Q&A with Jim Lucas

Words: Dan KamysCleaning natural stone can be a touchy subject for masons. You want a clean, beautiful surface without sacrificing the stone material’s natural state and condition.

To learn more, Masonry consulted with natural stone cleaning expert Jim Lucas, who represents PROSOCO, Mortar Net USA, Cortec Corp. and JE Tomes. Lucas has nearly 45 years of experience as an independent manufacturer representative in the industry. He has been a member of the Construction Specifications Institute since 1970. He also is a member of the Association of Licensed Architects, the International Concrete Repair Institute, the Wisconsin Chapter of the American Concrete Institute, and the Wisconsin Masonry Alliance.

Lucas’ awards include the CSI’s Brousseau Award and the AIA’s Chicago Chapter Distinguished Service Award. He has written articles addressing masonry cleaning, repointing and restoration for various industry magazines. He also is a speaker and AIA Learning Unit Provider for PROSOCO, Mortar Net Solutions and Cortec Corp. Following is what he had to say.

Masonry: Discuss different cleaning considerations for varying types of natural stone, including limestone, marble, granite, cultured stone.

Jim Lucas: The first step in cleaning stone is to identify the stone. Natural Stone can be silica based or calcium based. The silica stones are granite, sandstone (including bluestone), slate, gneiss, schist and basalt. The calcium-based stones include limestone, travertine and marble.

From a cleaning standpoint, the main difference is that the silica stones are insensitive to most acids, and the calcium-based stones are sensitive to most acids. The fastest way to identify them is with a drop of hydrochloric (or muriatic) acid. If it fizzes, it is a sensitive stone. If it lies on the stone like water, it is an insensitive stone. Cleaners containing acids are often appropriate for concrete pavers. Clay pavers can be treated like silica based stone.

Masonry: How important is determining pressure and volume for each project? What about accessories, like brush types? Also, talk about cleaning agents — when are they necessary?

Lucas: Water pressure is of little importance in cleaning stone. Water volume is very important. I like to see a power washer being used but I want a fan tip and pressure less than 1,000 psi.

Masonry: How is cleaning mortar from a newly finished natural stone project going to different from cleaning older, stained natural stone?

Lucas: The answer to this question is enough to fill a book. I can address the mortar issue easily enough, but stained, older stone is much more difficult to address. Not only do you need to identify the stone, but you need some info about the stain. Some common ones are tire marks, sealer blush (turning milky white), algae, moss, mold, mildew, leaf stains (especially oak trees), insect fecal matter (often called "tree sap"), oil stains from food, body oils or automotive fluids, deicing salt stains (commonly called efflorescence), hard water deposits (improperly aimed sprinklers), smoke and exhaust.

Then, you have the issue of water usage. If this is an interior application, we can't use much water. Churches and office lobbies are typical. Finally, you have stains that are actually part of the stone. Indiana Limestone often has quarry sap stains. Ohio sandstone often has metallic oxidation staining in new stone. Bluestone often exhibits a rusty orange discoloration. Quarry sap must just disappear as the stone reaches equilibrium with the environment. Metallic stains in Ohio Sandstone are just part of the beauty of the stone. Orange stains on bluestone can be chemically reversed.

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