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Need Advise on Building Large Arch Gate

I am trying to make a large arch-like gate out of foam. It would be about 8' high, it would have to stand on its own, it would have to be able to be broken apart into pieces and needs to be able to last in the elements. I was thinking of buying wet foam blocks (foam used by florists) and binding sets of them together and using spray foam to cover the outsides and paint it grey to make it look like rocks. It would be held together with dowels through each set of foam and have an anchor at the bottom using dowels hammered into the ground. 

Inspiration for this design came from the vault from the Borderlands game series 
http://i.imgur.com/DwMSsWb.jpg

I wanted to know if anyone has seen guides for making a fake stone arch or if anyone had ideas for making this (Especially if the ideas aren't too expensive)

Thanks

Toga_Dan1 year ago

theatre pieces are sometimes done with square steel frame faced with plywood, then styrofoam. Styrofoam is then carved, protected with cheesecloth and glue, and painted.

I have been trying now for about 2 hours but can't find the Youtube video again :(
For a similar project a guy used polystyrene foam blocks.
He did a 2D design model on the computer the same way a bridge or arch was done in the old days.
By getting the cutting angles on each piece right the pressure from the weight is distributed onto the mating surfaces and not outwards.
For extra stability he added sections of thin PVC pipe through the centre of each block.
Put together flat and feed a line through the pipe, line all pieces up and put good tension on the line - stand the thing up and enjoy.
Here is a basic picture of how it works, just ignore the stones around the arch.

http://old.bugsworthbasin.org/images/newslett/apri...

maybe wood then coat it with something to make it look like stone

https://www.instructables.com/id/Full-size-StarGate...

Floral foam is expensive, you can build it up cheaper with rigid insulation foam sheets from the home center and skin it with hardboard or even cardboard. Spray foam is expensive too in that volume. You could try to texture with a lightweight stucco or cement patcher mix. Good luck.