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What About Caulk, Filler, Wood Putty, and Sealers? Everyone is Using Them.

Updated: 6 days ago

Man incorrectly caulking exterior siding.

A common question is what caulk, filler, putty, or epoxy products are compatible with the traditional linseed-oil based products.

The simple answer: no modern caulk or similar product is recommended. Modern petrochemical-based products designed to keep moisture out will lose flexibility, fail, and eventually trap moisture instead. This is the inherent incompatibility of the materials themselves.

There are alternative solutions and strategies.


This article attempts to address a few different scenarios and offer an alternative to modern petrochemical-based caulk, filler, putty, epoxy, sealer products.


First and foremost, based on the products we promote the concept of “sealing” surfaces is the exact opposite of what is needed. The goal is to allow moisture to move efficiently away from a structure and then for that structure to dry out.


All modern petrochemical-based caulk, filler, putty and sealer products will lose flexibility, crack, peel and fail, trapping moisture and causing damage and deterioration in the years to come. As the compound is exposed to the elements, small hairline cracks form that let moisture in but not easily back out again. A real recipe for disaster.



Wood Rot or Damage:


If old wood is punky and a little soft, it may be possible to save and revitalize it with Purified Linseed Oil and a natural, linseed oil-based coating. Clean and apply a coat or two of the Purified Linseed Oil as a first step. Then evaluate the condition before moving forward.


If the wood is decayed and rotten, it must be replaced. In such cases, we advocate replacing bad wood with good wood i.e. a Dutchman Repair vs. a caulk, filler, epoxy, or putty product.

This technique, hands down, will achieve the strongest and the longest lasting repair of any alternate method or product.


Ideally, a Dutchman repair would use the same or similar wood species (matching strength and density) of what you are replacing.

It will move at the same rate as the surrounding wood based on seasonal changes.

After the repair is complete, Linseed Oil Putty can be used in the seam and/or surrounding cracks in the wood. Dust with chalk or a fine pumice powder and paint immediately with Linseed Oil Paint (Ottosson brand, Viking brand).


This may seem like a difficult technique for a beginner, but most Dutchman repairs can be done with basic hand tools. Do not be intimidated. Try it.

If you have some more complicated profiles that you need to replace, a local woodworker/carpenter may be able to recreate it for you, avoiding the need to acquire certain power tools and expensive knife blades.


Historically, a Dutchman is a common technique used for wood window restoration – an excellent project to practice the skillset and gain experience.




Sealing Around Windows and Doors:


It is really best to leave seams open so they can dry out vs. "sealing."

Especially if proper drip edge/flashing assists in moving water efficiently away from openings.


We recommend the flashing extends slightly past the opening and surrounding trim to prevent excess moisture from traveling in the vertical/horizontal seam between siding and trim.


We do not want water to get behind the siding. Rain should efficiently run down the siding and away from the structure. So, addressing gaps where vertical trim and horizontal siding meet, as well as similar scenarios found around a structure, is a worthwhile endeavor


If you have a big gap between your siding and your window trim, for example, a wood fill technique (like a Dutchman) is much more effective than a caulk or filler product.

It will last longer and it will look so much better, visually taking a finish nicer than if you tried to paint or stain a filler product.


For both new and old siding, cut a wood piece the same thickness and profile as the siding to fit in the gap. Work to achieve a snug fit but not too tight. Secure with a nail or fastener. Sometimes a pressure fit will work but it may pop out as the wood seasonally contracts/expands.

Exterior wood glue may work but use sparingly. This is not an ideal application for using glue/adhesives.



Sealing Siding:


Don’t do it. Clapboards are designed to expand and contract.

Sealing the seams will trap moisture and rot your siding over time.

It may also create an environment for mold to grow behind the siding and penetrate further into the structure.



Knot holes or wood pecker damage:


If you have knots that have fallen out of siding or woodpecker damage, consider using various sized wooden dowels. Cut to the thickness of the siding for example and fit into the hole.

A little wood glue in this case may work well.

Once dry, carefully scrape away any dried glue and spot treat with your exterior finish.

This is a quick-fix for such a scenario.



Small Holes, Wood Checks, Seams, Cracks, etc.


An exterior Linseed Oil Putty like DANA Linseed Oil Putty can be used to fill small holes, cracks, checks, small seams, nail heads, etc.

Apply with a putty knife, dust with chalk if needed and paint immediately with undiluted Linseed Oil Paint (Ottosson brand, Viking brand).


If you have very small wood checks or excessive texture or cracking of the wood surface, it is possible to thin the DANA Linseed Oil Putty into a syrup-like consistency with the Viking Purified Linseed Oil. More oil, the thinner and more flow the putty will have.


Brush this into the wood cracks to fill, dust with chalk or fine pumice powder and paint immediately with undiluted Linseed Oil Paint.


This video on a Quick-Fix Window Repair shows a version of this technique.



More on Linseed Oil Putty


While DANA Linseed Oil Putty can be used for small holes, cracks, nail heads, etc. for exterior applications, it is not structural so not appropriate for large repairs.

Anything larger than ¼ inch, a Dutchman repair would be required.

Apply with a putty knife, dust with chalk or fine pumice powder if needed, and paint immediately with Linseed Oil Paint.


Linseed Oil Putty must be painted in order to be protected from the elements.

Paint immediately so the putty and paint dries that the same rate, otherwise premature failure is possible.



Pine Tar


The Authentic Pine Tar will not cover well on modern caulk or filler products and does not offer enough protection to the Linseed Oil Putty. A wood fill or Dutchman for a Pine Tar application will always visually look the best.


You could use the Linseed Oil Putty and spot paint those areas with a matching Linseed Oil Paint color if really needed.

If you decide to try to spot paint repairs or filler/putty alongside the Pine Tar finish, do so with care. Be tidy to try and avoid visual differences between the two finishes, as well as paint drips, splatter marks, etc.

Linseed Oil Paint will generally be more opaque in appearance in comparison to the Pine Tar.

We do not like to encourage mixing materials like this if it can be avoided.


Simplicity is often the best option.


“Use like-with-like” is an Earth and Flax mantra.

Email with additional questions.


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