The difference between loose thickness behind the screed and final compacted thickness. A common rule of thumb for dense-graded mix is a quarter inch of roll-down for every inch of compacted lift, so a 2-inch lift goes down about 2.5 inches loose. The screwman sets loose depth to allow for it, and joint matching leaves the new side just high enough to roll down flush.
Figure a quarter inch of roll-down per inch, so carry it two and a half loose and it'll finish at two.
Also heard as
- rolldown
- roll down
Related terms
Screwman
Crew slang for the screed operator, who sets mat thickness, slope and width at the back of the paver.
Joint matching
Setting the screed so the new mat overlaps the old edge slightly and sits just high enough to roll down flush.
Lift
One layer of mix placed and compacted in a single pass of the paver.