The feelings of frustration were tempered by a discussion I had later with my roommate. It turns out that the vietnamese females were actually a bit upset about the day's work as well. They were not pleased that many of the American males were helping clean rather than helping do the manual labor. The American males were doing this because they knew that the American females wanted to help with the cement mixing and were being considerate by letting us pitch in. In contrast, the vietnamese students believed that we are working to complete a task as quickly as possible and that everyone should do the task they are most suited for. ie they believe that females are better at more fine detail tasks such as painting details on walls, whereas the males are better suited for heavy lifting.
This conversation led to much deep reflection on my part. On the one hand, given that we are ultimately trying to complete as much for the community as possible, it might make sense to put aside more principle based debates and do the work each person is best suited for. Yet, it is always possible to find an excuse not to stand up for gender equality. If you never make an issue of it, things will never change. Furthermore, the issue I had with this incident is that everyone was assuming that the males were stronger than the females. Just given that I am taller than the vietnamese males, it is certainly possible that I'm stronger than some of them. This incident was simply an interesting facette to examine gender relations in Vietnam, especially since while in Saigon I was surprised that I didn't experience much gender discrimination.