GRUNT! has been around a while, but following the release of a new formula, we thought it needed looking at again to see if it stands up to its claims for removing several common boating eyesores, from rust staining around fittings and yellow waterline stains, to exhaust stains and bird lime.

Now, the greatest aesthetic annoyance on my boat is rust leaching from the corners of a stainless plate I used to fill a big gap in the bulkhead behind my wind instrument.

Not only is it very visible, it’s also a constant reminder of why you shouldn’t use a grinder disc to cut stainless steel if you have already used the same disc on ferrous metal.

GRUNT! is applied with a paintbrush. Credit: Jake Frith

Because I cut the plate with an old blade that I’d used to cut mild steel with, the plate will forever have an edge containing enough mild steel content to leach rust down my bulkhead until I find time to replace it.

GRUNT! is applied with a paintbrush, left on to do its work for a few minutes, then rinsed off with fresh water.

Applying the product was easy, its gel-like consistency helping it stay put on this vertical surface.

The rust stains before GRUNT! was applied. Credit: Jake Frith

The product is as benign as promised in its application. It’s water-based and seems inoffensive to skin and nostrils.

It recommends on the packaging to leave it to do its work for 3-4 minutes, but I like living dangerously, so I left it for 15 minutes.

This, after all, is a stain that I have tried all manner of things to remove with zero success.

The rust stains after GRUNT! was applied. Credit: Jake Frith

The product was successful in removing a lot of the staining, but as the before and after pictures attest, it did not leave my bulkhead spotless.

It vastly improved what was an incredibly stubborn stain. It’s left me with a good feeling that multiple re-treatments with it might get the job done, so overall it’s pretty impressive. 

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