Connecting wood to concrete blocks

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Old 05-13-11, 06:34 PM
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Connecting wood to concrete blocks

What is the best way to attach pressure treated 2x4s to concrete blocks?

I tried using 3" long 1/4" tapcon screws. However, after I drilled holes using the tapcon drill bit, and thread the screws in, it bottoms out and spins. I can't get it to "bite" hard into the concrete. I drilled ten holes and eight of them are that way. Even drilling into the "middle" of the web does not always give good results. In some cases I thought I had a good grip, then I held onto the wood, and move/wiggle with my bare hands I was able to loosen up the screws from the concrete.

The application is to just extend the concrete surface out by about 2", to allow pipes and conduits to run along the top of the surface. I will attach Durock onto the 2x4s.

Is there a trick or a better fastener to use?

Also, I have a few 2x4 secured to blocks with the "ramset" tools by previous installers that I am trying to remove. Is the best way to do it with minimum damages to the block to pry them off with a pry bar?

Thanks in advance.
 

Last edited by MiamiCuse; 05-13-11 at 06:58 PM.
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Old 05-13-11, 07:04 PM
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One of two things is happening. Your bit may be wandering around and enlarging the hole. This might be true if it takes you a long time to drill each hole, as would happen with a weak hammer drill.

Or, you are thinking that you can "torque" the screw down and that it should hold, no matter how hard you turn the screws to it. Since CMU is soft and porous, you can't torque a tapcon down as tight as you might like. You need to slowly tighten it up and STOP when it gets snug. You should also use some construction adhesive for good measure. A few may still strip, but if you control how tight the screw is turned you will probably have better luck.

For your hardened nail, cut them off with a grinder and 1/16" steel abrasive disk.
 
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Old 05-20-11, 05:55 PM
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my hammer drill is fine, I am thinking may be one of the variables is the tapcon drill bit. It came with the box but may be worn out a bit? May be if I get a new one might improve the hole.

You are right once I drilled the hole, I changed the bit into a socket to drive the tapcon screw into it, and most times once it "bottoms" it spins.

If I am attaching a PR 2x4 lumber piece to concrete blocks, can I use the tapcon drill bit to drill through the wood into the block, or should I predrill with wood drill bit, then pull it out, change to tapcon bit, drill the concrete block, then take it out, change to a slightly larger wood bit, to enlarge the hole on the wood a little so the hex screw head can counter sink into the wood without protruding?

I noticed they have the white tapcon screws. Are those better? Will bite into the concrete better?
 
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Old 05-20-11, 10:23 PM
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or should I predrill with wood drill bit, then pull it out, change to tapcon bit, drill the concrete block, then take it out, change to a slightly larger wood bit, to enlarge the hole on the wood a little so the hex screw head can counter sink into the wood without protruding
That's probably the better way to do it.

However, if it wuz me, what I'd do is:
1. drill through the wood with a 1/8 inch twist drill bit,
2. change to a 1/8 inch masonary bit and drill into the horizontal mortar joints of the blocks (if you want to someday remove the PT lumber) or into the vertical webs of the blocks (if you don't).
3. Remove the wood and enlarge the holes in the masonary to 5/16 inch diameter with a masonary bit.
4. enlarge the holes in the PT wood to 3/16 inch
5. tap a lead anchor into the 5/16 inch hole in the concrete blocks



6. cut round tooth picks to length and put two or three into each lead anchor so the points are sticking out at you. The easiest way to do this is to push the toothpicks into the lead anchor, cut them flush with the end of the anchor using side cutters, then pull them out and push them back in so the pointed end is toward you.



7. drive a #12 or #14 (which is also 1/4 inch) screw through the PT wood into the lead anchor. Not only will the pointed ends of the toothpicks guide the screw into the middle of the lead anchor, but the screw will grip the wood of the toothpicks sumthin fierce, and the screw thread and toothpics will grip the ID of the lead anchor somethin fierce too.

That's how I attached electrical conduit to the exterior of my brick veneer concrete block wall, and it's probably the sturdiest way I know of to attach anything to brick, block or mortar. And, don't worry about the screws stripping. When I installed the electrical conduit for my parking fence, I used a 1/4 inch ratchet, 1/4 inch hex socket and #3 Robertson driver bit to tighten the #14 screws, not a screw driver. But, I didn't twist the bygeezus out of those screws either; I tightened them until they were tight, and no more.

So far as your experience with Tapcon screws goes, it's not typical. I don't know why your Tapcon screws are stripping, but I expect you'll have better luck tightening them by hand rather than using a drill and driver bit. And, of course, one of the most common problems of people relatively new to DIY is that they haven't acquired a feel for how tight is tight enough. The result is stripped holes become less frequent as one gains skill and experience.

If you want the PT lumber to be tight to the concrete block wall, use a spade bit to notch the back side of the lumber where the holes are.



PS: The difference between a wood screw and a sheet metal screw is that the wood screw will have threads typically about 2/3 of it's overall length and a smooth shank for 1/3 of it's length under the screw head. A sheet metal screw will be threaded all the way to it's head. And, just because it's called a "sheet metal screw" doesn't mean that it's short. You can get sheet metal screws 4 inches long. And, in my humble opinion, the Robertson or Torx head screws are superior to Phillips and (laughing out loud) slot drive screws that seem to be much more popular in the US than Canada. I live in Canada, and I rarely use anything but Robertson head screws, nor would I want to.
 

Last edited by Nestor; 05-20-11 at 11:00 PM.
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Old 05-21-11, 05:59 AM
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There are other differences between wood and sheetmetal screws. Thread pitch is different and sheetmetal screws are usually hardened.
 
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Old 05-21-11, 08:30 AM
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Robertson (aka square drive) are the best. I've worked in several shops that refused to switch over. It is very frustrating to work with anything but. I don't know why anyone would use slotted except for aesthetics.
 
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Old 05-21-11, 01:43 PM
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Nestor's way is very sound...and in good detail...
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Originally Posted by drooplug View Post
Robertson (aka square drive) are the best. .......It is very frustrating to work with anything but. I don't know why anyone would use slotted except for aesthetics.
.
I agree. Robertsons are the best and getting more use of late. I hate mixing types as well. Pretty much the only slotted ones I use are for electrical plate covers..- aligned vertically.!!
 
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