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6 mm ACM or MDO?

I have a sign to replace that is currently 4ft x 8ft double sided 1/2” MDO. It is attached bolted to angle iron on each end only, nothing on the top or bottom. It has been there for years this way though I didn’t do the original install. My question is could I get by going back with 6mm ACM attached at each end only, possibly add another piece of flat iron or angle iron to sandwich the sign board between it and the existing angle or should I go back with MDO bolted to the angle iron at each end like it was. I’ve used a lot of 3mm ACM but none of the 6mm. I just really don’t want to have to paint and prep the MDO if the 6mm ACM will suffice. Thanks in advance.


Active Member
We use 6mm ACM for site signs all the time. Though we typically frame it out on all four sides. Unless it's 4ft or smaller.


Old member
ACM will work if you frame it on the top and bottom as well as the sides. It just isn't designed for the stress load. It might work for a 4x4 or smaller, but a 4x8 will catch too much wind.

You might consider LustreBoard® or something similar. It has the modulus strength of plywood with an aluminum top laminate much like ACM. You will need to finish the edges (or glue on some plastic edge trim), but that material will be much more confidence inspiring!


Premium Subscriber
Go with 10mm..... or is it 16 mm ACM. I forget. Anyway, that will handle all your problems.