If Blob doesn't want to be moved then almost nothing can move him. It depends on the strength of his gravitational field. You can catch him off guard, by smashing the ground beneath him, or a surprise attack, but if he's 'planted', almost nothing moves him.
Classic WonderMan couldn't move an unconscious Blob. Hulk coudn't move him until he got really pissed off (and that time Blob was standing on a grassy field, i.e. not a very solid surface).
When he's airborne he seems more vulnerable, but the times Colossus has got him in that position, he's had help from Wolverine.
This a pretty even fight.