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I'm caulking a number of vertical fillet joints. I haven't used foam backer rod because (since the joint is vertical) it won't stay while I caulk. Bond breaker tape has been annoying to place evenly over both sides of the length of the joint.

Can anyone suggest an alternative? I was thinking of using a stick of wax and just running it along the joint.

  • A finger or a joint smoother (sold for filleting caulk joints) run just behind the caulk tip (done concurrently will keep it from falling off) and pushing the caulk in. For rough wood, you'll need a leather glove to prevent splinters – HerrBag Jan 25 '15 at 19:40
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Backer rod should be compressed in a joint. If it doesn't stay in the joint on it's own, then you need to get a wider piece. They come in varying diameters and you should choose one slightly wider than your gap.

  • @HerrBag I guess I was doing it wrong, but I'm still not sure that will work. This is for wood siding on a an old house, where the siding meets the vertical molding at corners. It looks like a little like this. The gaps average about 1/8" (some bigger, some smaller). The smallest backer rod I've seen is 1/4". That won't fit in some places. – StepByStep Jan 24 '15 at 3:29
  • @WebUser, you won't need backer rod in gaps that small. You might need it in a 1/4" gap, no smaller. Cut the tip of the caulk tube the same size as the gap to fill, it makes the job cleaner. I don't know what bond breaker tape is, but in cases I needed to mask a caulk joint, I used blue painters tape. In some cases, like on brick I have used duct tape. It is contrary, but better than messing up the brick. – Jack Jan 24 '15 at 7:47
  • I just seen the picture of the bond breaker tape. I can say I have never seen it used in all my days. – Jack Jan 24 '15 at 7:48
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Use a bond breaker/lumber crayon if possible. This will be easy to apply and still prevent that 3 sided adhesion.

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