Can you use expanding foam or quickcrete for new letterbox?

paho

I need to put a new letterbox and stand up. 

I am 75 F. with a replacement shoulder, so after digging a hole for said post, will probably be out of action for a few days. I had a brilliant idea of using expanding foam to set the post in. 

What do you people who know these things think of my brilliant idea? ( for some reason, very few of my brilliant ideas actually work).

Next easiest solution I can see would be that concrete you just add water to.

Which option would be the cheapest. I'm in NZ.

As an aside...

My old letterbox broke, so I built a new one,  but it was askew, but so what! Attached to a large Totara post which has been there over 50 years, but sadly that has rotted above ground, and a decent gust of wind will down it.

Thanks for any input about the mailbox post 

MitchellMc

Welcome to the Bunnings Workshop community @paho. It's delightful to have you join us, and many thanks for your question about installing a letterbox.

Your expanding foam idea would probably work, but it won't be particularly solid. I know they often use this method to set posts this way in America, but typically the post is dug quite deep into the ground to counteract the lack of weight from the foam. Once the hole is dug, that's the majority of the work, so using the foam isn't going to help all that much. Once the hole is dug, you need to fill it with the recommended amount of water and pour Cemix 20kg Fastcrete in. No pre-mixing is required, and once the concrete is in the hole, you only need to prod it with a thin piece of timber.

It would be cheaper to use concrete than expanding foam. Please use your PPE when adding the concrete, including a face mask, safety glasses and gloves.

Please let me know if you have any questions.

Mitchell