Is there any reason why I can’t use decking stain on a new wood floor indoors? The floor is untreated redwood. It seems easier to apply and doesn’t need a top sealant, why not?
There really isn't any reason why you can't use an exterior deck stain indoors. The only concern I can think of is the smell of the stain, but you would have strong smells with other finishing systems.
I suggest you buy some redwood, like your flooring, and do some samples of different deck stains. This way you can see the color before staining the floor and also see if this is the effect you are after.
Most exterior products are meant to be used outdoors therefore they have pesticides, mildewcides and other things that we are not supposed to to breathing in while we are indoors.
I used decking stain on my internal wooden floors 4 years ago and its still going strong with some wear evident now on high foot flow areas like the kitchen. But I say full-marks for using decking stain indeed! By the way I used Ronseal decking stain.