I am planning on installing 4"x6"x3/4" end grain wood tiles on a cantilevered three season porch (solarium). It has been sitting there with only OSB subflooring since I built the house over 30 years ago. It is a long, narrow room, approx. 8'x24', with a planned herringbone or basketweave pattern.

The question is can I just use tile adhesive over the OSB? Or do I need to add an underlayment such as cement board?

Any experience??

Depending upon the condition of the OSB, I think I would put down a layer of 1/4" plywood so your adhesive had a clean surface to bond to. I don't think cement board would be necessary but see what the instructions call for.

You will be amazed and stupified if it ever gets wet!

There ain't no instructions. I'm ripping the timbers on my bandsaw mill, and cutting the "tiles" with a cutoff miter saw. I'm thinking that 1/4" plywood is a good idea, probably in A/C Not nearly the pain of cement board and should provide a decent bond.

As far as getting wet, I ain't afraid: they will be well sealed.

If I was putting wood "tiles" on a plywood floor, I'd use wood glue, adhesive or epoxy rather than a tile adhesive. Normal shrinkage/expansion of wood products would seem to be asking for trouble with tile adhesive.

I hadn't yet considered the specific adhesive. This project is still in the planning stage. I still need to rip, cut, and dry the tiles. Probably won't be ready to install for another six months.

You have a very good point, though. I know there are plenty of wood adhesives available that get troweled on. Very similar to tile adhesive, but, intended for wood. Without your reminder I just may grabbed the wrong one without thinking.

I've seen the floor your talking about on YouTube and think it looks really cool. Thought about doing that myself one day but very labor intensive! Extremely durable no doubt!

Because of that in bold above, I think such a project is doomed to failure.
I worked in a cabinet shop with an end grain floor. The pieces were about 1 1/2" x 4" x 6"long. During humid parts of the summer the floor had a slight hump and in the winter cracks opened an filled with saw dust. It can be very hard to keep even the more stable species of wood from moving.
If a piece contains the pith(center growth ring), radial shrinkage/cracking will give you problems

Should make a nice floor , what wood are you planning to use or different varieties. Might consider whether to use heartwood and risk cracking or cants from a larger log. Also different shrinkage rates of different varieties. . I have a mill as well, sounds like a fun project. old 243

I don't know what climate you have there I check out some of the epoxies such as West system. It still needs to be UV protected. I think the OSB would give you a rather uneven surface versus a AC type plywood base or Baltic Birch. Are you planning on sanding the floor once you have it installed?

I'm going through my woodpile right now trying to make that decision. I have oak, ash, elm, maple, and walnut available. Strangely, though, I am leaning toward cottonwood. It is really a pretty wood, and not valuable for anything else. If I go with the basketweave I'll probably alternate with a much darker, or lighter wood, such as walnut or birch.
Sanding after installation will surely be necessary. Even with the best cutting jig, I know I'll have some variation in heights.
It wouldn't be my first failure! Oh, well, nothing ventured; nothing gained.

Cottonwood is very soft, one of our softest.

This room gets very little traffic, so, no concerns about durability as related to wear.

Being a deciduous angiosperm, cottonwood is grouped as a "Hardwood" but it is in practice way down the hardness scale, barely harder than most pines.
Balsa wood can be carved with a finger nail, but it is also in the hardwood group.

Realistically, with a Janka hardness in the 300's it isn't even as hard as some pines. I have no plans to press a .440" steel ball into it, though. Wood is usually rated for its bending and shear strength, This stuff is in compression, No forklifts are going to go rolling down it, so no worries.

Even as a dance floor I doubt Chubby Checker could phase it.

Good luck with the project. Please post lots of pics of the process and finished floor. Should look good. I hope it holds up for you. I

Creating a floor with the end grain up will expand from humidity in the air so severely, it will blow out your wall boards, and/or teepee high enough for a small child to sleep under.
Epoxy under it may reduce the possibility of the teepee effect, but you would be well-advised to leave at least an inch gap at all walls to prevent blowing out your walls.
A friend of mine had a similar disaster on a professionally installed conventional sawn hickory floor. Not the same scenario which you are trying to do, but illustrates the importance of proper installation, especially gaps at the entire perimeter.

I like your idea of the end grain wood floor. It's hard to say without looking at it whether your osb has a surface you can glue to. If it is solid and clean I would not be afraid to glue right to the osb. I would stay away from a rigid adhesive for this purpose as the floor will move and you need a little flexibility. There are plenty of commercially available flexible adhesives that also act as a moisture barrier and will seal the underside of the floor. They are a little pricey though. A 1" gap around the perimeter is a very good idea if you have a lot of humidity change. If you do have a lot of humidity variation you may want a 1"expansion gap across the middle of the floor to cut that 24' down to 12' of solid floor. If there is not that much humidity change I wouldn't worry about it. We are lucky here in the high desert of Idaho as the humidity is very stable and the only real movement we get in a wood floor is from water damage. You can pm with any questions.
Bob

While I have not seen that, I know that baseboard can cover a decent gap.

Expansion joint down the middle? Interesting! I'll keep that in mind as I work out the pattern. It just might be a natural with herringbone.

The floor in the shop I spoke of earlier had 3X3 angle iron along the walls to allow for expansion and shrinkage. The room was large but the six inches was often still too little along the walls with the pieces running width wise between them.