WHEN IT RAINS, BOARDS CAN BEND
Some porch wood at risk of changing size, particularly when hit by moisture, precipitation
A how-to guru advises a reader on how to deal with boards that buckle on a wooden porch when it rains.
Q We live in a row house. Every time it rains, our porch floor grows a hump. The rest of the porch is in good condition. I tried using primer to seal the ends of the boards, to no avail. Any suggestions?
A Traditional porch flooring is made of boards that have a groove on one long edge and an oppositely shaped tongue on the other long edge, allowing the boards to interlock. The design is an ingenious solution to one of the immutable properties of solid wood: Even if boards are kiln-dried, the wood fibres will always shrink or swell, mostly in width, as moisture changes. If the wood becomes drier than it was when the porch was installed, the boards will shrink, but the tongues are still in the grooves, so you don’t see openings in the floor. And when the boards swell, the gaps between boards just close up a bit — assuming there are small gaps to accommodate this.
In your case, three boards are buckling upward as a way to accommodate their added width. The tongue-and-groove edges are still holding them together, though, almost as if they are tambours rounding a bend in the curve of a rolltop desk. Several things could be contributing to why these specific boards are buckling while others on your porch stay flat.
The boards might be flat-sawn, meaning they were made from pieces sliced from a log in a way that shows the annual growth rings in the tree before it was cut. If you were to view the end grain of flat-sawn pieces, you’d see lines resembling smiles or frowns, depending on the orientation. Flatgrain boards expand more across their width than boards cut so that the growth rings are mostly up and down.
Or there might be a moisture problem, such as a leaky gutter downspout or a faucet with a hose connection that sprays water. It’s also possible there was a past leak that caused the nails holding the buckling boards to rust, making them the weak links that lift when surrounding boards swell.
Although your porch appears to be nicely painted, at least some boards might not be painted or at least coated with primer on all six sides — top and bottom, both edges and ends. Primer and topcoat paint help wood shed liquid water, such as rain and any condensation that forms on the underside of porch boards.
So, how to fix the problem? One solution would be to pull up all the boards, ensure they are painted on all six sides, and reinstall them when humidity is high so you know the boards are at their maximum width.
But that’s a lot of work, and you risk splitting the wood when you pull it up. Given that most of the porch is fine, a more practical option is to give these three boards a safe way to expand without lifting up.
Note that there is just a single board between the nearby brick pillar and the three boards that are lifting. Try creating a gap between that board and the brick with an oscillating tool fitted with a saw blade. The Fein MultiMaster pioneered this category of tool almost 50 years ago, and the German manufacturer has continued to improve it. It’s great, but pricey — $277 for the tool, sanding pads and one blade at Home Depot. If you don’t expect to use this tool for other projects, you might want a lower-cost model from another brand. The Genesis Multi-Purpose Oscillating Tool, for example, is $42.78 at Amazon.ca. Use a saw blade that is rectangular or slightly triangular, not circular, and has a cutting edge about 1.5 to two inches long.
An oscillating tool is easy and fairly safe to use, but practise on a scrap first. Then cut along the board where it meets the brick, until you have a half inch or so wide gap. If the boards still lift the next time it rains, try making the gap a little wider.
To help secure the boards so they don’t lift, nail through them into the joists (the framing under the floor). Use galvanized-finish nails, which have small heads. Use a nail set with a hammer to pound the heads about one-eighth inch deep into the wood. Then plug the spaces over the nail heads with wood filler and paint over that to hide the nails.