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Old 07-23-2016, 01:20 AM   #1
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How much torque to use on deck bolts?


I have a deck extension that uses 1/2" and 5/8" carriage bolts. I recently discovered the nuts were loose, almost all of them. I'm sure I re-tightened them a few years ago after the wood dried but since then the wood must have shrunk? The wood is southern yellow pine pressure-treated from home depot.

I used a torque wrench where I could this time and attempted to retighten. Where I couldn't use the torque wrench I guesstimated at very tight and I'll assume it was about 10-15 ft-lbs. The wood is so soft that anything past 10 ft-lbs caused the washers to sink into the wood. In the cases where the carriage bolt head was directly on the wood there was also sinking. To remedy that on the 1/2" bolts I used the 5/8" washers to provide greater surface. That is how I got to 15 ft-lbs on all of them without significant sinking.

So my quesion is, how much torque should I use and is 10-15 ft-lbs acceptable? Most torque spec charts I read have high numbers from 40 ft-lbs all the way up to 120 ft-lbs. Does that apply to decks? I don't think I can get to even 20 ft-lbs without a lot of sinking.
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Old 07-23-2016, 05:57 AM   #2
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Re: How much torque to use on deck bolts?


To prevent crushing and sinking in the wood, use FENDER WASHERS.

As for torque, I recommend German specs, I. E. Guttentight.


ED
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Old 07-23-2016, 07:47 AM   #3
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Re: How much torque to use on deck bolts?


it depends on how the deck was constructed.
if it was built correctly, they only need to be tight = finger tight and 1ish turns.
if it was not built correctly = tighten em till they go into the wood a little.
washers are a MUST either way.
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Old 07-23-2016, 10:53 AM   #4
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Re: How much torque to use on deck bolts?


general rule of thumb is that the wood should slightly compress under the torque.. no more no less
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Old 07-23-2016, 09:09 PM   #5
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Re: How much torque to use on deck bolts?


Wood compresses slightly, use LOCK washers. Ron
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Old 07-23-2016, 09:28 PM   #6
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Re: How much torque to use on deck bolts?


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Originally Posted by ront02769 View Post
Wood compresses slightly, use LOCK washers. Ron
Lock washers won't work, they need a solid surface to grip on, when the wood compresses it will release the lock.

Use ny-lock nuts instead.
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Old 07-24-2016, 12:19 AM   #7
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Re: How much torque to use on deck bolts?


Ok I will leave them as is. Concerning fender washers (also dock washers) I can't find any hot-dipped galvanized for 1/2 and 5/8 that are reasonably priced. Also nylock I can't find hot-dipped galvanized, and I would imagine if I could it would be expensive.
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Old 07-24-2016, 09:22 AM   #8
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Re: How much torque to use on deck bolts?


I would have thought there is no such chart. Lumber, esp the pt lumber used for decks, comes with too many variables to have a torque numbers. What I know is 15 lb/ft would be about finger tight on cars. Not good enough on lumber, maybe even on cars.
I would not use carriage bolts anyway. May look good, but it doesn't accept a washer and always crushed way too deep into the lumber. I use hex bolts, biggest washer for 1/2 or 5/8, and always have smaller washers if bigger washer is too loose for the head or the nut. There are different number washers - called for car parts - that are thicker.
Wet lumber would be crushed easily. So I tighten until I see the washer bend or sink slightly into the lumber. 6 months or a year later, tighten again using about the same pressure. It is ok to see the lumber crush a bit. If you want absolutely clean look, the framing lumber should be covered with finish panels.
Any framing is putting parts into a whole. Loose bolts does not necessarily mean the whole thing is compromised. Racking or such should not depend on the bolts anyway.
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Old 07-24-2016, 11:26 PM   #9
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Re: How much torque to use on deck bolts?


Thanks. I went back today and tested them and they all measured less torque than the 15 ft-lbs. Southern Yellow Pine is a softwood so I imagine there was some slackening or compression overnight. In an experiment reproducible on a number of bolts a 1/4 turn past finger tight was equal to approximately 160 in-lbs or about 13 ft-lbs. That is what I torqued all the 1/2 bolts to. The 5/8 bolts I left at 15 ft-lbs.
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Old 07-25-2016, 08:16 PM   #10
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Re: How much torque to use on deck bolts?


Quote:
Originally Posted by de-nagorg View Post
Lock washers won't work, they need a solid surface to grip on, when the wood compresses it will release the lock.

Use ny-lock nuts instead.
My bad, left out fender washer first, then lock washer, then nut. Has been working well for me for like 40 years or so. Ron
Y
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Old 07-30-2016, 11:52 AM   #11
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Re: How much torque to use on deck bolts?


I have never heard of anyone torquing wood lags/bolts. Not that they shouldn't perhaps but seems like way too many variables with wood to make it worth it IMO.
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Old 07-30-2016, 12:42 PM   #12
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Re: How much torque to use on deck bolts?


Agree with bob22, I have never heard of use of torque tables with bolts on wood. More common is tightening until the washer depresses the wood a little bit.

As the OPS has observed, PT lumber is often sold wet, and it will dry out over the course of several seasons. The result is that bolts initially installed tight will loosen, and should be retightened periodically. I never use carriage bolts on decks, as others have mentioned, it is hard to get a washer to work, the head pushes too deeply into the wood, and if you ever need to remove them and the nut is frozen onto the threads, it can be a struggle. Hot dipped galvanized bolts with washers and nuts works fine, and can be tightened easily by simultaneously using a wrench and a socket on either end.
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Old 07-31-2016, 09:11 AM   #13
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Re: How much torque to use on deck bolts?


Haven't seen this posted as an alternative. I've been using ThruLOK structural wood screws from FastenMaster. Can be driven with an 18v impact and require no predrilling. They're only a couple bucks apiece and the time savings is huge. My local inspectors accept them but check with your AHJ.
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