Oxalic Acid / Yellowish Gelcoat

[Ribtecer]

Last winter I cleaned the hull of a great condition, but slightly yellowish hull of a Rib with Oxalic Acid, it was then waxed twice with a high quality marine polish, it came up beautifully and looked like new.

However after quite a short time of being used from a dry stack, the yellowish stain came back beneath the waterline.

Before the cleaning process was done a small chip on the keel was filled and faired, that area was rubbed smooth with wet and dry paper and then polished up. Interestingly that whole area new and old gelcoat has not gone yellow.

Has this happened to anyone else? If so what can I do to protect it and stop this yellowing coming back next season?

Many thanks in advance.

 

[Graham376]

Just one of the annual jobs for me, oxalic on the yellow above boot line which I've found polish doesn't stop.

 

[Concerto]

I would suspect the original gel coat is not UV stable. This is a problem with Westerly yachts from the late 70's and into the 80's. When you sanded the gel coat whilst doing the repairs, you removed the top surface of the gel coat which had become discoloured. This article I presented to the Westerly Owners Association should give you plenty of advice for you to follow. Once the gel coat is white, then seal it with at least 3 coats of Meguiars Flagship Premium Marine Wax as this will provide UV protection.

https://wiki.westerly-owners.co.uk/images/8/86/Gel_coat_renovation_19May2020.pdf

 

[Yngmar]

If your sanded & polished area stayed white and your old unsanded & polished area has turned yellow again, it implies the whole thing is due for a coarser polish or wet sanding to get rid of the layer of old, damaged gelcoat on top. The oxalic acid will just turn it back white, but it doesn't improve the surface.