Acid wash

[craigb]

When acid washing new brickwork, what is the ratio of water to acid ?

I can just use hydrochloric acid (swimming pool acid) right?

TIA

Craig

[Eastie]

Short of any specific advice from the brick manufacturer the following is fairly common.

Hydrochloric is correct – I not sure that pool acid will be the required strength though ? – there lies the next question.

Mix between 20:1 water to acid for light bricks to 10:1 water to acid for dark bricks – always adding the acid to the correct volume of water. Like all things try and inconspicuous area first to see if any discoloring occurs.
The bricks must be washed down immediately before cleaning. Leave on for 3-5 minutes and scrub off – do not scrub the joints only the bricks as the acid only serves to dissolve the cement and will weaken the mortar lines.

[craigb]

Thanks Eastie that's just what I wanted :)

By the way, is just a stiff bristled brush ok or should I (or not) be using a steel brush ?

TA
Craig

[bookworm]

Originally posted by Eastie
Short of any specific advice from the brick manufacturer the following is fairly common.

Hydrochloric is correct – I not sure that pool acid will be the required strength though ? – there lies the next question.

Mix between 20:1 water to acid for light bricks to 10:1 water to acid for dark bricks – >>
always adding the acid to the correct volume of water.<<

Eastie, you NEVER add acid to water. If you do, there's a very good chance that the acid will be 'spat' back over you or into your face!!

You add the water to the acid!!!!


HTH,

bookworm

[Eastie]

You shouldn't need a steel brush - a stiff bristle scrubbing brush should work. Also forgot to mention to wash the stuff off well with water. You can also add bicarbonate soda to the wash down solution to neutralise the acid, especially good for light colored bricks.

[Eastie]

BOOKWORM - GET YUR BLOODY FACTS RIGHT !!!!!

Always add acid to water - very slowly.

Simple volumetric blending that if reversed will generally cause a lot more than a spit of acid in the face.

[bookworm]

Hi Craig,


Originally posted by craigb
When acid washing new brickwork, what is the ratio of water to acid ?

I can just use hydrochloric acid (swimming pool acid) right?

TIA

Craig

I've never heard of anyone using swimming pool acid. I doubt it would be strong enough and in any case it would cost you an arm and a leg.

"Spirits of Salts" is what hydrochloric acid used in the building industry is usually called. You buy it in twenty litre containers as a rule.

The object is to use the diluted acid to soften the mortar and remove the softened mortar using a reasonably stiff nylon brush and a paint scrapper where necessary. This assumes that you won't be using a high pressure pump which if you're doing it yourself is probably the way you'll go.

Don't leave the acid on too long. If you do you'll "burn the mortar" that is the mortar in the joints. It looks terrible!!!

Better to wash the acid off too soon and have to redo a panel of bwk than to leave it on too long.

Start at the top of the wall and work your way down. As the acid and later the water you use to wash it off, runs down the wall, it helps soften the mortar on the wall below. Just a little tip there.

Use the brush on a long handle. Its safer because it keeps you as far from the acid as practicable, its faster and easier on your back and shoulders.

In case you're wondering, although I'm a chippy by trade, I did brick cleaning back in the very early 80's when work down on the Mornington Peninsula (Vic) was very slow, so I've had quite some experience with it.

BTW, are your bricks clay or concrete? Concrete are harder to clean but not impossible.

HTH,

Mark.;) :D

[bookworm]

Originally posted by Eastie
BOOKWORM - GET YUR BLOODY FACTS RIGHT !!!!!

Always add acid to water - very slowly.

Simple volumetric blending that if reversed will generally cause a lot more than a spit of acid in the face.

Go back to High School and learn some basic chemistry! You do not know what you are talking about and consequently are dispensing potetially dangerous advice.

Oh and by the way, take your beligerent attitude and stick it where the sun don't shine.

[Phil Jennings]

Hi Bookworm,
it's a long time since I was in 1st year science class but I do remember always adding acid to water. A quick check on google "mixing acid and water" makes it very plain that you do add acid to water and not the other way around.

Best regards
Phil:)

[craigb]

Although I'm grateful for the replies, one of the few things I remember from my high school science is being told to ALWAYS add Acid to water because it won't splash.

Pool acid comes in 10l containers (black plastic) cost's about 10 bucks if you return the container, and judging by the fumes it puts out it's pretty bloody strong !

I guess I'll check on the label and report back the technical details.

Craig

[Rocker]

In the dispute about adding water to acid, or vice versa, I believe that Eastie is correct. Since hydrochloric acid does not react with water, the only risk is of splashing; obviously, if the acid is added to the water, the resulting mixture is going to be much less concentrated, and hence less dangerous when splashed, than if the water is added to the acid. If you look at a container of liquid pool chlorine, where similar factors apply, you will see that the instriuctions warn you to always add the chlorine to the water, and not to add water to the chlorine.

[cjr]

I just cleaned a stack of old red bricks. I used pool acid (as I have a pool and it only costs around $10 / 10 litres). I started out with 10% acid, however gradually made it stronger and found that about 30% acid was the most effective, as long as I washed the bricks with water as soon as I had cleaned them. It stuffed up my hands though and dried them out completely, so would advise some sort of rubber gloves.

Mixing acid and water (http://dev.nsta.org/ssc/pdf/v4-TS_30.pdf)

[Eastie]

Bookworm – I’ve no ill feelings towards you and it was not intended as a personal attack but a warning to those who might read it to think twice – very carefully.
Where advice is given that may be harmful I will generally speak out against such advice – as you have against mine.

Anyhow here is some more info for Craig (disregard the UK legislative references).

http://www.brick.org.uk/publications/PDFs/cleaning_site_safety_precautions.pdf

A material safety data sheet from the manufacturer will give you the ‘recommended’ safety precautions for the chemical you have – there should be a contact number on the container to obtain one (they will fax/email them through) – although the manufacturers of pool chlorine probably won’t have info on it’s safe use for brick cleaning. Keep a charged garden hose or bucket of water within reach in case you get some in your eye’s (or an eye wash bottle if you have one).


I've returned my belligerant attitude to my for safe keeping - hopefully it won't come out too often :D. I again see that any subtleness / irony / humour / tongue in cheek is often not evident in this medium.

Mark

[Theva]

Good references Eastie, Correct as usual.

Brickies acid (HCl) is available from one lit upwards, try Bunnies etc. Safety & mixing instructions are also on the label of the container. As one would expect, its nasty stuff so treat it with some respect & care.

These include adding acid to water (slowly), PVC / rubber gloves, safety glasses and having water readily available.

Regards,

Theva

[craigb]

Thanks Eastie, you can never be too careful when using toxic substances.

I won't be using pool chlorine, I don't know how that referance slipped in.

CJR, I'm suprised you have any skin left on your hands :rolleyes:

I thought I'd get some of those industrial strength rubber gloves when I do it.

Craig

[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!!