If you are planning to use linseed oil on your exterior finish, you will need to know how to apply it carefully so that you don't end up with a greasy mess. Linseed oil is a great staining liquid, providing a notable penetrating varnish to both internal hardwood floors and external wood finishing, and rather than acting like polyurethane and leaving a residue, linseed oil coats the wood naturally. Since the oil does not cover the wood in a tar-like way or places a gloss over the surface, you can use linseed oil to enhance the wood you are staining.
Step 1 - Sand the Wood
Before applying the layer of linseed oil you need to properly prepare the wood on which it will be brushed. If you have constructed the wood recently you can simply sand over it with a medium-grain paper, but if you have had the wood for a while and it has been previously painted, it might be worth using a delta sander to get rid of any previous paints or stains before you proceed. Once you have finished sanding down the wood, give it a light brushing with a clean cloth before you start using the oil.
Step 2 - Making the Oil
In order to get the right consistency for your staining, you will need to make a mix of the linseed oil with the turpentine. It is a good idea to boil the linseed briefly before you add it to the system, otherwise it can have trouble being applied to the side of the wood. Place four parts of your linseed oil to one parts of turpentine, and then boil it.
WARNING: Open all of the windows and doors before you start to boil this mixture, and use a gas mask as the vapors from the linseed and turps mix can pose a serious health risk.
Step 3 - Add the Oil
Once you have boiled the mixture for a few minutes, take the pan to where you will be adding the linseed oil. Using your brush, apply the linseed oil and turps to the wood. Use one thin layer at first, and then allow it to soak into the wood. Leave for about 30 minutes, and then wipe down any excess liquid using the sponge. Cover with a piece of aluminum foil and leave it to dry for at least two days.
WARNING: Linseed oil is highly flammable and its drying process releases heat. Store linseed oil only in metal containers, and keep the drying furniture away from any heat sources. Keep any rags or papers you use to apply the oil in a metal container filled with water.
Step 4 - Add a Second Coat
Once the 48 hours have elapsed, return and apply another coat. You should then wipe down the surface and allow the second coat to dry overnight. You will have to make sure that the first coat is fully dry before you proceed, and that there is no moisture on the surface of the second coat before you cover it over with the foil and leave it again.
Step 5 - Add the Final Coat
You can then begin to add a final coat. This should be applied to give a final shine to the wood.
TIP: Applying linseed oil too thickly or before the previous coat has finished drying makes it harder to dry. If you're unsure what to do, opt for a thinner final coat.