acid etching concrete

**yozza** · 16th Aug 2008, 05:09 PM

Gday all, i am a long time reader who has gathered an amazing amount of info from this forum, but now it is time to post.

After many years of dreaming about my perfect shed i have finally got it built, 9.15m by 11m barn with a mezzanine above the rear bay. I have got all of the wiring done now, heaps of power points, lots of lighting, all very neat and functional (well i have had about 3 years to think about it!!). The next stage is to paint the floor, I have done lots of research and finally purchased my paint (water emulsified 2-pack epoxy industrial flooring paint). As part of the preperation of the floor pre painting i need to scrub it with an alkaline cleaner, and then acid etch the floor. I have done a couple of test pieces on an old slab that is pretty clean and i found that while the acid did "fizz" when applied to the concrete it also appeared to stain the concrete.

My questions are:
1) Is it normal to "stain" the concrete?
2) How do people ensure that all of the acid is removed before applying paint? Copious amounts of water?
3) After etching and the concrete drys, i have heard that there is often a layer of fine dust on the surface that needs to be removed, have people experianced this, and if so what is the best way to remove said dust? Vacuum? Pressure wash?
4) Any other hints/tips people can offer would be greatly appreciated

Thanks all

Yozza

**Cementer** · 16th Aug 2008, 05:57 PM

Hi Yozza,
From experience I have found that acid washing leaves some sort of discolouration to the concrete. Usually the stronger the solution, the greener the stain. Using copious amounts of water removes the acid solution and helps dilute the run off but doesn't remove the residue or dust layer. That MUST be removed by pressure washer. I have seen so many jobs delaminate due to not pressure washing off the residue. At the very least, scrub with a firm broom and hose off. A water blaster will make sure though.
My method is a solution of 2:20 (1:20 is the usual for etching but I like to make sure)
Let the solution fizz before scrubbing with a stiff broom.
I'm sure others will give you more tips but this is a start.
Congrats on the new domain. Its a mans second home.

**Terrian** · 16th Aug 2008, 09:21 PM

^^^ Sounds advice, take note

**yozza** · 17th Aug 2008, 11:50 PM

Thanks Cementer for the advice
My plan (at this stage) for painting the floor is
1) Pressure wash floor
2) Scrub with alkaline detergent and pressure wash off
3) Mix acid and using a watering can apply evenly over floor, when it stops fizzing scrub with stiff bristled broom
4) Rinse off, and then pressure wash and scrub with broom
5) Let dry, then check for any crap left, and vacuum, pressure clean again
6) Let dry again to check
7) Moisten down concrete and then paint, very quickly!!!!

In regards to wetting concrete before painting the agent i got the paint from said to do it as it is a water emulsified paint, having the floor moist helps the paint "suck in" to the concrete, giving better adhesion.

The other problem i have got is that the shed is allready built and i am concerned about the acid reacting with the steel. I did some test pieces on scrap colorbond by scratching through to bare metal and then applying the acid sulution and then leaving it on there for times ranging from 5min to 20 min then rinsing off. So far after 2 weeks there is still no apparent reaction. Would it be safe to assume that provided i am quick with removing the acid there shouldn't be any real effect. I also did test piece on gal steel (simulate my posts) and there was a noticable reaction, with the final result that the gal dulled a little. Once again provided i am quick in removing acid solution can anyone envisage any issues with the gal?

And one more question (sorry about all the Q's)!!!! I have read that if you apply a weak solution of ammonia after acid etch and washing, it should change the ph to approx an even 6 -7. is this correct and if so would there be any residue after lots of water flushing?

thanks again for any help!!!!n

**GAM** · 18th Aug 2008, 02:22 PM

While on the subject, how would one REMOVE acid marks. I have a couple of yellow spots on outdoor granite tiles which I think may be due to hydrolchoric being spilt on to them.

Thanks
GAM

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