At Just Wood Furniture, we know that wood finish is a classic look that remains the most popular choice for cabinet doors and other pieces of furniture and home decor. But exposed wood surfaces can’t be left as they are because otherwise they will lose their colour, texture, and will have a shorter life. This is where finding the right finish for your wood becomes so important.
One of the most popular wood finishes is conversion varnish, also known as catalyzed conversion varnish. But what is conversion varnish? And what makes it such a good choice?
Conversion varnish is a finish that is popular for cabinet doors, and it is fast drying because it is chemically cured rather than air-cured. It leaves a similar finish to traditional lacquer but it is actually very different, both in terms of what it is made of and in terms of its properties.
Click to see contents
- 1 What Is Conversion Varnish Made Of?
- 2 What Are The Benefits Of Conversion Varnish?
- 3 Disadvantages Of Conversion Varnish
- 4 Conversion Varnish vs Other Wood Finishes
- 5 Do Different Finishes Work Better In Different Situations?
- 6 Final thoughts
What Is Conversion Varnish Made Of?
Conversion varnish is made of two materials. The first is the finish and the second is the acid catalyst. The catalyst is added before the varnish is put into the spray gun and it causes a chemical reaction (cross-linking) that makes the finish very hard and durable due to its higher solid content.
Conversion varnish is chemical cured and heat-cured, rather than air-cured, so after application, it needs to be kept at a shop temperature in the late 60s.
A resin is also often added to conversion varnish which contributes to the film build, hardness, and adds gloss. Without resin, conversion varnish doesn’t have the gloss finish that you would see with a traditional lacquer but with the resin, it will look exactly the same.
What Are The Benefits Of Conversion Varnish?
Conversion varnish is one of the most popular finishes for wood in a variety of situations, including cabinets, furniture, picture frames, and more. Let’s take a look at what makes it so popular.
Durability
Conversion varnish creates a highly durable finish. This is because it has a high level of dry film thickness and is made of 40% – 60% solid content that leaves it with a high solid film density.
Durability is important when it comes to finishes. First of all, a durable finish of course helps to maintain the integrity of the wood itself because it is a more protective finish. Secondly, it makes it much easier to clean because it is less likely to scratch. It can be cleaned with denatured alcohol or soap and water.
It is also resistant to heat and humidity which is, of course, important for kitchen cabinet doors where there will be a lot of cooking happening nearby.
Elasticity
Conversion varnish is also more elastic than many other finish choices. This is important for finishing wood because of wood joint expansion. Elasticity allows the wood to expand without causing any cracks.
Number Of Coats
Conversion varnishes require fewer coats than many other finishes. This is, again, because of its high solid content. Fewer coats will mean that it can take less time to finish the process.
Disadvantages Of Conversion Varnish
While conversion varnish can be the best choice for many people for all of the above reasons, it does have some disadvantages.
Difficult To Apply
Applying a catalyzed conversion varnish is a skilled task that can only be completed by professionals, so you can’t conversion varnish your cabinet doors as a DIY job. It is a delicate process and the correct ratio of the two chemicals needs to be used. The application and curing methods also need to be done perfectly if the finish is going to be as polished and durable as it could be.
Because conversion varnish is post-catalyzed, the person applying it needs to be able to use the right amount of the two chemicals. If the mixture is poorly done, this can lead to problems. If too much acid catalyst is added, this can cause a couple of problems. First, it can lead to colour-shifting of the dye stains. Second, it can leave an oily residue (known as a “bloom”) which can cause the final finish to crack.
The curing process also needs to be completed correctly. For example, if the shop temperature isn’t kept at a high enough temperature during the curing process, the conversion varnish won’t harden properly. If there is a lot of dust around during the curing process, this can leave marks on the final finish.
You can also only apply a maximum of three coats, due to the level of hardness, and if more than three coats are applied, this can lead to cracking and spoil the smooth finish.
Since the catalyst is added before the mixture prior to spraying, if too much time is left between the mixing and the application, the mixture can start to cure inside the spray gun.
Cost
Conversion varnishes are a relatively expensive finish when compared to other options. If you are finishing an entire set of kitchen cabinets and drawer fronts, using a conversion varnish can push the cost up by quite a bit.
But this is, of course, balanced by the increased durability and hardiness of the finish, which should make it last longer (assuming it is properly applied and left to harden properly).
Repairs
With some other finish options, touch up repairs are relatively easy. This often isn’t the case for conversion varnish because it is post-catalyzed so each application leaves its own finish. Small repairs are difficult to do without them being instantly noticeable, so often the only option is to redo the entire door.
Conversion Varnish vs Other Wood Finishes
Now we’ve taken a look at what conversion varnish is, let’s see how it matches up to some of the other more popular finish choices and the key differences between them.
Conversion Varnish vs Traditional Lacquers
Traditional lacquers are quite different from conversion varnish. Rather than being applied by mixing two materials together that catalyse, traditional lacquer is pre-catalyzed. Most lacquers leave a single component nitro-cellulose finish. Rather than being heat-cured and chemical-cured, they are air-cured.
Advantages Of Traditional Lacquers
Because the pre-catalyzed lacquer has already gone through the catalyst process, there is no need to mix any hardeners during the application. This means that it is easier to apply than conversion varnish and does not always require a professional to use it.
It also repairs more easily than conversion varnish and patch repairs can be completed without it being obvious. Most lacquers leave a naturally glossy and attractive finish. It is also much less expensive than conversion varnish.
Disadvantages Of Traditional Lacquers
Lacquer has a high VOC content, which can be harmful both for the environment and for humans. Conversion varnishes don’t have this content.
Lacquer has a lower solids content (12% – 18%) than conversion varnish because it is pre-catalyzed rather than post-catalyzed, and this can mean that its nitro-cellulose finish isn’t as durable. The low solid content can also make applying lacquer to cabinet doors and other woods much more time-consuming. This is because it needs to be reapplied many times to create a proper build and a hard finish.
Lacquer can yellow over time, especially if in direct sunlight, which is something that doesn’t happen with properly applied conversion varnish.
Conversion Varnish vs Polyurethane
Polyurethane is another form of varnish and it also has a high solid film density so is known for its durability. It is quite different from conversion varnish in some key ways, however.
Advantages Of Polyurethane
Polyurethane provides a more durable finish than many other finishes. It is water-resistant, heat-resistant, scratch-resistant, and is also resistant to alkalis and acids. This can make it a great choice for kitchen cabinet doors where it will be near to lots of cooking. It leaves an attractive finish and is highly protective of the wood underneath.
Disadvantages Of Polyurethane
While polyurethane is a remarkably durable finish, it does have some disadvantages. Like lacquer, it can yellow over time, which can make the finish look unappealing.
The application process is also time-consuming, although it is a pre-catalyzed formula like lacquer. Polyurethane needs to be sanded between coats to ensure that it bonds properly to the wood, but the varnish takes 24 hours to dry before the next coat can be added. This increased dry time can stretch out the entire process to several days.
It also needs to be brushed on and can’t be sprayed, unlike conversion varnish. It is more difficult to achieve a smooth finish with brushes than with sprays.
Conversion Varnish vs Shellac
Shellac was, in a lot of ways, the original protective wood finish. It isn’t used as much for entire kitchens worth of cabinet doors but is instead used for repairs and for smaller wooden pieces.
Advantages Of Shellac
Shellac is perfect for repairing scratches in the wood and leaving it looking like new again. It is a natural resin, made from the secretions of the female lac bug, so it is very mild and isn’t harmful to the environment in the way that many chemical solvents are.
Disadvantages Of Shellac
Shellac isn’t a hard or durable finish, especially when compared to conversion varnish. It doesn’t really have much water resistance or chemical resistance, nor is it particularly resistant to heat or solvents. This means that it will degrade quite quickly in high heat and humid environments.
It is also easily scratched and damaged, so will need to be reapplied fairly often, and it doesn’t cope very well with wood joint expansion. Its pot life is very short when compared to catalyzed varnish.
Conversion Varnish vs Tung Oil
Tung oil is another natural finish, similar to shellac, but it is plant-based. It is eco-friendly and it provides a natural finish through which you can feel the wood grain underneath, unlike the harder finishes provided by lacquer, polyethene, and conversion varnish. Like shellac, however, it isn’t as hard or durable as the chemical-based finishes so isn’t as suitable for wood that needs to take a lot of heat, humidity, or impacts.
Do Different Finishes Work Better In Different Situations?
We have laid out the benefits of conversion varnish here and highlighted the key differences between it and some other common finishes, but it is important to remember that the right finish can depend on the project at hand.
Surface preparation is an important thing to think about. When your surface is prepared, would a gloss finish improve the look of the final piece? If so lacquer could work well, as could conversion varnish with added alkyd resin. If you would prefer a matte look to the piece, then conversion varnish without alkyd resin is your best bet, otherwise, you would have to sand down the finish between coats to reduce the gloss.
Think about durability. How important is it for your piece to have a high dry film thickness? Is it likely to get knocked around a lot or be exposed to high heat? Conversion varnish or polyethene would work well in these situations.
Do you need something that is fast drying? In this case, conversion varnish is often the best bet. Would you instead prefer something that is slow drying but that you can apply yourself? Lacquers would often work well in those situations.
Also, think about your wood species. Darker finishes are generally better able to tolerate finishes that may yellow over time, whereas lighter finishes will show the yellowing much more easily. Do you want to be able to see and feel the wood underneath or would you prefer a thicker more solid finish over the top? The latter is achieved through finishes like lacquer and conversion varnish but the former can be achieved with other finishes.
Final thoughts
Conversion varnish is a water-based finish that is popular for a wide range of woods. It has a two-component finish because it is made of two chemicals: varnish and a catalyst. It has a quick dry time and is very durable due to its higher solid content. It is applied by spray but requires a professional to create a proper build using the correct ratio of chemicals and the correct curing process.
It can be the perfect finish that lasts a very long time and can have benefits over lacquer and other finishes in a variety of situations. It can, however, be a more expensive choice, but this can be offset by the fact that it tends to last for longer, which can reduce the cost long term.