Acid wash

[IanA]

On the subject of mixing acid and water, it is not strictly correct that there is no reaction. Concentrated acids release heat when mixed with water. (I think in a concentrated state acids can be considered anhydrous, adding water then allows water molecules to bind with the acid molecules.)

If a small quantity of acid is added to the water the increase in temperature is small.
On the other hand if a small quantity of water is added to the acid the temperature rise can be sufficient to cause it to boil. Being spat at by boiling acid can be nasty.

Maybe the concentration of the acid as it is sold is low enough to minimise the problem, maybe not, don't take the risk!!!!


Always add the acid to the water.

[Marc]

Concentrated cloridric acid distinguishes itself by its high affinity to water. Mixing the two components results in massive heat emission, which can be traced back to the exothermic production of various hydrates from the acid.

Safety Precautions: The acid should be added to the water, as illustrated above. Reversing this order and adding the water to the concentrated acid can lead to splashing due to the intense production of heat that will make the smaller ammount of water boil.

Remember the following phrase:
"First the water, then the acid, otherwise it won't be placid!"

Or you may prefer this one:
Do what you oughta,
Put the acid in the watta.

Adding water to high concentrated acid or base is used in bomb making.

[Rocker]

I must apologise for posting my assertion that water does not react with acid. However, it is true that there is no reaction if you add water to the dilute acid (37% concentration by volume) that is sold as pool acid. I have just tried adding water to it, and it does not boil or spit.

[Marc]

The increase of temperature in the water due to the action of the acid molecules depends on the number of molecules available in the solution. The more concentrated the solution, that is the less water present, the more reactive the acid will be to an addition of water.

Since the concentration of commercial acid for cleaning purposes is either unkown or is printed in small print and in a way that is not clear the the user, it is a must to remember that strong acid like cloridirc or suphuric are strong because they are highly reactive, mainly to WATER. If needing to dilute 1/20 that is you need one litre of acid and 20 of water add the acid slowly to the full ammount of water needed.

In case you needed to dilute just 1acid /2 H2O, extra care is needed. You would need to take the whole ammount of water in this case 2 litres and add real slow the liter of acid, allowing for the new solution to cool down several times in the process.

[nesbit]

Bringing up an old thread here. But how long should you wait until you begin the acid wash process? I just filled up a hole in my wall after the removal of an old air conditioner on the weekend. I noticed this morning that there are some stains that have appeared on the bricks. Would it be safe to do it this weekend?

Thanks in advance.

[Bleedin Thumb]

Just give it long enough so the mortar has gone off enough 2 weeks to cover yourself. You can do it now but be carefull not to weaken your new work. One thing that wasnt mentioned above unless I missed it amongst the biffo was that you should wet your walls down first before you add your acid mix. Just a quick hose it stops the acid mix from getting sucked into the dry bricks - you only want it on the surface. My prefered mix rate is 12 water to 1 acid and yes acid to water!!