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Pinto Concrete

Pinto is a relatively infrequent problem but one that leaves all parties in a project disappointed.

Pinto concrete drivewayIt is a phenomenon that occurs from time to time all over the country, and no cause has been established despite investigations by most major industry players. It happens regardless of concrete company, location, season, cement, admixtures, aggregates, and importantly for us happens in jobs both with and without colour. For this reason, we are quite certain it is not a fault of or caused by the colour we supply.

It is highly unlikely to be caused by the concrete supplied either as jobs supplied before or after jobs that result in pinto are always fine.

Because of this lack of common factors, it is generally accepted that it is likely to result from a combination of environmental factors at the site and/or the placing, finishing or curing process.

But to blame the contractor is also unfair as if it was known what combination of factors caused Pinto, they would avoid this.

Despite being a global issue there is very little information on potential causes, but there is this article from the U.S. Essentially most literature on the subject suggests such a long list of potential causes, that they aren't actually any help.

We are open about the risk (even though it is very small) as we don't intend to mislead customers as you can see here, http://www.peterfell.co.nz/colour/about-colour.html, and we also include this information on each of our Inspiration pages (for patios and paths, floors, drive etc)

Pinto typically has an appearance of puddles or a cloudy appearance suggesting it is related to moisture. There are many opinions and theories but for each of these we have heard, there is usually a case disproving it.

Usually pinto occurs in exterior slabs and we are aware of only two internal floors that have had a problem. In one of these, the floor was given a very light grind which removed the darker areas suggesting it's only a surface issue - see the pictures below. The key difference between the way interior and exterior slabs are finished is that for interior floors there is polythene below the concrete, vibrators are usually used and power floats are usually employed.

And it's not just concrete - pinto can also occur in pavers as the following shows, one from Auckland and one from Dunedin and different manufacturers:

Pinto concrete pavers Pinto concrete pavers

It's obviously extremely disappointing but the functionality of the concrete is unlikely to be compromised as Pinto should only be an appearance/aesthetic problem only.

Possible fixes

The following headings show some examples of jobs where different solutions have been successfully employed. BUT, we know that there are also cases where these solutions have not been successful - unfortunately there is little certainty around which will make a difference.

Our advice

Our advice is to do an acid wash and wait, then do a second acid wash after a few months. We suggest this because it is fast, easy and cost effective, and has proven very effective in a number of cases. If after this time there is little or no change then try the vinegar, and then one of the other options.

If there is no time to wait then a tinted sealer can be used to cover the problem up.

Acid Wash + Time

The project below was in Whangarei, at left about three weeks after it was poured and the picture on the right shows the day after it was given a light acid wash (20:1)

Pinto concrete acid wash Pinto concrete acid wash after

Tinted Sealer

Where a quick fix is required a tinted sealer can be used to cover the Pinto. Tinted sealers have their strengths and weaknesses and it's important the owner appreciates these, but it was quite successful on this project in the Hutt Valley.

Pinto with tinted sealer

White vinegar

Some of the American literature on Pinto suggests trying White Vinegar. The owners of this house in Morrinsville tried that and while some shadowing remains the final result was acceptable to them.

Pinto concrete white vinegar Pinto concrete white vinegar after

Do nothing

These photos were taken four months apart and the effect was considerably reduced. We know of a number of projects where the effect disappeared after year or two, but not all.

Pinto after a three

Light Grind

The before and after photos below show that for this project in Wanaka, the pinto was able to be removed with a light salt and pepper grind

However, we know of another project in Auckland where the grinding removed most of the pinto but some still shadowing remained.

Pinto before grinding PInto after grinding

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