Any tips for cleaning GRP?

[cozzykim]

I have a project, to restore this old family Sailfish 18 to sailing condition.
It has been neglected for about 20 years and is completely coated with lichen and algae.

Powerwashing has left a lot of grey rings on the white gelcoat, does anyone have any tips for removing the lichen residue without doing too much damage?
Thanks.

 

[MoodySabre]

There are a couple of boats that have bad marking like that in Bradwell. It looks as though it has etched into the gelcoat. If that is the case then I imagine a sanding down and a painted finish will be necessary.

 

[DavidTav]

I would recommend to try using Oxalic acid or a product which includes this as an active ingredient. Persdonally, I wouldn't be too quick to resort to a painted finish.

 

[Searush]

I got a bottle of Simoniz(?) Marine Cleaner & one of Marine wax from the local car accessory shop for about a tenner total. It took a fair bit of graft (hand polishing with damp rags) but in a day I did a 32' hull (shipsides only) in a day & got excellent results. Not quite such bad marking as you clearly have, but there was a lot of deep staining that took extra work, but it did come up OK in the end.

 

[pouch]

Just been doing some refreshing of GRP gel coat myself.

If you have a resonable depth of gel coat you can flat back using 1000grit wet and dry paper with water. Then after use a cutting compund like Farecla G3 (more abrasive) or G10.
Decent coat of wax after and it looks like new!

 

[cagey]

I have a project, to restore this old family Sailfish 18 to sailing condition.
It has been neglected for about 20 years and is completely coated with lichen and algae.

Powerwashing has left a lot of grey rings on the white gelcoat, does anyone have any tips for removing the lichen residue without doing too much damage?
Thanks.

use the black Harpic no joke it is brilliant at remomoving stains from grp. For years have used the oxalic/ paste and other methods but they needed hard work to get a result.
For the last 2 years I have used a combination: Evode Brick Cleaner for Calcium type fouling. Oxalic for ferrous stains, Evode Patio Cleaner for organic stains, and then Harpic. The only hard work is putting the polish on and then making it shine.
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