Hi everyone,

I will be laying down one layer of 3/4" CDX to my slab using Tapcon concrete screws and I'm looking for advice on which size screw to use. A two layer system of 1/2" CDX is not an option due to door and window issues. My first choice was to use a power nailer as recommended by NOFMA, but some folks here have talked me out of it. The flooring I will be laying over the subfloor is unfinished #2 Common white oak.

I was not able to find any info on how many screws per 4x8 or 4x4 sheet should be applied and what holding power would be enough to do the job? My plan is to use 20 1/4" x 1 3/4 inch screws every 2 feet, inbedded 1 1'4 inches into to concrete per 4x8 sheet of CDX. After drilling the hole for the screw, someone here suggested I add some roofing sealer to the hole prior to screwing the Tapcon as an added measure to prevent moisture issues It has been recommended that 3/16" x 1 3/4 inch screws with a penentration of 1 1/4 inches should do the job. But after looking at the spec sheet (info below) from the Tapcon website, I'm at a loss since I do not know how to interpret the data. My thinking is more holding power, the better and maybe I should use the 1/4" screw. I can't get about 400 1/4" x 1 3/4 inch screw online for about $50.00.

Size Embedment Concrete 3725 psi
3/16" 1" 380 lb.
3/16" 1-3/4" 1090 lb.
1/4" 1" 800 lb.
1/4" 1-3/4" 2100 lb.

Some also recommend that I use Redi-Drive anchors. Nice product, but after talking with the tech folks, their feeling was that once the anchor is in, it ain't coming out. So if I make a mistake, I'm pretty UAC.

With the flooring I'll be applying, any thoughts on which size Tapcons and how deep to drive them would do the trick?

Best...Stan

Who were the "tech folks" who warned you against using the better fastener?

Tech folks at Ramset- Redi-Drive. They didn't warn me against using their product. They were just stating a fact that once their anchor is in, it would be darn near impossible to remove the anchor. Whereas with the Tapcon's, you could just back them out with a drill. As well, with the Redi-Drives, I would need to make a countersink for the anchor head to set in.

Stan

3/16" X 1 3/4", 32 screws per 4 X 8 sheet (1 per sq foot), you'll need a good hammer drill.

I'm with Sean on the screws/amount. I use sceaming dewalt hammer drill one guy on hammer drill one guy with cordles with countersink bit another guy with old wards varible speed drill screwing down. Countersink guy would kept the cords untangle/an supplys of drill bit/screws. Went threw alot of filips #2 bits if i recall other then that we move right along. GOOD LUCK WITH YOUR FLOOR

Steve is dead on, I always use a countersink bit. sometimes the tapcons dont seat themselves below the surface and the countersink is a big help.

Just finished installing 1400 SF 3/4" sub floor on 3250 psi crete, with TapCons, 6 mil plastic sheeting works for me, though others prefer mastic, #15 Felt and mastic on subfloor, drying time and then HWF install.

Screw spacing, 19.2" (truss center, that little black diamond on your tape) on the 8' side, 5 screws, and 16" on center on the 4' side, total screws = 20 per sheet. attach with 2 1/4" x 3/16", using the supplied crete bit and Dewalt 1/2" electric Hammer corded Drill (Sears $79). !/2" Dewalt 24 Volt VSR with a #3 philips, set at 14-15 tork setting. No problem self sinking Philips, flush or better. 875 screws @ $10 box of 100 with drill. Install rate alone is $1 / SF. VB or #15 felt with Mastic extra. Start in the middle of the sheet and work to the edges, stand up a 6p nail for spcaing, and go to town. I find a mechanics sitdown creeper with shelf invaluable for us old guys with bad backs


Paul
P.S. Whear a dust mask, that crete dust is a killer.

Thanks to everyone who helped with my inquiry. I'm ready to go.

I'll probably go with 32 per sheet to see how things go. Thanks for the tip to start in the middle of the sheet and work outwards.

What did you mean by "6p nail for spacing"? Space what?

I'll send pictures as I progress.

Best...Stan

He means spaceing between each sheet of plywood for expansion you need that for sure

hey Steve, Sorry for the miss print. 6d brights are just long enough to make for easy, pickup and provide the nescesary expansion between sheets

Slab prep is of utmost importance. give it a good sweeping for for the
big stuff and a good vaccume for the dust.

Tack a 6d into a corner and wrap a string line around a piece of 1/2"
from bottom up. Swing an ark acouple ft. wider than than the room, wrap another 1/2" and weight it with a bucket halffull of water. Take another piece of 1/2 " and slide it under the string line Sure beats measuring with a tape.

Common practiceis to fill 3/16"Depressions, and dimple 1/4" High Spots




Paul

From all this I'm thinking that T-nailing the subfloor to the slab is not a good idea?