Question re concrete curb for fence

I am taking down my 3' white picket fence to replace it with an 'iron' fence of the same height. (I can weld so I'll make the new steel fence.)
I want pour a continuous curb that will go under the fence. The fence posts (steel) will bolt onto the curb. I think I need to make the curb between 6 to 8 inches wide--haven't figured this out yet. I reckon 6" would be okay in the sense that there is no substantial weight bearing downward onto the concrete. However, the fence posts will have base plates welded to them and I might need a wider curb so the bolts do not get too close to the edge (to prevent cracking the edge of the concrete out where the bolts go in). Comments on this hoped for and welcomed.
Also, I am not sure how deep to go with the curb. We live on southern Vancouver Island with a climate like Seattle. We don't get much in the way of frost and it never goes deep. So, I thought I probably could go down around 16" below the ground surface and not have to worry about frost problems. (I think I'd like the curb to come about 2" above ground.) I don't know if this is right thinking or not so I'd be happy to get comments.
Finally, I think I need to also be concerned about going deep enough so the fence could not be pushed over if somebody leans on it. Is 16" deep enough for that?
Thank you in advance, David Todtman
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my concerns wopuld be the posts rusting causing thew curb to crack. that happened to my and all my neighbors homes all the concrete porces had to be replaced or another work around found
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I don't think the posts will rust. If they were set into the concrete, then there is that risk. I've seen what you are referring to--the metal just 'melts' away from rust where it enters the concrete. My posts will not be set into the concrete but rather they will be fastened to the top of the concrete by base plates. The base plates will be welded to the bottom of the fence post. The posts will be painted which will protect the surface from rust.

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_Something_ will be going into the concrete: just make sure that it's rust free and you're good to go: concrete won't keep out water on it's own for the most part: so steel in it can rust and destroy the concrete work.
As to the curb, the issue isn't the amount of weight yo're going to be putting on it, but how big and deep it needs to be to keep from moving about. This is non trivial. But are you planning on putting these in yourself? I have vague recollections of concrete guys with reasonably automated curb making devices offering ther services for lawn/garden edging who would both have a good idea what you need and be able to give it to you fairly cheap.
John

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Hi David. Ken from Maple Ridge here. I'm a concrete contractor and here is my 2 cents. You have asked how high, wide and deep, right?
#1 Height Here's something to ponder: Is there going to be grass next to the new fence? I'm asking because you could actually set the elevation of the concrete curb to your desired lawn height. Then mowing is much easier. (you'll be able to drive or push your mower on the curb.) Personally, if you don't mind weedwacking, it will be more visually pleasing if you do pour the curb slightly higher than the lawn or any other landscaping.
#2 Width Since you DO know how to weld, why not make up some small steel plates with anchors on the bottom and actually pour them into the new concrete at the required spacing? After the forms are stripped, you'll be able to weld your fence posts to these. Not very nice if you ever have to remove a section, but it may work better if you will never have to remove them. With the plates installed in the curb, you'll be able to go with a 8 or maybe even 6" width.
#3 Depth
DO NOT get a curbing company to do this for you. They do not pour the curbing deep enough for adequete frost protection and you'll probably be able to just push over the fence after you mount it on the curbing. IF you want a permanent fixture, I highly recommend a small (but necessary) footing under your curb. You can easily get away with 16" wide and 4-6" thick. Pour the curb on top of this to whatever finished height you decide on.
#4 One More Thing A couple rows of 10mm steel in the footing and a couple more in the curb will reduce movement in the curb after it cracks. IT WILL CRACK! You didn't mention the length of the fence, but it will have to crack to release stress due to freeze/thaw and shrinkage.
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