ᐅ Protect XPS insulation from UV exposure

Hello, we have some XPS insulation in a few basement window wells that is not covered with plaster or anything else. Since XPS is not UV resistant, it should actually be protected against that.
We contacted a few plastering companies, but the prices for this small amount were surprisingly high.

Would it be enough to simply apply some filler, or what would be the easiest way to protect the insulation from UV light? Or is it actually not necessary since there is relatively little sunlight reaching the area (because it’s a basement window well)?

I attached a photo. Thanks and best regards

Hausbaer

Order an HPL panel in your desired color (available in almost all RAL colors) with a thickness of 2–3mm (0.08–0.12 inches) cut to size and simply glue it on – done! These panels are completely weather-resistant and UV-stable. Polycarbonate sheets could also work. However, none of these options can be done for 50€.

What about buying and applying the plaster yourself? At this point, appearance should be secondary, and it’s quite manageable to do the work on your own. Including painting, it should easily be doable for under 100€, with a six-pack of beer already accounted for ;-)

One tub of solvent-free black paint, a brush or roller, and you're all set.

So far, we have only received quotes above 1000 € for plastering companies. One company said that corner beads and mesh are necessary to be able to apply the plaster at all (otherwise it supposedly won’t hold due to moisture). The exterior plaster is very expensive, and the work is difficult to carry out because it is in the basement shaft.

Is there any truth to this, or is it just a rip-off?

Working in the basement shaft is always uncomfortable, that’s true, but charging over €1,000 (about $1,100) for plastering and painting just 1 square meter (11 square feet) is outrageous. The mesh comes in 25m (27 yards) rolls for around €100 (about $110). The 2m (6.5 feet) of mesh and 5kg (11 lbs) of filler, plaster, and paint might cost generously around €100 (about $110). Small materials like corner beads, and so on, about €30 (about $33). Asking for €870 (about $960) for two half days of work (including drying time) is really steep, in my opinion.

This kind of job is perfect for posting as a task on a DIY platform. Experienced DIYers who know a bit about plastering should be able to handle it. I would never pay more than €500 (about $550) for plastering a light shaft. For €200-300 (about $220-$330), you can get very good quality HPL panels as I mentioned before, and with the €800 (about $880) you save, you can do something better.

Edit:
Take a look at colored stone plaster as well — it’s a cool alternative and UV stable with the right resin.