Mortero Blanco Capa Fino Impermeable

Originally there was a gap of ca 1 cm around the window frames that was filled with some kind of gypsum plaster. The builders that looked at it made a sucking noise, because gypsum loves water. It does not rain here often, (29º and lovely today), but still. There was a water resistant wall paint over the gypsum, that probably saved the day.

And here is how I do it: I stick a trowel along the wood of the window frame, and fill the rest.

That leaves a gap of ca 2 mm, that I will fill later with a non-silicone caulk, so we have a water resistant elastic junction. Clever, huh.