Guide · St. Augustine
Cleaning coquina and historic surfaces.
St. Augustine has building materials almost nowhere else in the country has. Coquina, tabby and centuries-old lime render do not behave like modern masonry, and treating them as though they do destroys them.
What coquina actually is
Coquina is sedimentary rock formed from compressed shell fragments — quarried on Anastasia Island and used through the old city for centuries, most famously at the Castillo. It is porous, comparatively soft, and held together by nothing stronger than natural cementation between shell pieces.
Put a pressure washer to it and you do not clean it. You erode it. Material comes off, and it does not grow back.
The rule for anything historic: lowest possible pressure, gentlest possible chemistry, and test somewhere invisible first. If there is any doubt at all about a protected or listed structure, the answer is to stop and ask a masonry conservator — not to try a corner and see.
Tabby, lime render and old brick
- Tabby — a colonial concrete of lime, sand, water and oyster shell. Same porosity problem as coquina, same vulnerability.
- Lime render and lime mortar — deliberately softer than the masonry it protects, because it is meant to be the sacrificial layer. Aggressive washing removes exactly the thing doing the protecting.
- Soft historic brick — pre-modern brick is far softer than anything fired today, and blasting it strips the fired outer skin and leaves the porous core exposed.
Acid is the other way to ruin it
Coquina, tabby and lime are all calcium carbonate. Acidic cleaners — including several sold as general-purpose masonry or efflorescence removers — dissolve calcium carbonate. The surface may look brighter briefly while the material is being eaten.
The same caution applies to travertine pool decks for exactly the same chemical reason, which is why an acid-based product should never be the default on stone.
If you own something old in the old city
Properties in and around the historic district may sit under local review requirements for exterior work. Cleaning is usually less restricted than alteration, but "usually" is not a basis for proceeding — check with the city before work starts on a designated structure.
For everything else in St. Augustine built in the last century, none of this applies. Modern stucco, block, vinyl and Hardie are the normal job, cleaned the normal way.