Acid Etch

Thought I’d better explain that last timelapse video!

While talking with Michael – a friend who visited today, we were looking at the instructions for the Shield-crete, and specifically at what was needed to prepare the surface.

Although the concrete slab is brand new, it was finished almost too well, and was really polished smooth by the multiple helicopter applications.  What we found was a drop of water had difficulty penetrating the surface, not because it had been sealed (it hasn’t), but it was too smooth.  For the sake of a small job, it was worth giving it a quick acid wash to make the surface a little (microscopically) rougher so the Shield-crete could key into it better for a more durable finish.

I headed down to Masters and bought the rollers etc that I will need when the time comes, a cheap bucket, a $3 broom, and 5l of hydrochloric acid ($12).

After clearing the floor and wetting it down (according to the (brief) instructions on the HCl container), I watered down 1 litre of acid with 10l of water.  This was then applied to the first section of the floor, where it steamed and bubbled (you can see that in the video – it is the very white areas that appear just after the acid is poured on).

The broom is used to brush the acid around, and when it stops bubbling, the job is done and the residual is hosed off/watered down.  This was then repeated for each square (so I could keep track of where I was up to).  Had no idea how much to buy- turns out it was exactly the right amount.  1l of acid + 10l water for each 10m2.

Now this is done, the floor is ready for the next stage, which I will do once construction is completed (tomorrow!!)

2 Responses

  1. Hi Stu
    Was there a requirement to mask off the lower extremities of the shed before proceeding with the acid wash?

    • I gave it some thought, and decided I wasn’t going to be concerned in the end. The acid is not incredibly strong, and is only on for a few minutes before being hosed off and down.

      I’m expecting it to have as much impact as pouring coke on it (perhaps a bit stronger!) I did’t leave it on, and hosed it down with copious amounts of water to dilute the acid to useless.

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