Sister form is similar to edge forms, differing only when panels are cast side by side, separated with only a common form. This statement describes sister form as:

• A. A type of steel support
• B. Identical to edge forms with no differences
• C. Similar to edge forms, differing only when panels are cast side by side with a common form
• D. A temporary form used only for foundations

Answer: (C)

In Tilt-Up, edge forms shape the exposed edges of wall panels. A sister form is basically a close cousin to edge forms—set up to produce the same edge characteristics—with one key distinction: when two panels are poured side by side and share a common form between them, the formwork arrangement changes. That shared boundary is what differentiates sister forms from edge forms, while outside of that shared boundary they behave like edge forms.

So the statement is the best description because it acknowledges the overall similarity to edge forms plus the specific condition where panels are cast next to each other using a common form, which is precisely where the difference lies. It isn’t a steel support, and it isn’t identical to edge forms in all cases, nor is it only a foundation form.