Replies

1. 
   calvin | Sep 12, 2010 02:38pm | #1

   Bill

   If you still want to try.  Use 1/4" tapcons, drill deep-go in more than an inch and a half.  Don't go over too far and take a third or half the bow out-install another screw.  Move on over in shorter intervals to get it where you want it.

   Or, get a straighter 2x8.

2. 
   calvin | Sep 12, 2010 02:41pm | #2

   Bill

   further clarification.  Is this board you're fastening going on the vert. edge of the slab or laying flat on the floor?

1. 
   BillA | Sep 12, 2010 04:04pm | #5

   the board is on the vertical edge, and is a little less than 10' long

1. 
   calvin | Sep 12, 2010 04:10pm | #6

   What's it going to be used for?

   Could you get the same use from 2-5' if the bow is too stiff to straighten?

3. 
   DanH | Sep 12, 2010 02:43pm | #3

   Note that a lot has to do with how the hole is drilled.  If drilled with a good impact drill & a steady hand the hole will be correctly sized, but if drilled with a regular drill or a shaky hand it will be oversized and you need to use a smaller bit to start with.

   Also remember than you need to go deeper than the screw and clean out the hole (ideally with compressed air).  Otherwise the screw will bottom out and even the best-drilled hole will strip out.

4. 
   JTC1 | Sep 12, 2010 02:57pm | #4

   Tapcon says

   ......the following:

   "Ultimate pullout in 4000 psi concrete:

   3/16" diameter - 1" embedment = 650 lbs; 1-1/4" = 870 lbs.; 1-1/2" = 1090 lbs; 1-3/4" = 1460 lbs.

   1/4" diameter -  1" embedment = 800 lbs; 1-1/4" = 1340 lbs; 1-1/2" = 1820 lbs; 1-3/4" = 1670 lbs."

   This is from the "Tapcon Anchor Performance Data" card packed with the fasteners.

   Yes, they are approved for use with ACQ lumber, so you are OK on that score.

   As you can see from the above data the pullout strength is greater with 1/4" diameter fasteners than with 3/16" fasteners.

   You did not mention the length of fastener you tried or whether you provided any supplemental clamping to reduce the bow before driving the screw, or how the hole was bored - hole needs to be drilled cleanly without wobble.

   As you can also see from the data the pullout strength rises very quickly depending upon embedment.

   What I would do:  Get 1/4" Tapcons in a length which will provide 1-1/2 to 1-3/4 final embedment (3" or 3-1/4" sounds right) with the hex / washer head style.  Drill clearance holes in the wood (1/4" D.) - 2 screws, not 1.  Clamp the wood by some  means to get it as close to contact as possible (creativity may be required) Bore the 3/16" pilots into the concrete using your 2x8 as a template; these holes should penetrate the concrete by at least 2-1/4" (final embedment + 1/2"); clear as much concrete dust as possible from the holes - either by suction or by blowing out with compressed air - dust left in the holes will cause the screws to "bottom out" - guaranteed to strip.

   Drive screws alternating  between tightening # 1 and # 2, do not overtorque - when the washer head compresses the wood by about 1/8", you are tight enough.  Release clamps.

   By asking the screw to pull the bow out of the board, you have reduced the amount of embedment by 3/8" - see table above to see what 1/4" less does to pullout strength - typically 500 or so pounds per 1/4".

   OPTION # 2 - buy a straighter board or straighten the one you have.

   I have used Tapcons for years with good results.

   Others will be along to argue for lead anchors, etc.

   Jim 

1. 
   BillA | Sep 12, 2010 04:18pm | #7

   Thanks for the advice. I used 2 3/4" screws, which leaves 1 1/4" embedded if the gap is pulled up, but less than 1" when trying to pull-up the board, hence an "ah hah" moment. My nearest reaction point  for "pre-pulling" the board is about 17' away, and don't have a board long enough to do that. I think your advice on the larger and longer Tapcons is good, and I will install 2-3 of them and alternate.

   I think I did do a good job of drilling, and used the recommended bit with a hammer drill. But I did goof by forgetting the step of making sure the hole was clear of debris.

   I'm using the phillips head screws instead of the hexhead screws so I can get a flush look against the board.

1. 
   JTC1 | Sep 12, 2010 04:41pm | #8

   Is the face of the board visible once the project is complete?

   If not, you might consider counterbores deep enough to accomodate the Tapcon's hex head plus a 1/4" SS or HDG flat or fender washer.

   OR, a temporary "reaction point" such as a truck bumper or board between the two front tires......might not be feasible, just a thought.

   Good luck.

   Jim