Can you acid stain an existing concrete patio in NB?

Yes, you can acid stain an existing concrete patio in New Brunswick — but the results depend heavily on the condition, age, and history of the concrete. Acid staining is one of the most popular ways to transform a plain grey patio into something with rich, variegated colour, and it works well on sound, clean, uncoated concrete that is at least a few years old.

Acid staining works through a chemical reaction between a metallic salt solution (typically iron, copper, or cobalt compounds in a hydrochloric acid base) and the calcium hydroxide in the concrete. The reaction creates permanent, translucent colour that is essentially part of the concrete itself — it cannot peel or flake the way a coating can. The result is a mottled, marbled appearance unique to each slab, with natural variation based on the concrete's original mix, curing history, and surface texture. No two acid-stained slabs look exactly alike, which many homeowners love.

The critical variable is surface preparation. The concrete must be free of any previous sealers, coatings, paint, oil, grease, tire marks, or curing compounds — all of which will block the acid from reacting with the concrete and create blotchy, uneven results. Old sealers require chemical strippers or mechanical grinding to remove. Areas that have been patched with different concrete or mortar will react differently and show as distinct patches in the finished colour, which can be a design element or an eyesore depending on your expectations.

In New Brunswick's climate, age matters. Concrete that has experienced many years of freeze-thaw cycles may have surface scaling, micro-cracks, or spalling that will show through the stain. Acid staining does not hide imperfections — it enhances them. A rough, pitted, or patched surface will look rough, pitted, and patched in a darker colour. The technique works best on smooth, structurally sound, consistently poured concrete.

In terms of timing, plan your acid staining project for the May through September window in NB. The acid-staining process and the subsequent sealer application both require temperatures consistently above 10 degrees Celsius for proper chemical reaction and sealer cure. Patios in Moncton, Fredericton, or Saint John that catch afternoon sun can be stained well into early October, but watch nighttime temperatures.

Expect to pay $4-$8 per square foot for professional acid staining of an existing patio, including surface prep, staining, neutralising and washing, and a quality penetrating or acrylic sealer topcoat. DIY acid staining is possible but carries real risk — the chemicals are hazardous, the timing is unforgiving, and a botched application is difficult to undo. If your patio is large or prominently visible, professional application is strongly recommended.

Need help finding a decorative concrete professional in your area? New Brunswick Concrete can match you with local contractors for a free estimate.