Drain blocked with caustic soda

water dissolves it. Vinegar dissolves it faster, but beware of splash from caustic, a chemical that can blind you.

NT

Whatever you do, do it slowly and do not use boiling water to try to speed things up. Caustic soda solidified in a drain might have a layer of sodium carbonate covering it (it is very efficient at removing carbon dioxide from the air). That carbonate layer dissolves a lot more slowly than caustic soda itself. Once the caustic soda is exposed, it can react unpredictably and sometimes almost explosively with boiling water. As NT says, it can blind you if it shoots out of from the drain hole as a hot, concentrated, highly corrosive solution. At the very least, good eye protection is essential, and a full-face mask makes sense if you already have one.

Some brands of caustic soda 'harden'. With others, there's a rapid, heat-producing reaction with the water, and dissolve totally without a trace. Why is this? Have the former been 'cut' - ie something has added to bulk it out (such as washing soda)?

I always use a kettle of hot water. But don?t peer down to see how its working!

The same bottle has IME done both depending in the concentration of added water. .

It's probably due to the amount of water added and the complex hydrates sodium hydroxide forms with water, particularly the eutectic mixtures of varying solubility:

"A hot water solution containing 73.1% (mass) of NaOH is an eutectic that solidifies at about 62.63 °C as an intimate mix of anhydrous and monohydrate crystals."

Yes, seriously, I know of a drain that was blown apart by the reaction, which was not nice for anyone in splatter range. Brian

Thanks. I'll study that. One thing I didn't mention was that my water is extremely hard, and it may be the calcium that does it. However, it does seem that some brands of caustic soda are worse than others.

My guess would be the size and shape of the pellets and the rate of adding water would be important factors. Aren't you supposed to gradually add the NaOH to the water and use the solution?

And, as with any dangerous solid or liquid (eg exothermic in contact with water), always add solid/liquid to an excess of water rather than water to an excess of solid/liquid. Had that drummed into me in chemistry lessons!

Agreed. That's what I meant by 'gradually' - but I could have stated it more clearly.

That's the namby way to do it, yes, but Real Men? fill the u-bend up and pour a boiling kettle down. That shifts any fatbergs

you get superheated pure NaOH and lots of pressure.

It's the safe and less useful way, yes.

As I said, try it the other way after making sure you have old clothes and eye protection.

Which might be a problem with modern plastic drain pipes.

It isn't

One end is always free

It's the heat that would be the problem, not the pressure. Solid NaOH (crystals) gives out a lot of heat when it dissolves in water. Added to the fact that the water is already boiling, you could cause the pipe to soften or even melt.

The water can't get above 100C, it just forms steam to carry the excess heat away. Harmless to any drain pipe.

As for pressure, you can't make any when there's only one blockage, there's nowhere closed. If you artifically made 2 blockages, even then the materials blocking drain pipes won't contain any significant pressure. IOW the alarmism is bs.

NT

It clearly isnt if there is lots of pressure.

It never has yet

As you probably do not understand, plastic waste pipes can take boiling water, and boiling solutions of caustic sodoaq boilss at approximately the same temperature.