View Full Version : Subfloor delaminating?

12-14-2006, 01:11 PM
This past summer, I changed my 1950's ranch into a 2-story, which was a major project. (And no, I still don't live in the house yet). While the roof was off and the 2nd story was being added, rain had gotten the old 1/2" to 9/16" plywood flooring wet. The plywood sits atop 3/4" solid wood planks running at a diagonal, and all of the original subfloor is still in place.

Now that it's winter and getting dryer, I'm noticing that the plywood is crackling as I walk over it, and I think it's delaminated in many areas, even though, from the surface, it looks fine. I would like to finish the floor with 3/4" hardwood, with tile in the bathroom and possibly kitchen, but I'm concerned about the crackling plywood. The noise is more of a crackle than a creak or pop, but I'm thinking that the sound may still transmit through the hardwood and/or tile when we walk over the floor. I'd be putting backerboard down under the tile, but does anyone have any experience with delaminated plywood? Also, as a side note, I've been told by a high-end builder that they don't use backerboard under tile, but rather, just another sheet of plywood. What's up with that? Well, maybe that's another thread.

Anyways, is there anything I can do, other than to just replace all of the old plywood (leaving the 3/4" solid planking), and putting down new? It's about 1600 square feet of old floor, and that amounts to a bunch of money for "new" underlayment, but I also don't want to be kicking myself later, after spending even more on the finish floor.


12-14-2006, 05:27 PM
In my opinion, delaminated plywood will never be "right". I look forward to some other input. Maybe someone will have a suggestion.

12-14-2006, 05:52 PM
I'm with jimbo. Delaminated plywood is just a little better than heavy cardboard.

12-14-2006, 06:06 PM
Take it out where needed. For those areas that are going to be tiled, don't let that guy who tiles to the plywood do it for you. The only approved method for doing that requires two layers of plywood, properly installed and quite expensive thinset to do right, and everything has to be just right to last. Use either a membrane (something like Ditra from www.schluter.com (http://www.schluter.com)) or a cbu. Make sure the cbu is installed per the specs, which requires thinset and roofing nails or special cbu screws. Check out www.johnbridge.com (http://www.johnbridge.com) for tiling help. Also note, if the joists weren't designed for tile, they may not be sufficient.

12-14-2006, 06:30 PM
I'm not convinced that the plywood is delaminated without actually seeing it. If it looks okay from the top then it might still be good if it has thoroughly dried. I'm thinking that it possibly swelled and loosened some nails and that what you hear is the squeaky noise from the nails rubbing against the plywood. To test this "theory" you can locate an area where there are squeeks then put in a handful of deck screws thru the plywood and try to get them into floor joists. If that stops the annoyances then you can figure out what to do next. If the plywood has trapped moisture and can not dry out then you could have rot .... definitely need a good thorough investigation before loading it up with expensive flooring. You might also consider using a circular saw to make cuts between sheets of plywood to relieve any stress from the probable swelling which could be causing bucking of the wood resulting in the crackling sound.... kinda sorta maybe.....

Bob NH
12-14-2006, 07:00 PM
The diagonal subfloor was what was used in most houses before plywood. Much of it had hardwood installed over it. If someone If someone wanted vinyl instead of hardwood, plywood might be added at a later date.

You could probably put hardwood right over the diagonal subfloor, IF you are using standard 3/4" thick oak or equivalent. It would not be acceptable for the thin stuff they sell at Lumber Liquidators.

If you are going to use ceramic tile, then the experts may say you need two layers of plywood.

Your solution in the end might be related to what you need to get both proper support and floor elevations throughout the house.

12-14-2006, 08:16 PM
I tend to agree with Randy. My dad ran into the same problem you did when he built a small garage behind his house about 8 years ago. Same exact thing you are hearing. It got wet from a storm and about 3 months later here come the squeaks.

What we did was exactly what Randy advised, but with a small twist. We isolated 4 main sections that were suspect. In each section we screwed evenly spaced 3" deck screws on each joist. My dad is a design engineer and we tossed around the idea of contraction once the floor was complete. Based on a few good assumptions we made 3 cuts in the plywood between each joist on both ends. Since then there has been no sound.

FYI - depending on the quality of the product, and the size, some of the glueing agent used does not fair well when water comes into contact with it. When you couple weather along with that the variables on destortion compound dramatically. Once the agent releases, the fiber in the wood will begin to pull back from the seam and eventually pull every lamination apart.

12-14-2006, 08:43 PM
If you use a membrane or cbu, you can get by with one layer of plywood. Two layers are always required if doing stone tile, or tiling directly to the plywood. The second layer must be installed offset from the first so no edges line up - the end should be offset 1/4 span (i.e., 4" offset from the end of the other if on 16" joist spacing).

12-14-2006, 11:12 PM
I'm not a highly experienced tile guy but I am a very experienced handyman and pretty decent plumber. I've had to do several remodels for my mom to get her out of the "slum lord" business and into the rental house business. I've seen several floors like this and lots were tongue and groove that bucked after years of high moisture...and I fixed them like I described. The plywood just adds a twist. As long as it is dry, no sign of rot (if there is mold you can kill it with lots of stuff off the shelf...or if you're really a tight wad you can use 1/4 cup Clorox per gal. water and a pump up sprayer to saturate and let dry before proceeding (get a gas mask for the fumes). As for the tile job. IMHO two layers of plywood sux. But, like I said, not highly experienced... I would insure that the floor has plenty of strength and is solid (jump up and down on it..Does it bounce? Can you feel it move under you if someone else walks on it?) add Durock or Wonderboard which probably will cost a few bucks more than plywood and IMHO is worth it and will help make the floor more solid. Hardibacker has impressed me but probably is not as good in a high moisture area... then throw on the mortar and lay the tile. In baths and kitchens I'd at least put plastic or roofing felt under the concrete board for a moisture barrier. Even if the laminations separate...as long as there are no humps to warp your floor then it can be worth salvaging. Repair as necessary and let'er rip.

12-15-2006, 06:01 AM
Wow - Thanks for all the quick responses!

Randy - Just to make sure we're talking about the same type of noise, my noise is more a crackle. It's not a squeak. I'm trying to think of a comparable noise, but the closest I can think of is walking over plywood that has dryrot. In general, the floor still seems to be solid and OK, but in some places, such as some edges and a few small areas, the very top layer is loose, leading me to think it's delaminating. The plywood is not T&G, and the sheets are butted up against each other with no gap. (There are 1/8" gaps in the diagonal subfloor, however.) Actually, the plywood was used as the finish floor for quite a few years when the house was first built.

I've tried using 2" drywall screws to screw down the crackling areas, with some success in reducing the noise, but I don't know if this is really a good idea, or if it will even help with delamination. Or, should I just rip up the old plywood and put down new? To add another twist, a new subfloor was added in front of the house during my renovation, and for some reason, the framers made the top of the new OSB subfloor 1/8" higher than the top of rest of the old plywood. When I confronted them with this, they said that I should just sand down the 1/8" between old & new to a gradual slope before putting down the finish floor.

Also, regarding the cutting of the plywood, I'm a little confused as to the location of the cuts. Is it along the seams? Along the joists? Either way, it seems like the noise isn't coming from the seams as much as it is from the "meat" of the plywood.

Thanks again.

12-15-2006, 06:36 AM
As for where to make the cuts. They are simply for stress reduction IF the floor is bucking. You could actually cut anywhere but it's "prettier" and helps hold the integrity and strength of the full sheet if you cut just barely thru the plywood along the seams. Normally, half of the seams would be right on top of the joists. With the good subfloor underneath you can probably just put a screw anywhere but in the joists will tighten up the subflooring too which is a good thing. even if the delaminating has occurred you've probably still got strength. As long as it has remained strong and even with a 1/8" difference in floor height you can minimize work. If you are seeking perfection you can use this stuff that looks like mortar mix.."floor leveler"... pour it out and it levels itself then keep on going... if the delaminating is where you're doing tile then putting CBU on top and using a few extra screws can fix that. If you think it needs to be replaced... you call that shot... I ain't there to take a gander at it. If you're doing real hardwood you need a sturdy surface that will hold nails without question. If using composites, Pergo, that sort of thing with a floating floor system then you can get away with alot and still have a really good job. If someone else is getting paid to do it... I'd make then give me a NO SQUEEK guarantee....and don't pay that last bit of money until there are no squeeks. It's amazing that when you get concerned and paying attention you can learn alot about a floor just by looking at it and walking across it. You'll notice all kinds of things other people never pay attention to.

12-15-2006, 06:41 AM
If you want to sleep well rip it out and replace it.

Then there will be no wondering or should the floor fail, no regrets.

Since it is on top of a good sub floor it should be a fairly easy job.

12-15-2006, 07:55 AM
I agree, tear it out since you can see some delamination, the rest is suspect.

Tile hates movement, and that is why you can't tile to planks and expect it to last. You can tile to plywood, but only if you do it right. The Tile Council of America (TCA) is usually the agency called out that sets the standards for tile installations in the USA. They require two layers of plywood, properly installed for stone installations AND if you are going to tile directly to the plywood without an isolation membrane or cbu. If you use cbu, all of the manufacturers require you set the cbu in a mortar bed and allow it on a single layer, if all else is up to specs. The mortar under the cbu is not to adhere it to the plywood, but to fill any minor imperfections in the surface so it is 100% supported. Again, tile can't handle movement - you need to isolate it from the subfloor when it is wood. A membrane or cbu will do that. The screws or nails used to hold down the cbu will eventually actually crush the cbu a little as the floor moves, but the cbu floats. That is another reason why you need to reinforce the seams of the cbu with the proper alkaline resistant fiberglass tape - you need that cbu sublayer to be monolithic. If the entire floor structure is thick enough to prevent excessive deflection between the joists, and the joists are strong enough to prevent deflection along their length, then the floor should outlive the occupant. Anything else and you are on borrowed time.