Webber, who was on pole at Spa last year and celebrates his 35th birthday on Saturday, then set the day's fastest lap of 1:50.321 in another rain-hit session after lunch, with Schumacher fading back to 11th.
Ferrari's Fernando Alonso and the McLaren pairing of Jenson Button and Lewis Hamilton followed the Australian with Red Bull's champion and runaway leader Sebastian Vettel back on 10th place.
Heidfeld to take Renault to court
Nick Heidfeld plans to take High Court action in London against Renault in a bid to force the British-based team to honour his contract as their lead racing driver.
Heidfeld was ousted from his seat in the team on Wednesday by Brazilian Bruno Senna, nephew of the late legendary former champion Ayrton Senna.
An interim agreement has given Senna an opportunity to race for Renault at both this weekend's Belgian Grand Prix and the Italian Grand Prix next month.
But Heidfeld is not prepared to take the slight lying down and intends to fight back and regain his seat.
In a statement on Friday, the normally mild-mannered racing driver said: "I was surprised by the team's intention to replace me and regret that things have developed this way. I cannot be very specific as something is pending.”