Previous in Forum: Conductive Liquid   Next in Forum: GE Ultem 9085 Resins for Lighter Weight Aircraft Interior Parts
Close
Close
Close
7 comments
Participant

Join Date: Apr 2007
Location: France
Posts: 1

Practical problem with acid and granite

04/21/2007 1:52 PM

This is my first post on this forum so I hope I do everything right.

I am restoring a french farm house. The stone around the windows are in a standard granite. The granite was covered in old cement which I have been cleaning with concentrated (at least at to Consumer standard) Hydrochloric acid. The acid bubbles up green when in contact with the cement. This worked fine and I repeated the process many times with no problems, until the tempreture increased and under direct sunlight it has left a very definate yellow stain on the granite. Now I cannot get rid of it. I am not sure what the stain is: a safety dye in the acid or from the reaction with small amounts of cement still in the granite.

Can anyone suggest a course of action? This yellow was caused chemicaly, surely it can be chemicly undone. Note that granite porros and the yellow is several milimeters deep into the stone.

Register to Reply
Pathfinder Tags: granite hydrchloric acid
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru
Hobbies - HAM Radio - New Member United Kingdom - Big Ben - New Member Fans of Old Computers - Altair 8800 - New Member Canada - Member - New Member

Join Date: Jun 2006
Location: Toronto
Posts: 3968
Good Answers: 119
#1

Re: Practical problem with acid and granite

04/21/2007 11:26 PM

photos, stained area and unstained area if you can. Use flickr and post URL here if you cannot do it here.

there are a lot of trace elements in the granite, expecially if it is porous. Some can have a valence state changed. You mah have bleached an item to an acid state.

Of method is to take a piece of the same granite that you do not need on the wall, (if you can get it). Mark a strip and treat with acid and make the stain. Use this as a test piece.

Then try a drop of drain cleaner to neutralize the acid. Let sit and then wash...see if any difference. Try other neutralisers. Try a few drops of oxalic acid. and H2O2 Hydrogen peroxide

Household ammonia might also work as the NH3OH might be more mobile in the granite than NaOH. Ammonia is also less risky

__________________
Per Ardua Ad Astra
Register to Reply
Guru

Join Date: Mar 2007
Location: Etherville
Posts: 12334
Good Answers: 115
#2

Re: Practical problem with acid and granite

04/22/2007 7:07 AM

Hello Cromwell. I'm not a chemist but I did a quick google on 'restoring granite + acid ' and found such links as https://www.baneclene.com/professionals/Content.aspx?xps=NDYy.

My limited knowledge is that chemical reactions are not necessarily reversible. Also it seems that granite can be confused with other materials. Testing limited areas is always the best method. I wonder from the description if the cement on the granite was accidental, or there for some reason? It may give a clue perhaps. Best of luck - I'm quite envious of you having such a great project to do! Kris

__________________
For sale - Signature space. Apply on self addressed postcard..
Register to Reply
Anonymous Poster
#3

Re: Practical problem with acid and granite

04/22/2007 9:15 AM

Someday, someone will enjoy and celebrate your mistake as a craftsman's artifact. Leave it alone and move on.

Register to Reply
Guru
Popular Science - Weaponology - New Member

Join Date: Feb 2006
Posts: 962
#4

Re: Practical problem with acid and granite

04/22/2007 8:35 PM

This a photo reaction (sunlight warmth) due to the chlorine in the acid, reacting with minerals in the granite and UV light from the sun. (yellow colour) Have you tried mild detergent these are often ammonia based. Polish with steel wool.

__________________
There's them that knows and them that just thinks they know, whitch are you? Stir the pot and see what rises up. I have catalytic properties I get a reaction going.
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30313
Good Answers: 817
#5

Re: Practical problem with acid and granite

04/23/2007 5:14 AM

Is there scope to use mechanical removal, such as a high-pressure water jet, rather than a chemical method of removing the cement, perhaps?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Mar 2007
Location: Etherville
Posts: 12334
Good Answers: 115
#6

Re: Practical problem with acid and granite

04/23/2007 5:47 AM

'Granite' like most rock types can mean a whole variety of materials . If it really is Granite , porosity and permeability are relarively low compared to other rock types (note that porosity ≠ permeability ). Several mm penetration doesn't sound consistent with Granite . I still think it's worth being certain what it is , although that still leaves you with the stain - which I will stick my neck out and say you are stuck with. As a last resort , can you add tone to the yellow stained bits to camouflage a bit - Do you have a chunk in a skip you can experiment with.

http://www.asgranite.com/counter-faqs.html

__________________
For sale - Signature space. Apply on self addressed postcard..
Register to Reply
Commentator

Join Date: Apr 2007
Location: Montreal, Canada
Posts: 56
#7

Re: Practical problem with acid and granite

04/24/2007 8:52 PM

Hello there, I think you are going to be stuck with the stain... chemical reaction cannot be reverse all the time. You can try water jetting 5000 PSI with a TSP solution at 1% concentration, sometimes it works.

I would use a wet sandblast (the small one) and locally try to remove the stain or I should say attenuate the color of the stain. Then apply some colored stain matching the original color. This is a job for an artist... take your time and you should get good results.

Register to Reply
Register to Reply 7 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Copy to Clipboard

Users who posted comments:

Anonymous Poster (1); aurizon (1); BrainWave (1); Kris (2); Madmax1997 (1); PWSlack (1)

Previous in Forum: Conductive Liquid   Next in Forum: GE Ultem 9085 Resins for Lighter Weight Aircraft Interior Parts
You might be interested in: Cement Boards, Lead Acid Batteries, Cement Tiles

Advertisement