Colleague in Nigeria wants to cast holes in concrete for 3″ diameter tennis net posts but can’t get chunks of polystyrene to cut into cylinders then burn out. I’ve suggested getting a can of expanding foam and casting a 3″ cylinder inside a roll of cardboard but he doesn’t think he can get that either.

Any clever suggestions for a low-tech solution?

Water bottles 😀

Pop a couple of pieces of soil pipe in the hole and pour around it?

tennis net post, wrapped in a (or 2) plaggy bag ?

PE pipe?

Plastic or cardboard tubes is what they use round here. Plastic stays in, cardboard gets burnt or peeled out.

Ice? 🙂

4 inch pipe, or ducting, cast in to concrete. Put net posts in place and fill round with sharp sand, compact and then put a 1 inch sand/cement cap on. No need to burn/cut anything away and removable in future if needed. This is how we put sign posts in situ

tennis net post, wrapped in a (or 2) plaggy bag ?

+1 – you can always add a mm or two with foil or plastic or cardboard.

I like the sand idea. How much will that resist movement as the ball hits the net?

I like the sand idea. How much will that resist movement as the ball hits the net?

It’ll be fine if properly compacted, or even use grit sand to compact better – do a decent strong mix of your concrete/sand, cement cap – leave the sand an inch below surface and fill to surface with your cap. 15mtr lighting columns are even installed using this method

That sounds suitably low-tech thanks! He could even compact the same crushed terracotta tiles that are spread and rolled to make up the clay surface.

3″ OD diameter capped pipe smeared in grease with lots left proud. Quick twist and it should just pull out after concrete has set enough to walk on.. Or use 3″ID pipe and leave in the concrete flush to surface.