Have read quite a big on the site, VERY glad I found it.

Hello to you all and thanks for reading in - I have a few questions I'm really hoping to get some insight on. First, here is what I'm working with:

Early 70's Portland, OR home with 4x6 Fir joists (propped with 4x4's on concrete in a ~ 2' crawl space covered with 6 mil. The joists are spaced 48" OC. The subfloor is either 1 and 1/4" OR 2" (I have not found a spot to verify yet but I do know its > 1" thick for sure) x 5" (as measured) T/G Fir nailed perpendicular to the joists.

On top of that is a 5/8 particle board that I will be pulling up. Here in lies topic #1. I am working with Lumber Liq 3/4 x 4 3/4 Tobacco Road Teak (acacia). Per the install instructions, I am advised to lay a minimum of 3/8 CDX over any existing subfloor that meets their recommendations in order to meet height requirement. I am pulling up 5/8 particle so i wouldn't mind going with a 1/2" or 5/8" plywood replacement just to have a more rigid floor and such.

I"m really just trying to determine which underlayment would effectively equal or surpass the 3/8" + CDX min requirement while providing all the things we want in a nice plywood - rigidity, holding power....etc I am asking as I've read on here that CDX and OSB are not so great...etc What should I be looking for if I wanted a better underlayment that CDX?

I am installing about 22 sheets of this so cost is a bit of a concern, though not nearly as much as selecting a sheet that will provide all the benefits the current shitty 5/8 particle board does plus adequately hold whatever fasteners I use for the 3/4" Acacia.

I have installed this Acacia in the past with the Bostitch, using 1 3/4 staples @ 15.5 gauge and had good success. A few cracked tongues that I was able to work with. Considering that I will be installed new underlayment of my "choice" I wouldn't mind trying cleats to try and avoid the cracked tongues this time.

Please advise on underlayment vs. staple/cleat

Thank you very much in advance!

Here's more than you probably want to know about plywood and grading. http://www.plumcreek.com/Portals/0/down ... fo/J20.pdf

For fasteners I would go with 18 ga cleats.

Cracked tongues can happen with any material and can be affected by a "weak" part of a board, but don't let that alarm you. Trying to explain why is another story, but probably best seen if you look on the bottom of some boards. I had one crazy customer that wanted to send back some Mirage because of that. "It has knots in it."

Cleats seem to be more preferred these days, good suggestion.



Nothing wrong with CDX. It's used all the time. But what I don't get is the recommendation. Does the sub floor have gaps in it? 48 inches on center? Okay, now it's making more sense. Sorry no experience with that.

Thanks for the link, I will get to reading.

The Fir T/G subfloor is in outstanding condition, no gaps. The beams are spaced 48" OC. The "recommendation" I speak of is direct from Virginia Mills install PDF of product. The type of subfloor I have is constituted as "old style" (not used any longer) and laying directly atop is not recommended. Instead they recommend the usage of min 3/8" thick CDX atop the subfloor prior to install (as an underlayment).

My hesitancy just comes from several negative reviews of OSB and CDX (though OSB more so) that I have read about from installers ON LINE (no real world experience from myself).

There are a few options for acquiring some 1/2 or 5/8 cdx in the $13-16 range per sheet - I may go that route. I suppose I just want to feel rest assured that the cleats I go with will hold this 3/4 teak down to the CDX for the long haul.

Thanks guys.

there were way too many numbers and factors in these replies to make any sense.

what I can decipher is this.

4x4s 48" on center?

I'm sorry..but instead of adding on over the top,.I would shore up underneath instead.

add some Cats and cross bracing..

James, I am not so worried about movement as there isn't much. The original joist/subfloor system is surprisingly strong. Somewhat common to the Northwest during the 60's and 70's (tri level home, where only the main level is supported this way ~ 650 sq ft). 4x6 support joists that are 48" OC with 2x6 t/g fir subfloor.

My concern is just selecting the appropriate underlayment to go atop the subfloor. And actually if I have the subfloor exposed, would it be adviseable to lay 15lb felt between that and the new 5/8 underlayment and also on top of the underlayment underneath the finished floor? Or is it just one or the other?