What is the best exterior clear coat for wood? If you have this doubt, then this guide is for you!
One unique thing about exterior clear coats is that they protect your wood furniture from moisture and sunlight while giving you the freedom to showcase the unaltered beauty of the piece.
Unlike paint, clear coats don’t build an opaque blanket on your wood. They function by creating a film-like cover over the wood surface or penetrating it.
Clear finishes can be generally grouped into two, namely film-formers and penetrators.
Types of Exterior Clear Coat for Wood
Both clear coats differ majorly by their mode of operation and layer structure. We will discuss their pros and cons.
Film-formers are known for their ability to enhance the tone and beauty of wood surfaces without leaving the wood furniture to the mercy of moisture and sunlight.
They prevent the wearing and tearing of wood.
Film-forming clear coats require regular maintenance annually or triennially. Failure to sand and recoat regularly can cause the coated surface to crack and peel.
More often than not, varnishes contain a blend of resin, volatile solvent, drying oil, and drier. They form a hard transparent film when used in coating wood material.
After application, the solvent part evaporates into the thin air while the remnants go through a process of oxidation or polymerization to create a lasting transparent film.
Varieties of varnishes include lacquer, acrylic, conversion varnish, two-part varnish, polyurethane, pseudo varnishes (drying oils), spar varnish, alkyd, shellac violin varnish, and resins.
- It protects the wood from moisture and sunlight
- During maintenance, the wood material is unaltered
- It requires more time to dry
- It requires sanding between coat layers
- It is delicate to apply
Penetrators, as their name suggests, operate by getting absorbed into the wood. Unlike film-formers, penetrators do not crack or peel.
During maintenance, there’s no need to sand or scrape, as the soaked finish just fades away. They help damp wood dry and require less maintenance compared to the film-formers.
Good examples of penetrators are hardening oils and polymerized oils.
- It is easy to setup
- It takes less time to dry
- No sanding is needed between coats
- Its surface does not crack or peel
- It is not effective in protecting wood from moisture and sunlight.
- It requires regular maintenance and supervision
The Madison Formula and Birth of Oil-varnish Blend
In 1950, the Madison formula was invented at the Forests Products Lab. This formula is used to create a linseed-oil-based finish that could be made from natural and available ingredients.
This formula solves the issue of cracking and peeling associated with varnishes and the easy wear and tear problem commonly experienced with oil-based finishes.
The resulting mixture derived using this formula was commonly known as penetrating sealer finish. The oil-varnish blend contains paraffin, linseed oil, earth pigments, and mildewcides.
The oil-varnish blend is the best of both worlds.
This hybrid varnish possesses the desired attributes of the varnish and penetrating finish.
The soft texture of the oil makes the penetrating sealer easy to apply compared to varnish.
Also, the film-forming feature of varnish makes the hybrid finish effective in protecting the wood furniture against moisture and wearing.
However, the pure varnish is more effective in reducing the effect of sun rays on your wood furniture.
Things you need to make an oil-varnish blend
- 1/3 boiled linseed oil or tung oil
- 1/3 mineral spirits.
- 1/3 varnish.
- Spray bottle
The Madison formula is still relevant today since most companies built their hybrid products around the basic concept of the formula.
The developments were fashioned around three factors.
Resistance to Moisture
The addition of oil gives the hybrid product all the resistance against water and moisture. These oils include linseed oil, tung oil, and resins.
The primary issue with penetrating sealers was that the average varnish is more effective in protecting the wood from sunlight than the hybrid ones.
Why? Their layers are not really thick to bounce back harmful UV light.
Therefore, the best way out is not to improve the thickness but to combine the UV light absorbing with blocking materials.
This way, they are able to protect the wood surface for some time before breaking down.
When the lignin holding the wood fibers is down, it will completely degrade, so also the wood fibers. The degradation turns the film cover grey and rough.
Quality penetrating sealers contain a preservative that helps protect the wood against attacks from microorganisms such as moss, mold, and mildew.
Such ingredients include zinc, borates compounds, iodine, and other similar compounds.
What Is the Best Exterior Clear Coat for Wood?
The inability of users to access the table of ingredients of the manufacturers is a major setback in the clear coat industry.
There is no way to know the quality of a product unless you buy and test it.
The only way to get a rough estimate of the applied ingredients is by checking the manufacturer’s safety data sheet only made available to retailers.
You can get the rough sketch by removing the solvent mass from the overall product mass.
Every sealant has its own pros and cons. The varnish is the best for protection against moisture and UV light. Followed by penetrating sealers, then, oil-based sealants.
Regardless of the sealant used, nature will always find a way to call for maintenance. The best you can do for your wood is to extend the lifespan of the sealant since no sealant lasts forever.
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