On 25/07/2012 16:46, stuart noble wrote:
On 25/07/2012 16:20, Martin Brown wrote:
On 25/07/2012 15:57, stuart noble wrote:
On 25/07/2012 15:37, Martin Brown wrote:

Lawn sand will also wreck concrete paths the same way with iron stains.
There should be a warning on the side of the packet about spills.

I don't think there's any chemical reaction with softwoods (pine etc),
but hardwoods are a different matter.

There is a lot less tannins in softwoods so they tolerate it much
better. But there will still be some rust orange ironstain with no
tannins although it may not be obvious on wood it marks grey concrete.

If and when acid doesn't work, it can't hurt to try alkali. Try some
washing soda on a small patch, or even bicarbonate of soda

No good. Iron carbonates are insoluble. The only chance is a reducing
agent with a soluble iron salt - most fruit acids will do.

I'm sure you're right, but I have a distant memory from my wood
finishing days of alkali at least changing the colour to a more yellow hue.

Actually that rings a vague distant bell, but I think that for it to
work the alkali has to be pure household ammonia solution.

--
Regards,
Martin Brown