UKC

I've just recently bought a wooden Lapis brush on an impulse purchase. I'm probably going to be climbing sandstone because that's what's in my local area, will a horsehair brush be fine to use on sandstone?

Just wack it with a t-shirt or tea-towel. I doubt anyone will condone using any type of brush on sandstone. Damage from using brushes is apparent all over the sandstone in my area.

Just use less (or no) chalk. 
It's for your sweaty hands, the rock doesn't need it. After dibbing wipe your hand on your trousers. 

You shouldn't brush sandstone, and don't need to if it's properly dry. Flicking it gently with a beer mat and blowing on it removes the sand dust. Sand only tends to stick to it when it's wet, and if it's wet you shouldn't be climbing on it.

More importantly thoroughly clean the soles of your rock shoes with a rag/beer mat and use a beer mat or similar to stand on when you start.

You definitely shouldn't be brushing chalk off sandstone - if you are then someone is using way too much.

You still need something to remove the sand and dust though.

& in the real world where every single hold is plastered with so much chalk as to render it pretty much unuseable ... what's the solution?

A beer mat or similar is ok if that's all you have, however it's only useful in starting a climb with clean shoes. The problem with tea towels (or nothing at all) is that the force into the ground when starting a route erodes the soil. As SS regulars will know, some routes are over a foot lower than they were a few decades ago. Using a bouldering pad slows that process down significantly. Whilst many may not wish to fork out for a full pad, a sit pad (much cheaper) is still useful as it spreads the force into the ground. I don't think the issue is just about clean shoes protecting the rock. We need to look at the whole process and our impact on the crag as a whole. Apologies if I'm teaching anyone to suck eggs here

Being a boulderer almost exclusively apart from the odd SS trip (including a good one today at Harry's), I learnt from trad climbers how to use slings etc effectively to protect the top of the crags. Maybe it's time sport and trad climbers took a couple of tips from the bouldering community before our SS crags are better known for caving?

If the ground is a foot lower, the climb is a foot longer. That's a good thing isn't it?

To the OP, people have climbed for generations without a brush. So no, it's not necessary it is a choice, just give it a blow and get on with it. 

But previous generations didn't have to deal with the current fad for applying chalk with ( apparently ) a shovel! Again what's the solution? A slap or a blow is fine for removing sand it will do nothing to remove half an inch of chalk build-up.

ban chalk?

Aha! A thinly veiled excuse for cheating when you can't do those elusive first moves eh?

Just kidding

The secret of my success

The beermat should have been soaked in a lager frenzy ...

Regarding Toothbrushes

The ones being described are band. Have a look here for more info.

http://www.southernsandstoneclimbs.co.uk/2016/10/toothbrushes-and-boulderin...

The issue with chalk :

http://www.southernsandstoneclimbs.co.uk/2015/05/chalk-on-sandstone-eco-bal...

The Southern Sandstone Climbs Guide has a detailed intro and on page 45 has examples of what you can and can not use. The into is available to be download.

https://www.rockfax.com/climbing-guides/books/southern-sandstone-climbs/

Surely this rather depends on what sandstone? The Torridonian stuff is rather different to stuff i've climbed in the West Midlands where looking at it too long erodes holds!