Sealing Wood End Grain

By Robert Robillard on Workshop tips

Window sill replacement

On decks or porches you can seal all rip cuts as they are installed and seal the end grain after the decking in in place.

Painting Wood End Grain

The end cuts in siding, deck boards and trim all need to be sealed at installation. 

The biggest reason for sealing wood end grain is because the wood end grain is exposed on an end cut and it absorbs liquids up to 250 times more rapidly than other wood surfaces.

Why Sealing End Grain Is Important

Grab a bunch of straws and hold them together – that is how I envision wood end grain.  These tiny straws wick up moisture over time from rain, snow and roof splash off.

The days of old growth lumber, “bullet proof”  lead paint, and leaky breathable house walls are gone.  All of these things help prevent or slow wood rot.

Today’s wood is different and not as insect and rot resistant, the paint is not nearly as durable and houses are constructed so tight that sidewall moisture problems are prevalent.

By sealing and back priming all wood trim or decking you are giving the trim or decking a better chance to endure the elements by slowing water infiltration.

Wood trim often rots due to improper installation methods, and from not priming or painting the end grain.  Trim wood exposed to the elements soak up water which start the rotting process.

Wood trim should be installed:

  • Decoupled from the masonry with flashing or an air gap
  • Installed with an air gap spaced off  a roof, masonry or the ground

Wood trim and decking should:

  • Siding should have proper joint flashing
  • Decking should have adequate spacing for drainage and air flow
  • All wood sealed on all six sides

Seal End Grain At Installation

Priming and sealing end grain during the wood siding, deck or trim installation can be easily accomplished and does little to slow down a job.   All it takes is a little can of paint or sealer.
Spray cans or primer or disposable cans and brushes with primer can be used to prime the end grain once installed.
Most of our exterior wood siding and trim comes pre-primed or finished with at least one coat from the factory so all we have to be concerned with is end grain.
 On our deck installations we seal all six sides but start by sealing only  the top, bottom and edges.  We do this on saw horses prior to the decking installation.   We seal the end grain after the deck boards are cut to final size or after the deck boards are fastened, if accessible.
On decks or porches you can often seal all rip cuts after they are installed.  Many times the carpenters will run the boards long and cut them in place –  sealing the end grain can then be done with the decking in in place.

A Better Product Lasts Longer

Best practices dictate sealing wood end grain – it doesn’t add on much time, just like adding strips of building paper behind the joints ad results in a better quality, longer lasting installation. 

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About the author

Robert Robillard

Carpenter / Remodeler / Editor

Rob Robillard is “The Concord Carpenter” Rob is a builder, general contractor, carpenter, woodworker, and editor of Concord Carpenter and ToolBoxBuzz As a General Contractor and carpenter, Rob owns and operates Concord Carpenter LLC. A full-service remodeling and construction company. Rob is a recognized leader in home building best practices and a source for how-to information for building professionals. On this website, Rob covers all aspects of home construction, building science, home improvement, woodworking, remodeling, and some of the best product and tool reviews. Rob is in charge of our Tool and Product Review series - Concord Carpenter Videos where we post all of our tool reviews and video tutorials. Rob approaches remodeling and building construction with a pragmatic and problem-solving approach. He enjoys using his knowledge and experience to help and educate building professionals as well as DIYers on best practices in the construction and remodeling industry. He's a strong advocate for "raising the bar" in the construction trades and promoting the trades to youth. #BeAMentor #Green2Great Craftsmanship, quality, and pride guide his journey on this channel The Concord Carpenter's motto: "Well done is better than well said!" : Read more about Rob

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