How To Get A Smooth Glass Finish On Wood
Before I get into whether a dry or wet sanding is better to obtain a smooth wood finish we need to detail industry standards. This process is not something a painter will do before staining and sealing the wood trim of your house.
If you have the money for doing it then great, but the cost would be more than you imagine. I thought I would save some poor soul out there by adding that little bit in here before a home owner reads this.
What I will detail is for fine woodworking in either furniture or wood art. Much will depend on what you want the texture to be in the feel of your hand. If you have struggled with getting that glass finish on wood there is no need to turn to epoxy.
What I will offer here is an alternative to epoxy methods which have become so popular in recent years bringing back some old school techniques which seem to have been forgotten. Better yet is that what you will need to accomplish this you will most likely already have in your shop.
Smoother Grain Is A Cleaner Finish
The obvious reason for sanding is to smooth the grain. Typically one will begin with a heavier grain sandpaper depending on what is desired. If one is shaping wood you may see paper grits near the 100 range or perhaps 80 if it is getting serious. At those grain levels you are not trying to smooth anything. Here one is altering the contour of the wood for a purpose.
In terms of smoothing wood for a glass like finish more can be done than just sanding. A paste wood filler such as Mosers Grain Fil can be used before the finishing process begins but is not required. The purpose of this type of filler is to seal the wood fibers closing them to allow for sanding to create an even surface on rough grain species. Even does not mean leveling the wood from corner to corner.
To better define an even surface understand how wood fibers lock into each other. Some grains are more open than others in how they grow together. In other words there are more peaks and valleys between the grains in a micro view. This is in part what creates a rougher feel to some wood grains than others.
The wood paste filler aids in evening the wood grain. Note that when you apply these wood pastes you need to go cross grain. Moving with the grain will not help fill the gaps as well as a cross grain pull. After it is applied you allow it to dry overnight to be worked the next day. Just be sure to get any excess removed from the surface before allowing to dry. It should not be pooled anywhere on the wood surface.
The next day you are ready to dry sand. Whatever you do stay away from heavy grit sand paper. You need near 220 grit paper and here you want to dry sand lightly. I would even consider going up to 300 grit depending on the wood I am working with and how smooth it felt before beginning this process.
Once you have sanded you have a choice to make. It is typically best to apply the paste once again and then allow to sit overnight and then sand once more. This will depend on the wood species and its grain as well as how slick you want to make the finish. For the smoothest finish possible you may even go a third time around.
In the event you do not use a paste such as this, most of us do not, the sanding process for preparation is virtually the same. Sand to achieve a clean surface and smooth feel to about the 300 grit level. Know that the smoother the wood is before staining the lighter the stain will be on the wood color when applied. If deeper or darker color is desired you may want to max out at the 220 grit level.
Here you will have to make a judgment call but typically two times around is sufficient.
Sealer Helps Create A Smooth Wood Finish
If I were to use a polyurethane as a wood sealer on newly stained trim within a house I would not go to this extreme. In fact it could be a headache. On smaller projects such as wood art or furniture it is perfect. When you open a new can of poly it is thin and will run all over the place. Yet there is a trick, thin it.
I like to mix my poly 50/50 with thinner or if water based use water. Does it sound crazy? Try it. Yes it will want to run like crazy. Yet if one uses a fine brush or foam brush the results are amazing. There is a drawback which require more work as a result.
You will need to apply more coats than normal. How many more depends on what you are looking to achieve in terms of feel and appearance. Nevertheless dry sanding in between coats will produce a beautiful finish in the end. So what does thinning the sealer do to help?
While the natural state of the sealer seems very thin to us, in terms of its ability to penetrate the wood it still is thick. By thinning the poly it becomes easier to seal the fibers as it soaks down within the wood rather than sitting on top of them. This is important for allowing the future sanding to smooth these fibers once the sealer is dry.
Sealer does more than act as a protective coating against the elements. It locks the fibers together on the surface creating a barrier. If the sealer is allowed to penetrate deeper into the pores and fibers of the wood it forms a more uniform barrier. By doing this it aids in “raising the grain” more evenly for sanding on a micro level. Sanding between coats is best done in that 300 grit range again depending on species and cut.
There is a hidden benefit. If a fine brush or a foam brush is used you can minimize brush marks. Indeed this all equals more time on the project. Again it depends on how far you want to take this to achieve the best appearance. Yet after multiple coats with light sanding between it really helps the last part of the process.
When Should Wet Sanding Be Used?
Some may ask if wet sanding should be used at all? The truth is to get that slick finish it is almost a must. I have heard many say that it is not an absolute.
Yet here we are next stepping into the 500 grit range and up of sand paper. The grit levels of sand paper at this point perform better with some kind of lubricant working with them.
Some applications such as with wood epoxy resins require fine wet sanding and also applies to many wood hardeners. Experimentation from product to product may be needed. Yet wet sanding helps to polish this surface.
The issue with not wet sanding at these levels is that the dust will begin to form a layer on the paper itself preventing it to work as efficiently as it otherwise would. When you have reached the point of having stained and sealing the wood to your satisfaction the wet sanding is for two factors.
We are removing any last remaining blemishes from our application method such as brush marks and we are also giving the wood a massive smooth over with each pass. You will want to soak the 500 grit paper in water. I always like to add a little dish soap to the water. The purpose of this is to decrease the surface tension of the water. This will allow the water to further act more as a lubricant when sanding.
Once the paper has been soaked we apply another light sanding to the surface. Once this is completed you are again left with a choice to make. Do you want to get really crazy with this and make this as slick as possible? Then lets keep going.
Apply another light coat of poly and allow to dry. The next time light sand with 1000 grit paper, yes we are in the automotive category of finishing at this point. Yet to continue getting crazy apply another coat of urethane and then continue this process until you reach near 2000 grit in wet sanding. It sounds crazy doesn’t it? Indeed crazy slick and smooth. Yet now we have another choice to make.
What To Call The Last Finish?
After the wood is slicked up with our automotive sanding techniques you can choose how to finish the piece. One option is to apply another coat of poly and call it done, but there is a better option that may sound crazy. Nevertheless it works.
Try applying an automotive wax or a hardwood floor wax finish rather than another coat of poly. I would use wax made for wood but in a pinch automotive can work. It would surprise you to the finish you will achieve. This process will give wood a glass like finish that is absolutely beautiful and no doubt protective to elements or spills.
The purpose of using the automotive wax as compared to additional polyurethane is due to the nature of what urethane does to wood.
Ultimately as the urethane dries it always wants to leave behind some kind of artifact where the sheen is uneven or a slight raise in the grain creating a slightly uneven rough spot.
Woodworkers know the drill well. We buff and coat, then coat again and again until the sheen is uniform.
Still in doing this the urethane is not perfect in its finish. It never will be. This is why people have turned to other types of finish to achieve that smooth look and feel. Yet the automotive wax is easy to use and can be reapplied as needed. All you do to finish it is buff it out.
How Realistic Is This To Use?
If you have a piece that you want this look and feel on it is very realistic but it requires some time. What I like about this process is that it is resource efficient with items we already have.
There is no need to go out and purchase an additional finish application. Most woodworkers use some kind of car wax for their table saw top and have it sitting around. Polyurethane is like the bread and butter basics of the wood world.
In this way we can use what we presently have reducing costs on projects we wish to use it on. The more important question is do we want this kind of finish on our projects? Table tops I love this kind of finish. It is almost important to have them for protective reasons especially if a dining room table or coffee table.
In terms of wood art I never use this system. In fact when it comes to things such as my box art I want the box to retain its natural wood texture in the hand.
The problem with the process is that the further you go the less it feels like wood on the fingertips. Some people love that, I personally do not.
In all of my wood art I love to have a rougher feel to my work. This includes my wall art where I leave the end grain cuts a little rougher than most would. Indeed I sand, yet part of the appeal is the wood itself. Needless to say I am a firm believer in allowing wood to have its beauty and its feel for it is a part of the appeal.
An additional difference in sanding wood art is the sanding tools one will use. Some offer more in refining art than smoothing a surface. Each tool has its place yet there are differences in how they are used.
Despite what I like or do not like I had to figure out a way to accomplish this and I wanted to do so with common things we all would have ready at hand. In my opinion it is definitely better than epoxy finishes which can be expensive and often do not turn out as picture perfect as we would like.
The one benefit to the wax finish is that if something is wrong it is easy to buff out and reapply. If epoxy messes up you might as well pull out the wood chisel and then start the project over. For this reason alone I find the wax method more appealing and forgiving than other alternatives.
The one benefit that epoxies have over this method is when one is using the epoxy to form the table itself. We have all seen how forms are made and the wood is essentially an accent within an epoxy table top. These creations have a cool factor yet never appealed to me as again I want to feel the wood in my hands.