Metal Tie Holder design?

[Duffy]

Aluminum and wet concrete is BAD news. The pH of wet concrete is very high and it will aggresively attack the aluminum producing a bulky oxide salt. a bit like salty ice melt on roadside concrete. Coated sheet steel about 18 Ga would probably be a better and cheaper choice. Remember, the washers dont HAVE to be round! Square is quicker, cheaper and as easy to index for the "crossed hole" step.