# Bowed Slab



## Dan M (Feb 21, 2017)

I bought an 100" x 40" x 1.75" dried Oak slab from a friend to make into a table. Before I had a chance to connect it to a frame, it bowed down the center. Tonight I turned it onto its top and put a bunch of weight on it to help flatten it. I plan to use a bunch of screws up through the bottom to keep it flat once I'm able to. That frame sitting on top of it, is what I want to use (the whole table is upside down right now). Is this going to work? Is there a better method? Or do I now have a huge worthless/bent slab?


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## Steve Neul (Sep 2, 2011)

The first thing you need to do is get it off the floor. The slab needs air to get to both sides. 

If there is any chance to flatten the slab you need to dry the side that is up now and wet the side that is down. If the bow was due to storage there may be a imbalance in moisture content. If that is the case moisture from the air has gotten to the side that is up but not to the other side. It's kinda like a kitchen sponge, if you just wet one side it will curl up. 

If you get it flat what ever you make from it be sure to put a finish on both sides of it to prevent it from warping again.


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## Tennessee Tim (Dec 15, 2010)

A few beginner issues may be happening...we'll start there.

1) what was the moisture content of the slab when purchased and now?

2) appears it may have been stored on something flat as the floor or a benchtop.

3) placing any lumber directly on a floor or anything flat is usually a bad thing to do. The concrete slab usually holds some moisture if not kept at a constant MC in the room and a lot are poured without a plastic or vapor barrier below because the cause the concrete to set up slower ( BUT in actuality the plastic/vapor barrier makes it cure better by holding moisture longer as it ages to it's full strength). on a flat surface it prevents that side from changing MC as fast and creates a bow (the center touches)due to the other is usually drying faster. IF it cups than the opposite side is gaining moisture.

PLEASE get it OFF the concrete and up to where both sides are evenly getting the room air at the same time. Put it on dry 2x4's on their edge on a bench with a little air movement and it should straighten back out.

DO NOT anchor the frame to the top with screws (or glue) as you suggested as this will also cause bowing issues. You may screw it with elongated holes in the frame as this will allow the top to move. ANYTIME 2 woods are placed cross grained (one running opposite than the other) NEVER glue or secure solidly to prevent any movement....IT WILL MOVE and destroy the top!!!

search all the post about bowed tops here....your not the only one!!!


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## woodnthings (Jan 24, 2009)

*I'm gonna have a different approach*

All the advice about moisture and one side drying faster is true. However, I think you won't have much luck correcting the bow in that large slab. So, I would rip it into 3 separate pieces, joint square and straighten the edges and reglue them on a flat surface. If you don't square the edges you will have another cupped slab. If you are careful, you won't be able to see the glue lines. 

If you don't have the necessary equipment to joint 10 ft long and 1 7/8" thick pieces, you may have to seek help. We can give advice, but we can't loan out our tools....:frown2:


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## Tennessee Tim (Dec 15, 2010)

woodnthings said:


> All the advice about moisture and one side drying faster is true. However, I think you won't have much luck correcting the bow in that large slab. So, I would rip it into 3 separate pieces, joint square and straighten the edges and reglue them on a flat surface. If you don't square the edges you will have another cupped slab. If you are careful, you won't be able to see the glue lines.
> 
> If you don't have the necessary equipment to joint 10 ft long and 1 7/8" thick pieces, you may have to seek help. We can give advice, but we can't loan out our tools....:frown2:


You could be correct IF it's been correctly dried and stored BUT from his info we assume it was flat on purchase then something happened which would be a moisture issue. Let's get the MC correct and balanced prior to any ripping, IF we rip now and reglue now then the MC gets corrected after then it's gonna move again. Correcting the the MC first may or may not correct all the bow BUT it has to be balanced for any corrections to stay stable.

THEN we would suggest the slicing and regluing after it's stable IF it's still slightly bowed.


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## Dan M (Feb 21, 2017)

Update: I raised it up off of the concrete by 2.5 ft, bridged across some bar stools with the bowed side up, put fans and a dehumidifier around it for the last 2 weeks while I continued sanding and working on it. It slowly flattened back out! Thanks for all your advice! I'll be sure to post a final pic.


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