HCl concentrqtion to clean cement mixer?

[tonyjeffs]

One skill I don't have is cleaning up after a long d-i-y session. I'm ashamed to say that after my block making project, my cement mixer is now 30kg heavier, and a lot smaller inside, with concrete. I'm going to buy some HCl from a local supplier, but don't really know what to ask for. What is reasonable safe to use with caution, and a good read of the COSSH documents, but powerful enough to corrode the unwanted concrete. I thought maybe 1litre of 34% HCl, 66% water. Is that anything like reasonable. And is that even the correct terminolagy. Should I be asking for a 0.3molar solution?

I have a few ideas about safety, but aany advice on that too would be most welcome.

Thanks

Tony

ps I'll put a video up on youtube on how I got on with making the exposed aggregate finished concrete blocks as soon as I get aroudn to splicing it all together. Not a job for a sunny day like this!

[Tim S]

tonyjeffs coughed up some electrons that declared:

Just ask for "brick acid". Conc HCl is about 30-odd% (as HCl is a gas, so it's the limit of what you can dissolve in water)

Sorry, don't know for sure. But I would guess your solution is a fairly good staring point. You don't really want to use 30% HCl as it gives off HCl gas like a bugger which isn't good for your eyes or lungs.

Too weak and it will take longer. Gut instinct and a vague recollection of chemistry lessons suggests 10% HCl (close enough to what you suggest) should be relatively un-smelly but still reasonably effective.

Try a small amount of trial mix on a stationary bit of the drum and see what it does to the cement.

Goggles, preferably non-ventilated and fully enclosed (eyes are hard to replace), gloves and good thick overalls. Have a hose handy just in case you need to wash down in a hurry. HCl isn't poisonous as such and in very dilute form it's pretty innoculous (it's produced and used in weak form in your stomach).

Cheers

Tim

[The Natural Philosopher]

First step is to fill the thing with water and a few bricks and get spinning, then bash the outside with a mallet to crack off most of it.

Then just chuck in neat brick acid. Whatever they allow you to buy. Its not that concentrated.

Continue chucking it in till it stops fizzing.

Then hose the whole thing down extensively. It corrodes steel pretty well does HCl.

I think you are getting altogether too concerned. What is sold as brick acid is relatively safe. You can wash your hands in it. Not for long, and any cuts will sting like bejasus, but thats the sort of level its at. Eyes and clothes are your primary sources pf concern, so make sure its tatty old clothes, and a glasses if you intend being cavalier with the stuff.f it does get in your eyes, total and instant flushing to reduce concentration is the way to go, with maybe a mild antacid like bicarbonate - maybe someone medical knows better - and off to A and E fast. It wont be nice, but it wont blind you instantly. The eye surface hurts like hell, but repairs quickly.

But on skin - it will let you know if its doing damage: it stings. But once washed off Ive never seen any permanent damage from it.

Just be sensible and make sure it doesn't splash, or if it does you arent where it does.

IT acts very quickly on cement presumably turning some carbonate into some chloride. I guess the end result is H2O and CO2..anyway, when it stops fizzing, youve either run out of carbonate, or HCl :-)

The actual residue is pretty harmless.

[Dave Liquorice]

Maybe this is a lesson you will learn from?

It'll take a lot of HCl to dissolve 30kg of concrete... And you'll still have some fairly acidic waste to get rid of. Have you tried taking a cold chisel and lump hammer to the concrete inside the drum? If you can get a few cracks in it or better still a lump or three out the rest will fall, perhaps with a little persuasion, off the drum.

[The Natural Philosopher]

Established practice is to fill the drum with water betwen mixes, and leave it turning, or at the time of the last mix of the day, and then add bricks. These chip most of the dross off the drum and blades. The rest usually comes free with a few good whacks of a mallet.

What doesn't probably isn't worth worrying about.

[Lobster]

Agreed. I spent a happy(?) morning years ago spent crouched inside a concrete mini-mixer with hammer and chisel... I remember the noise being absolutely deafening!

David

[Tim S]

Lobster coughed up some electrons that declared:

SDS + chisel bit + the bestest ear defenders in the world?

[Lobster]

For sure, but I don't think SDS drills were even around back then - if they were, my employer certainly didn't have one (or ear defenders either, for that matter!)

David

[Tim S]

Lobster coughed up some electrons that declared:

Does the OP have an SDS?

[Andrew Gabriel]

I imagine it will diossolve the drum first.

[The Natural Philosopher]

No, it won't.

Ive used it to clean cement of trowels and the like It goes for cement, and only slowly attacks the steel.

[The Medway Handyman]

Clearly a need for 'percussive maintenance'.

[Dave Liquorice]

Yes, best not to let it build up a 30kg layer of set concrete in the first place but the OP by his own admission said he was hopeless at cleaning...

[Andy Dingley]

Mid-70s from the patent, but rare.

[tonyjeffs]

Thanks all. Not heard of an SDS hammer drill before, but will buy one next time around. How does it work in a way that is so much more efficient? Have today had great success with hammer, earplugs and chizel. (Figured the technique. Cut a radial slot outwards from the centre, and widen it. If you try to cut concentric circlese, the concrete jams up like an arch.) Have identified local supplier of brick acid, but if the chizelling goes well (a bit at a time ,so itll take a few days ) I might not need it.

tony

[Lobster]

you're familiar with a conventional hammer drill?, then the difference between that and an SDS is massive - I'd say go and buy one now, you won't regret it. Would certainly make your current job a doddle.

David

[The Medway Handyman]

As long as its a 3 function SDS drill of course.

[meow2222]

It'll get harder each day, so dont hang about.

NT