Applying a coat of varnish finish is the last step when it comes to finishing wood.
If done right, it will seal and protect the natural good looks of timber for years. And if applied incorrectly, you’ll have a hell of a job on your hands trying to remove and redo that finish all over again.
So its no wonder why you’ll want to make doubly sure that your varnish coat will stick well and evenly to your wood craft masterpiece.
Now, luckily, varnish is one of those types of finishes that will work well over anything. You can apply it over paint, stains, and even over another varnish.
But can you varnish over linseed oil?
Provided that the linseed oil has properly cured, you can apply an oil-based varnish over it. The varnish will then offer an extra layer of much needed protection to the wood underneath.
Now the main thing to remember here is that the linseed oil has to be ‘cured’, and not simply dry (there is a difference between the two). This is important because linseed oil takes incredibly long to dry (compared to other natural finishing oils).
But let’s dive a little deeper in discovering more about getting the most out of that Varnish + Linseed Oil combination…
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What Can You Put Over Linseed Oil? (Can You Really Put Varnish On Top Of Oil?)
You can put almost any oil-based finish you want over a natural oil such as linseed oil. Anything from polyurethane, lacquer, and of course varnish, will happily sit atop a finishing oil and seal it in.
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However, all of this comes with one caveat… you have to be sure that the linseed oil has fully cured.
Now, drying and curing may appear to be the same thing. However, they describe two very different and separate processes that oil finishes go through.
What Do We Mean When We Say Linseed Oil Is ‘Dry’
When linseed oil is dry it has gone through an evaporation process. The solvents in the oil finish have evaporated away into the air (leaving that strong wafting smell in their wake).
Once the solvents have evaporated away, all that’s left behind is a film that no longer feels tacky to the touch.
A single coat of raw linseed oil can take up to three days to dry.
Boiled linseed oil dries much faster, thanks to the extra treatments that it has been put through. Boiled linseed oil can take as little as 24 hours to dry.
Related Post: Boiled Linseed Oil vs Thompson’s Water Seal: Which One Is Better For Wood?
What Do We Mean When We Say Linseed Oil Is ‘Cured’
Now, once linseed oil has cured we are referring to the fact that it has been through a chemical process. The chemicals in the film have undergone a change that have turned it into a hard abrasive-resistant resin.
A single coat of raw linseed oil can take up to 10 weeks to dry (depending on the temperature in the environment around it). Boiled linseed oil, on the other hand, can take roughly 4 to 6 weeks to dry.
Related Post: How To Make Linseed Oil Dry Faster (What You Need To Know)
As long as you are sure that linseed oil has cured into a hard resin, (and it isn’t still in its soft film form), you can go ahead and add that coat of varnish.
Can You Put Water Based Varnish Over Linseed Oil? The old saying goes that ‘oil and water don’t mix’. And this is none more true than when it comes to varnish and oil. A water-based varnish won’t stay on top of a linseed oil finish. And that is regardless of whether it is a raw linseed oil or boiled linseed oil finish.
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To Sum Up…
At the end of the day, linseed oil is a finish that can enhance or rejuvenate the look of wood. However, on its own, it doesn’t offer real durable protection from everyday wear and tear.
So, adding an extra oil layer of a durable varnish isn’t a bad idea. And it can work out well provided that you stick to a couple of rules;
- Only use an oil-based varnish over oil finishes like linseed oil.
- And make sure the linseed oil has cured properly before applying varnish.
Long-term behavior of oil-based varnishes and paints I. Spectroscopic analysis of curing drying oils | SpringerLink
Drying and oxidative degradation of linseed oil – ScienceDirect