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Remove bolts with hydrochloric acid

PostPosted: Wed Mar 25, 2015 6:39 am
by rhyolite
Hi guys,

Just wanted to share this with you, maybe it's something which could come in handy one day.
Currently working on my 1975 astre safari, and I needed to get the rear seatbelts out ..
The seatbelts are bolted through the floor, with a T47 bolt ... and those things GET STUCK !!!

The bolts come out of the bottom behind the rear wheelwells, and they are almost unreachable with
any tools. Ofcourse you can heat them, hit them with a hammer .. but I noticed no real difference.
I :censored: up 2 T47 sockets, so I started a little experiment :

The problem is that these bolts are in a tight spot, and they are exposed to water, salt and whatever
you can think of ... They rust and get really stuck .. and drilling them out is very hard.

This is what the problem looks like :

My experiment involves Hydrochloric acid ... Maybe you know or didn'tn but hydrochloric acid is fantastic
rust desolver ... It is mild corrosive to metals but it will attack rust first.

About Hydrochloric acid ... Yes it is the same stuff known for melting faces and all that kind of stuff, but that
is only with a concentration of 40% or higher ... you don't want to use that (if you were able to even get it)
What I'm using is <-10% solution .. it is widely available in DIY stores ...
Although it is only 10% should be carefull, wear rubber gloves, don't get it in your eyes .. it's still nasty stuff !!!!

Ok, I poured a little HA in a small plastic container .. and placed it on the bolt from below,like this :


Immediatly when you place the container, it's starts to produce bubbles ... The HA is reacting with the rust and crap ...

After a day or so, the chemical process is finished ... Which will look something like this :


Most of the crap is in the container ... I know, crappy picture but you get the idea :


Now the bolt looks pretty clean ... so I gave it another shot getting it out ...
I used no heat, no banging with a hammer ... just a high-quality T47 socket (snap-on, only one I could get),
and took the biggest wrench I had ... And must say, it came out without any struggle ... piece of cake :)
The bolt isn't damaged by the acid, but it was offcourse rusted ... But it can be used again ...


Extra information :
I'm using hydrochloric acid, I had that in my garage. You can use more types of acid but i'm not to comfortable
with having even more aggresive stuff ... Citric acid and acetic acid will get the job done too, but takes a little longer.
Even vinegar will get it done, but that would take several days.

I will do some more of this kind of chemical experiments, Im currently derusting the inside of my fueltank with
elektrolyse, and after it's done I will zinc-plate the inside with a process called elektrolytic galvanizing...

Just FYI :)


Re: Remove bolts with hydrochloric acid

PostPosted: Wed Mar 25, 2015 12:34 pm
by cjbiagi
Nice job Tiemen... :th:

Re: Remove bolts with hydrochloric acid

PostPosted: Wed Mar 25, 2015 7:37 pm
by spencerforhire
Pretty neat idea for removing rust from the bolt threads before it's out. I use a small sandblaster sometimes to perform the same function.

Re: Remove bolts with hydrochloric acid

PostPosted: Mon Mar 30, 2015 9:50 am
by dindin
I use Evaporust on rusty parts..stuff is incredible..


Re: Remove bolts with hydrochloric acid

PostPosted: Mon Mar 30, 2015 10:38 pm
by ol55
How would this work with PB blaster or Kroil already on the bolt?

Great idea!


Re: Remove bolts with hydrochloric acid

PostPosted: Thu Apr 02, 2015 4:45 am
by rhyolite
Hi Larry,

Both are penetrating oils if i'm correct ? :)
Shouldn't be a problem, I also tried several products like that, WD-40, brunox and IMAL (all similar european products)

If you want to be sure you don't get an unwanted chemical reaction with those products, clean it a bit.
But you're working with very small amounts, so no real danger there :)
It can also be done with sulfuric acid (same as battery-acid).

To other comments, yes i'm aware there are more solutions to this problem, I just posted this idea because
these bolts are always stuck like :censored: . And penetrating oils just don't cut it most of the time.
Heating it up was a problem because the beltsystem is covered with plastic, which would start to melt.
And because these bolts are accessible from below, this approach could work without damaging the
bolt, the thread and the car.

And a whole lot of commercial products out there are/were based on acids, but because of environment crap most
of those products lost there true power. And basic acids (some, not all) are widely available and plain cheap.


Re: Remove bolts with hydrochloric acid

PostPosted: Thu Apr 02, 2015 11:03 pm
by Monza Harry
So T, Do you think that muriatic acid would work and are you familiar with it? That is very easily available here! Pool stores/area in big stores and in/near the concrete section in the home big box and hardware stores. Thanx T and that does open up some possibilities, even if only for "Emergencies" Harry

Re: Remove bolts with hydrochloric acid

PostPosted: Fri Apr 03, 2015 6:05 am
by rhyolite

Had to look it up, but muriatic acid is the same as hydrochloric acid. It seems to go with more then one name :
Hydrochloric acid, acidum salis, muriatic acid, and spirits of salt.
In NL we call it "zoutzuur" which is directly translated into "salt acid ... so somehow salt has something to do with it :)

So it's the same.
You were absolutely correct finding it in concrete related sections, overhere it can also be found there.
It is most commonly used to clean concrete/cement hazes from walls during construction.


Re: Remove bolts with hydrochloric acid

PostPosted: Fri Apr 03, 2015 6:24 pm
by Monza Harry
That will be handy to know T and Thanx! I know many acids by name and never found out one of the most commonly used ones . Thanx again Harry

Re: Remove bolts with hydrochloric acid

PostPosted: Wed Jan 13, 2016 4:01 am
by robert123
Neat idea and great photos and story. :th:

You can also try Jasco Prep and Prime (phosphoric acid). It is only $7.00 per quart/liter at Home Depot/Lowes. Really strong stuff... STOPS rust
asap -- should dissolve it also. Easy, just spray it on and works overnight. * Put it into an old Windex spray bottle and spray under dash...or inside front
frame rails......etc. Also, Heat is supposed to help the acid work faster (heat up the acid in warm-hot water -- they will equalize in temp.

REMEMBER, if needed/possible..... to soak the metal part in some Baking Soda to Neutralize the acid (stop the acid from eating the metal).
(Approx. 1 tablespoon Baking Soda for each quart of water.

For example -- depending on the metal & thickness & degree of rust --f you leave rusty metals in Vinegar (its' acidic) over 3-7 days ........ you'll see how it starts eating the good metal.

Good luck