How to cut fiberglass shower for fixtures?

A new fiberglass shower is being put in. How do we cut the holes for the plumbing fixtures without damaging the fiberglass.

Grit-edged hole saw.

Is this the only thing that works? We own the regular non abrasive hole saws. We’d have to get two different sized bits which would run a lot of money. The holes don’t have to have a perfect smooth edge. We just need to be sure that what we do doesn’t make a giant crack. We can back the fiberglass with a block of wood for cutting purposes.

A regular hole saw will work, but it will dull the blade, and maybe ruin it in short order. I don’t think you are going to crack fiberglass - it’s a woven material and very, very tough.

I doubt it will crack either. Tryasking here instead.

It looks like we’ll try the hole saws we have. Thanks.

It worked.

Awesome. One trick is to cover the area you will be sawing with masking tape. It seems to help preventing problems with drilling/cutting into a lot of surfaces.

For future reference, you can also use a RotoZip tool on light fiberglass, but it is pretty much of a pain.