A varnish coat will protect wood from moisture, scratches, and other damage. But, can you use varnish over wood oils?
You can apply varnish over wood oil as long as the wood oil is fully dry. But, it’s better to use oil-based than water-based varnish over wood oils. And, you must sand before applying it.
That’s because oil-based varnish contains a high amount of oils, making it compatible with wood oil. However, you must sand with fine-grit sandpaper before applying varnish.
Varnish doesn’t stick well to oiled wood. That’s because oiled wood tends to accumulate dust over time that can prevent varnish from sticking.
Also, most wood oils dry hard, meaning that the varnish can’t penetrate or soak into the wood. Since it can’t soak into the oiled wood, it won’t stick properly.
You must sand the wood oil to help varnish stick better. Sanding will create pores over the wood oil that the topcoat can penetrate and stick. Also, sanding will remove dust and imperfections from the wood oil.
Oil-based varnish sticks over wood oil better because it has a high amount of oils that are compatible with wood oils. On the other hand, water-based varnish doesn’t contain oils and isn’t compatible with any type of wood oil (but still can be applied over it).
Related Read: Varnish vs Wood Oil
Sanding is Necessary
You shouldn’t varnish oiled wood without sanding. That’s because wood oil, such as Linseed oil, penetrates the wood deeply. So, if you don’t sand to remove some parts of wood oil, varnish won’t stick over it.
When you sand wood oil off, you create pores and holes in the finish that the varnish can penetrate into. Sanding removes imperfections and bumps from the surface that can prevent paint adhesion. Also, sanding smooths the surface, helping to create an even layer.
However, some types of varnish don’t need to penetrate to stick. For instance, acrylic varnish doesn’t need to penetrate the surface and can stick over wood oil without sanding.
Wood Oil Dry Time Before Sealing
You must wait until wood oil cures before applying varnish over it. Different types of wood oil have different drying times. But, on average, it takes wood oil 3 days to fully cure. Once the wood oil cures, its particles harden and become compact enough to withstand another coating over it.
If you seal oiled wood too soon, the finish will turn sticky. That’s because a wood oil that hasn’t cured yet is still drying. This means the solvent is still evaporating, and if you seal it you will prevent it from evaporating. This leads to a sticky or tacky finish.
How To Varnish Over Oiled Wood?
Here are the tools you need:
- Clean rags
- Paint scraper
- Paintbrush or spray gun
- Paint thinner (optional)
1. Scrape The Finish
First, clean and scrape the oiled finish. Scraping will remove some parts of the coating and create pores that the top coat can soak into. Cleaning will remove dust and filth from the surface, which can prevent paint adhesion.
To clean an oiled wood, use soapy water and a soft brush to scrub the filth off.
2. Sand Wood
After scraping, sand the wood. Sanding will create tiny pores and remove imperfections from the surface; this helps with paint adhesion.
To sand an oiled wood, use fine-grit sandpaper. Fine-grit sandpaper will smooth the surface, but won’t remove the oiled wood. Avoid using medium or coarse-grit sandpaper as it can remove the entire finish.
You must sand the stress areas of the wood. The stress areas are the parts on the surface that will be used regularly. For instance, on a table, the stress areas are the tabletop and edges.
3. Apply Varnish
Thin varnish before applying it. To thin water-based varnish, use water and to thin oil-based varnish, use mineral spirits or turpentine. Thin it in a ratio of 4:1 (4 parts varnish and 1 part paint thinner) for a sprayer, or in a ratio of 3:1 if using a paintbrush to apply it.
Apply 3 coats of varnish over wood oil. Wait until one coat dries before applying the next one. Optionally, you can sand between coats to improve the adhesion between coats. Wait until the final coat of varnish fully dries (cures) before using the wood. It takes oil-based varnish 1 week to cure.
Different Types of Wood Oils
You can varnish over Danish oil, but Danish oil is a penetrating finish and will soak into the wood grain. So, it’s best to thin Danish oil before applying it or use a type of varnish (such as water-based) that doesn’t need to penetrate the surface to stick.
You can apply oil-based varnish over linseed oil because both finishes are compatible. That’s because they both have a high amount of oils in the formula.
You shouldn’t varnish over Teak oil because it’s a natural oil that dies hard and prevents liquid from penetrating its coating. To seal Teak oil, you must use water-based varnish or another type that doesn’t need to penetrate to stick.
You can put varnish over Tung oil because Tung oil is compatible with several types of varnishes. Spar varnish especially works well over Tung oil but ensure to sand first. Also, ensure the Tung oil has fully cured before varnish.
Osmo oil is a hard wax finish that doesn’t accept top coat properly. So, to seal Osmo oil, you must sand the coating and use water-based varnish over it.
Related Read: Can You Stain Over Wood Oils?
Mixing Varnish With Wood Oils
You can mix oil-based varnish with wood oils. That’s because both of these finishes use the same solvent (oil) and are compatible. However, you shouldn’t mix water-based varnish with wood oil because they have different solvents (water and oil) and aren’t compatible with each other.
Mixing oil-based varnish with wood oil creates an oil-based finish that has improved durability and water resistance. Since varnish is a clear coat (with no paint pigment), mixing it with wood oil will create a tinted (or colored) finish. However, the mixture will have too much oil content that can turn yellow after a while.
If you mix water-based varnish with wood oil, the finish won’t have a consistent flow, color, or dry time. The mixture will be unusable.
You can varnish over oiled wood, but clean and sand the wood oil first. Cleaning will remove dust from the surface and sanding will remove imperfections and help varnish stick better.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,