DIY Arbor Swing: How to Seal Wood Posts

We’re sharing step by step as we build a DIY arbor swing in a beautiful backyard! This is Step 1: how to seal wood posts with liquid rubber coating before setting them in the ground footings.

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Sealing Wood Posts for an Outdoor Arbor Swing

This arbor swing is in an area where it will get a fair amount of sun and also a fair amount of water (from precipitation and from the yard sprinklers) so we wanted to make sure that these 8×8 cedar posts are going to withstand the weather and last for years to come. Our first step to making these posts weather-resistant is sealing the posts where they will be below-grade (below ground level).

As you can see in the video, we chose to use FlexSeal liquid rubber coating on the posts. This rubber sealant is ONLY applied to the portion of the post that will be set in the ground and slightly above the ground (above grade), to ensure that the footing stays secure and the post doesn’t rot prematurely due to ground contact, moisture, or bugs. I calculated the hole depth and applied the sealant so that it would cover the post below grade and the entire section of the post that will be set in the concrete footings.

Later in the process, I’ll show you how I sand and seal the wood’s surface above ground to ensure that the natural wood shines and is durable against the exposure to direct sunlight and weather. Sealing above-ground exterior wood extends longevity and helps prevent warping. This rubber coating step is to protect the below ground wood from the moisture which can cause mold and mildew to rot the post below the surface.

How to Seal Wood Posts with Rubber Coating

The rubber sealant can be applied with a paint roller, like we did, or by using a paintbrush – or you can also dip the material or pour the coating right on the surface, depending on the need and the manufacturer instructions. Clean and sand the post surface with a medium grit sandpaper, and use a brush or tack cloth to remove any residual dust or grit. Then, apply the wood sealer rubber coating, and then let the coating dry to cure for 48 hours, typically, as recommended by the manufacturer.

Why to Seal Below-Grade Wood Posts

Rubber-sealing wood posts that will be installed below grade will help them last longer. We love building with redwood and cedar posts since they are naturally rot resistant and beautiful, but any type of wood below ground level, treated or untreated, is more prone to decay over time. Apply sealant helps ensure that the posts stay secure in the footing and don’t degrade from the moisture in the concrete footing and in the ground surrounding the footings. Even pressure treated lumber will benefit from the extra step.

Stay tuned and subscribe to see how we set the footings for the swing arbor, stain the posts, and more – right up until the finished project reveal!

FAQs about Outdoor Wood Posts

Where can I find FlexSeal or similar liquid rubber coating for protecting in-ground posts?

You can find FlexSeal liquid rubber coating at Home Depot, Ace Hardware, or even at your local Walmart. It comes in black, white, gray, and clear finishes to fit the project you’re working on.

FlexSeal and similar rubber sealant products are typically used for sealing concrete foundations or for sealing roofs, so be sure to check the label for suitability for use as a below-grade sealant for wood. Some similar products to consider:

If you like the look of it, you can even use it to seal outdoor wood furniture or other exterior wood. The rubber coating will obviously cover up the wood’s grain (as opposed to a traditional oil- or water-based polyurethane stain, lacquer, shellac, or natural oil like linseed oil, tung oil, or danish oil) but it can be an option depending on your needs.

What size posts should I use for an arbor swing?

We used 8×8 cedar posts for this arbor, and for any 2-post arbor to support the weight and movement of the swing, I wouldn’t use anything smaller than 8×8 (with secure, appropriate depth footings).

Finding a post that large typically requires visiting a local lumber mill or lumber supply store. Big box stores like Home Depot, Lowe’s, Menards, or Sutherlands may have posts in stock depending on the local market, but visiting a local lumber yard will typically give you better options and a higher quality lumber.

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How And Why To Rubber Seal Wood Posts For Outdoor Use Prior To Setting In Footings, Remodelaholic
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I am the husband of the amazing Cassity of Remodelaholic. I love to problem solve and to design and build things inside and outside the house to make life better. I am a professional Landscape Architect by trade and love the outdoors.

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Lorene has been behind the scenes here at Remodelaholic for more than a decade! She believes that planning projects and actually completing them are two different hobbies, but that doesn't stop her from planning at least a dozen projects at any given time. She spends her free time creating memories with her husband and 5 kids, traveling as far as she can afford, and partaking of books in any form available.

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