problems with Tapcon screws

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Old 02-11-12, 07:55 AM
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problems with Tapcon screws

I'm trying to secure plywood to a concrete floor as a base over which I'm going to nail down some flooring. Obviously I want to secure the plywood as well as possible, so I'm spacing 2-1/4" Tapcons a foot apart to maximize securing the sheets of ply. Unfortunately I'm having all sorts of dramas getting th Tapcons to work. I either have some of them spinning on me with zero grip when they get fully inserted, or they lock up on me before they make it through to the end, requiring me to redrill the hole. Probably only about a third of them are securing properly. I'm using the bits that came with the Tapcons so that can't be the issue. I'm getting concerned because I really need these panels to be locked in as securely as possibly, otherwise if they come loose the flooring will be compromised.

Any suggestions on what I could be doing wrong? The only thing I can think of is that the side of the cartons suggests using a hammer drill to screw the Tapcons in - I only use the hammer drill to make the holes then use a conventional drill to screw them in - wouldn't using the hammer function strip the holes and make them loose?
 
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Old 02-11-12, 08:17 AM
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If you are using 3/4" plywood, a 2 1/4" screw is too long. Your screw should go into 1" of cement. If you are using the 3/16" screws, I have found that they are pretty light duty and will sometimes want to strip like you describe... I rarely use them. I prefer the 1/4" screws, they seem to grip better since they have better threads. When you suck the screws down tight, you will probably strip the holes out too unless you countersink holes in the plywood, creating a tapered "pocket" for the head of the screw to sit in. If the hole isn't countersunk, the tapered head of the screw puts so much pressure on the wood (trying to crush it) that it will usually pop the threads out of the cement, stripping your hole.

For a countersink, you can either use a wood countersinker after you drill your hole, or just smack the hole with a cold chisel/ punch to make an indentation for the head of the screw.

I'd also recommend that you use PL adhesive under the plywood in addition to your screws.

You will also have better luck using a rotary hammer (heavy duty hammer drill) and a 5/32" SDS bit to drill your holes for the 1/4" screws. With so many holes to drill you will love it. And yes, an impact does help a little with driving the screws in. Mainly it helps to keep the bit from slipping as much.

When setting the screws there is a fine line between making the screw tight enough and stripping it out. So start with the 1 3/4" screws and if you strip a few of them out, back them out and try a 2 1/4" screw. Hopefully this will help you out.
 
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Old 02-11-12, 08:28 AM
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No expert...but what I have found is that you need to be very careful to drill straight with the hammer drill. Moving it around too much will make the hole too big. You also need to blow the dust out with air.

I also found that it is better to use hand tools to install them. I've never done more than 10 or so at a time...might take a while in your job. I don't mean just a screwdriver...I'll use a 3/8" ratchet with a bit installed. Once it's snug...that's it. If using phillips head tapcons, it's important to countersink under the head so it will be flush or slightly below flush.
 
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Old 02-11-12, 09:17 AM
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I should have pointed out that I have used a countersink through the operation, because I didn't want to have any heads sticking up even slightly to interfere with the laying of the flooring.

I might switch to the thicker screws as suggested if that will give me a better grip. Hopefully that may work better.

As for the extra length I'm using, there's a reason for it. I had to put down a new layer of concrete over the old one to level it out (it's between 1/2" and 1" in thickness). We had a contractor do it the first time, and he made it even worse. I then went over it myself with another layer and got the floor billiard table level. However, with two new layers I thought it best to count on the original concrete floor underneath for the best grip, which is why I went for the longer tapcons.

One other question - should I predrill the ply before using the tapcon drill bit? I'm just going through wood and concrete with the hammer drill to make each hole, even though I know the bit isn't technically designed for wood. Could this be possibly causing any issues? I know one thing for sure - cheap hammer drills are NOT designed for this kind of work! I made it through two sheets of ply before the drill started overheating and stripped its gears! Have to go and buy a new one this morning.
 

Last edited by timbo59; 02-11-12 at 09:32 AM.
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Old 02-11-12, 10:07 AM
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If you were going to predrill the plywood, I'd do it before I laid it on the floor. Or if you prefer to do it after it's laid in place, put a stop collar on your drill bit to prevent it from going ALL the way through the plywood and hitting the cement.

Sorry about your drill. Like I said, for that amount of holes I'd recommend the rotary hammer. 7/8" is the small variety, I have a 1 1/8" that I really like, and 1 1/2" ones are pretty heavy duty, almost like a mini jackhammer.

You can drill through plywood with a masonry bit, but it's not really "drilling" through the wood since it doesn't have a wood cutting tip on it. It basically smashes and tears the wood away, and isn't as fast as a wood drill bit as you probably have learned. If I was using a rotary hammer to drill the holes I probably wouldn't bother drilling the holes in the plywood first either.

Got a Harbor Freight nearby?
 
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Old 02-11-12, 10:14 AM
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I'm trying to secure plywood to a concrete floor as a base over which I'm going to nail down some flooring.
Around here this is often done with 2X4s (flat) spaced 12"- 16" apart perpendicular to the final floor boards. The 2X4s are glued to the concrete. Once the the top flooring is nailed in place you basically have a solid mass so not much is needed to hold the bottom boards, weight alone is almost enough.

I swear the first time I tore one of these out it looked like the had poured hot tar on the floor and set the 2X4s in it though maybe in retrospect it was cut-back asphalt flooring adhesive. I have use construction adhesive under the 2X4s and it worked fine. I have never seen plywood used or the substrata screwed or even nailed. If height of finished floor is a concern 1X4s could be used, just need really short nails for the finished floor boards.
 
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Old 02-11-12, 11:05 AM
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@Xsleeper. Yeah, it was one of their cheapies I used for the drilling that burnt out on me after about 50 holes! Still, I'm not going to complain given the price - they're just about throwaways for the $$. On the other hand, they can also work out well - I have a nailer I bought from them for $20 which I've used to put crown molding throughout our entire house and it's still going strong.

Went out and bought a Makita to finish the job. If that burns out I'd be surprised, as they're usually pretty good.

@Ray2047. I know that method. It's considered a bit dated these days, as it uses up too much height and can compromise doorways as a result. That's when they started coming up with direct glue down for flooring, or of using either floating plywood bases or the fixed variety I'm trying to use.
 
 

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