Property prices

[lazerlab]

Hi, The bricks are apx. 25x10x10 cm of solid rock. We imported it from Laos. The price is only 700 thb. per. square meter. We glued them together with the green concrete (i do not remember the name) BRAND. I am not in the construction buisiness yet. But i will soon be. We have some 4+ Rai to develop. I do not now the english name of the acid we used. In Norway we call it BLÅSYRE (blueacid) very toxic and strong. Be carefull if you are going to use it. It is very dangeorous to handle.
PS. We only used the stone on 2 exterior walls, not the entire house. Concrete are mutch cheaper.

[Khundon1975]

Lazerlab


That was nice and cheap 700Baht per M2.

What glue did you use. Was it a 2 part epoxy resin glue? Or do you mean by "glue" that you set the stone in a mould and poured concrete onto the back of stone.


I have been involved in building many Acid etched concrete buildings in London and elsewhere, so the acid you mention will most probably be one of the two I mentioned.

I am intrigued to know what made the colour of the concrete turn from grey to black, as acid alone would not do that.

I have dyed concrete many colours including black but that was during the mixing stage, not after it had set and cured.

[Norseman]

The acid in question is hydrocyanic acid, also known as Prussic acid.

[Khundon1975]

The acid in question is hydrocyanic acid, also known as Prussic acid.

Hi Norseman

H-C-3m is that the Prussic acid, which you are talking about.

I know it is used in the manufacture of organic chemicals and sometimes in agriculture as a fumigant.

I'm surprised to hear it used as an etching/colouring agent on concrete.

In it's liquid form it is a weak acid, but I am mystified as to how this affects the colour of concrete, unless it is a reaction with crystalline salts or soluble metallic salts in the concrete mix.

I know it can be formulated using calcium cyanide and sulfuric acid, so it would do the job, but be a very volatile mix, unless a stabilizer such as phosphoric acid was added.

Well, I have learnt something today.

Thanks Norseman.

[Khundon1975]

Lazerlab

Just done a bit of googling and now I understand the Acid etching process.

I was under the impression from your post, that the acid itself was what caused the colour change, but I now know (thanks to some help from Norseman) it is just a carrying agent, which allows the concrete surface to be etched and allow the ingress of the chosen colour in the solution into the surface structure of the concrete walls.

[Norseman]

H-C-3m is that the Prussic acid, which you are talking about.

I don't think so, but you are very close.
The formula is HCN (Hydrogen, Carbon and Nitrogen).

We call it among other names, cyanide.
The Nazis called one variant of the HCN Zyklon B.

[Khundon1975]

Norseman


Cheers for that, my last chemistry lesson was at school, and that was more years ago that I would like to mention.