Subfloor Questions

jflan the house was build in 1979. The picture I put up was the best place to take a picture of the bridging that is there today. The side of the house I will be dealing with has some wire but also carrys all the plumbing for the house but the worst is the lines for the heat pump run through all of the joists in the area plus duct work that covers about 3.5 feet so sistering the joists is really not a good option.

 

Any chance the stamp is also labeled " T+G " or " This Side Down " ?

 

This is all that I can get off the stamp that I can read.

Sturdi-I-Floor 20 OC
19/32" inch Interior (APA)
Exterior Glue NR8-108/FHA-UM-66

And another stamp that has this on it
2-2-2-2-2-2
K-K-K-K-K-K

And one more question. For nailing the joist to the block what size nail is reccomended or will screws work?

 

1. don't assume ditra is going to "stiffen" things, ...it won't.. it is an isolation membrane that may help w/ any lateral movememnt, ..but not vertical movement/deflection...

2. here's an interesting article on reinforcing joists.. http://www.finehomebuilding.com/PDF/Free/021184090.pdf

 

The blocking will stiffen the floor , the Ditra will let the tile float , increasing it's ability to deal with movement without cracking .

 

Thanks Wiley the subfloor itself is pretty solid and thanks for the article. No I will make sure to install the blocking correctly. The only difference between what was suggested here and the article was that I glue and screw the blocking into the subfloor as well as nail from the sides. Also I didnt assume that the ditra would stiffen the floor. I am at the minimum subfloor thickness for using ditra but I called them and gave me the OK to use it in my application. Doing the blocking is an extra precation.

 

So what is the best way to get the vinyl adhesive off the subfloor. Or should I just put 1/4" ply on top?

 

Depends on how well it's stuck but a scraper works. It looks like a shovel with a flat end. It's tedious work but usually will get the job done.

 

well then the wife just fugged up the whole planning she wants 3/4" hardwood in the adjacent rooms. Looks like if I use 3/8" ply screwed and glued on top of the subfloor with the 1/8" ditra + the tile at 5/16" I will be just 1/16" shy of the 3/4" mark. The 1/16 will be less since the thinset for the tile is not factored in.

If I go this route should I also add the blocking to the joists as well? If so should I do the blocking before or after I add the 3/8 ply.

 

If you do the blocking last you can screw through both layers of plywood into the joists and blocking , just make sure to keep the screws you use to laminate the two layers of ply together out of your blocking line so that you don't have to fight screw points to get the blocking in later .

FWIW , Ditra comes in a thicker 1/4" mat as well as the 1/8" , it's called Ditra XL , this product is great for gaining a bit of height to flush to adjacent flooring materials .

When you apply the Ditra , wash the plywood surface to remove contaminants and dampen it's surface slightly .

 

OZ what should I was the plywood surface with and should I dampen the surface before as I am installing the ditra?

When laminating the two layers I know I need to place screws throughout each sheet of plywood but how far apart should the screws be placed? Also what type of 3/8" ply should I use.

 

If the plywood is new you can just wash it with a sponge and clean water .

In between the joists I would put screws about 6" apart . Make sure to use subfloor adhesive liberally between the plywood layers in a 1/4" bead .

 

Sounds good OZ. Is there a recommended type of plywood I should be using?

 

Standard sheathing will be fine

 

And one last question, when I lay the new plywood how much spacing should I leave from the walls? How much spacing should there be between the sheets of plywood?

 

1/4" from the walls , 1/8" between sheets

 

And should the gaps between sheets be filled with anything prior to installing the ditra?

 

No , the thinset will key in there

 

Excellent. And 16d nails to attach the blocking to the joists?

 

Or 3" screws