13 April, 2008

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?

24 comments:

Amalie said...

It is the bane of my home. I'm not entirely opposed to white brick, but I know there's red underneath. In fact, part of our screened in porch has a stippled effect-- it's buff brick and only the raised parts were painted. It's pretty. Cottagey. I'd even be happy with that on the rest of the house.

But alas, power-washing and sand-blasting scare the crap out of me. Our mortar's already in less than excellent condition.

Sigh. Why, oh, why...

Jennifer said...

Did you get my message on your last post? My father-in-law is a stone worker- limestone specialty. Try just sanding it off. Or the K2R...

Don't try anything with oils in it. Good luck!

Green Fairy said...

Jennifer--Thanks so much for the tips! What's your father-in-law's opinion on sealing the stone? I'm finding conflicting info online about sealant coats.

Amalie--Your painted brick sounds quite pretty!

Jennifer said...

I'll have to ask... we need to seal our limestone patio this summer anyway.

I don't think they seal any outdoor architectural elements, though... I'll let you know if they do, and what sealant we will use on our patio.

For now, I think you would be find leaving it as is... you can always seal later.

Green Fairy said...

Most Web sites I encounter say to let stone breathe, still, I'm finding products for sealing limestone. But maybe that is for patios. Thanks for passing on my questions! :-)

Anonymous said...

From my own personal experience -- absolutely do not power wash the limestone, Mine is now horribly etched.

Green Fairy said...

I'm sorry to hear that!

We've held off on stripping the limestone to do more research. I picked up a product--I forget what it's called, offhand--but it's supposed to be good for stripping paint off limestone and brick. I'm going to try it in an inconspicuous spot in the back sometime in the next few weeks, and will let y'all know how it turns out.

Anonymous said...

Hi, maybe yo finished ny now, i live in malta and nearly all house untill a fewyears ago were built with lime stone and still are, i recently did some work on a pre- war house many fell during ww2, i had a limestine coving/cornice to strip of the old paint, i found a burner usefull, but was told the heat might crack the stone so i used a paint stripper, chemicals i know nut it works, sanding is still needed to remove most stubborn parts but aslong as u done break the skin to deep which is a layer that for between 0-3 cm thick which is a natural reaction with air the stone should keep its integrity, MLT

granite-sealer said...
This comment has been removed by a blog administrator.
Brigid Keely said...

I found your post while looking for ways to remove paint from limestone. The stuff you've quoted is from the same sites I've found. Have you made any progress in stripping the paint off the limestone? Has anything worked for you?

We're moving to an apartment with a decorative brick and limestone fireplace. Previous owners put plastic brick veneer over the actual brick, and horrible brown paint over the limestone. I'm having a hard time finding actual, proven ways to get paint off of limestone... but lots and lots of hits instructing people on how to PAINT limestone! Don't do it! Ugh! Limestone is awesome!

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