Heathrow and Gatwick airports have said they are monitoring porous concrete found on their sites after school closures linked to the material.
The airports had previously found the reinforced autoclaved aerated concrete (Raac) before extensive news coverage over its use.
Heathrow said it had the means to keep it safe until it can put “permanent solutions” in place.
Gatwick said it has found no cause for concern.
The discovery of the concrete, which can crumble, in schools and public buildings has led to a number of closures since the start of September.