Red Blazer X:
The biggest problem that I'm having here is that all the tub surrounds I've ever seen stop at the top of the tub and don't extend below the top of the tub to cover the drywall beside the tub. That is, they look like this:
So, when you say you've got a hole in the floor, but you've pulled the tub surround away to check the drywall, then I'm thinking you're checking the drywall above the tub to see if it's wet.
I have already pulled the sheetrock around the tub surround and pulled it out a little bit to see if there was any damage underneath it but didnt see any and cant see any from the crawl space.
Does this mean you removed the drywall at the front and back of the tub surround and pryed the tub surround away from the remaining drywall to see if the drywall behind the tub surround was water damaged?
If this is what you did, then doing that wouldn't really tell you anything. You see, a bathtub has a lip (about 1 inch high) that runs along the top of the front, side and back of the tub. You can see that lip in the following picture:
The tub is pressed snug with the wall studs so that tub lip will (hopefully) be flat against the wall studs. When they install drywall or tile backer board or anything around the bathtub, they won't drop the drywall down in front of that lip, or at least they shouldn't. They will hang the drywall so that it extends down to a point about 1/8 to 1/4 inch ABOVE that lip like this:
Notice that the bottom edge of the cement board is a short distance ABOVE the lip of the bathtub. The ceramic tiling in the drawing (or in your case, the tub surround) drops down in front of the tub lip and silicon caulk seals the bottom edge of the tiling (or tub surround).
(Also notice that the drawing is wrong in that it says the tiling should drop down to 1/8 to 1/4 inch above the top of the tub. That's way too much. It's the drywall, greenboard, cement board or whatever that is fastened to the studs that should drop down to 1/8 to 1/4 inch above the tub LIP. The tiling should drop down to about 1/16 of an inch (or so) above the tub top. Having a 1/4 inch gap between the tile and the tub would mean you'd have to use an awful lot of silicone caulk to seal that joint, and that would detract from the appearance of the tiling.
If it's an insulated exterior wall, the polyethylene vapour barrier behind the drywall will be stuck to the tub lip with accoustical sealant to form a moisture barrier around the tub. Even if it isn't an exterior wall, it's a good idea to have polyethylene behind the drywall or cement board just to act as a moisture barrier. They make waterproofing membranes (like Mapei's Kerdi) especially for this purpose, but it goes over the drywall or cement board.
If there is any water penetration through the wall, (such as at penetrations for the faucet handles or tub spout) that water will dribble down the back side of the tub surround (or the back side of the drywall) and drip into the gulley formed by the tub lip, the top surface of the tub and the back side of the tub surround.
Since that gully extends all around the tub, any water penetrating through the tub surround will flow around the tub in that gulley and come out where the lip ends at the front and/or back of the tub. The result is normally that the wall below the top of the tub at the front and/or back of the bathtub is water damaged, as well as the underlayment and/or subfloor in those areas.
Since the water flows in the bottom portion of that gulley, well below the bottom of the drywall, you won't see any water damaged drywall unless it happens to be leaking in right where you pried the tub surround away from the drywall. If the leakage past the tub surround occurs somewhere else, the drywall where the tub surround has been pried away will be perfectly dry since the bottom edge of that drywall is about an inch or more above the water in the gulley.
The size of the damage is about 6"x8" and is in the corner of the tub and nearby wall and about a 2" hole that I pushed through to see how strong it was.
Is the 6X8 inch area of damage on the wall or on the floor? Is the 2 inch diameter hole a hole through the drywall, or a hole right through the floor so you can stick a finger into your crawlspace?
If the wall is damaged right under where that gulley ends at the front and back of the tub, and you haven't seen too much water splashing on that wall from the tub, that's a pretty good indication that the wall is getting wet from behind because of water running along the tub gulley. That means there's water penetrating through the tub surround, probably around the faucet holes, or the silicone caulk at the base of the tub surround is leaking.
If the 6X8 inch area and hole are in the floor, then most likely it's only in the underlayment, but it's possible that the subfloor has started to rot, too.
Here's how they built my building (but there are probably other ways of building a floor):
IN THE BEGINNING were the floor joists
Over they floor joists is the subfloor, which is typically either 3/4 inch tongue and groove plywood or 3/4 inch thick pine 1X6 boards.
Over the subfloor they build the walls typically out of 2X4's.
Within each room, they install thin (1/4, 5/16 or 3/8 inch) plywood or particle board "underlayment" over the subfloor. (except in the bathroom. in the bathroom the tub goes in first and sits on the subfloor. the underlayment is cut to fit up to the tub.)
Then they do everything else, including install the drywall and paint...
Then they install the flooring over top of the underlayment in each room.
It's been my experience in my building, that it's typically only the underlayment that rots when there's water leakage at the front or back of the tub, but I have seen the 1X6 fir boards of the subfloor start to rot.
I was wondering if I could just repair it from the crawl space underneath the house. I can get to the area easily. I was thinking about taking a small sheet of 3/4" plywood and place it between the joist and nail some supports between the joist to sandwich the plywood under the old subfloor and the 2x4's or 2x6's.
You can do that. However, if this section of the floor really isn't in a traffic area, you're better bet would probably be to just replace the flooring in the bathroom, and in so doing you'll expose the underlayment. Typically, if there's a contour to the side of the tub, they'll set the underlayment down in a full sheet close to the tub, and then cut a piece to fit between that full piece and the tub. You can just replace that cut piece, or if you can cut part of that cut piece out, replace only part of it. The underlayment will be nailed, stapled or screwed down to the subfloor. It should never be glued down.
Removing the underlayment will give you a good idea what condition the subfloor is in in those areas. If it's rotted, I'd give it some time to dry, scratch away any rotted wood, and if the remaining wood is still fairly thick, repair it with epoxy.
The above kit is sold at Lee Valley, and most of what you get in it you don't need. However, they also sell the liquid epoxy and hardener separately as well as the paste epoxy and hardener separately. But, I think the whole kit costs a bit less than all 4 purchased separately.
If the subfloor is rotted, I'd scrape away all the rotted wood you can find with a sharp paint scraper. Then, allow plenty of time for what's left to dry completely. Now, mix equal quantities of liquid epoxy and liquid hardener, and paint that mixture onto the wood you want the paste to stick well to. (That liquid will penetrate into the deteriorated wood and make it harder and stronger as it cures.)
Before the liquid epoxy you painted on cures (in a few hours), mix up some paste epoxy and paste hardener, and apply that to replace the wood that has rotted away. Since the liquid epoxy hasn't completely cured, you should get cross linking between the liquid which has penetrated into the deteriorated wood and the paste epoxy, ensuring very good adhesion of the paste to the wood. The paste will dry to the strength and hardness of good wood, and you can sand/scrape it down so that it's flush with the surrounding subfloor (especially when it's still relatively soft before it fully cures). Apply several coats of the paste to get it flush with the surrounding subfloor. (Even if it's not perfectly flush, when you install the underlayment on top, then any good sheet vinyl will still install reasonably well over that area of the floor.)
Then screw or nail your piece of underlayment down and install new linoleum (which is relatively easy).
If it's not a traffic area, you could also get under your floor and drywall screw a piece of plywood to the underside of your subfloor where the damaged area is. Always remember that plywood is strongest in the direction of the grain of the OUTSIDE plies, so the grain of the outside plys should probably be parallel to the floor joists and just run the plywood out far enough on each side to screw into healthy wood.
Swinging a hammer between floor joists can be difficut, especially when you're laying on your back. You could instead use an X-tra long 7/64 inch drill bit to predrill holes (and counter sink them with a countersink bit) using an angle drill to screw fir 2X2 cleats to the sides of the floor joists with 3 inch long drywall screws to support your piece of plywood.
Not sure if this helps.