Acid Etch concrete

[Arch Stanton]

I am going to paint my new shed floor. The word on the street is, you have to acid etch the concrete first. That sounds fine but I'm concerened about the effects the acid may have on the shed when it inevitably comes into contact with it.

Are there any precautions I should take appart from wash the steel well?

[artme]

That's about it Arch.

The acid you use wo'nt be very strong and a good was should take care of it.

[BobL]

Rather than following the "word on the street" I would follow the directions on the can. For example, for Berger jet dry if it is new concrete there is no need to etch new concrete.

[Optimark]

I concur with BobL, whilst the word on the street and on the can is an acid etch prior to painting, if the concrete is new it doesn't require an acid bath to prepare the surface and rid it of oils and other stuff that happens to stain concrete over time and thereby stop a good adhesion of the sealant with or without a coloured tint.

The Staseal stuff I used, suggests an acid etch prior to sealing, except when the concrete is new.

Mick.

[Eowyn]

I've been misreading the instructions. The instructions for Bondal Garage & Factory Floor Protector starts a paragraph with "new concrete", so I assumed that whole paragraph was irrelevant to old concrete.

so old unpainted concrete needs acid etching and wait two days before painting.
so old painted concrete needs cleaning and a test patch to check the new paint will stick.

One third of my workshop floor is painted already but it is black, so i intend to redo it, as soon as I get access in a few weeks.

[Arch Stanton]

Beauty,

that saves some time and worry. Thanks gents.

[GraemeCook]

Rather than following the "word on the street" I would follow the directions on the can. For example, for Berger jet dry if it is new concrete there is no need to etch new concrete.

Good Morning Arch

Also agree with Bob. I have used Berger paving paint and Berger factory floor paint on very old concrete (50+ years ??) without any etching and with excellent results. My technique was to give the concrete a good blasting with the Karcher, let it dry and then a couple of coats of Berger with an extremely woolly roller. Ten plus years between repainting - light Karcher, let dry and repaint.

Unless the chemistry of whatever you are going to use is radically different from Berger then I cannot see why it needs to be etched. Perhaps its a ploy to sell their proprietary acid etching compound. Or am I being cynical?



Fair Winds

Arch

PS: The Berger paving paint also works well over epoxy and in a marine environment. Use it on the deck of my yacht!

[Master Splinter]

The etching chemical is citric acid. $8.25 per kilo. A kilo should be plenty for a double garage.

[Arch Stanton]

Rather than following the "word on the street" I would follow the directions on the can. For example, for Berger jet dry if it is new concrete there is no need to etch new concrete.

I have now decided to use the Berger Jet Dry. I wasn't sure if I should get the "Garage" version or the "Heavy Duty". I went to Bunnings and had a look at the can. I found the help line number and gave them a call. The number was for Dulux. The bloke I spoke to was helpful and he said the Jet Dry was my best bet, Garage version. I can only assume that it is a better product than the other Dulux products in its class. The big thing he said was, that the Jet Dry relies on the concrete being acid etched for it to work properly.

[doug3030]

The reason behind acid etching concrete prior to painting is because of efflorescence, which is water-soluble salts leaching through the concrete and being deposited on the surface of the concrete. While not all concrete is affected, it can really happen to any concrete surface.

In bad cases of efflorescence white deposits of salty crystals can be seen on the surface. In mild cases it may not be very visible if it can be seen at all. It is the salt deposits that cause problems with the paint adhering to the concrete.

As the salts are alkaline, the treatment is to wash the concrete with acid. If there are any alkaline salts on the concrete the surface will bubble when the acid is applied. Washing the concrete with acid can only make the paint adhere better and cannot have a derogatory impact.

It is a very simple and cheap process and I would do it whether it is old or new concrete and then paint it within a few days before any efflorescence has a chance to reappear. Once painted, the concrete is sealed so there should be no further passage of water through the concrete meaning no more alkaline salt deposits.

All you need is a litre or two of hydrochloric acid, a plastic bucket and a nylon broom. Dilute the acid 10:1 water:acid in the bucket and apply the acid to the concrete with the broom. You can tip some on the concrete and spread it with the broom if you like. Keep applying the acid until the bubbling stops. If you are careful you wont get any of it on the shed walls etc. If you do just rinse it off. It wont do any immediate harm. It is advisable to rinse the concrete once the acid washing is completed.

It is advisable to wear rubber boots as you will likely have to walk through the acid while it is wet.

Put it this way, I would rather spend an hour and $20 doing this before painting rather than sit and watch the paint slowly lift. How soon do you want to have to empty the shed and strip the floor?

Google "efflorescence" for more background information.

Cheers

Doug

[aldav]

I agree with Doug. Concrete is an alkaline product and will neutralise the acid - when brushing the acid on to the concrete you will notice it loose its power once you have brushed it over a relatively small area. Consequently any damage to steel will be virtually non-existent. Just wash the surface down with clean water when finished. When making up your hydrochloric acid/water mixture add the acid to the water, NOT the water to the acid. The wrong way round can lead to an unexpectedly strong chemical reaction. This is a wise move whenever diluting chemicals with water - evidence those who have had granular chlorine blow up in their face!

[doug3030]

When making up your hydrochloric acid/water mixture add the acid to the water, NOT the water to the acid. The wrong way round can lead to an unexpectedly strong chemical reaction. This is a wise move whenever diluting chemicals with water - evidence those who have had granular chlorine blow up in their face!

Thanks for adding that Aldav. It is a good safety point which I overlooked, as it is just second-nature to me having become familiar with the process. It would never occur to me to do it any other way. I am pleased you brought it up as many might not have known.

Cheers

Doug

[Poppa]

I acid-etched one half of my new garage/shed on the weekend. Used 50 litres of water with 5 litres of acid to do about 50m2 of concrete. I mixed it in a big bucket, then sloshed it on the concrete and went over it with a firm broom to make sure all the surface was thoroughly covered. Then left it for about 20 minutes or so, until it was no longer bubbling at all and washed it off with a lot of water. I was careful to wash any nooks and crannies thoroughly and probably used way more water than I needed to, but I was happy with the result. Now leaving it to dry for the week and will paint next weekend. Using Staseal Premium matt. I think I need to start my own WIP thread for my shed...

[Hermit]

When making up your hydrochloric acid/water mixture add the acid to the water, NOT the water to the acid. The wrong way round can lead to an unexpectedly strong chemical reaction. This is a wise move whenever diluting chemicals with water - evidence those who have had granular chlorine blow up in their face!

Also, by adding (liquid) acid to the water, if there's a splash it will only be water that splashes up and cops you in the face.

If adding water to liquid acid, the acid can splash up.

[Christos]

..... I think I need to start my own WIP thread for my shed...

Yep.