On 26/07/2017 19:50, Chris Hogg wrote:
On Mon, 24 Jul 2017 15:17:30 +0100, wrote:

My workshop floor has been power floated and I believe I need to etch
the surface before painting. Is this just a case of wetting it, brushing
on some hydrochloric acid, and then hosing it out after about 20 minutes?
How can I estimate the amount of acid for 30 m2 floor area?
How do I know when it's sufficiently etched?

Here's a sequence of URLs

https://www.promain.co.uk/blog/how-t...ncrete-floors/

This has a link:

https://www.promain.co.uk/flag-acid-...tion-8572.html

Click on the TECHNICAL tab, and you'll see the acid has a specific
gravity of 1.1

Click on the DATA SHEETS, and then on the Safety Data Sheet, or click
on this
https://www.promain.co.uk/amfilerati.../file_id/2495/

Scroll down to Section 3 Composition/Information on Ingredients,
where it tells you it's hydrochloric acid.

The sum of all that is the etching solution is hydrochloric acid, aka
Brick Acid, of specific gravity 1.1

A hydrochloric acid solution with a specific gravity of 1.1 is about a
20% solution by weight.
http://www.handymath.com/cgi-bin/hcl...i?submit=Entry

This particular Brick acid on ebay has a strength of 18%.
http://tinyurl.com/y87ef2e3 Note that other strengths are available on
ebay, some stronger, some weaker. This one is close enough not to
matter.

The instructions for the Promain acid say

"When applying Acid Etch to a floor you will notice the solution will
fizz this is the acid reacting with the concrete, the Acid Etch needs
to be applied until this fizzing stops. After application of Acid Etch
to a floor the floor will need to be rinsed with clean water to wash
the acid etch away and allowed to completely dry before the floor
paint is applied. This is especially essential when applying solvent
based floor paints or line marking but when applying water based floor
paint it is not as critical. When calculating the amount of product
required we would suggest you base your calculations on approximately
20m2 per litre".

The 5l container of acid on ebay will treat 100 sq.m.

Just be careful when you're using it. It's quite strong acid. Read all
the precautions for the Promain acid, and follow them. Wear rubber
boots, rubber gloves (Marigolds?) and goggles or better, a full face
visor. If you get any on your skin, rinse it off immediately. Don't be
cavalier with it. Keep the kids/pets indoors.


Thanks! That's all extremely useful - A-level chemistry was a long time ago.