Install a torch down modified roof on the osb. No kind of outdoor finish is going to waterproof partical board. John

It's not partical board, it's OSB which does stand up to moisture quite a bit better than partical board. Instead of a torch down roof, I thought about using a product called Sanitred. This is a pretty neat product that has a lot of uses. I even know a lot of people who have built koi ponds out of concrete blocks and coated the interior with Sanitred to make it hold water. Another thing I was thinking about is putting down cement board and seal with fiberglassed joints, and then tiling it using exterior grade mortar. Any thoughts on either of those two methods?

One thing I forgot to mention. the Sanitred comes in colors and is attractive enough to be the finished surface. I'll keep a large sisal rug over most of it to protect the finish.

osb is partical board that is pressed wood particals combined with a few resins, it is not by any means made to be exposed to the weather.

With cement board/fiber glass/tile you will be fighting movement. One poster over here tried it over plywood as the pictures showed the tile was cracking and coming up in a short time.Even using high grade construstion adhesive to place the tile movement between the layers will cause the joint to fail. Another problem is the grout water is going to get thru it same as it does in a Shower stall but unlike a shower that has drain holes installed down below, that water is going to slowey get into your project and cause failure.

Movement will be caused by weather changes and exposure to uv as well,a basement sealer is not ment to be exposed to outside heat/cold exchange or uv.

Now dont shoot the mesenger, I my own self have been trying to figure out a way to tile an outside deck without using a slab for a few years now. In fact Im still working on it. John

OK I'll forget the tile idea. I wasn't too sure how well it would hold up outside. I think my only viable option is to try the Sani-tred. I know it is sold as a replacement for flat roofing systems, so it might work well. It will cost me around $500 to do the 14' x 16' deck but that is if I use the lifetime warranty directions. I'll let you know how it works. I sure wish I had decided before framing that I wanted a screen porch on this end of the house!! LOL!!

O Man!! there has gota be a way,, anyone who gives a lifetime warranty is total full of s#%t it cant be done.

My progress>> use one layer, the more layers the more movement, say 1 1/2'' plywood T&G tape the seems with fiberglass use tile with really close clearance I am thinking 12'' tile but then much smaller tile would fan out the stress but then they require more joints so I am at 12'' tile. Put it down with construstion adhesive and use tilt up expandtion joint material for the grout, its kinda messy but it makes a real good joint that moves as the weather changes.

Take these guys that run hot water thru the slab inside the house and tile the floor there is a fair amount of temp change when its first cranked up during the first freeze. The wife of John Mon's Father did this, He bought some high $ tile,like Com stuff 5/8'' thick and perfect sizeing the grout line is like 1/8'' they used a simular material for the joints.Thats where Im at,another thing the Ccooms needs to ponder.. how to drain your project I am thinking there is no fall in the framing. Mabey some slots in the bottom plates and a flat mop?

Still Thinking John Mon

I know that Sanitred holds water really well over a long period.....people are using it to line koi ponds!! Since it is a rubberized product, movement should not affect it. I would plan to periodically re-coat the porch too. I know that lifetime guarantees rarely last a lifetime.

You're right about the drainage...the project was not designed to drain. It is a totally flat floor. One big plus....this corner of the house rarely has rain blowing towards it. Rain blows onto the front of the house but not the back, except for the rare freak storms.

Go Get Em man. I am intersted in how it holds up over time. J

Cindy, you will be trying to change the nature of the partical board,that is keeping it together when exposed to moisture and weather exchange.A perservative offers no effort with these things.

After the basement sealer is on the same forces will work on it combined with Folks walking on it,tables and chairs landing on it and being moved around things like that. Combined with different kinds of weight will be the 3/4 partical board landing on joists 24'' on center or even 16'' on center, floor joists are usually 24, anyway there will be movement inbetween the joists as Folks walk around on the floor. That stuff is an underlament/sheathing not a finish floor.

On the other hand no one I know has ever tried what your planing, it might work! J