When you have been using wood for construction, furniture or flooring, you will likely have to enhance the resilience and durability of the natural material. Polyurethane is one of the most common and effective finishes that provide a protective final coat for the wood. However, there are two different types of Polyurethane (sometimes referred to as “Poly”): water based and oil based polyurethane.
Both types consist of different ingredients and come with their respective pros and cons which we will cover in this article.
- The Uses of Polyurethane as a Wood Finish
- Characteristics of Waterborne and Oil Based Polyurethane: Overview Table
- Water Based Polyurethane vs Oil Based Polyurethane – the Differences
- How to Apply Polyurethane
The Uses of Polyurethane as a Wood Finish
Polyurethane is an effective wood finish that provides a protective coat for all types of wooden objects. Around the house, it is often used for (re)finishing hardwood floors, all kinds of furniture, in particular, if it is heavily used or located in damp rooms. Poly can also be used for exterior wood installations such as doors, windows or fences. It comes with different degrees of sheen, such as satin, matte and gloss.
Alternatives to polyurethane are mainly lacquer and varnish but also the different types of oil finishes for wood. If you consider using lacquer, do not miss our comparison of polyurethane and lacquer.
Characteristics of Waterborne and Oil Based Polyurethane: Overview Table
Refer to this table for a quick overview of the different characteristics of both types:
|Water Based Polyurethane||Oil Based Polyurethane|
|Appearance||Almost colorless||Amber hue, darkens over time|
|Drying time||2-6 hours between coats and to the first careful use, 2-4 weeks to fully cure||At least 24 hours between coats and to the first careful use, 2-4 weeks to fully cure|
|Application||3-5 coats, can often be done within 1 day||2-3 coats, stretched over several days to let it sufficiently dry between coats|
Read on to learn more details on their differences.
Water Based Polyurethane vs Oil Based Polyurethane – the Differences
Both water based (acrylic) and oil based polyurethane offer great protection for a wooden surface. The main differences between them are the appearance, the drying time and the cost.
One of the main differences, however, is the look of the surface after treatment:
If you are looking for a natural finish of your floors or furniture, then the water based polyurethane would be a good choice. The water based finish might look milky in the can, but once you have applied it, it will look clear and remain clear. However, some water based products might create a slight hue on the wood.
Oil-based polyurethane, on the other hand, often provides an amber hue which you may or may not appreciate. For certain woods and layouts, this amber shade is perceived as being warmer (source). Over time, oil based finishes tend to become darker while water based poly coats retain their colorless appearance.
Drying Time and Application
Water based polyurethane dries much faster, multiple coats can even be applied within a single day. It usually takes 2-6 hours for waterborne poly to dry to a point when you can apply another coat or even carefully walk on it with socks.
Oil based poly takes at least 24 hours before you can apply another coat.
In addition, water based polyurethane is not as smelly as the oil based one. For instance, a room with a hardwood floor treated with water based poly can therefore be used much earlier.
As a rule of thumb, acrylic poly needs to be applied in 3 to 5 coats while oil based polyurethane requires 2 to 3 coats only. While this requires more working effort for the water based coating, it can usually be done within 1 day taking the short drying time between coats into account. For oil based poly, usually 3 to 5 days are needed to apply the different coats and let the smell go away.
Hardness and Durability
Generally, oil based polyurethane is said to be the harder and more durable finish thanks to a higher concentration of solids as ingredients. Yet, it is also less flexible to adjust to the natural movements or changes of the wood. In practice, most people consider both water based and oil based polyurethane as being similarly durable and protective. Therefore, durability may only play a minor role when you decide which one you are going to use.
Acrylic polyurethane is significantly pricier than the oil based counterparts. Depending on individual product and the numbers of coats, finishing a floor with water based poly can be up to 2 to 3 times as costly.
However, it may yet be worth the additional cost: You will be able to apply the several coats faster (thanks to the short drying time) and it does not produce a strong odor as the oil based ones do.
How to Apply Polyurethane
Water based polyurethane does not work well on top of oil based ones. If you are refinishing an object with an oil based poly coat, you should sand it down and remove it entirely.
However, you can always apply water-based polyurethane over oil based stain. You need to sand the existing coat to allow the polyurethane to stick on it. You can use some synthetic steel wool or fine-grit sandpaper for this (if you are working on a floor or a larger object, you will want to use a powered sander though).
3 Steps to Apply Water Based Polyurethane
Follow these 3 generic steps to apply poly on a sanded wooden surface:
- Apply a very thin layer of the water based polyurethane with a foam pad, brush, or cloth. Make sure that you do not raise the grain of the wood and do not apply excessive polyurethane.
- Once the initial coat is dry (within a few hours) you can apply the second coat.
- If you are applying the layers repeatedly, after allowing them to dry you do not necessarily need to sand the surface in between. However, make sure that you apply at least 3 to 5 coats to get the same protection level as provided by oil based stains.
Tips for the Perfect Polyurethane Finish
Now that you know the difference between water based and oil based polyurethane, you might be wondering how to master its application on floors and furniture. Here are 4 tips to achieve a finish like a pro:
#1: Stir and Do Not Shake
While you are using the finish, stir it after regular intervals, especially with water based poly. Additionally, avoid shaking the can. This would create bubbles, which will affect the application and the protective effects.
#2: Apply Thin Coats
For each round of coating, apply a thin coat of finish only. Once it has dried, you can apply another coat. Otherwise, thick coats would extend the drying time and affect the natural look of the finish.
#3: Remove Drips and Excess Immediately
When you are applying the finish there might be an excess or even drips if you are working on a vertical or uneven surface. You should remove those imperfections immediately (acrylic poly can be removed with water). If you are using oil based poly and it has already dried, sand it out or use a sharp razor blade. After you have used the blade, use a feather to remove the remaining blemish.
#4: Look at you Workpiece from Different Angles
When you are applying polyurethane, both oil based and water based, make sure that you look at the floor (or the type of surface you are finishing) from different angles. You can also use a bright light to identify excesses as well as parts that you might have missed. This is a final step for each coat to make sure you achieve an even finish for the whole surface.
#5: Allow Sufficient Drying Time
Let oil based polyurethane dry for at least 4 days before you move your furniture back (water based: at least 2 days). Although you may carefully use a finished object after around 6 hours (waterborne) or 24 hours (oil based poly), both types need 2-4 weeks to fully cure (source). Try to avoid intense uses during that time. The longer you wait for the first use, the lower the risk that you damage the protective coat.
Comparing water based and oil based polyurethane, it becomes obvious while the waterborne type is so popular nowadays. It dries quickly, is not as smelly and offers a good level of protection. The advantages of oil based poly are the warmer hue (if desired), the lower cost and the slightly better hardness,
However, most DIYers choose water based (acrylic) poly. If you prefer a less smelly and fast-acting finish, it will probably be your first choice as well.
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