Grinding Down Fiberglass

There’s so much of our boat we’ve ripped out. There are no cabinets or bulkheads left in the back portion of the boat, other than the structural ones that run port-starboard. Most of the cabinetry came out relatively easily (once we remembered the simple tool of a lever!) with the fiberglass tape providing less grab than full cloth would have. For once not completely overbuilt!

When the shelving and bulkheads come out with tape attached, it’s relatively quick work to clean it all up and prep for paint or a new bulkhead. Where we have to use the oscillating tool to cut through the fiberglass (in areas where we worry about pulling apart something that is more structural), a ridge is left that needs to be ground down.

Grinding is, the way I’m describing it here, a form of really, really aggressive sanding. There are also angle grinders you can use as a cutting tool; the spaces I’m talking about here are against the hull where a tool like that just doesn’t fit. If it fit, we’d do that instead of an oscillating tool as it is more powerful.

Note: we also have to spend some time removing old carpet adhesive that someone (ahem, Nica) in an ill-advised move used to adhere well, carpet, to the hull way back when. I’ll use this same method on that, but the sanding discs will gum up way faster than they wear out. In addition, I don’t need to be AS precise because all that adhesive is inside cabinets and will be painted over.

How can you grind fiberglass more safely and easily? Here are a few tips.

Have a vacuum cleaner (shop vac might be more powerful!) running. For us, a second person to hold the vacuum nozzle makes it far more effective. If you don’t have a second person, maybe duct tape the hose to the grinder so it captures as much dust as possible.

*Regular sandpaper, but you get the idea with the vacuum (and a second set of hands!)*

Wear a respirator to protect your lungs from the fiberglass dust
Wear a tyvek suit or other easily-removed set of protective clothing. Those fibers get everywhere and are itchy as heck!
Use a sanding backer pad or attachment for your drill, with 40 or 60 grit paper. We’ve found the self-stick stuff to be cheaper and easier to install as opposed to the hook and loop variety, but it’s all up to you. Be prepared to go through this stuff fairly quickly; if you don’t, great. If you do, though, you’ll have enough to last the project!
A headlamp helps keep an eye on the area you’re focusing on, even if there is good lighting otherwise.
Using a sander doesn’t remove the need for elbow grease. You’ll have to apply pressure against the ridge to make progress in removing it. Make sure you’re in a comfortable position, or at least get yourself as comfortable as possible.

Grinding down fiberglass is not a lot of fun, frankly. It’s hard work even with the right tools, makes a horrible dusty mess of fine slivers of glass that get everywhere, and takes way longer than you think it should. Still, not grinding it down would mean leaving a very sharp ridge of fiberglass behind. Be safe!

Note: links here are to show you what I mean, in case a tool or idea is not familiar to you. They are also affiliate links. As an Amazon affiliate, I earn through qualifying purchases.