and then run into an unforeseen problem.

  • Thanks for the info! I tried upvoting your answer but I don't have enough reputation. Do you have any recommendations on which grain filler to use? I have already sanded and stained all stairs and risers at this point, so I need something that will not affect the color. I saw that clear grain fillers exist, but I'm not sure if they work well. Do you have any brand recommendation? – Kevin Jul 3 '17 at 16:20
  • Sorry can't give a brand recommendation, I'm in the wrong part of the world for starters and I don't know what would be tough enough for this application. As Ashlar indicates above, I believe it's most common not to fill grain on stairs. – Graphus supports Monica Jul 4 '17 at 11:19

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