With all the varieties of wood finish available on the market, you could get confused as to which one is most suitable for a particular job as a woodworker. No woodworking project is complete without applying a wood finish to the surface of the wood. One of the most widely-used types of wood finish is polyurethane varnish, which we call merely “polyurethane” or “poly.”
Polyurethane is an extremely versatile type of wood finish. It is also widely used to coat surfaces made other materials as well. As a woodworker, you would be interested in the best ways to use it as a finish for your woodworking projects.
Here, we highlight the advantages and disadvantages of two types of polyurethane – wipe-on and brush on poly.
Wipe-On Polyurethane vs. Brush-On
Polyurethane is best-known for its durability and impressive finish; hence it is a preferred choice for most woodworkers. Whether you use a wipe-on or brush-on process, you want the result to be more or less the same – your project should look smart and the wood surfaces well-protected. Each of these types of polyurethane shares more or less identical properties. The main difference between the two is the method of application.
The procedure for applying wipe-on polyurethane is relatively more straightforward than that which we use with a brush. It is because you don’t have to be too concerned about brush strokes and excess drips. We apply wipe-on polyurethane with a cotton rag, and provided you use the correct quantity of finish evenly on the surface of the wood, you will quickly get good results.
You can get adequate protection from brush-on polyurethane with two coats. However, one of the biggest challenges is to apply this type of polyurethane devoid of brush marks and drips. You will achieve the best-looking finish when you apply it on horizontally-flat surfaces. You need to apply brush-on polyurethane in multiple coats. The time taken for it to dry in-between coats is a minimum of four to six hours. But you can get the best results if you leave each coat to dry overnight before applying the next coat.
Wipe-on Polyurethane Vs. Brush-on: Pros and Cons
Each type of polyurethane and the process therein has its advantages and disadvantages as follows:
Wipe-On Polyurethane Pros
- It is suitable for slender, vertical surfaces.
- You can apply it faster to round and carved surfaces.
- It is easy to apply.
- The applicator comes from waste material, which can be thrown away after use.
- Wipe-on poly dries faster than brush-on polyurethane.
Wipe-on Polyurethane Cons
- It is a messy process.
- We need to apply more coats than brush-on polyurethane.
- The polyurethane-soaked rags are a fire hazard if not handled properly.
- Premixed wipe-on poly is extremely expensive.
- Your finish may not be as good as a brushed finish.
Brush-on Polyurethane Pros
- It is a neater process than wipe-on polyurethane.
- You don’t need to apply the number of coats that you need for wipe-on poly.
- It is a faster process than that of wipe-on polyurethane.
Brush-on Polyurethane Cons
- You have to sand and smoothen the surface between coats.
- It has a tendency to form drops and streaks
- It takes longer to dry than wipe-on polyurethane
When to Brush and When to Wipe?
Some woodworkers prefer wipe-on polyurethane because they have developed a high skill level in applying it. You will rarely see such people using a brush. But in general, woodworkers prefer to apply polyurethane using a brush. They use wipe-on poly only in situations where it brushing isn’t practical.
If you have a thin, rounded surface or an intricate lattice, you will find it cumbersome to use a brush. Similarly, you would find it impractical to use a brush for applying polyurethane to carved surfaces like moldings. In such a case, wipe-on poly comes to the rescue.
With brush-on polyurethane, you can apply the finish in a more sparingly and controlled way. But if you have a vast surface like a tabletop or a double bed, you would be better off brushing or spraying the polyurethane onto the wood.
How to Apply Polyurethane
Whether you use wipe-on or brush-on polyurethane, other than the application method, the related procedures are more or less the same. Here some useful tips that could make your life easier while applying polyurethane:
By applicators, we mean cotton rags and paintbrushes for each respective method of application. Your applicator should be clean of contaminants like dust, lint, moisture, and grease. In the case of a wipe-on application, wearing latex gloves is mandatory. However, you can also use gloves while brushing the finish to keep your hands clean.
It is a good practice to cover all the surrounding surfaces with drop cloths or old newspapers. After use, ensure that you store or dispose of applicators as required.
The Thickness of Coats
The rule of thumb while applying polyurethane by any method is to apply a thin coat. If you want a durable thickness, you can best achieve it by adding multiple coats. A single thick coat will create blemishes on the surface, which can be challenging to rectify after the polyurethane has dried and cured.
To apply thin coats of the finish, you have to dilute the polyurethane to the desired consistency and use a light hand while applying it. The approach of applying multiple thin coats is both cumbersome and time-consuming. But it is the only way that you can impart a professional touch to your wooden surfaces.
The Dust Factor
Dust is your primary foe. You need to scuff the surface between coats. After scuffing, wipe the surface with a rag dipped in thinner for removing dust particles. Once the thinner has thoroughly dried, you can start to apply the next coat. A useful aid for removing dust and debris from the wood’s surface is tack cloth, which is cheesecloth treated with a sticky substance.
The dust and debris stick to the cloth, leaving a clear, uncontaminated surface. While rubbing the tack cloth on the wood, brush it lightly. If you rub it too hard, you may transfer some of the sticky substance onto the wood surface, which could disrupt the next coat.
How to Mix Polyurethane
Before you apply polyurethane, you need to mix it with the desired quantity of mineral spirits. After dust, the next difficulty that woodworkers face while using polyurethane is bubbles. From when you first touch the liquid until you complete applying the finish, you need to prevent air from entering into the liquid, especially on your paintbrush.
Remember, the thinner the bristles, the more chance of bubbles forming. So, use a brush with thicker bristles. A good ratio is three parts polyurethane to one part mineral spirit to avoid bubble formation. For wipe-on polyurethane, the proportion should be 1:1. Take care not to shake the product while handling the tin. And while mixing the two liquids, mix gently with a paint mixing stick.
A good idea for preventing bubble formation is to dip the paintbrush in some mineral spirit for about ten minutes. Then, you can remove the excess mineral spirits by blotting the brush on an old newspaper. There is little chance of bubble formation with wipe-on polyurethane.
Applying the Coat
The first coat of polyurethane is not likely to be impressive. It may contain flaws, and the surface may not seem uniformly coated. Do not be discouraged. As you apply the subsequent coats, the finish will take on a better appearance.
Another thing you will notice while applying the first coat is polyurethane raises the grain, and you will see fibers popping up. It is a common occurrence with most wood finishes. You can feel the aberration on the surface when you gently slide your hand over the surface, and it feels fuzzy. It may not occur with subsequent coats, but you can smoothen the surface by sanding with 220-grit sandpaper or #0000 steel wool.
To impart a uniform and bubble-free coat on your wood surface, always move your brush very slowly. Start from the center of the piece and move to the end, along the grain. Then, go back to where you started and move the brush slowly in the opposite direction along the grain and continue till the other side.
Repeat the process with successive coats, ensuring to sand the surface adequately between each coat. Also, clean the wood’s surface between each coat with sandpaper or steel wool, as we described above.
Now you have seen the different aspects of both types of polyurethane – wipe-on polyurethane and brush-on polyurethane. If you were not clear about the difference between these two types of wood finish, we hope that you now understand more about them. The information that we have provided here should help you make a wise decision on which type of polyurethane to use for your wood projects.
As we highlighted here, although brush-on polyurethane is less labor-intensive and time-consuming, you get a much more satisfying result with the wipe-on variety. However, sometimes it is more practical to use brush-on polyurethane in preference to wipe-on polyurethane. Once you are aware of each process’s pros and cons, you can surely make the right decision. It will now be possible to get the best possible polyurethane wood finishes in your future projects.