Vasconcelos - having been dropped twice as he progressed to 37 not out - batted right through the morning session at Wantage Road to add exactly 50 for the third wicket with Zaib, who posted an unbeaten 22.
That stand enabled Northamptonshire to reach lunch at 86 for two, with Luke Fletcher and Dane Paterson taking a wicket each, but further progress proved impossible after a heavy downpour during the interval left the playing surface saturated.
Umpires Neil Pratt and Richard Illingworth abandoned play for the day shortly after 3pm.
James Anderson starred as Lancashire got off to a strong start against Somerset before rain dampened the first day of their division one clash at Emirates Old Trafford.
Anderson, playing his fourth consecutive four-day game for the Red Rose and his final match before the sole Test against Ireland, gave notice of his readiness for England duty with a brilliant eight over opening spell during which he bowled five maidens, was hit for five runs and claimed the wickets of Steven Davies and Tom Abell.
Although Somerset had recovered from 12 for three to 109 for four by the time torrential rain hit the ground at 2.45pm, it was Anderson's spell that will have England supporters hoping for brighter days with the Ashes beginning in just over a month.
Day one of Leicestershire's division two match against Sussex at Grace Road also fell foul of a wet outfield.
The game is the second of Australia batter Steve Smith's three-match stint at Sussex, ahead of his country's World Test Championship final against India at the Oval on June 7 and the Ashes versus England, which starts at Edgbaston on June 16.
