Hi,
First time posting after reading for hours about slabs and subfloors and solid hw flooring.

I'd love to be able to put down a 3/4" plywood subfloor, then nail the 3/4" thick, 8" wide reclaimed fir planks to that. My problem is that the added 1.5"+ to do it correctly is all but a deal breaker in my house.

I'm contemplating gluing down the planks to the slab as has been done in retail stores using reclaimed boards from this same vendor. I know it's not a good idea but it may be our only chance for solid hw floors. I haven't yet found an engineered floor that would look right in our very casual, sort of shabby, beach house, or else I'd go that route. Every engineered floor I've seen looks so finished and neutered of its wood origins.

I'm in southern California and the slab is at grade.

If I went the glue down route, which glue would you recommend? Also, would you lay down a 6 mil poly vapor barrier first and then glue to that barrier? Will the planks stick to the vapor barrier?
Should I treat the underside of the planks before gluing them?

Lastly, I don't need a hundred year floor, which is why I'm considering this option. If it lasted 10-15 years, I'd be happy with the investment.

Thanks.

You would need a manufacturer's "system" consisting of their vapor barrier and their adhesive, to even stand a chance. Here they are:

1) SIKA ( http://www.sikaconstruction.com/con-prod-app-wfa.htm )
2) Bostik's ( http://www.bostik-us.com/markets/floori ... fault.html )
3) Dritac ( http://dritac.com/home.php )
4) Franklin Titebond ( http://www.titebond.com/IntroPageTB.ASP ... prodcat=13 )

Each manufacturer makes a "moisture barrier" product and an adhesive that works with it. They are expensive. Laying down plastic will not work unless you install a plywood underlayment over it. Alternatively, I saw an article about some "contractor" that screws the planks down directly to the concrete over the plastic vapor barrier. He laid the vapor barrier and then laid each plank by drilling holes every 16" OC, one on each side of the board, about 1.5" in from the edge. He used Tapcon concrete screws. He then plugged the holes and had the floors sanded. I can't say if this works. It might. It would sure be time consuming.

Thanks for your suggestions.
I'll look into them.

Okay, I read up on all four manufacturers and their products at their websites. They all sound like they are the best thing since sliced bread.

Do you have a preference amongst them?

Here's a fly in the ointmint...

I'm partial to Mapei Planniseal WFM, & 990 Adhesive.

http://www.mapei.us/

We use the Sika system, but because it is readily available, not because it is better. All the systems Gary recommended are fine, go with what you can get.
The Mapai system also presumably is as good as the others, never used it so cannot personally attest to that, but Floorologist wouldn't take a chance on an inferior product.
Good luck with the install, but you are gonna need clamp straps or floor jacks, I am sure.