It doesn't freeze much down here. The Oklahoma sandstone isn't hard like stone but it isn't the softest stuff around either.
I will be using a sealer. It's the same stuff I use on stuff around fountains. The reasons for using the sealer is a fear of moisture finding a fissure and freezing--expanding or just weakening a section.
The stone is pretty solid with no visible fracture lines. So I am comfortable with it's integrity.
Around here we have soft limestone. Every now and then you'll see a newbie want to use it for landscaping. About three years later after repeated freeze--fracture-powdering they'll have a pile of dust. So I am aware of what you're talking about.
I once noticed a limestone boulder about the size of a car out in a pasture after they'd went through with a large water line. I asked the farmer why he'd allowed them to leave it. He explained that it would soak up water, freeze, break apart, soak up water again, refreeze, break into smaller pieces. In no time at all he'd have limestone which he'd plow into the field and all would be well.
The stone is done and ready to be installed into the gate. I'll be doing that later in the week. We got really lucky on it. When you see it I'm sure you'll agree.
I'm serious about getting lucky. Lucky is different from being good. Good only takes effort. Luck is like on the rock when I accidently turned it over moving it around and found the underside is the side I really wanted to work with. Luck is taking the cutting torch while doing something else and burnishing a scrap piece of the gate rock. Luck is a good thing!