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Lichen on Lime??  RSS feed

 
David Cameron
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Does anyone know of any lichen that will grow in a high-lime environment? Building with hemp-crete is way cool, but would be even cooler if some surfaces could be coloured using lichen. Nova Scotia has a generally humid environment so lichen grows well, especially along the coast where one sees the brightest orange and yellow lichens on rocks and old concrete. Hmmm, old concrete-that should contain significant lime, perhaps the varieties that grow on concrete would grow on a lime surface??
 
Neil Layton
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Location: Edinburgh, Scotland
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It depends what you mean when you say "lime".

I think the limiting factor would be the pH of the substrate.

Hydrated lime (calcium hydroxide), the stuff used by builders, is extremely alkaline (ph 12.4), which is an irritant to most plant and animal tissue and would probably be quickly lethal to all but the most extremophile organisms. Calcium oxide (quicklime) has a pH of 12.8, and has been used as a weapon: https://en.wikipedia.org/wiki/Calcium_oxide#Use_as_a_weapon.

Garden lime (limestone or calcium carbonate) has a pH of 9.4, and lichens will grow on this.

In terms of concrete and mortar (which contain hydrated lime or sometimes quicklime) this has been largely neutralised by the chemical reactions that take place as it sets. There are lichens that will grow on concrete, cement and limestone. Here are some growing in Ireland (where limestone is also a common rock), separated to species: http://www.lichens.ie/view-lichens-by/lichens-by-habitat/limestone-burren-lichens/

I'm not sure how you'd go about putting together a mix that would encourage lichens (see http://www.permies.com/t/55379/fungi/Loving-lichens for a discussion ) for such an alkaline substrate, but I would suggest one aiming for a pH around 9.4, which would be the most likely pH of the natural substrate of these lichens.
 
Joseph Lofthouse
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Lichen growth tends to be inhibited by acidity and by acidic rocks such as granite. They tend to grow fine on basic rocks such as limestone, shale, dolomite, or old cement.

Cements are basic because of hydroxide ions, which convert over time into carbonate ions, which are much less basic and much less reactive. Rain and carbon dioxide in the air tend to wash away or lock away the hydroxides on the surface of fresh cement so that lichens can then grow. Around here, 2-3 year old cement grows lichens fine.



 
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