My current prototyping project involves an air ram which I use as a pump. Its cylinder is drawn copper tube (150mm nominal) and its head and tail are 3D Printed (polylactic acid, PLA). Its working pressure is only 0.1Bar.

My problem is that the head and tail leak air right through the PLA.

My printer uses 0.8mm nozzles and the wall thicknesses involved are 4mm (with the current printer settings this means that the walls are solid PLA, there is no matrix infill involved).

I find it hard to believe my eyes, but it is true. Air escapes right through the printed PLA walls. It gets worse ... I have painted the pressurised surfaces of the head and tail with Rust-oleum sealant and the air still gets through!

Does anyone have a solution to this problem?
I'd love to hear it because I'm all out of ideas.