Oxalic acid again, sorry

[Spyro]

I have some rust stains on my grp deck that I want to remove. I have purchased oxalic acid crystals. What proportions should I mix with water and how long should I leave it on before I see results? I have read about mixing with wallpaper paste but as it's on a flat surface will I need to do this?

Thanks

 

[Clyde_Wanderer]

It would be better to add a wee bit of wallpaper paste as it gives it a better chance to do its job.
Mix it in hot water, about 250grms to 1ltr of water, ( what you dont use can be used at another time if stored in a sealable glass jar) as most oxalic available is only about 20% pure.
Let it cool before adding about 1 table spoon of wall paper paste.
Apply and leave for about 15-20 min then wash off.
You can always use a nail brush or similar to help scrub satins, but wear gloves, and a mask (while mixing it) as it is poisinious.
Someone posted a link for AGW wood care, which has a COSHH sheet for oxalic, which makes scarey reading, but will relate to pure oxalic I would imagine.

 

[VicS]

The simplest way of dealing with stains on the deck is to make it wet and just sprinkle some oxalic acid on them. It should remove light stains within a few minutes, then wash away with more water. Repeat if necessary

If you really want to use a solution make it saturated or nearly so as the more concentrated it is the quicker it will work. The best figure I can find for its solubility is "1 part in 8 parts water" I assume that means 12.5 % so disslove at the rate of around 12 g in 100 cm³ water. It is a bit slow at dissolving so use warm water .

Yes to make it thick enough to use on vertical surfaces add wallpaper paste to the solution.

Remember that it is very toxic so keep solid and solutions safely stored and <u>labelled!</u>

 

[FullCircle]

Caution, I wouldnt use HOT water, just warm or tepid even.

 

[VicS]

[ QUOTE ]
as most oxalic available is only about 20% pure.


[/ QUOTE ] Why do you say that? If it is bought as oxalic acid then I would expect it to be much nearer to 100% than that. It will however be supplied as the dihydrate. You can check the arithmetic to find the percentage of oxalic acid in that but I make it 71.4%.


AGWoodcare quote a purity of 99% (But that will obviously be as the dihydrate).

The safety data is very scary but with common sense, some rubbergloves and some safety specs there should be no problems. It is not even horrendously toxic. The lowest recorded lethal dose (in women) is 600mg / kg of body weight.

 

[ianabc]

Absorbed thru the skin.

Causes kidney damage/ stones

 

[santeana]

Made enquiries last week at local chemists for supplying crystals and mixing. After consulting supplier data gave me a ratio of 1 part to 5 parts of water.

 

[jimbaerselman]

I do it the lazy way. Shake up too many crystals in a re-labelled 500ml fizzy drinks bottle with water. Pour off from the top as required, leaving un-dissolved crystals at the bottom. Top up with water. When the crystals disappear, add more . . .

Simple system - gives a saturated solution - permanently to hand.

 

[santeana]

Neat method - thanks.

 

[Spyro]

Thanks for all replies, now I only need to decide which method to use.

 

[Gunfleet]

If you've got kids (or illiterate friends) you might want to give Jim's method a pass. /forums/images/graemlins/frown.gif