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One other advantage of Citric acid is that it is safe to pour down the drain after use. Phosphoric acid is widely used in the dairy industry as a milk stone (calcium deposits from the milk) remover and can be bought at a reasonable price from farm supply stores, just check that the one you buy is phosphoric and not nitric acid, it may also contain surfactants which leave a white powder on the surface.
I did something similar last year, I removed the rear subframe first, IIRC only one snapped bolt but the front one was totally different about six snapped off even though both subframe bolts had been soaked with Plus Gas for a couple of days and had been heated with a MAP gas torch. A previous owner had also been at mine and snapped one of the front mounting bolts, he didn't drill the old one out but instead drilled a new hole at an angle. I had my subframes galvanised, it's a mixed blessing, every captive nut needs to be re-tapped, the extra thickness of the zinc means that it was absolute hell to get the front wishbones into the subframe.

That’s useful information especially the possible source of phosphoric & the caution of nitric being supplied in error. The disposal of residue is also interesting; I’ve always disposed of the exhausted acid by using it to clean the concrete & hosing it away, more thought in that area required.
M

Airportable wrote:

That’s useful information especially the possible source of phosphoric & the caution of nitric being supplied in error. The disposal of residue is also interesting; I’ve always disposed of the exhausted acid by using it to clean the concrete & hosing it away, more thought in that area required.
M

It is surprisingly easy to buy chemicals, its a question of understanding what you need and how to use it. We bought Sodium Hypochlorite and Sulphuric acid in 205 litre barrels and caustic soda and feed grade Urea by the tonne, all for cleaning dairy equipment or feeding dairy cows. When you use these in their most concentrated forms you quickly learn to respect them. I give this information in the belief anyone reading it will have equal respect with their use. Sometimes chemicals have very diverse uses, for instance Urea is the densest source of nitrogenous fertiliser, it is also the most concentrated source of protein for ruminants and when dissolved in water it becomes "Ad Blue"

Add blue, the most expensive pig piss you can find. Who found out that adding it to cars reduced emissions. Buying solvents has become difficult, I've used trichloroethylene for parts cleaning but no longer, try buying that or carbon tetrachloride & the phone would be ringing in the police station! Pro-solv is claimed to be a "drop in replacement ", I use paint thinners but I've always preferred trich'.

One last post before this thread returns rightfully to the originator

Airportable wrote:

Add blue, the most expensive pig piss you can find. Who found out that adding it to cars reduced emissions. Buying solvents has become difficult, I've used trichloroethylene for parts cleaning but no longer, try buying that or carbon tetrachloride & the phone would be ringing in the police station! Pro-solv is claimed to be a "drop in replacement ", I use paint thinners but I've always preferred trich'.

It was Mercedes that discovered that Ad Blue would enable diesel engines to comply with emissions regulations, like many of their safety innovations they gave the technology away FOC to anyone who wanted it. If you have read how supermarkets ripped us off with fuel then that pales into insignificance to what they are doing with Ad Blue. Although I wouldn't suggest anyone does it but one tonne of Human feed grade urea and two thousand litres of de ionised water make three thousand litres of Ad Blue. I have seen IBC's of Ad Blue for just twenty seven pence per litre.

Quite frankly, I am horrified by some of the comments in this thread regarding the use and disposal of dangerous chemicals.

The disposal of acids in to any public drainage system is illegal.

The allowed range of ph of waste water is 6-10. All acids are way lower than this and can adversley affect not only the integrity of the drains themselves by degrading the pipework, but also the working of the end sewage treatment works. The vast majority of sewage treatment is a biological process, meaning ph outside the 6-10 range can result in degrading or wiping out the treatment works ability completely.

Further, many road and surface water drainage systems discharge directly into the nearest watercourse, especially those on newer housing and/or trading estates.
An example is that the road drainage in my village is directly connected to the local beck, and any non surface water discharge into the system is likely to destroy any biological life in the watercourse. Many small rural villages have rudimentary and/or tiny sewage treatment works that are easily wiped out by such discharges.

In a previous life I spent many years as an Investigating officer for what is now the Environment agency. The number of prosecutions we undertook for exactly this type of thoughtless behaviour was uncountable. The worst offenders, by far, were farmers and small businesses.
I have many stories of the havoc created by people ignorant of the consequences of discharging acids into public drainage systems. One of the worst was a dairy/cheese maker who managed to totally dissolve a public sewer such that 50 yards of road collapsed into the space where the concrete pipework used to be!

I apologise if this comes over as harsh, but in the current environment where the water companies are being severely criticised for their failures, it really is a case of 'he who is without sin casting the first stone.'

I think we’ve had our wrists slapped chaps.
When we get a rebuke from the Head Master we should all sit up & listen & with due cause.
The comment on the dairy was prescient, we’ve just returned from a short break up near Grassington & one of our regular walks having caught the bus to Kettlewell is to walk back through Grassington & back to the site. We use a lesser path which takes us past a large dairy & the runoff has increased over the time we have visited. I’m unaware of any treatment plant between the dairy & the river.
Between the three who be should be shame faced but there is an undercurrent of caution & an acceptance that we knew there were reg’s but not what they were (I speak for myself only here). So I will in future seek out the appropriate channels & use those. It did bring up the concrete up nicely thought.

Sadly my response disappeared into the ether or was erased, suffice to say that I installed a total containment system way back in the 1980's, no contaminated liquids that entered the drains ever found their way to any river. In 1999 a newer installation was made and as with the earlier one was approved by the EA, with that one we could store over two million gallons of waste (both solids and liquids) one store of 360,000 gallons was 1500 metres away with a system of underground pipes and automated pumps. I no longer farm myself but my two MG's are kept on an ex dairy farm, again all liquid waste is stored in tanks and irrigated onto the fields, again as approved by the EA. I have no idea what happens up north but forty years ago down south the EA took a responsible attitude towards farmers, they only prosecuted repeating offenders, with the others they offered advice on how to reduce and then stop water pollution from farm sources, I didn't need a rebuke as a responsible ex farmer I know how to dispose of waste.
EDIT
However I will still defend the use of citric acid for rust removal, it is a naturally occurring acid found in all manner of plants. It is widely used in the food industry and in pig foods it reduces the amount of ammonia in pig dung. In households it is used in cleaning products, in medicine as a preserver of antibiotics and widely used by the food and drinks industry. It does not attack concrete or the materials used in drainage systems.
When used for rust removal it only attacks the oxides (rust) leaving the base metal undamaged, it leaves a sediment of ferrous citrate. After the acid has been used it naturally degrades and I have found that within a week it is supporting the growth of algae. Now compare that with the degreasers used before the acid treatment, where does it all go?
There are 28 million households in the UK, most will put thick bleach (sodium Hypochlorite and caustic soda blend) down their toilets once a week. Less often they will use a limescale remover (Hydrochloric acid) drain unblocker. I have never seen at our recycling centre a disposal point for the likes of white spirit used for cleaning paint brushes or thinners after spraying you car

I was going to post about the latest updates but it seems like I have caused a few issues.
Thank you everyone for your advice but it's probably time to close/delete this thread.

This thread can assist advise and entertain and all comments and posts are taken as that. Our own actions dictate who we are not what we read, that is unless specific guidance is requested. Although I am an Incorporated Engineer, in my time I have made many errors of engineering judgement but learning is the name of the game. Life is an education. Death even more so! Don't strop posting your experiences< I for one really enjoy the updates.

Don't cut us off mid restoration, your rebuild is a proxy for the jobs I'm unable to do without industrial quantities of Deep Heat being applied having clambered out of the pit.
You carry on, only try & avoid topics that might upset the Headmaster.
M

I for one see no need to close the thread, just because some issues have been raised, indeed these issues are informative and educational.
Unless they are raised, how will those who don’t know ever learn.