How to Apply Boiled Linseed Oil Properly -Tips & Techniques

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Boiled linseed oil provides a lustrous finish to any wood project. It is a full-proof system that any level of finisher can do without fear of failure! While there’s a slight learning curve rest assured its pretty hard to mess this process up.

Pure linseed oil is extremely thick and very slow to dry. Boiled linseed oil (BLO) has chemical driers and thinners added to enhance the application and drying processes. BLO provides a rich oil finish that adds character, depth and beauty to virtually any wood surface. BLO has a definite place in a woodworker’s arsenal.

flax-plant-flower-seed-and-oil

BLO has been around for a long time and is a favorite of many woodworkers and wood finishers. It is a product of flax-seed. A plant renowned for its health benefits and floral beauty. Raw linseed oil is a eco-friendly, green product. Boiled linseed oil is not.

Unfortunately, raw linseed oil is not workable in its natural state due mostly to its heavy viscosity and extended drying times. Once applied it can remain “sticky” for years.

Linseed products suitable for wood finishing on the market today are sold as “Boiled Linseed Oil” or “Purified Linseed Oil”. Originally linseed oil was boiled in a vacuum to remove molecules of oxygen and breakdown its food components, principally fatty acids. This process accomplished a few things: it enhanced drying time; reduced stickiness; and it helped reduce the tendency of the oil to turn rancid.

Today the term boiled linseed oil is in many cases is a slight misnomer and in other cases a total misnomer. Most BLO products sold today as boiled linseed oil are no longer boiled but are instead replaced with chemicals that increase drying time, thin the oil to a workable state and impair rancidity. Because of this it is no longer a green product nor is it classified as a food-safe product.

There is a new system (actually a very old process re-introduced) of refining raw linseed oil. The product is most frequently label “Purified Linseed Oil”. Producers of PLO have reverted back to simply boiling the oil in modern pressurized cooking pots and market it without chemical additives. Purified linseed oil is green and food-safe.

natural-oil-finish-on-a-wooden-bedside-table

There are a number of advantages BLO and PLO over pure Tung oil. While all three are known for adding character and depth to wood there are some strong advantages to Linseed Oil. BLO is faster drying, easier to apply, requires fewer coats and costs less. Unfortunately I cannot comment on PLO as I have never personally used it. (I am open to product information and product donations for experimentation and review).

The downside to BLO is the tendency to yellow with age, the possibility it can turn rancid, the fact that it will mildew if used in damp environments (typically outdoor use) and is not food-safe. Linseed oil offers “water protection”. It is a natural water repellent. There is an ongoing debate it may or may not be waterproof.

That said for the right application, in the right environment, the advantages of linseed oil far  outweigh any disadvantages.

Applying Boiled Linseed Oil – What You’ll Need to Get Started

For New Wood – 2 Grades of Sand Paper (120 – 180 – 220 – 320 – 400)
Old Wood or Damaged Surfaces –  Sandpaper (80-120-180 – 220 – 320 – 400) and a mechanical
sander
Tack Cloth
Between Coats – 400 grit paper or #0000 steel wool or grey scotch brite pad
Applicator (choose one)– Cotton Rag or Stiff Natural Bristle Brush
Boiled Linseed Oil
Suitable mixing container with a lid for air tight storage between coats
Clean rag for wiping excess

Applying Boiled Linseed Oil – Properly

Proper BLO Application and Surface Preparation

When oiling wood the surface should be first finish sanded to anywhere from 320 to 400 grit sandpaper. Surface coatings (polyurethane, lacquer, shellac) hide 180 grit sandpaper scratches whereas oil will accentuate them. So when oiling wood a finer finish sanding is highly recommended.

Raising Woods Grain – A necessary Step for a Fine Finish

Think of prepping wood for finishing like getting a haircut. The first wash after your barber visit results in a whole bunch of split ends that suddenly pop. Well, wood fibers are a lot like hair strands. After all the sawing, gluing, planning and sanding many of the wood fibers are damaged and torn. Adding moisture (like shampooing your hair) pops those broken strands and they need to be removed for a really nice finish.

For that better finish the grain should be intentionally raised before staining or finishing. I always wet my woods after my 180 grit sanding (for a complete sanding explanation see my YouTube videos Sanding Efficiently <for beginners>, and Choosing the Right Grade Sandpaper for Your Woodworking Project <for all levels>). Wetting the wood raises its grain (kinda like split-ends in hair) which can be sanded down with the last or next sanding of 180 or 220 grit papers.

Raising the Grain entails wetting the wood’s surface, letting it dry and then re-sanding to knock down raised wood fibers. You can use a spray bottle or a wet rag to moisten (not soak) the surface. Let it dry and then come back and sand or re-sand with a 220 grit sandpaper (if you are staining or applying a surface coating use 180 grit to level the grain).

TIP: First time with BLO? It’s always best to get the feel of any procedure by practicing in an unnoticeable area on your project like the bottom of a table, the back of a dresser, the inside of a cabinet, etc. I’ve done thousands of projects over the last 30 plus years and “ALWAYS” follow this rule on every one of them.

BLO can be applied with a soft clean rag, a piece of #0000 steel wool or a grey scotch brite pad. It can be applied to by pouring directly from the can to an applicator but you will have better control and less waste by pouring a small amount in a bowl and dipping the applicator.

Start with the hardest to reach spots first to avoid contact later in the application. Apply in circular motions across the grain of the wood. The object of the first coat is to saturate the wood as deeply as possible.

Apply a generous but controllable amount of boiled linseed oil to your applicator especially for the initial few coats. The surface should look very, very wet but not puddled. Older and reclaimed woods will suck it up like a camel drinking water in the dessert. All areas should look wet but if any areas have standing puddles spread them out or wipe them off.

On the flip side if your wood sucks in your application, reapply again and again keeping the surface wet (but not puddled) with oil for the next 30 minutes. After 30 minutes your wood should be saturated with oil and any excess wiped off.

Watch for the next couple hours and if any excess oil has bubbled to the surface wipe it off. At this point allow to dry overnight before applying the next coat.

Re-application Timing – Subsequent Coats of Boiled Linseed Oil

Wait time is based on how quickly the surface dries. This is a factor based on temperature, humidity and thickness of the coat. In most cases overnight dry is sufficient. However if the next day the surface is still tacky allow more time. The surface should feel dry and somewhat slippery to touch before re-coating.

Boiled Linseed Oil Re-coating – Sanding Between Coats

When the surface is no longer tacky to touch you are ready to do a very lite sanding following the direction of the grain (operative word is lite as we don’t want to cut through the very thin layer we just put down previously). Use either a 400-600 grit sandpaper, a #0000 grade steel wool, or a grey scotch brite pad (grey pads are rated 400-600 grit).

Follow this method for the next coat. Typically you would lay down three coats.

Applying Boiled Linseed Oil – The Final Coat

The only difference in this coat is you don’t sand after the final coat. I allow it to cure and then depending on the look I am looking for I might apply a coat of paste wax. Paste wax on wood is just like paste wax on your car. It offers minimal protection but adds depth and smoothness to your wood project.

TIP: Avoid waxes with silicone additives. Silicone (like WD-40) adds a slippery texture that feels nice to the touch but fouls refinishing coatings and becomes an absolute bear to remove should you ever decide to touch-up or refinish your project.

Boiled Linseed Oil – Repair

You won’t believe how easy this is. Clean the damaged area, apply BLO undiluted to a soft cotton cloth and wipe it on. If it soaks it up quickly apply a little more and repeat until the wetness lasts for 15-20 minutes. After 20 minutes, with a little elbow grease, rub the BLO into the damaged area for a few minutes. Wipe any excess and you’re done.

Boiled Linseed Oil – Rag Disposal

Oily rags are volatile and should be hung to air dry. Rags have been known to spontaneously combust when balled up in a refuge container.

Boiled Linseed Oil – Dry vs Hardening

Boiled linseed oil dries in a few days and can be put in moderate service. Boiled linseed oil does not fully cure or harden (dry all the way through) for 30-45 days. It’s okay to put your project in service once dry but you should refrain from heavy use until hardened.

Tags:applicationchina oilhow to applyoil finishsurface preparationthinning tung oiltung oilwood finishwood oil

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