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What is Alkali Burn?

Alkali or pH burn is a condition that occurs when fresh mortar, cement mixes and/or concrete is too fresh (New), been improperly hydrated, or an improper formulation was used. This causes the breakdown of oil-based or vinyl-acrylic based coatings binders. When using. 100% Acrylic coatings tinted with organic colorants, it will result in color loss due to the colorants reaction with the lime in the concrete mix. Color loss and deterioration of the coating film is most likely to occur when coatings are prematurely applied to masonry surfaces that are less than one year old. After the above have cured, any moisture being introduced into these substrates may cause efflorescence, blistering and peeling of the coating film due to the reactivation of the high alkalinity. A pH reading of 7-10 will allow for improved coating success.

What is pH?

pH is the measurement of acidity or alkalinity. A pH of 7 is neutral. The pH values from 0-6 indicates acidity and from 8-14 alkalinity. The value of water is 7, thus regarded as neutral.

How can I eliminate or prevent Alkali Burn?

All masonry surfaces should be allowed to cure a minimum of 28 days and ideally for one (1) year prior to the application of any type of coating and even then the pH should be checked. Proper surface preparation and testing can help avoid alkali burn. Coronado makes available a pH pencil (IMA.1220) to perform this pH test. Always try to use inorganic colorants when tinting a color. Organic colorants (AX, D, E, M, R, or T) are more sensitive to alkali burn than inorganic colorants. The use of alkali resistant primers like Coronado 43-11 Elast-O-Meric Masonry Primer-Sealer Pigmented (Non OTC Compliant), 48-10 Elast-O-Meric Acrylic Masonry Sealer Clear or 48-11 Elast-O-Meric Acrylic Masonry Sealer can also help in the elimination of the phenomenon.

What must I do if Alkali Burn occurs?

The source of the moisture must be repaired by removing all failed coatings, caulk, etc and replacing caulking and patching compounds as required
Remove all efflorescence and allow the surface to dry thoroughly.
Apply one of the Coronado alkali resistant primers listed above.
The application of a flat coating will allow for best performance due to its ability to allow for vapor transmission through the cured coating film. Non permeable coatings are more likely to blister and peel due to their lower permeability.

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* Pro Tips *
Exterior facing walls can be cooler than interior walls leading to color variation and touchup problems. Be sure interior is fully heated when painting during cold exterior conditions.