This is a spin off from an other topic. I was wondering what size blocking folks are using? 4x4's, 6x6s' or 8x8's, maybe a combination. What species of wood, hard, soft, pine, spruce, cedar? Hard wood seems a bit heavy to handle in vast amounts, or is it required in some sitituations? How about lengths? Durability, if it sits around will it rot? I know it does, what can be done to help slow it down? Tim

I think I saw a power point presentation at a guild conference once about restoration work and the subject of cribbing was discussed.
The presenters' company used 6x7 blocks and I think they were 4' long but I'm not totally sure. They could be 3' long.
The reason the used 6x7's is that they would stack them with the 7" being the tall dimension to create a cribbing stack, as shown in the photo below:



Then if they needed to jack some point up to level, repair, or restore the frame, they would slide some pieces into the standard cribbing stack with the 6" dimension up. And with the 7" space between layers this was easy to do.
They would gang several 6" thick pieces together to get a "platform" to place a screw jack, or bottle jack onto and then raise the intended timber for the repair.

Something like this:



In the above drawing you can see the two 6x7 on their sides to make a jack platform between the layers.
And the jack is shown on top.

Using a jack in this fashion if the jack fails then the frame can only settle to the top of the cribbing stack. And you can jack up the frame in short steps, that is a little at a time.

Hope this helps.

Jim Rogers

Nice post Jim,

And the photos help explain things. I can see how the use of the 6x7 timbers is quite effective to be able to slide in a jack platform, etc. But unless you have access to a mill (like yourself) getting these "odd sized" cribs would be a challenge. Not to mention expensive... standard sized cribs are probably easier to get. All you'd have to do is get a few smaller ones for a jacking platform or insert layers of planking.



As to Tim's question about crib rot,

It didn't take me long to realize that most timber restorations (at least that I've seen) shun pressure treated stock. One guy I asked this to who specializes in only restorations said "there's no strength to it... it's just pine."

But I think most PT is southern yellow pine, which is plenty strong--much stronger than white pine-- Anyway, he chooses larch (tamarack) for ground- contact replacement timber. (he found a steady supplier for this somewhere). Maybe this would be a good choice for cribbing?

I like choosing something other than PT simply for the aesthetics. It aint traditional, you know... but PT would make good cribbing!

What about cedar? I used to be able to get eastern white 6x6 "cut-offs" random legnths from a fencing company--- post ends. They actually had stuff 2-3' long most times.

Linseed oil has always been a tried-and-true preservative, too.

About the cribbing sizes, it really depends on the timber framer. If he has a regular supplier of timbers then this supplier has probably made him many different sized timbers before. It is not that unusual to have 5x9 or 4x7's or other none traditional sizes in a timber frame stock list.
And to make a sale, these days, I'm sure a mill would make some 6x8's and cut off an inch of 1x6 and keep for themselves to make up an order of 6x7's.

I have made some cribbing before for jacking up a camp and sold this cribbing twice. Once to the customer; and after he was done with this I helped him sell it to another customer who does timber framing restoration work. It was white pine.

Some companies like hemlock for cribbing as it is very rot resistant as well.

I have made cribbing out of oak for highway bridge repair companies, many times. That stuff is heavy....

I could see having a mix of wood, hard and soft. It looks like 6x7 x a crisp 4' is the way to go, and gobs of it. Tim

Here's a couple pics. (one was posted earlier) One shot is of a good sized crib tower. Only part of the tower is shown. The barn has a basement and the tower went clear to the cellar, probably a 30-foot tower at least... i.e., lots of cribbing!


A rafter snapped:






And here is how they re-supported the purlins:






Can someone chime in and share their thoughts on using pressure treated timber in restorations. And it seems like a good choice for cribs, but you hardly ever see it used.

???

I walked into a 1765 barn that had been restored with 8x8 PT sills and repaired post bottoms. The flourescent green of the PT was so distracing I forgot to look up at the frame. It was disgusting, and sacreligious, in my opinion. If that's all you've got, that's one thing, but there are many alternatives, and they don't have fastener issues. I'm not a fan of 2-3 growth rings to the inch, but then I'm biased, I saw a lot of black locust.


Dave

I think Dave and Derek just about covered pt. If I have to use it on a job I leave the scrap for the client/owner for their future use. I wish black locust was more plentiful around here, some yard trees once and a great while, never straight or long enough.

I will keep my new blocking on stickers and under cover. Tim

I second the PT negatives for a frame repair. I hadn't really noticed how wide spaced the growth rings are on that stuff. But I've looked in the last day or so at my deck and was at Lowe's today and saw some... it's true.

Imagine an entire frame of the stuff. (sorry for the image!!)

Anyway, I see nothing wrong w/ PT cribbing.

Didn't see this thread in my quick fly by the other day Tim.

We use Red Pine, good strength to weight ratio, and it trades at a fair price when its available seasonaly, Usually order twelves and sixteens and buck up the pieces that promise to wind into block, and keep the ones the the strait checks for needles and track.