Larger holes can be repaired using pre-made clom bricks or blocks bedded in a weak lime mortar and pinned together with non-ferrous supports.
Gellir atgyweirio tyllau mwy o faint drwy ddefnyddio brics neu flociau clom a wnaed o flaen llaw sydd wedi'u gosod mewn morter calch gwan a'u dal ynghyd ag ategolion anfferrus.