How to Waterproof Cedar Lumber

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Things You'll Need

  • Sandpaper (50-60 grit)

  • Paint brush or roller

  • Water repellent preservative


Follow manufacturer's recommendations for selecting a compatible waterproofing and paint combination.


Use caution when working with cedar. Cedar splinters can be especially irritating.

Cedar has a number of characteristics that make it desirable for outdoor projects including decking, siding and construction. Cedar takes on a wide variety of colors, is low in pitch and resin, has a pleasing aroma, and resists decay and rotting. The aromatic compounds within cedar discourage most wood-damaging insects.

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The treatment of cedar with a waterproofing can prolong its life and enhance its appearance. Waterproofing material is most effective when applied to newly milled cedar.

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Step 1

Clean any dirt accumulated on the wood. If the cedar has a very smooth finish, scuff slightly with 50 grit sandpaper.

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If the cedar has been exposed to weather for more than two weeks after being cut, sand the surface and clean thoroughly before treating.

Step 2

Procure a wood waterproofing material. These are available at most home centers and hardware stores.

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Waterproofing treatment is available in clear or with various colored tints. Cedar will absorb a variety of tints quite well.

Step 3

Apply the waterproofing with a brush or roller, as per manufacturer's instructions. Backbrushing, a technique in which the dry brush is stroked in the opposite direction from which paint was applied, will even out the coat.

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If you are applying the waterproofing on installed cedar, pay close attention to treating horizontal surfaces where water can accumulate.

Step 4

Recoat with multiple coats. Cedar typically needs to be retreated every two years, but this can be extended with multiple waterproofing coats. For maximum lifetime, apply as many coats of waterproofing as the cedar will absorb.

If you plan to paint the cedar after waterproofing, do not treat with more than one coat.