Material and install recommendation

What's the overall size including the arch to the top.... of the green portion..

 

That looks like a hard coated eps foam sign. Do not try to screw into it. If you pull off the glued letters without breaking the hard coating over the foam you should be able to glue on a new lightweight face if the new face is small enough, maybe 2'x2'. Getting off the old adhesive from the existing letters will be difficult. These types of jobs are easy to lose money on.

 

ACM should work fine. Probably Lexel and mechanical fasteners so you don't have to worry about high winds "air freighting" the panels.

 

Not sure what your sponge background is, but you will hafta figure that out, so you can secure the new substrate to it or some buried backer in there.

For me, the look of the stones and cement, I would not use ACM. In no time at all, it's gonna streak and chalk out. At that size, I'd probably use a good piece of cedar or redwood and either sandblast or carve it and make it elegant. If they don't have the budget, then offer up some cutout letters on just about anything, but not ACM, unless you're gonna wrap it, but then again, you have a permanent sign, that's only gonna last 4 years. The other stuff will last 15 years and maybe need a cleaning every so often.

 

It's something like a Peachtree City Foamcraft Sign.

Home Depot sells 3/4"x 4ft x 8ft PVC panels with a wood grain imprinted in it for $99. Probably one of the better choices for a job like this.

I'd go with glue and screws to hold it down.

 

Whatever substrate, hand pattern and hand cut, or at least hand pattern and then do an endless number of patterns until it is nearly perfect. It's hard to figure out how much of a curve a designer randomly threw on this sort of panel, and everytime we have done it the curves match poorly. We have done this before with 090 aluminum with studs popped on the back, siliconed in place. Since it's recessed, there is almost no windload, but a healthy serving of silicone is never frowned upon. (Or lexel, everybody here loves that stuff)

 

Yup. We have a "stud gun" that you attach a ground to the panel and the gun onto the metal and POP, it welds a threaded stud (or a female threaded stud) onto the metal panel. Studs are limited in length, so in this case I would pop a female stud, .75" tall for a 1/4" piece of all thread. Then once on site, I would drill the holes and decide how long to cut the all thread, thread it in, then bend them slightly in opposing directions so it doesn't want to fall right off, coat the back in silicone, and force it in the holes.
It's really a fantastic addition to a welding shop, but if you do not have the capability in the first place, you can achieve a similar effect with glue and pads, just not as flush necessarily. Here's a picture. Please disregard the dust, and the circle that the stud is surrounded by is a mark that the router makes. We stopped making marks this size as it tends to dimple the face with all the heat and is very hard to align under the guard of the stud gun. Now the marks are 1.5" or so in diameter, but more precise.

 

Ive covered quite a few of those up over the years I usually use .032 or .040 aluminum (acm would also be fine) when you finish the panels you can lay it horizontally and silicone all letter to it Easy! I always just silicone my panels onto the structure using Gorilla tape or a couple screws that are placed discreetly

 

Great. We get our stud gun and studs from southern stud weld, and I'd wager a skilled welder could tack these on if this is a one off project. But the gun will weld a threaded stud that will twist in two before it breaks the weld.

 

Is the 3rd picture the finished sign?

 

How did you cut the metal?
Looks great, it's always nice to have a contractor who is willing to work with you!