Eastern Spruce planks prone to split

[Greenie]

Greetings!
We mill spruce into 2x10 planks each spring. The planks are stickered and air dry until August or September when we plane and size them (usually the planks are around 12-15% moisture). The planks are used for picnic table tops and seats and are stained prior to service. Many of these planks split once in service. Once the split opens rain and moisture go to work and in a few years the table look terrible.
We're in mid-coast Maine and I've heard that spruce trees along the coast tend to split because of windy conditions.
Is there anything in our process that could be changed to reduce splitting?

Many thanks!

[beenthere]

How about some pics of the split planks?

What size spruce logs are you sawing?

How do you check the moisture content to know it is 12-15%?

How are the planks fastened down?

Do you see any cupping or do the fasteners prevent that?

Is it a water repellant semi-transparent stain?

[barbender]

A wide spruce plank out in the weather, and especially the sun, will be likely get a wide check in it.

[Jeff]

I would think you would need to make sure your fastening methods allow for movement in such wide boards, otherwise splitting is probably inevitable.

[Greenie]

We use Torx screws to fasten the planks to white cedar cross members. The tables are 7 feet long, 3 screws per plank at each of the three cross members. There is approximately 1" gap between the planks. The stain in dark brown - which absorbs heat from the sun and doesn't help matters, but I have no choice in the color. The stain is Woodsmen from True Value. I'll try to post pictures in a few days - I'm not there right now.
Thanks for your interest.

[Ianab]

3 screws per plank is likely the main problem. As your planks heat up and dry out in the sun, they are going to shrink in width and there is nothing you can do to prevent this. If you have fixed them to a cross member with 3 widely spaced screws, the wood can't shrink, and so a crack has to open up (or the screws pull out)

Can you change the design so it has the screws all near the centre of each plank? That way the board is able to shrink, the 1" gap opens up slightly more, but the board has a better chance of staying intact.

[Bruno of NH]

The dark stain doesn't help.
Jim/Bruno

[GeneWengert-WoodDoc]

Two of the three screws should be in slotted holes so the screws can move easily as the wood shrinks and swells...do not fasten these screws really tightly.

[SwampDonkey]

Yep, it is the root cause. Spruce is not really prone to split real bad even if double nailed. I have built picnic tables as well from spruce. My trouble is to get spruce that is actually dried. If I go to a lumber lot of a hardware and pull boards from a bundle out in the weather where the wrapping has not been removed, thus acting like a bath tub collecting rain, the table will be rotten in 4 years. That seems to be the method of lumber storage at small outfits around here.  Or the shed so leaky that they might as well be out in the sun. :

[Greenie]

We make as many as 100 tables a year. We used to use galvanized nails to secure the planks but switched to torx screws a while back. The nails, when used now appear to allow some lateral movement that the screws don't. Putting slots in 300 top planks and 200 seat planks isn't time efficient - I'm not sure how we could do that quickly.
I do appreciate the insight and advice; I had initially thought our drying process was at fault but now see the more likely reason our planks split.

[Ianab]

Yes, nails can flex a bit more and so the problem is less.

Maybe go back to the nail gun and keep the nails closer together, nearer the centre of the board?

The problem is pretty well understood, the tricky part is coming up with a practical solution.  ??? :P

[kwendt]

So relatively ignorant question here... In general, if I were to cut and store Spruce logs in my barn to dry and be available for tables, replacement or rebuild studs, etc... How long would be reasonable amount of time to let them dry? Bark on or off?

[beenthere]

Stored spruce logs will split when they dry. Is that what you want?
Best saw them close to the dimension you want to use the lumber, and then dry that in the barn.  But not as logs.

[kwendt]

Stored spruce logs will split when they dry. Is that what you want?
Best saw them close to the dimension you want to use the lumber, and then dry that in the barn.  But not as logs.

That's what I wanted to know. Thanks. Some will get peeled and stored whole for replacement purlins, some cut for stud, building. Checks are ok.

[Magicman]

I have never sawn Spruce, but I do have a pointer that goes back to sawing.  Always look at the log end for any sign of a natural or "felling" check.  Orient this check vertical for the first face opening.  If you turn 90° it will be horizontal for the final face opening and saw through. 

This method hides the check within a couple of boards and will cause no harm.  If you do not follow this procedure, then each board will already have the beginning of a split when it is sawn.  There is no way to prevent further splitting as the board dries.

I have sawn over 18Mbf of Cypress during the course of the past three weeks.  Every log has been examined for even the smallest sign of check before sawing and oriented accordingly.