Leaks in oak barrels unfortunately happen once in a while. Wood, being a natural material, can have spots in the grain where liquids try to escape.
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At the cooperage, we pressure check each barrel to check for leaks, prior to sanding the barrel and preparing it for shipment. In the video below, Master Cooper Douglas Rennie shows how the coopers inspect the barrel. And then in the case of leaks being present, how the coopers repair them.
Douglas explains: we begin with two gallons of 140 degree water (°F) and then a test bung. The bung has a one-way valve on the inside, which opens and then allows air pressure in. It closes when the air pressure is removed, trapping air and water inside the barrel.
The pressurized air will force the water through any potential weak spots in the barrel.
Douglas begins by checking around the head and the ends of the staves for any leaks. He then checks the body of the barrel, finding eventually a leak on the chime—the ridge or the end of the barrel.
First, he scrapes away the leaking water, using a scraper, which will allow him to see the exact point at which the water is being forced through the wood.
He then uses the pick and the hammer. With the pick, he punches a hole where the water is coming through. Next he takes the pick out and fills the hole with a wooden spile.
Essential tools: Wood chisel, Small chisel, Hammer, Sandpaper, Spiles, Wedges
Douglas hammers the edge of the spile off and inserts the spile into the wood at an angle. He hammers it in to the hole. He explains that he listens for the barrel sound that tells him it is all the way in prior to trimming off the spile with the wood chisel – first one side, then the other.
Then comes the sandpaper, which he uses to smooth over the wood. Douglas explains that wherever we scrape wood, we open the pores. He uses the sandpaper to close the pores on the edges of the stave.
He then checks the barrel again for leaks, because now the pressure is wont to find another weak spot.
After he finds a grain leak on the barrel head, Douglas explains that will take a completely different fix than the earlier chime leak. He scrapes the wood—when the movement is smooth, going with the grain, and then the movement is rough, going against the grain.
To fix this particular type of leak, Douglas has to go with the direction of the grain. He moves the chisel to 1/2 an inch above the leak and hammers the chisel in until it will not go any further. He then checks that the wooden wedge is a little bit wider than the chisel. If they were the same length, it would leak on either side.
He also notes that when inserting the wedge, you will always go across the grain and never lengthwise with the grain, otherwise the stave would split all the way up the headpiece.
Next Douglas hammers in the wedge and then trims the excess wood with the chisel, cutting from both sides. He hammers the middle part of the wedge further in before trimming off excess wood and then scraping the wood. He finishes by closing the wood pores with sandpaper.
Lastly he inspects the barrel one last time for leaks, before releasing the air pressure and letting the water drain.