Frequently Asked Questions

#AskaConservator Day 2023

On November 4, 1966, the Arno River burst its banks and flooded Florence, Italy, severely damaging or destroying many of the Renaissance city’s cultural and historical treasures.  The devastation left in the wake of the flooding served as a poignant reminder of the necessity to intentionally take steps to preserve sites of cultural heritage. Since 2019, the American Institute for Conservation (AIC) has used the memory of the tragedy to ignite a passion for conservation and connect with those dedicated to this cause through hosting #AskAConservator Day. Conservators work hand in hand with a wide range of communities to protect and preserve historical sites, valuable artifacts, and cherished traditions. These collaborations with diverse communities are invaluable for fostering stewardship, promoting cultural understanding, and driving forward research. This year, we are thrilled to have our very own Architectural Conservator and AIC Professional Associate, Anthony Hita, ready to field your questions. Here are his responses.

Before planning an intervention for water penetration, you must determine where the water is coming from. Often, you’ll find that the water is coming from something wrong on the building, like a lack of gutters or gutters shedding water on or too close to the building. Other times, it may be an inappropriate mortar trapping water in the wall. It can even be something like a lack of proper insulation, allowing the inside faces of the wall to reach the dew point. These different things have different interventions, and you can sometimes address a water problem without touching the bricks themselves.  

The most usual thing prescribed for exterior liquid water penetration is a siloxane sealer. These are great for resisting wind-driven rain or liquid water intrusion. Still, it’s vitally important to remember that siloxanes have an extremely long service life and limit what kind of cleaning or painting you can do in the future. Sometimes, we find siloxanes that are still effective from the 1970s or 1980s that prevent liquid cleaners, mineral paints, or other sealers from being applied. If you do go the route of a siloxane, I advise only using it in areas you know need it and keeping some documentation you can pass on to a future owner or occupant so they know what is there.

For below-grade applications, you may need a system that combines some parging or vapor barrier with graded gravel and a french drain. This solution can sometimes also help moisture penetration from rising dampness. 

Without knowing the type of stone, it’s hard to say for sure. In general, you want to use a repair material that is strong enough to hold the stone but weak enough that if the stone breaks again, it will snap at the old break and not the new one. You also do not want the repaired area to act as a capillary break and trap moisture, ice, and salts below the repair, where they might cause damage to inscriptions or the base of the statue. Assuming your stone is of moderate strength and absorption or stronger, our Lithomex®-based Casein Glue is usually a good option. Alternatively, you may be able to use small dots of epoxy with the rest of the void filled in with a lime-based injection grout. However, remember that epoxies generally cure very hard and may not allow the stone to separate at the original break should the damage condition reoccur.   For sugaring marbles and incredibly soft stones, it can be challenging to find a product soft enough. Compromise in those situations is sometimes necessary, knowing the repair may be stronger than the stone but with few other options. The exception is if the damaged area has to resist gravity (i.e., a projecting arm on a statue). In these cases, you usually need to use a titanium or stainless steel pin inserted into a bed of epoxy.

Assuming your house is masonry, I’d keep it simple. Source a piece of local stone, carve it, and insert it with a period-appropriate lime mortar such as our Ecologic Mortar. Using techniques and materials available to a 1740’s builder helps to ensure compatibility. Remember, though, that if your building didn’t already have a date stone, you are adding something anachronistic. That’s fine, but I believe it’s essential to find some way of acknowledging that the stone isn’t original, perhaps by carving a small inscription of the year and your initials. If you don’t want your acknowledgment visible, you could always do it on the back or sides so the mortar will hide it. In doing this, you add your own chapter to the story to the building rather than attempting to rewrite the existing story.

The first and best thing you should do is to remove the paint. The method you choose in paint removal should be informed by what damages the building the least. You may need to test several different methods. I’d generally avoid aggregate/media blasting and power washing as these methods can do extreme damage to historic masonry quickly if not performed by an experienced operator. After the paint is off, you can assess the masonry and determine what to do. A common intervention is consolidation of the remaining sound host material followed by surface repair. Most likely, you’ll minimally want to do some surface repair with a product like our Saint-Astier® Lithomex®. Follow that with repointing. Sometimes whole unit replacement in extreme situations is required. I advise whole unit replacement where over 50% of a brick or stone is lost, or where compromised materials may be leading to structural problems. If you think you have structural issues due to the damage, you will want to consult a qualified structural engineer for advice.

It sounds like you probably have a lime plaster base that was finished with gypsum plaster at some point–a common situation in old houses that have been continuously occupied. First, make sure the plaster itself is good and solid. Often, cracks and holes are a sign of failing plaster where a layer has become debonded or the keys (what hold the plaster to the lath) have crumbled. You can get a good sense of this by knocking on the plaster. If it makes a solid thunk, it’s usually good. If it makes a hollow thud, it’s usually a sign that it’s failed and hasn’t fallen off yet. Remove the bad areas, and you may find the damaged area is bigger than you realized.

For the smaller holes around an inch or so, as long as you are sure the plaster is on lath and is good and solid, you can fill in small holes easily with a mixture of 3  parts hydrated lime and 1 part gauging plaster. For deeper holes that have small widths, you can add a bit of fine masonry sand into this mix to help give it some body. If the holes are on a plaster wall direct to masonry, you’ll want to use one of our Ecologic TOPCOAT Platinum products instead–usually Ecologic TOPCOAT(F) Platinum mixed with a bit of our Ecologic TAKCOAT® Platinum product for extra adhesion. A good ratio is 1 part Ecologic TAKCOAT® Platinum to 3 parts Ecologic TOPCOAT Platinum. Gypsum in gauging plaster is water soluble, so except in some specialized cases, you normally won’t use it anywhere moisture might move through the wall, like on a direct-plastered masonry wall or an exterior.  

For bigger holes or cracked areas, you will likely need to expand the void a bit to give yourself room to work. Start using our Ecologic TAKCOAT® Platinum product and then one of our Ecologic TOPCOAT Platinum lime-based plasters. For repairs deeper than 1/4″, use Ecologic TOPCOAT(G) Platinum and do it in two coats. For repairs less than 1/4″, you can use one of our fine or Ecologic TOPCOAT(XF) Platinum varieties directly on the Ecologic TAKCOAT® Platinum to bring the plaster back up to the surface.  

Of course, you can avoid all this minutia work if willing to recoat the whole wall. In that case, you can skip filling smaller holes using some self-adhering fiberglass tape. Then, recoat the entire wall with a layer of our Ecologic TAKCOAT® Platinum product, followed by the finishing grade of Ecologic TOPCOAT Platinum of your choice or even one of our mineral paints. The main downside is that you may gain ⅛-¼” on your wall’s height. Larger cracks still require you to do some filling, as previously mentioned.

All walls contain moisture, even if there isn’t a moisture problem. That moisture will move through the mortar joints to the surface, where it will carry its dissolved minerals that are left behind when the moisture evaporates. Generally, moisture will move from areas of higher density to areas of lower density. In a traditional historic mass masonry wall, mortar joints act as this lower-density evaporative surface. Over time, if the wall was pointed with denser materials like Portland cement mortars, the moisture will experience more trouble escaping, and you may get salts building up in the wall invisibly (subflorescence). In some cases where the masonry units are weaker than the mortar, you may have the salt grow on the stone/brick instead or cause internal damage that causes faces or layers to fall away. This is why it’s essential to always use a mortar that is weaker and less dense than your masonry.

Once you point an area with lime mortar, your wall can breathe again, maybe for the first time, and moisture and salts will begin to escape. If you only point a small area with lime mortar and the rest is denser mortar materials like cement, the small area of lime will be where all the moisture and salt wants to go, and so you’ll see an over-dramatic expression of salts (efflorescence) in that area compared to other places. While unsightly, this is a sign the mortar is working as it’s moving the salts away from the masonry units. If your wall does not have an active moisture problem and is not adjacent to a high salt area, the salts will diminish over time once the critical mass of built-up salts in the wall is allowed out. You can clean the area by lightly brushing away the salts with a firm (but not metal) bristle brush. Vacuum up the salts. Avoid rinsing if you can. The salts are water soluble, so rinsing will put them back into the solution and they’ll get sucked back into the wall. Likewise, if you leave the salts on the ground and don’t clean them up, moisture may cause them to wick them right back into the wall. If you live in a place with high-ground salt (old farms, salted sidewalks or roads, near cemeteries, significant waterways, etc.), you may consider repointing more of the wall in lime to help the salts get out and even use a parging or limewash to protect the wall better if the aesthetic changes are not a problem.

Yes, it’s possible to render over logs.  Chink the logs till they are about flush with the face of the log, and scratch the chinking in preparation for rendering.  Use a lime-based render and mix chopped hemp, straw, or animal hair into your first coat to give it extra flexibility and crack resistance.  Alternatively, you can secure fiberglass lath to the logs and render over that.  Logs expand and contract at a higher rate than masonry materials, so it is vital to either use lath or have that fiber in the base coat to minimize the possibility of cracking as the logs swell and contract over time.

Whenever you are combining polymerized materials like tile grout into an area where they weren’t originally, you could potentially run into issues. In an interior, it isn’t likely to be as problematic as an exposed exterior. However, you should still probably understand what, if any, moisture is interacting with the tile and if any sealers were originally used on it. This seems like a non-answer, but you do need to understand more about the system the tiles are a part of before choosing a product to not only minimize the chance of damage but also maximize the long-term performance of whatever material you select.

ASTM standards for job site practices are usually broad, and while they give definitions, targets, and guidelines, they typically do not offer tutorials on means and methods. This is because there are often many ways to accomplish a task, many of which may lead to equally valid results, or may not be universally applicable. In the case of a skim coat, the procedures and products you use will heavily depend on A) the substrate, B) the skim coat material, and C) the conditions and exposure of the wall system. Without knowing more about the specific application, it’s difficult to say what products may be suitable. Gypsum, Portland cement, and lime will all have different products and procedures, and the right thing for one can be ineffective at best, harmful at worst, to a different one. You’re always welcome to contact us directly with the specifics of your project for more individualized help.

In certain situations, if a lime mortar is pointed too deep or used to lay particularly thick walls where air or water-borne dissolved CO2 cannot penetrate, the lime mortar will not set. It could have implications on the performance of the wall system since carbonation is part of what grants lime mortar its durability and strength. You’ll often hear the anecdote of European castle walls with unset mortar at the wall’s core where air and moisture never reach. Historically, masons would use natural hydraulic limes or add various pozzolans to the lime to give it a slight hydraulic set. Surveys of historic lime mortars have found at least trace amounts of hydraulic material (added or natural) in a good cross-section of mortars, suggesting hydraulic lime of one kind or another was widely used. However, even hydraulic limes depend on carbonation for their long-term properties. The good part about this process is that for a time, there is available unreacted calcium hydroxide that, when exposed to water, can migrate into microcracks and give lime its vaunted “self-healing” effect. The downside, however, is that lime mortar’s properties change significantly over time and are disproportionately affected by things like depth, exposure, and joint finish style.

The consequence of this to historic structures is that doing a mortar analysis on an extracted surviving historic mortar is only sometimes going to give you an actual picture of what kind of mortar might be best compatible. Due to carbonation, lime mortars will initially gain mass and decrease porosity. However, because calcium carbonate is soluble, over time, water movement in the mortar will increase the porosity and eventually lead to mechanical deterioration. Thus, a mortar that is, say, 100 years old will not necessarily represent the mechanical properties of that mortar at 50, 25, or 1 year old. So it isn’t quite as simple as saying, “This lime mortar is crumbly, so we want a weak lime replacement mortar” because the weak mortar with 50-150 psi now, may have at one time reached 900-1200 psi. It also ignores how the materials on the building have weathered in the intervening years, which may necessitate a change in mortar composition. An oversimplification of the historic use of lime has led to a proliferation of questionable advice on lime mortars that tends to result in people using mortars that are far weaker than what was plausibly the properties of the original mortar. For example, right now, there is a common misconception that assumes all pre-20th century historic lime mortars were non-hydraulic “hot mixes,” and so advises people to put back only a modern slaked aerial lime mortar. These modern mortars may be putting something in the wall that at its peak is far weaker and far more vapor permeable than the original mortar, which may allow water and the deleterious materials deeper into the wall than the original mortar, starting a process of weathering in materials that have not historically weathered as such. To me, it seems the automatic assumption that only weak aerial limes are valid for historic structures is an overcorrection to our equally inappropriate use of Portland cement mortars in historic buildings–neither extreme considers the building as a unique system that needs to be contextualized and understood to choose the most sympathetic replacement materials.

Unlike today, where porches are mostly pleasure spaces, porches historically were a significant social and functional portion of the house, so almost all structures would have had some porch, even if that meant cutting a few corners like a proper foundation. In a time before widespread building and zoning regulations, people could do and get away with a whole host of practices we find problematic today.  

I’m a pragmatic preservationist. I acknowledge the value of keeping a building as authentic as possible, but I believe some modifications are necessary to allow the building to be safe, comfortable, and habitable. The best way to preserve a building is to keep it in use. Things like safe electrical wiring, indoor plumbing, and, yes, a foundation under the porch are all modifications I’m okay with as long as they are thoughtfully and intelligently done to minimize the damage to the original fabric of the building and don’t substantially change the ability to interpret the building in its historical context. In many cases, adding a foundation will also preserve the historic porch and so can be a win-win for both continued use and preservation.

I assume you mean a Type S hydrated lime and not a Type S cement-lime mortar which should definitely not be used. If so, be aware that a Type S hydrated lime and sand alone will produce a relatively weak and crumbly mortar that can work to a degree in sheltered areas but may not hold up well in your basement. Hydrated limes are primarily meant to be combined with Portland cement to add plasticity and control the setting time and are not generally appropriate to use independently due to the inability to reach strengths needed in exterior environments.. To my knowledge, Virginia Lime Works was selling hydraulic limes, not hydrated limes. The names sound similar but are quite unlike one another. If you are attempting to source products similar to what Virginia Lime Works used to sell, I recommend using our Ecologic Mortar, which is a pre-blended mortar containing sand and lime, or purchasing just the Saint Astier® NHL 3.5 and mixing your own sand with it.  

Parging is an excellent option to help with dampness and cohesion in a masonry wall on a foundation or in a basement, but is not a replacement for repointing. Parging will generally consist of one coat of material, and lime-based parging will typically be 1 part lime to around 2 parts coarse sand. I recommend using a hydraulic lime for this, either a properly produced pozzolanic hydraulic lime (PHL) or an authentic natural hydraulic lime (NHL) with a proven track record. If you are going to use hydrated lime, be aware that you’ll likely get cracking and have to redo sections of the work relatively frequently as the hydrated lime and sand will not resist the moisture and salt of the wall to the same extent a more appropriate hydraulic lime would.

It is good you are installing what sounds like a french drain system leading to natural drainage away from the foundation. Still, given the amount of salt and moisture infiltration you’re describing, it may also be necessary to assess the slab and see if other remediation techniques are required. You’d likely need a slab expert to come out and help you assess what kind of water drainage systems would work best for you (perhaps an interior perimeter drain)  and if any other remediation is necessary. You might consider a breathable earthen floor or a pure lime concrete floor system if you are seeking a vapor-permeable floor system, but these would be replacements for your current slab.  This will not be as simple as sealing the top, as you are correct that it would likely force the water elsewhere, but it’s hard for me to get more specific than this because there are a lot of factors that can go.

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