The door that divides two halves of the building here is on a mag
catch linked to the smoke alarms and has a small spring loaded arm to
close it when the smokes trigger and the catch releases.

Trouble is it closes but with quite a thump, that has to be there to
ensure it closes properly past the intumescent seal. Is there
anything like the soft close buffers you can get for kitchen unit
doors/drawers? These gently stop the closing door then compress over
a few seconds to let the door/drawer close fully.

This is a standard sized 40 mm engineered solid wood door so has a
reasonable mass.

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Cheers
Dave.