Sometimes when designing a set you have to change the type of material the set is made of. This could happen for a number of reasons; it's too expensive (number one reason), it's difficult to work with, it may affect the lighting design or it wasn't what you thought it would be.
This happened just this past week. Don't panic it will be OK! It might not be 100% the way you want but no one will really know the changes but you and your design team.
Example, I had to change all of the muslin walls to luan walls (thin plywood). I know it would have looked flawless with the material but I had to make the change. I had to ask myself a couple of questions before making this decision. Did it change the integrity of the design? No. Does it really look that different? No. Can the lighting designer work with new change? Yes. Does it fit within budget now? Yes. Answer: It's OK then. Just make sure the producer is happy and knows about the change.
I know the show, in my mind, would have looked like more of want I wanted but sometimes these things happen. It part of the design process.
Enjoy reading my encounters in and around theatre set design.