Oxalic Acid

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On the advice from here I have purchased a tub of the above, I’m after some general advice on best mixing practice - using to remove stains.

Best to dissolve and spray on and make a paste or ?

I understand that I need to wash it off afterwards - roughly speaking, how long should I leave it to work, mainly concerned about making matters worse rather than anything else.
It’s rust and some general black staining on the gel coat that I can’t get off.
 
I just mix the powder with a little water and paint it on.

Let it stand 10-20 minutes and wash off with soapy water.

Nb it doesn't work in cold weather.
 
Baggywrinkle said:
Poignard ist definately right, works best in warm weather and direkt sunlight.

I also add a bit of cheap washing up liquid to the mix so it foams and I can see where it is already applied.
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I'll try the washing-liquid tip. It can be difficult to see if you have missed any areas. I was thinking of trying a weak temporary dye of some kind that would wash off but I don't know of any.
 
I have heard of users making a paste like substance so it's not so runny and sticks to vertical surfaces much like the green jelly of y10 does . I guess it depends on flatness of surfaces to be treated.
 
Add a little bit of wall paper paste to help it adhere to vertical surfaces ie side of hull.
You usually can actually watch it start to work a few moments after application.
My tip is for best results is repeated applications rather than leaving one coat on for long time.
Use an old paint brush to work solution into area or item to be cleaned and if needed do it again.
 
Poignard said:
I'll try the washing-liquid tip. It can be difficult to see if you have missed any areas. I was thinking of trying a weak temporary dye of some kind that would wash off but I don't know of any.
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I have been using Oxalic Acid for a number of years; great staff for removing stains of all kinds and for bleaching wood. I would be very careful mixing dye in case it has a reaction and you end up with a permanent stain.
 
Yes it good stuff, I've heard the mix it with wallpaper paste trick but never tried it.
I tend to use 'Grunt' now, it's a bit more expensive but it goes on like a paste and a little goes a long way.
 
I have often used mixed with wallpaper paste, worked well to keep it on the vertical areas. Don't use too much paste, one year ended up with paste stuck to hull that needed hot water cleaning off afterwards. Last year had no paste to hand so used washing up liquid, also helped it to stick but found less effective at bleaching: perhaps the detergent was too alkaline and reduced the acid's effectiveness.

You need at least 10C temperature for good results.
 
I guess it shouldn't need saying, but oxalic acid is nasty stuff and you should wear appropriate protection (inc goggles) when using it.

As mentioned, the warmer the better, 10C is a minimum really. I use Y-10, it's very convenient and a tub lasts for ages. I find it dries on the surface and needs running water and slight brushing to get it off.
 
Wow. That’s a lot of responses. Thank you all.
Clearly idea of whacking it on next month may well not work if the temps drop.
 
jasperthedog said:
Could anyone recommend a mixing ratio for cleaning down fiberglass, no major rust marks just want to try and get the surface as clean as
possible ready for polishing.
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I wouldn't use oxalic acid as a general cleaner, only to remove any brown waterline stains or rust spots. To prepare for polishing, I just use lots of warm sudsy water, a sponge, a tiny squirt of Tesco own-brand "cream cleaner" (about 75p a bottle), and a running hose to rinse it all off.
 
jasperthedog said:
Could anyone recommend a mixing ratio for cleaning down fiberglass, no major rust marks just want to try and get the surface as clean as
possible ready for polishing.
Click to expand...

If you must use oxalic acid
From a post on the ribnet forum a few months ago:

Cleans rust stains and returns yellowed and stained GRP to original colour in 10-15 mins, washes off with a light pressure wash.​
​
1 litre of luke warm water​
200g Oxalic acid powder (ebay)​
50mls car wash detergent (any mild liquid detergent)​
Wallpaper paste powder (to required consistency)​
​
Add the acid to the water. Slowly add paste powder until mix starts to gel. Go short and leave it a while - it thickens for a few minutes. Then add detergent. Brush on, leave 10-15 mins and pressure wash off.​
 
I've used it with and without wallpaper past, with past is preferable for topsides.
Proportions is easy , 1/4 bucket of tepid water then add oxalic acid until you get a saturated solution i. e. you cant dissolve any more.
I put it on with a soft broom.
If adding wallpaper past, you don't need much, a 1/4 of what you would use for wallpapering.
If it's a windy day, make sure you hose it off before it dries.

Plank
 
I buy it by the bucket load, and use it on club boats as well as mine. I make up a saturated solution. The undissolved crystals in the bottom just go into the next mix
I definitely don't use wallpaper paste any more. If you let it dry and make it too thick it can be a lot of water, and hard sponging to get it off.
For me it's tepid water, crystals and a good squirt of washing up liquid.
I apply it to my topsides with a squeegee type sponge that you use for mopping the floor.
Been doing it like that for 14 years now with good results, and no problems.
 
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