TIL: 9th September 2023 — how to scrape off a hardened polyurethane foam

A few months ago I went on a mission of tidying up some cables I had running outside of my house's boiler/server room. This involved drilling a major hole in 600mm of hard wall in order to guide the cable (and a massive connector) to the equipment inside. Needless to say I left more than one hole during the course of entirely botching several attempts.

After finally completing the cable work I filled the "extra" holes with polyurethane foam, which is a great insulator and works its way to fill all the crevices while hardening. Having almost no experience in this I didn't take precautions to cover the surfaces onto which it might drip. Neither did I know that after hardening, it can't be easily removed.

So next morning, predictably, I found the hardened foam all over the porous plastered exterior wall and some more on the composite decking. Nothing apart from cutting it off could be done at that point, but I didn't want to damage the affected surfaces too much.

Several months of procrastinating later... I found this gem — a PU remover (e.g. from Soudal).

It's basically magic. Apply the paste, wait 30-60m, scrape it off and wash. Repeat if needed. It's gone from the porous plaster — no marks or stains, like nothing happened!

Although composite board wasn't as good after two passes due to many small grooves that are very hard to scrape :/

Lessons learned: don't wait for PU to harden — clean it off immediately, always cover the surfaces when there's a risk of spillage.