Rust marks on GRP

[Ammonite]

Whats the best way of removing rust specks from white gelcoat and off white / grey moulded non slip deck caused by grinding mild steel (not me!) Oxalic? Thanks

 

[C08]

I have used Oxalic acid a few times but I find the Starbrite Rust Removal spray more effective.

 

[pvb]

Yes, oxalic acid. An easy way to do it is to buy a tub of Y10 or similar.

 

[Baggywrinkle]

Oxalic Acid got rid of the rust stains left by my old gas bottles.

 

[Fimacca]

|Expensive options are out there. I tried a cheap ebay powder, but the gel is much easier.
The below is the best I have used. - I don't know them - from dartmouth - and you get a decent amount of it. y10 expensive for what you get.....

BRIGHT COAT - GEL COAT DE-STAINER TREATMENT

 

[GHA]

Phosphoric acid works well, wickes used to do some called grout film remover, data sheets would show if they still do it.

 

[Ammonite]

Ive got a large tub of oxalic so will give that a try. Its great at removing waterline staining but I havent used it on rust before. Thanks

 

[Momac]

Unless of course hot metal has burned into the gel coat.

 

[Ammonite]

Unless of course hot metal has burned into the gel coat.

It was when the keelbolts were being replaced so Im hopeful this isnt the case and that the guys were just covered in the stuff as they walked in and out

 

[PaulRainbow]

When mixing powdered oxalic acid, mix it in warm water.

 

[Jamie Dundee]

When mixing powdered oxalic acid, mix it in warm water.

And if you mix with wall paper paste you have Y10

 

[PaulRainbow]

And if you mix with wall paper paste you have Y10

I also found using hot water and cornflower worked, but went thin again after a time. Might thicken make up after a few seconds in the microwave.

 

[Momac]

For rust and other stains on GRP I have used bar Keepers Friend Power Cream , which contains oxalic acid .
Apply to the stained area using a brush if required - go make a cup of tea or leave as long as is necessary and come back later and rinse off .

 

[masterofnone]

Whats the best way of removing rust specks from white gelcoat and off white / grey moulded non slip deck caused by grinding mild steel (not me!) Oxalic? Thanks

Y10 and a green pan scourer

 

[Jamie Dundee]

I appreciate its non slip decking but if you use oxalic you really need to re-seal the gel in some way or it will stain again. Starbright deck wash or similar perhaps.

 

[Mistroma]

Oxalic as everyone says (even the people suggesting Y10, Barkeeper's friend, Starbrite etc. because the active ingredient is virtually always oxalic acid). I think that one Starbrite desk wash contains EDTA which will act as a chelating agent to react with any metal ions on the surface of the deck.

Please note that the rate of reaction falls off a cliff at low temperatures. A stain will shift in minutes at 25-30 deg. C but take hours or even days at low temperature. I would say anything below 10 deg. C will be pretty slow to work. I used to slowly pour warm or hot water over the hull in cold weather, or sponge with pretty hot water. Dissolve in hot water as suggested to give a decent reaction rate or simply sail to Greece and use it on a sunny day.

I have used phosphoric acid to remove rust from steel and it should be good on very small metal particles on the surface of GRP. It was handy for spraying inside hollow sections on a car chassis and then just left there forever. The acid will convert the surface steel to a white phosphate powder (probably a mono-molecular layer) and excess does nothing further unless the surface is scratched to expose fresh metal.

You will be rinsing off excess phosphoric acid and I would imagine that it might disguise metal particles initially but rub off later and let more rust develop. It is just a theory as a lot will depend on the size of the metal particles. Oxalic acid is a first step and did permanently remove small rust flecks from the deck of my previous boat in fairly cold weather (probably March/April in Scotland). I had a pretty good moulded non-slip surface on the deck and that made it difficult to scrub out the metal particles.

 

[richardbrennan]

Just had exactly the same problem and have had good results with "Magica" rust remover. A little goes a long way.

 

[Mistroma]

Just had exactly the same problem and have had good results with "Magica" rust remover. A little goes a long way.

I haven't seen that one before and don't think it is commonly available in UK. Most other cleaners are an expensive way of buying oxalic acid with some surfactants and little else.

A quick check shows Magic contains.
1) Oxalic acid
2) Potassium tetroxalate dihydrate (The hemipotassium salt of oxalic acid)
3) Citric acid
4) Ammonium bifiuoride
5) Isopropyl alcohol

I have mixed citric acid and oxalic acid before and not surprised to see it here. Ammonium bifiuoride can be used to etch silica and I imagine it will have quite a strong effect on gelcoat. I might try mixing some of it up in future if I have a stubborn stain. I'll skip the Ammonium bifiuoride but probably have most of the other components in my garage along with some malic acid.

 

[longjohnsilver]

And if you mix with wall paper paste you have Y10

You most certainly do. At a fraction of the cost. But don't then spread it over the entire hull of a 48' boat. It will set and be very hard work washing it off. Don't ask how I know this! But the hull was very clean afterwards. All the stains disappeared.

 

[oldgit]

Bag Oxalic acid 250g £5.00
250g Oxalic Acid•Hull•Deck•GRP Cleaner & Rust Remover-99,5% | eBay

Y10. about 8% Oxalic poss. 25 g. £15.00

Large horizontal areas decks etc , including cracks around stantion bases, go for a bag and mix yourself.