Cedar wood is ideal for many outdoor projects because it contains natural oils that protect against insect infestation and rot. Along with this natural resistance, cedar is very durable. Even though cedar is a softwood, it is 80-percent as strong as oak, a notable hardwood. However, despite its natural benefits, cedar shakes used for roofing can eventually succumb to mould and mildew damage as the wood repeatedly comes in contact with rain and snow. Luckily, there are methods available for waterproofing cedar shakes, further extending the life and durability of your cedar roof.
Sand the shakes using 100-grit sandpaper and an electric sander; this will smooth out the surface and prepare it for waterproofing. To ensure full water protection, you’ll want to prepare all sides of each shake. Sand even the backside of each wooden piece. If your shakes have already been installed, then you can still sand and seal the outward facing side of the shake, but keep in mind that waterproofing only one side will not offer as much protection.
Rinse off the shakes by running them under a running faucet or a garden hose. The water will help remove excess sanding dust. Do not use a power washer on the shakes; roofing shakes are often thin and they could crack from a high-pressure burst of water.
Wait at least 24 hours for the shakes to dry. Even if the shakes appear dry beforehand, it’s best to wait a full day to ensure that there isn’t any moisture trapped in the wood’s natural grooves and knots.
Apply a coat of general-purpose water-repellent wood sealant to one side of the shakes. Most general wood sealants contain synthetic resin, but a few brands are fortified with epoxy; either variety of wood sealant will work as long as it is labelled “water repellent.” You can use either a foam brush or a regular bristled paintbrush to apply the sealant.
Wait one hour, and then apply a second coat. For most cedar items, one coat works fine, but cedar shakes come in regular contact with moisture, so an extra coat is ideal for the best protection possible. Avoid touching the first coat, since it will still be slightly tacky.
Wait at least 12 hours for the second coat to dry, and then turn over the wood pieces and apply sealant to the back of the cedar shakes.
Apply a second coat to the back of the shakes after one hour.
Allow at least 48 hours for the water-repellent sealant to dry before you attach the shakes to your roof.
The waterproofing effect of sealing your shakes is not permanent. The Western Red Cedar Lumber Association indicates that a coat of water repellent sealant will only last for one to two years. Make sure to apply a fresh coat of sealant to your shakes every 12 months.