New wood threshold install; spray foam underneath a good/bad idea?

Hi,

I've watched Tom Silva's method for installing a wood threshold (re: https://www.thisoldhouse.com/how-to/...-new-threshold ). I really like the fact that he is able to do so without the use of nails or screws.

Tom Silva uses spray foam under the threshold--both as an insulator and an adhesive. When I look at my new threshold, however (see attached image), you can see very deliberate grooves or channels. It makes me wonder if those grooves are there for a good reason--perhaps to allow an air space to promote drying. If I use foam, I'll be filling those grooves and, if they really are there for a good reason, I'll be defeating the purpose.

If it matters, I'm planning on using a clear marine finish (Epiphanes) on all six sides.

So, what are your thoughts; go with the foam or allow the underbelly of the threshold to "breathe"?

Thanks in advance.

 

I think I would be inclined to face nail but that's me.

The groves are just part of the milling process and not intended for anything else, just like the back side of most wood flooring.

 

I don't know for sure about thresholds but flooring and moldings often have relief cuts on the back so it will set better on whatever substrate it's nailed to. That said, the back door to my shop has a homemade threshold with no relief cuts and has worked fine for over 15 yrs. IMO the main thing is to make sure there is some sort of sealant across the bottom side of the threshold.

 

Thanks @Marq1 and @marksr.
BTW @marksr, I did hear your recommendation for going with an aluminum threshold, but my wife wasn't having any of it