Garage cracked joist repair


Old 11-28-10, 01:59 PM
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Garage cracked joist repair

I noticed that one of my garage 2 x 6 joists has cracked all the way through. The crack occured right where a knot is. I was thinking I should just sister sandwich a couple of pieces on each side of it. Not sure if I should use 1" plywood strips or 2 x 6 treated lumber and /or if i should glue it all together in addition to some wood screws. The garage was built about 40 years ago. I remember a lecture from my old high school woodshop teacher where you had to be careful about glueing wood of different species, grain, age, etc, or you could induce splitting. I should be able to reposition the cracked piece ok. What's the recommended sister material of choice here and should I use glue? what kind, carpenter's glue or liquid nails? I'm leaning towards the plywood since that should be strong and stable. Thanks!
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Old 11-28-10, 03:25 PM
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Is this a ceiling joist?

You should sister a joist the entire length. Use liquid nails and through bolt the joists together.
Old 11-28-10, 03:48 PM
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And plywood would be the best choice. Treated lumber is about the most unstable thing in the world. Most of it is filled with knots and cracks as well.

I agree it would be best to go whole length, but if it hasn't sagged (or if you can get it right), then the sistering should make it better than new.

And though I'm sure drooplug knows better than I, I'd probably PL adhesive it, clamp in place and use deck screws. Once the adhesive sets, it's not going anywhere. Just seems like through bolting 2x6 might be overkill...if there is such a
Old 11-29-10, 04:04 AM
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Just a "jump in" to make things more complicated for you. I would take the advice of both drooplug and Vic. Use a plywood strip AND a full length 2x6, all PL400 or 375 together and use 5" carriage bolts through the whole sandwich in at least 16" intervals, scattered up and down the sister, sort of offset, if you will. As Vic says, most all dimension lumber will have knots and weak points in it. The plywood gusset will add substantial strength.

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