I have done some looking but haven't found an answer to this unique problem so I thought I would ask all of you.

I have some boards (they were the backs of church pews), red oak, 3/4" thick that are 14' by 21". The length is made up of two, 7' sections finger jointed together. The widths are made up of 6 or 7, 3-4" boards. They are lacquered on both sides and are kiln dried and probably 20 years old from my neighborhood.

I would like to use these, as they are, for flooring without ripping them down. The boards are square edged. What would be the best way to attach them? I'm thinking of screwing them down using a T-slot that would be covered with a plug. I'm thinking two per width and every three feet. This would allow for expansion/contraction yet hold them firmly in place.

Any suggestions?

It is recommended to fasten flooring at least every foot along the length.
I would go with four screws across the width. One at each edge and two in the field. You could fasten alternating rows of the planks in the field, also.

Thanks Pete,

Would you recommend an adhesive? I know they say the adhesive will allow for expansion/contraction but a 21" board will move and I'm concerned about the adhesive restricting movement and causing cracks.

I'm not married to the screw idea. Would suggest another?

Dave:

You'll still need to get those boards to lay flat if you consider adhesive. 21 inches wide is scary to begin with...and 14 feet long! wheew. Okay, I see the rest.

Sealed on the underside will give some protection. How much it is sealed could work against you with adhesive when thinking of glue bonding. What's underneath the planned floor area? That's where many problems begin that few really understand. Is it dry?

You must have a ton of this stuff if you're using it as flooring?

I have 23 of these boards. They are surprisingly flat, given their use. The subfloor is 1" board run diagonally with 1/2" ply on top. They are 50 years old in Colorado, so very dry.

The easiest way to add glue to your installation would be to get some of the Bona sausages and one of their guns. Put a bead across the "plank" under the screw rows. It's less messy than a full trowel glue. The glue remains somewhat flexible so it will give with traffic and flex. When the whole floor is covered with your planks that are acclimated the glue will help prevent minor cupping which could occur during a high humidity event, and hold them in place to the underlayment during a dry winter season.
Remember that flooring has a built in tolerance for seasonal change from the way the surface touches before the bottom. Slide a couple of T&G planks together and you can see how there is a tiny gap between the pieces at the bottom. You might want to put a chamfer on the underside of each plank as they are laid so the top edge can compress if the plank swells a little, before you start to get cupping.