How to Finish Wood
Why the coating and its application matters
The finish you apply to your wood is one of the first things you notice. A great finish applied right will bring your hard work on your project to life. However, if the finish is not applied well you will notice immediately. Additionally, a properly applied finish will provide protection from moisture, scratches, and more. With that in mind, we will cover the most common mistakes that are made when you are applying a finish to your wood and how to finish wood to achieve the maximum finish quality.
Before Applying Finish You Must Properly Prepare the Wood Surface
The finish you apply will only be as good as the quality of preparation you perform to the surface. When you are preparing your wood for coating there are two key steps you should perform to ensure your wood is ready to apply a coating. Please read below to learn the 3 key steps in preparing your wood for coating.
The first step when finishing wood is to smooth the surface through sanding. The grit of sandpaper you should use will depend on the surface defects present in your wood project. Sometimes people will immediately start with a coarse sandpaper like an 80 grit paper when in reality the surface does not have significant defects and sanding time could be reduced by starting with a 120 or 150 grit sandpaper. The key principal to understand when sanding is that the rougher the surface is left the more you will see the effects in the surface finish. Additionally the darker the wood will color when applying a finish, especially if your using a stain with dye in it. Typically a good ending grit will be 150,180, or 220 depending on your preference. The end goal is to have the surface not show machine marks or sanding scratches after a finish is applied. A key point is that while sanding you should always try to sand with the grain otherwise you can create cross marks which will show up when your finish is applied. To best understand the different types of sandpaper, their material make up, and related information there is a great resource here.
Dewhiskering the wood also known as raising the grain – Unless you plan on using a non grain raising stain you will want to make sure to raise the grain before any stain is applied. This is typically done after you have achieved the proper degree of smoothness from your initial sanding. The purpose of dewhiskering is to properly prepare the wood to accept stain without causing the grain to raise up, which will ultimately leave a rougher looking finish than if the wood is properly prepared for stain. The wood grain will raise up due to moisture accumulating whether it be from stain or the environment. By wetting the wood to about the point you intend on applying a finish (so the wood is close to puddling), letting it sit overnight, and in the next day taking sandpaper about the grit you finished sanding with that is slightly dull and sanding you will have removed the grain. Dull sandpaper is important because you do not want to remove any more of the surface, rather you only want to remove the grain that has become elevated due to moisture exposure. By removing just the grain, you will reduce any further swelling from future exposure to moisture like when your applying your stain. Of course you could also use a non grain raising stain.
Prior to applicaiton of your stain and topcoat remove any saw dust by blowing the product off with air. You should also consider a brief solvent wipe with the approrpiate solvent for your coating to prepare the wood (this will be done after you have raised the grain on the wood surface.
After Surface Preparation You Should Choose the Appropriate Stain or have it Chosen prior to Beginning Preparation
Stains come in a balance of dye and pigment. The degree to which each is present in your coating will be one key determinant of the coating appearance. For a greater in depth coverage of stains refer to this article. Essentially the more dye a stain has the more uniform and non obscuring the finish will be. Meanwhile, a pigmented stain will prevent UV discoloration and improve durability but might obscure the way the wood finish appears as well as a have a slightly uneven appearance to the products surface compared to a primarily dye stain.
Next You Should Use the Appropriate Application Equipment
Depending on the type of stain and top coat you use you may need a spray gun. If your coating is hand applied the application equipment will be less applicable. However, if you will be spraying your finish a few key things will be needed. Ultimately you will want to choose between a compressed air system or a turbine HVLP spray gun. To help decide which is right for you we have put together a guide here.
First is the proper volume of compressed air also known as CFM. To spray finishes with a spray gun you will want 20 CFM of air to be able to use most spray guns (less air will often yield issues atomizing the coating or the gun not working as it should).
Second you will want your compressed air to be filtered that is feeding the spray gun. This can be achieved by a refrigerant dryer or a oil water extractor called a 2 stage air filter.
Third you will want to select spray equipment that is right for your coatings and production. If you are spraying a lot of product you may want to consider an air assist airless outfit. For most other wood finishes you should consider an HVLP or LVMP spray gun. If portability is key a turbine Gravity Fed HVLP Spray Gun could be right for you. For most low volume wood finishing work a gravity fed spray gun will be great, or you can consider a pressure fed spray gun. To learn more about gravity and pressure fed here is a good overview. To learn more about HVLP vs LVMP here is a good article.
Finally Apply the Stain and Top Coat Correctly
Application of stain mostly only requires proper mixing and spraying technique to apply well. However, one key mistake that is often made is that more product is added when the stain dry’s because it appears to light. Remember the color the stain will appear after applying a top coat over it is similar to the color of the stain when it is still wet on the wood. The type of top coat you select will determine important things to consider which are highlighted below
Shellacs and Lacquers – Should be applied in thin coats and can be applied while underlying coats are still wet
Varnish (includes polyurethane), conversion varnish, catalyzed lacquer – For these types of coatings you need to wait for each coat to dry before applying a new coat, with excessive drying (more than a few days) you need to scuff the existing coating layer
Water Base – You have to wait for underlying coats to dry and if to much time goes by you should scuff the existing coats surface.
By properly preparing your wood surface, selecting the stain that will meet your performance and visual needs well, selecting proper equipment for your particular finishing need, and appropriately applying your stain and top coat you can ensure that your finish will be top of the line and last for a long period of time.