Pig, Quelk or Gorret? All three are regional terms used to describe a deviance in level between the two skins of a cavity wall.
According to the textbooks the skins should be at the same level, as every three bricks laid on the outer skin should match the height of one block laid on the inner skin. The reality is different.
It is common for skins to drift out of level and one can witness the tell-tale signs to correct the levels on the inner skin where lintels are encountered and most prominently at plate level. The use of conventional dpc within a cavity wall at changes of level and abutments can be problematic at the best of times. But when skins are out of alignment the undertaking is even more challenging. And if a shaped cloak is used that requires building into both skins, it cannot be incorporated correctly if the skins are adrift.
The photograph captures an example of skins running adrift despite both being constructed of the same sized block work.
Cavity Trays manufactures preformed cavitrays with adjustable cavity upstands. These are self-supporting so do not require building into the inner skin. Therefore if the levels are adrift it does not affect the functionality of the tray. Each upstand is hinged so it can take up the cavity width encountered as opposed to the cavity width anticipated. It means the cavity is always fully protected. Not penetrating the inner skin means laying of that skin can proceed more easily. The bedding courses remain uninterrupted so possible air tightness (or lack of it) is not compromised.
Cavitrays with adjustable cavity upstands permit the contractor to overcome pigs, quelks and gorrets or whatever the mason chooses to call the discrepancy!
European Technical Approval has been awarded to Cavity Trays Ltd and the Type X cavitray is just one of a range of trays offered with the adjustable tray upstand.