[steveri]

I went for a wander up to my local green traverse last night and found a whiff of bleach in the air. Is this a thing now? Looks like someone has been doing some zealous spring cleaning.

Can someone brighter than me comment on the chemistry, what this might do to the strength of the rock, etc?

[tomtom]

I've heard of it before - not that uncommon at the beginning of the season.

Not really sure what it does to the rock.. Neat its not good for the person applying it - but 10% dilute its probably not that harmful...

Remember that 50-60 years ago all the rock was nice and clean as all the air pollution (and how it also worked its way into the rain) killed of lots that grew on the rock...

[steveri]

Oh indeed Tom, it's pretty green right now and funnily enough my first thoughts were 'the factories stink a bit tonight' before realising it was the rock.
Bit slow on the edit button, but this one probably shows it better

[tomtom]

I seem to remember someone telling me that one of the old grit wads (those from the 70/80's) used to go around the circuits at their local crags sprayign with bleach solution at the beginning of the year to keep em clean...

From my own experience of de-greening the outside of a house (once white - then green) the most effective way was 5-10% bleach solution sprayed and scrubbed...

Its an interesting question whether or not this is better or worse than brushing the green off for example... A Q I can't answer!

[remus]

Its an interesting question whether or not this is better or worse than brushing the green off for example... A Q I can't answer!

From an ecological perspective surely it's worse? You're going to significantly alter the chemistry of the environment, potentially fairly long term depending on how long the bleach solution hangs around (could be a while on porous rock types?)

[Will Hunt]

It's an interesting one, this. There might be no damage done whatsoever, but bleach? At the crag? It doesn't feel right. I suppose if used sparingly it's unlikely to do any environmental harm as it would be so dilute in any runoff. Maybe there's some harm to the rock? Anywhere else you'd just brush it off with a stiff brush but that's not going to be good for sandstone. Folk in the North York Moors extoll the virtues of dabbing some chalk on the holds with a chalk ball and brushing it in and repeating, then coming back at a later date. I suppose this might have something to do with the chemistry of the rock and the chalk being different, thus the lichen doesn't like the alkalinity of the chalk?

[tomtom]

Magnesium carbonate has a pH of 9.5 and bleach of 12.

So both are alkali. THB I think a mild bleach solution sprayed carefully (from a mister for example) is probably pretty benign..

Sloshing on domestos from the squirty bottle is liable to be less benign...

Tomorrow I can ask my colleague in the office opposite who is a carbonate sedimentologist... who seems to know about all of this stuff

[steveri]

Always good to have a carbonate sedimentologist on call! There's some other holds nearby I suspect have had the treatment previously and have that real dead-rock look of a massively popular area that's seen lots of traffic and lots of chalk, like the plantation. Just looks a bit 'denatured'. There's no run off to speak of and the rock only really gets wet from soaking through from above/behind. Not calling foul just yet, more curious and protective.

Also nervous about Touch ID on my phone not working if my tips burn off

[SA Chris]

I've used it before on pebble beach polished granite (friction co-efficient close to zero) that had a layer of seaslime on it so never got properly dry.  Actually worked quite well lasts for about a month or so before the slime grows back. But this was next to Aberdeen Harbour, so not like a few drops of bleach in the sea would be noticed. Actually the gel stuff worked better, stuck around for longer and did the job more effectively. I did the project and not bothered reapplying though.

[tomtom]

OK - spoke to my colleague. A geologist with a strong chemistry background (poor thing...)

DON'T USE BLEACH ON SANDSTONE/GRITSTONE

It breaks down the silica in the cement holding the grains together. His words were "if you put bleach on sandstone, then let it wash off and repeat - eventually you'll be left with a pile of sand". Its not going to cause it to fall down, but regular use of bleach will eventually break it down causing it to crumble.

[Will Hunt]

Good knowledge, TT. Wadded.

What is it that breaks down the silica? Is it the pH difference? Is it a corrosive property of the bleach? If it's the pH difference, will chalk not have a similar effect on sandstones as it dissolves into rainwater and works its way into the porous rock?

[tomtom]

What is it that breaks down the silica? Is it the pH difference? Is it a corrosive property of the bleach? If it's the pH difference, will chalk not have a similar effect on sandstones as it dissolves into rainwater and works its way into the porous rock?

Yes its the pH - but Chalk (Magnesium Carbonate) has no pH unless its in solution. Even then my colleague describes it as 'very sluggish'. Its the spare OH's in Bleach that are readily available to react with the Silica.

I followed this up by asking about repeated application of chalk and washing off - and he thought the effects were negligible. Same for applying to damp rock. Basically there is not enough time for the weak effects of any chalk solution to really do anything. It would just wash away. So he thought*

*I really know very little about this

[steveri]

Quality reply Tom, thanks. Sounds like this kind of information should be better known.
Elsewhere on the Friends of Pex FB page people are talking about a 10% solution and that venue would at least be subject to rain. Overhanging algae-riddled buttresses less so. Bleachers beware.

[Will Hunt]

The stuff that is being advocated on the Pex Hill Facebook page is this:
https://www.taylormclure.co.uk/q-clear-algaecide-231-p.asp

Which says it is based on Benzalkonium chloride: https://en.wikipedia.org/wiki/Benzalkonium_chloride

I'm a complete chemistry ignoramus, but the chemical composition on Wikipedia doesn't show lots of OHs (though maybe these are formed by reaction with the lichen?). Is this stuff an acid? I know that sandstones are acidic rocks, but presumably the rock will still be affected by a strong acid?

[tomtom]

Probably not as bad as bleach in his (very brief) view.

He also said Chlorine Bleach wouldnt be as bad as Peroxide bleach..

Mild acid on sandstone is fine (according to my colleague). Vinegar on sandstone/gritstone would be fine - but bad for limestone!!

Personally - as someone who climbs quite a lot on sandstone, I think using bleach is being lazy. Dry weather and a soft brush has always worked for me.

[andy popp]

Personally - as someone who climbs quite a lot on sandstone, I think using bleach is being lazy. Dry weather and a soft brush has always worked for me.

I agree. If this isn't sufficient then the rock isn't in condition and shouldn't be climbed on.

[AndyR]

OK - spoke to my colleague. A geologist with a strong chemistry background (poor thing...)

DON'T USE BLEACH ON SANDSTONE/GRITSTONE

It breaks down the silica in the cement holding the grains together. His words were "if you put bleach on sandstone, then let it wash off and repeat - eventually you'll be left with a pile of sand". Its not going to cause it to fall down, but regular use of bleach will eventually break it down causing it to crumble.

I think this may be true (if, a very slow reaction) if you sat the sandstone in a bleach solution, but i’m not sure it is representative of the situation described - the sodium hypochlorite solution will react preferentially and completely with the huge excess of organic material present (algae) - assuming of course that you’re spraying a dilute solution of bleach on localised holds - I don’t think there’s a problem if used judiciously. And you could always spray with some water after 30 mins or so if you were really worried. But I’m a geochemist so probably not to be trusted...

[SA Chris]

Vinegar on sandstone/gritstone would be fine - but bad for limestone!!

Don't know, might actually create some friction!

[mrjonathanr]

Quality reply Tom, thanks. Sounds like this kind of information should be better known.
Elsewhere on the Friends of Pex FB page people are talking about a 10% solution and that venue would at least be subject to rain. Overhanging algae-riddled buttresses less so. Bleachers beware.

They have no business applying bleach to Pex. What is wrong with people?  Just use a brush. And water.