Yellow/Brown marks on white GRP Hull

[nigelstgeorge]

I keep getting yellow/brown patches on my white GRP hull which is cleaned and polished every year. Nothing removes the marks except either oxalic acid mixed with wallpaper paste which is amazingly quick and good or Y10 (expensive)

See photo attachment.

My question is how can I stop these marks appearing.

regards Nigel

 

[pvb]

About the only sure way is to stop taking the boat to sea!

You might experiment with different polishes. I use Meguiars #45 Polish followed by 2 applications of Meguiars #56 Pure Wax. Still get yellow stains, but not as bad as with other polishes.

 

[peter2407]

Try this for cleaning

Can't answer the prevention thing, but as for cure I last used the GRP Renovation System fro Wessex. I ended up using it neat rather than diluted, but did the whole boat with only a third of the contents, which at less than £20 was a bargain. The latest web site content says for professional use only, don't know why the change.

http://www.wessexchemicalfactors.co.uk/marine_exteriorcleaning.htm

 

[Lakesailor]

It almost looks like a design. I wonder if it's from an incomplete cleaning of the mould before your hull was layed-up? Almost like some bloke had been using a cloth in swirly motion to buff up the mould and didn't remove something that has pentetrated the gel coat, which goes on the mould first.

 

[pvb]

It almost looks like a design. I wonder if it's from an incomplete cleaning of the mould before your hull was layed-up? Almost like some bloke had been using a cloth in swirly motion to buff up the mould and didn't remove something that has pentetrated the gel coat, which goes on the mould first.

Might that be the result of uneven polishing?

 

[Lakesailor]

As he keeps getting them the uneven polishing may have been pre-production and the stain is locked into the gel coat. It migrates out after every cut'n'polish

just a thought.

 

[Stu Jackson]

We call that a "mustache." As the wax wears off, chemicals from the water grip the gelcoat and create a brown stain. We remove ours with a Davis product called FSR. It's an oxylitic acid in gel form. Ketchup has also been reported to work. Once cleaned off, rewax.

 

[charles_reed]

As he keeps getting them the uneven polishing may have been pre-production and the stain is locked into the gel coat. It migrates out after every cut'n'polish

just a thought.

Agree it's probably Gel-coat contamination.

If oxalic acid works - why bother any more - I've just been cleaning my hull with it - it's amazing how yellow white gelcoat becomes when exposed to UV reflected off the water.