Bowed live-edge slab

[Duncan Brown]

I have an 80" x 21" live-edge slab of English elm from Berkshire Products that I'm installing in my basement as a bar top. The slab is 1.25" thick, is flat sawn, and the slab will be installed bark-side down. The slab was vacuum kiln dried to between 6-8% by Berkshire and has been sat raised up on 2x4s in the basement for a few months to acclimate to the humidity level down there (about 55-60%). It's been sanded to 80 then 120 grit and will be finished with Rubio Monocoat.

The slab has no cupping but it is bowed down its length with the center raised about 0.5" higher than the ends. From reading the posts here, it seems like the best advice is "do nothing," as this level of bow is not terrible and the slab is too thin to level with a router. The bar top feels level and you only really notice the bow when you look under the bar and compare it to the pony wall that is dead level. The bow means that the slab only sits on the end two brackets, but since they are Centerline brackets rated for 100lbs each and the slab weighs 50 lbs tops, that should be fine.

I was hoping to get some advice from the experts on the following questions:

1. Is my "do nothing" approach reasonable? Posts here seems to suggest that 0.25" of bow over 7' is entirely expected and that even the 0.5" bow that I have is not too much to worry about.

2. Should I add a shims so that the slab also rests on the middle two brackets or just leave it alone?

3. The brackets don't have screw holes, so to stop the slab tipping when someone leans on the edge, I am planning on attaching a 4" mending plates with #8 or #10 screws that sandwich the bracket between the mending plate and the slab. I'll do this with the two end brackets, since they are the ones that make contact with the slab. Since the slab will be able to move relative to the brackets and will only be fixed along its center line, I think I'll be fine for expansion across the grain and any small movement along the grain. Does this sound reasonable? I'm trying to avoid drilling into the 0.5" inch steel bracket to make a slotted hole as I don't have the metal-working gear to do this.

Thank you in advance for any advice.

[Scott T Smith]

Duncan, If it were me I'd figure out a way to pull the bow out of the slab via my mounting system. However, this is a very subjective answer.

My main reason for responding was to advise you to finish all sides of the slab with the same finish and same number of coats. This is extremely important for wood stability when working with wide slabs.

Best of success to you.

Scott

[Duncan Brown]

My main reason for responding was to advise you to finish all sides of the slab with the same finish and same number of coats. This is extremely important for wood stability when working with wide slabs.


Will do, thank you. I have enough Monocoat to finish all six slides of the slab so I'll make sure it's evenly finished.

[Frank Pratt]

I too would pull the bow out of it when mounting. That's a lot of bow to just leave as is. Shouldn't be too hard to do. When securing it, be sure to allow for seasonal wood movement across the grain.

[Duncan Brown]

I too would pull the bow out of it when mounting. That's a lot of bow to just leave as is. Shouldn't be too hard to do. When securing it, be sure to allow for seasonal wood movement across the grain.

Thank you, I will try that. The steel brackets are secured into the 2x4 pony wall with four 2.5" #10 screws so they should be able to handle the force of pulling the bow out (they can handle me sitting on them).

I'll add an additional mending plate across the center bracket and screw it into the slab to try and pull the bow out. The slab will be screwed in at three points along the grain (parallel to the pony wall) but it's free to move across the grain so hopefully that should be fine to accommodate seasonal movement.

[Bill Dufour]

Location and expected humidity for more then two months? I would expect humidity to change with the seasons if your climate is like mine.. I would support it at the ends and see how much it will sag over time. Maybe put some heavy stacks of plates or statures on the high ends.
Bill D.