Historic Masonry Seminar -- Repair, Remediation, Cleaning

Eight o'clock in the morning is probably not "early" for most of you; but if you are an independent contractor who is used to getting up at noon and going to bed at five a.m., it's pretty freaking early. Still, Ted and I managed to drag ourselves up in time to attend a free morning seminar at the Garfield Park Conservatory called "The Care and Maintenance of Your Historic Masonry Home," hosted by the Historic Chicago Bungalow Association and Neighborhood Housing Services of Chicago. It was well worth the effort.

I'll post the class description here, because they do have another workshop coming up in April.

From greystones to bungalows, Chicago residential neighborhoods are defined by brick and stone buildings. However, many homeowners are uncertain of how to best preserve, maintain, and repair their historic masonry homes. Presented by Mario Machnicki, president and founder of Marion Restoration, this workshop will cover: common conditions and deterioration problems, identifying priority repairs, establishing a scope of work for masonry repair projects, best practices for cleaning and tuckpointing, and financial resources to fund rehab projects. With over 30 years of experience, Mr. Machnicki has been featured in This Old House and The Chicago Tribue.

Next seminar:
Saturday, April 25, 10 a.m. to 12:30 p.m.
Avalon Public Library
8148 South Stony Island Avenue
Chicago, IL 60617
RSVP to greystone@nhschicago.org, or Blanch at 773-522-4637

We learned a great deal about masonry in general, and Chicago building practices in particular, during the two-hour presentation, which was followed up by a Q&A where they welcomed specific questions about your own building. It covered the types of building materials commonly used, such as limestone, sandstone, and brick, and the types of mortar and style of mortar joints. It also provided links to some excellent online preservation briefs, including:

Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings

Repointing Mortar Joints in Historic Masonry Buildings

Dangers of Abrasive Cleaning to Historic Buildings

There are nearly fifty briefs in all, on a wide number of topics, so check it out.

The key to preserving a building all comes down to one thing: the mortar. (Well, two things, the other is keeping out water.) To ensure that The Box House will last another eighty years, we should be repairing our masonry with like materials, and get our mortar matched exactly. We kind of knew that already--although, amazingly, most contractors do not seem to--we just needed more direction in how to go about mixing new mortar and where to get our mortar analyzed. There is a company called U.S. Heritage Group, Inc. that can run a chemical analysis on our mortar and give us the exact composition.

A previous owner repaired some of our mortar joints with Quikrete--we found the empty tubes in the basement. This product, like many modern mortars and cements, is rigid and doesn't breathe. Areas of our brick garage have a layer of cement smeared on the surface, which now prevents it from breathing. It's probably only been a few years since these bungles were performed, but we're already seeing issues related to these bad repairs--spalling, cracking, efflorescence. If we don't remediate them, over time the brick--which can no longer expand with weather variances--will completely break and crumble against the inflexible mortar.

Other things we learned which are directly applicable to our building:

The paint on the walls of our brick basement can only be removed chemically. It is a tedious process, but he recommended three products to try: Soy Gel, Prosoco, and Dietrich. Under no circumstances should we use mechanical means. What surprised the two of us is that sandblasting is actually illegal in Chicago. Not that we would try it, the historic brick is too soft, but it's illegal because of the lead dust the paint might contain, which will coat the neighborhood. We were shocked because we had just read an article in the Tribune about a couple who had renovated their basement by sandblasting the walls. It seems to be a common practice; I guess contractors either don't know about it or assume they won't get caught.

I neglected to ask specifically if we could use those same chemicals on the limestone outside, which still has its coating of paint because I haven't decided exactly how I'm going to remove it. We've been simply watching it flake off and "helping" it along.

However, Machnicki did mention that these same companies sell detergents to clean exterior masonry; the trick is to soak your masonry first so that the chemicals don't soak in, and to rinse it thoroughly with water. He mentioned a 900 psi as being okay, but he also strongly cautioned testing areas when cleaning first. Yellow brick, for example, is extremely susceptible to damage, and he's seen brick that has been bleached out from improper cleaning. We have some green biological growth on our portico, and he recommended trying water first.

Someone else asked about finishing off a brick foundation basement, and we were told that the furring strips should be placed an inch away from the walls to allow the masonry to continue to breathe.

Another person asked about insulation, but we were told our buildings didn't need it. With walls a foot thick, it wasn't necessary. He did mention insulating plaster, but we didn't get the chance to pursue the topic. I'm not certain what that means.

All in all, it was a very enjoyable morning--definitely worth getting up at the ungodly hour of eight.

Plus, we got to spend some time at the Garfield Park Conservatory, which just celebrated its one hundredth birthday.

Don't let this picture fool you; it's still pretty chilly in Chicago.

Repair and Maintenance of Historic Limestone and Marble

I had relatives over today, and should be catching up on some work-work now, but instead I've been surfing the Net for more info on removing paint from the exterior of The Box House. Here's a brief summary of what I've found if anyone else is working on something similar:

I found what looks like a good article on the subject of limestone repairs, originally written by Hoffman Architects: Maintenance of Historic Limestone and Marble

Unfortunately, it doesn't cover paint removal. An excerpt reads:

Marble and limestone are relatively soft stones and can be easily scratched and marred. This softness means chemical cleaners, sandblasting and wind-driven grit will take their destructive toll.

I imagine if chemical cleaners are going to be harsh, than chemical stripping will take its toll as well. Old House Journal agrees:

As opposed to kiln-dried masonry materials such as brick and architectural terra-cotta, building stones are generally homogeneous in character at the time of a building's construction. However, as the stone is exposed to weathering and environmental pollutants, the surface may become friable, or may develop a protective skin or patina. These outer surfaces are very susceptible to damage by abrasive or improper chemical cleaning.

From a message board I found this method for removing paint from limestone:

Try some liquid cooking oil. Rub a coat on and let it sit. It should soften and swell the paint. On another site, I was asked how to remove paint from rocks without harming the moss on them. I wasn't sure, but suggested the cooking oil. It worked, the person was very happy...The oil will soak into the pores of the rock. It will take repeated washing with soap and water over a period of time to remove it. I cringe every time I hear of somebody going to paint brick or stone.

Oil seems like it should be mild, but messy. I found a number of sites praising it for removing paint, tar, etc., but haven't come across anything "official" sounding.

From another architectural site I found this, geared toward graffiti removal:

For the removal of the paint from the limestone follow these steps:

1. Saturate the wall. This is to prevent driving the paint further into the porous material when solvents are applied. The easiest way to do this is to set up a lawn sprinkler or garden sprayer and direct it onto the wall above and below the graffiti. Let the wall absorb water overnight. There is some possibility that water will saturate all the way through the wall.
2. Apply a poultice that is a mud-consistency mix of a solvent (if toluene doesn't work try xylene or methylene chloride) with diatomaceous earth (obtained from a water treatment supplier) or commercial clay. The poultice must be of a consistency that will adhere to the wall.
3. Tightly cover the poultice with plastic sheeting taped to the wall and leave for three or four hours. This will allow the solvent to remain in contact with the paint without evaporating.
4. Remove the plastic sheeting and allow the poultice to dry. This won't take too long on a sunny day. Once dry, the poultice will begin to crack and fall off. At this point you can use a vegetable (not steel!) brush to remove the admixture. As the poultice dries, so will the wall, and as the water migrates toward the atmosphere it will help carry out loose particles of paint
5. Spray the wall with a high-pressure water jet to clean the rough surface. This equipment is available at most rental outlets.

You may need to repeat the process several times.

The cautionary notes that I emphasize strongly are: DO NOT apply the solvent directly to the paint without first saturating the wall. Solvent alone will drive the paint deeper into the limestone. DO NOT use a caustic stripper because it will etch the limestone or brick and leave what, from a distance, will look like an embossed version of the graffiti. DO NOT try to physically remove the paint with brushes, scrapers or high-pressure sprayers alone, because you will remove more stone than paint

All of the solvents are commonly available at hardware and paint supply houses. I would avoid the environmentally friendly paint removers because they are usually non-solvent based material and rely more on acids, which are caustic. They also tend to be expensive and viscous, making them difficult with which to work.

So I should probably stop scraping, too. We had used a scraper on the loose bits that were obviously coming off--just had to slide it under the paint and flip it up. When I tried to press a little harder, I noticed some teeny tiny flecks of stone came up, too. I'm not sure if this was because the surface wasn't cleaned before painting, or if it's damage from moisture getting under the paint.

At the Chicago Bungalow Forums, they had a few more suggestions, ranging from steam to power washing. The Chicago Bungalow Association had a PDF on it.

Sigh. It seems like there's definitely some conflicting info out there, with some saying "no" to power washing, chemical strippers, steam, etc., and others saying "yes, this worked for me," trying all of the above and even using sandpaper to smooth the surface. I don't know anymore. I think I'll have to call around some and get a few more opinions from the pros.

Why, why, why do people paint stone and brick?