Glue it to the masonry with expanding foam behind. Won't even warp.
It's what we call a bodge job or cowboy carpentry. If foam is overused it can also bow the casing. Also no longer meets fire regs.
Can you explain that more for me? Isn't foam inherently more fire retardant than the air that would otherwise be behind the casing?
In independent testing by both labs and various fire brigades many expanding foams have been found to combust readily at far lower temperatures than was previously thought, as well as producing toxic vapours/smoke in a number of instances Even some of the pink "fire foams" are little better - only a burn test of the complete system can prove the combination of elements (and obviously that isn't a goer for one-off doors). Mineral wool, an old tried and tested packing, in conjunction with intumescent caulk are now the preferred approach for untestable situations as this has been proven to be effective over a very long period. This came up when a couple of us were required to undertake the FDIS Diploma in Fire Doors training in order to insect and pass the doors our teams were installing (another royal PIA)
Yes, and if it is 1 hour rated a 10mm layer of intumescent caulk (fire mastic or fire stopping) is required between the wool and the back surface of the architrave
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