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Can I Use Polyurethane Over Linseed Oil? (Quick Answers)

Linseed oil, also known as flax oil used to preserve woods, apply them as varnish, or stains. Since it is organic and non-toxic, it is highly popular as a wood finish for wooden furniture and the interior.

In this article, we will discuss if you can use polyurethane over linseed oil.

Can I use polyurethane over linseed oil? 

You can apply polyurethane over linseed oil. Since polyurethane is a synthetic polymer, you can simply use a canned spray bottle to spray polyurethane over your linseed furniture. Applying polyurethane over linseed oil will mix and create an oil-varnish blend that will enhance the color. 

Linseed oil is a great element used in wood to prevent scratches and deformations of wood. Before you apply polyurethane over any oiled wood, make sure to apply it once the oil has dried properly.

Once the oil over the surface is dried, it will help the polyurethane to stick to the surface properly. Maintaining oil-ratio in polyurethane is important because linseed oil is also a slippery content.

You need to cure the surface properly before you put the polyurethane over linseed oil. Use 180-grit sandpaper and rub the surface off. After that, remove the dust and apply the first coat.

After applying the first coat, let it sit for a couple of hours to dry and wipe off the excess oil. And repeat the process. Failure to execute the procedure properly will cause the surface to become sticky and unfinished.

Applying polyurethane over linseed oil makes the surface waterproof. Also, it will harden the surface and make it more durable. Polyurethane itself is an oil-based topcoat finish that can be applied over linseed oil without damaging the texture.

The following shows whether a different type of polyurethanes sets on linseed oil or not:

Spar urethane:

The problem with Spur urethane is that it can lose its longevity due to exposure to ultraviolet light in the presence of sunlight. The presence of direct sunlight can cause purine to rise above the surface.

Therefore, it may need to be refinished every few years to maintain quality. Using expensive and high-quality finishes is fairly long-lasting.

Water-based polyurethane:

You might face some difficulties when mixing polyurethane over linseed oil. When you apply polyurethane over linseed oil, if the oil is not properly dry, they both might get mixed.

As a result, they create a blend of oil and varnish that will never become hard and peel off. 

Can I put polyurethane over boiled linseed oil? 

Raw linseed oil takes months to dry. So, it’s better to use boiled linseed oil when applying polyurethane over it. During the procedure of applying polyurethane over boiled linseed oil, apply the first coat and let it sit for 10 to 15 minutes.

Wipe off the excess oil after this. You can use a roller, brush, or even cloth to apply the polyurethane.

If you do not wipe off the excess oil, it will cause a sticky surface to build up. Repeating the same procedure 2 to 3 times and between an interval of 24 hours is the best option for you.

The advantage of using polyurethane mixed with dried linseed oil to finish the wooden surface is, it will provide you with a water-resistant finish, is easy to maintain, and helps enhance the beauty of the grain.

It will take very minimal maintenance. You might need to refinish the surface once a year to make it look new.  

3 reasons why you can use polyurethane over linseed oil

There can be many reasons why polyurethane over linseed oil. Applying polyurethane over linseed oils causes no damage to the surface. Rather it seals the pores of the wooden surface making it more durable.

Also, linseed oil provides a glossy finish to the surface and increases the longevity of the wood.

But make sure to maintain the oil ratio between the polyurethane and linseed oil because polyurethane itself is an oil-based material so failing to balance the proportion will damage the texture and finish.

Reasons, why you can use polyurethane over linseed oil, is discussed below:

Protects against cracking and breaking:

Polyurethane itself works as a good finishing top coat over any varnish or element. So, applying polyurethane over linseed oil will protect the surface from cracking, breaking and make it more durable.

Polyurethane is dedicated to hardening the surface. It will extend the lifespan of the wood and provide a glossy look. 

Makes the surface waterproof:

One of the key specifications of polyurethane is, it makes the surface waterproof.

So, when you apply polyurethane over linseed oil as a finishing topcoat, it will make the surface waterproof as well as prevent the linseed oil texture to remain intact from water.  

Increases the lifespan:

When you apply polyurethane over linseed oil, it will generally increase the lifespan of the wood.

Generally, linseed oil will require refinishing after a year or so, but adding polyurethane over linseed oil will extend the time limit of refinishing and increase the lifespan of the wood.

Does linseed oil need to be sealed?

Linseed oil needs to be sealed to prevent moisture from accumulating on the surface. Since linseed contains natural essences that make it more eco-friendly, non-toxic, and odorless so it does not harm the environment.

However, many people who use to coat the wood do not care about sealing the linseed oil texture. When applying polyurethane over linseed oil, it works as a sealer by creating an extra layer of protection and hardening the surface.

Besides, it also makes the surface scratch-free. In addition to that, linseed oil gets damaged due to UV rays coming from sunlight, so keeping the linseed oil-coated wood in the open will damage the wood.

Using polyurethane over linseed oil will work as a sealer and block the UV ray. So, sealing the linseed oil to avoid moisture from accumulating and blocking the UV ray is recommended.

Can you clear coat over boiled linseed oil? What finish to use over boiled linseed oil? 

There are some noticeable advantages of applying a clear coat over boiled linseed oil. First of all, using clear varnish over linseed oil will prevent the oil fume to roll down from brushes to the floor and create a mess.

Besides, when you apply the clear coat to your furniture, just in case your furniture fabric gets stained, you don’t have to worry about taking so much hassle to clean them up. Simply rinsing off with water will do the job.

You can use any type of varnish you want to use over boiled linseed oil. You can use clear varnish, tung, or even Danish oil.

But the best is to use water-based polyurethane. Water-based polyurethane dries quicker, which enables you to save time and focus on more projects. Also, it is easy to apply and requires very minimal maintenance.

So, water-based polyurethane is the best choice to use over linseed oil.  

How to apply polyurethane over boiled linseed oil? 

Unlike the other topcoat finish where you can apply multiple coats of finish, you can apply not more than two coats of polyurethane-based topcoat finish over linseed oil to get the best results.

If you are satisfied with the color, texture, and gloss after the polyurethane has dried up, simply use a final varnish coat to seal the entire surface. This will not only extend the lifespan of the wood; it will also prevent it from water or dust.

The polyurethane layer will also help to prevent the UV ray from causing any damage to the linseed oil texture.

To apply polyurethane over linseed oil you will need some materials such as a brush, a paint sprayer, gloves, and mineral spirits. The procedure is shown below:

Sand the surface well:

Start your work by sanding the surface well. You must need to sand the surface as a part of the preparation. Use 320-grit sandpaper to sand the surface thoroughly.

Make sure to maintain proper direction, keep sanding towards the direction of the wood grain. Finally, clean the surface and let it dry in case it is wet.

Apply the polyurethane:

When applying polyurethane, try to reduce the density of the polyurethane by 10 percent by adding mineral spirit in it.

Thinned polyurethane will help the sprayer to flow the finish smoothly and in case you are using a brush, the strokes will be even. Apply a thin and even coat in the beginning. 

Wait for it to dry and repeat:

Once you are done, wait for the surface to dry and again repeat the process once. Water-based polyurethane takes 6 hours and oil-based polyurethane takes 24 hours to dry.

Final Thoughts 

You can use polyurethane over linseed oil. It will not cause any damage to the texture of the linseed oil. Rather it will prevent the ultraviolet ray from damaging the linseed oil. So, polyurethane will protect the linseed oil, harden the surface and give it an extra glow to your wooden surface.