Hi, I've watched Tom Silva's method for installing a wood threshold (re: [URL="https://www.thisoldhouse.com/how-to/how-to-install-new-threshold"]https://www.thisoldhouse.com/how-to/how-to-install-new-threshold[/URL] ). 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.

Three or four years ago I power washed our three or four year old redwood deck and treated it with some kind of oil that had a very light transparent stain in it. It now needs cleaning and re treating. The wood is in good shape, just very dirty and covered with a lot of mildew. I've decided not to do it myself this time and got two bids from painting contractors. The first basically suggested doing what I did: power wash, light sanding, treat with oil (transparent stain added if desired). The second said that it needs chemical cleaning, followed by brightener, then treatment with the finishing product. He claims that if any existing stain (color) is left in the wood, a transparent stain and oil treatment will just sit on the surface of the wood and stay sticky forever, ie, it will not penetrate properly. Who to believe? Obviously one approach is cheaper than the other. PS, we are not interested in non transparent stain.