How to clean mixed masonry facades properly – what you and your contractors should know.
By David W. Boyer
For many building professionals, the final clean-down of newly constructed masonry would seem to be a fairly simple task – a task best delayed until all of the important work is done and the ribbon-cutting ceremony is just days away.
Those same professionals presume that a cleaning contractor armed with the right product should have no problem removing hardened mortar and all varieties of unsightly contaminants from “masonry” with little risk of damage. Why then can you travel to any city in North America and find recently constructed masonry façades that are irreparably damaged or left with significant construction soiling in place? The reason is simple: Yesterday’s masonry façades bear little similarity to masonry façades today.
Yesterday vs. today
There once was a time, before World War II, when grey mortar and red clay brick dominated architectural masonry. Back then, you could use raw acid to remove smears of Portland cement mortar from newly constructed buildings with little risk of damage.
Those days are long gone. Today, removing excess mortar from clay brick is a different story. Present-day brick producers achieve an impressive variety of colors and textures by varying their clay blends, modifying firing temperatures, incorporating metallic colorants, or applying surface finishes. Each variant introduces additional challenges when removing hardened mortar smears. And then there are the added variables created by the particular mortar, mortar additives, cure time, temperature and surrounding materials.
The fact that these variables often differ from one job to the next may explain why producers of proprietary masonry cleaners offer a growing variety of cleaning formulations for clay brick alone. But alas, today’s masonry façade is rarely composed of clay brick alone.
Today, it is not uncommon to encounter new masonry façades that blend clay brick with architectural CMU, cast stone and manufactured stone. Some buildings even sport accents of thin natural stone just to complicate matters that much more. Given the investment of time and money that goes in to designing and erecting a building, it is ironic that ultimate responsibility for a cleaning program that needs to consider the varying degrees of acid sensitivity of blended masonry façades, falls on the shoulders of the cleaning contractor.
Many times, those same cleaning contractors are not granted access to a building site until after all other trades have completed their work. By then, the excess mortar they are asked to remove may have hardened for months. To remove the unwanted mortar smears, the contractor has to resort to harsh cleaning solutions and high rinsing pressures that damage the surface being cleaned, and destroy adjacent surfaces.
So who’s to blame? The designer who created a complicated blend of dissimilar masonry materials? The construction manager who delayed cleaning too long? The cleaning contractor who approaches every job the same way? The product that removed unwanted soiling from one surface but damaged nearby surfaces?
The blame for poorly executed new masonry cleaning can be shared by many parties. It stems from a failure to recognize the important role that new construction clean-down plays in a building’s final appearance. For mixed masonry façades to continue to compete with alternative building systems, it is imperative that we change the way building professionals approach the task of new masonry clean-down. It’s time for some new rules.
The first one is – Know your surface. Here’s a look at some of today’s most commonly encountered masonries, followed by the new rules for cleaning them.
Compared to other masonry materials, cleaning architectural CMU is decidedly different. The goal is not only to wash away excess mortar and jobsite soiling, but also to remove any excess colored cement paste that obscures the block’s natural texture and aggregate color.
You want to reveal a more color-uniform, still weather-resistant surface. In fact, when cleaning integrally colored CMU, the color intensity you want is that of a split cross-section of the CMU itself. Allowed to stay on the block face, that excess colored cement paste weathers and streaks. It also contributes to what many block producers call “secondary efflorescence.”
Removing the paste reveals the blocks’ intended appearance and produces a more attractive and maintenance-free façade.
The good thing about cast stone is the relative consistency of color and texture through the body of the unit. Some of the most forgiving cast stones – from the cleaner’s perspective – are actually ground or profiled in much the same way as natural stone, or split to reveal the colored matrix and aggregate within the stone.
Whether your project includes cast stone produced with Portland cement or calcium silicate, all cast stone is somewhat acid-soluble. This means that cast stone can be damaged beyond repair by cleaning procedures that are perfectly safe for clay brickwork or rough-textured architectural block.
Clay brick comes in a wide variety of colors and textures. Many get their effects from components not found in simple red clay brick. A cleaner used successfully on one type of brick may react with another, causing stains. For instance, many white or light-colored brick contain vanadium salts. They’ll react with some cleaners to cause ugly green, gray, brown, even purple vanadium stains. Cleaning contractors should get on site as soon as they get the job, and find out exactly what kind of brick they’ll be cleaning. In many cases, brick producers include cleaning recommendations on pallet tags. Make sure your contractors or construction crews follow them!
Concrete brick is available in a wide variety of colors, but generally sports a fairly smooth surface. It’s essentially a smooth, colored architectural CMU. Any cleaning operation will alter its appearance and expose some of the fine aggregate cast into the face of the units.
Done in a controlled way, cleaning can improve the overall color uniformity and weathering resistance of the finished wall. Because concrete brick is acid-soluble, if you clean it like clay brick, you’ll do irreparable harm.
Be careful! Some concrete brick closely resembles clay brick. It can be so convincing that people clean it like clay, only to discover the difference when the damage is done.
Produced from a lightweight concrete mix, manufactured stone is wet-cast in rubber molds that are created to simulate the appearance of natural stone. Though many incorporate integral color, much of the accent color that makes manufactured stone appealing is applied to the surface of the cast units. Many producers of manufactured stone use accent color, which is washed or etched easily from the surface of the individual “stones.”
This makes cleaning manufactured stone a very delicate process. In addition to selecting the best cleaning product, every effort should be taken during installation to minimize the need for cleaning. Carefully “lay” or adhere the manufactured stone as cleanly as possible. Avoid bonding agents whenever practical – they make mortar drips that much harder to remove. Installers should clean as they go – carefully – with a little fresh water and a soft brush.
During the cleaning process, the type and texture of the stone are important considerations. Some stones – sandstone, slate, quartzite, granite and gneiss – are fairly resistant to the acidic cleaners needed to remove excess mortar. For these, the care taken when cleaning clay brickwork pretty much applies.
Many common building stones, however, are acid-sensitive. Limestone, marble and travertine can be irreparably damaged by cleaners appropriate for the acid-resistant stone varieties. To tell whether you’ve got acid-sensitive or acid-resistant stone, use a drop of vinegar or a dilute acidic cleaner. If it bubbles, it’s acid-sensitive. If it doesn’t, it’s acid-resistant.
This knowledge will help you choose the right cleaner and level of care you need for cleaning.
Thin fired-clay units, often referred to as “thin brick,” are increasingly popular as interior and exterior wall-coverings throughout residential and commercial markets. Although usually 1/2- to 5/8-inch thick, thin brick has face sizes similar to conventional brick. Installed, it gives the appearance of a conventional brick wall.
Thin brick comes as individual units, which are adhered to a substrate and the joints filled in with mortar or grout, or as cast-in-place panels. When mortar and grout are used, post-construction clean-down is needed to remove the excess and clarify joints, just like conventional masonry walls.
Unlike conventional masonry, thin-brick walls often use a latex-modified grout or mortar that gives the joints a degree of water-repellency – as well as a degree of resistance to conventional masonry cleaners. This type of mortar or grout requires cleaners specially made for removing them.
Cleaning guidelines: New rules for new masonries
1. Know your surface
Concrete brick and manufactured stone are designed to look like clay brick and natural stone. As already noted, cleaning them like clay brick and natural stone can cause problems. As soon as a cleaning contractor gets a job, it should get on site and determine beyond doubt what materials its crew is going to clean.
2. Use the right cleaner
Always use products made specifically for the type of masonry being cleaned. Results may be unpredictable if you use anything else. If you know what you or your project team is cleaning, it’s easy to find out what the right product is. Masonry manufacturers usually are glad to tell you what cleaners to use to make their masonry look its best. The distributor of the masonry for your project also can be a good source.
Many distributors carry or can order the cleaners appropriate for the masonries they sell. NEVER USE RAW ACID TO CLEAN ANY MASONRY.
3. Always test before cleaning.
Even if you know the surface and have the exact cleaner made for it, test the cleaner on a small, out of the way, but representative section of the wall. Testing helps determine the most efficient dwell times and dilutions. More importantly, you’ll avoid costly, unpleasant surprises.
4. Use the mildest dilution that gives effective results.
The higher the dilution with fresh water, the safer your masonry will be. It’s really important on clay brick walls that have concrete or natural stone trim. How do you know what the effective dilution rate is? See rule #3. Limestone and manufactured stone components on masonry walls should always be protected from the cleaner, no matter how dilute. If the product literature has specific dilution instructions, follow them.
5. Clean early.
Don’t let the mortar cure too long – particularly high-strength mortar. The longer unwanted mortar smears cure, the harder they get and the harder they are to remove. It’s a big problem on sensitive surfaces. In general, for smooth or acid-sensitive surfaces, clean within seven to 14 days after the mortar joints are tooled.
The window is seven to 21 days for acid-resistant or rough-textured masonries.
6. Follow the basics.
The fundamentals of new construction cleaning still apply in most cases. They are:
- Use lots of water to pre-wet the brick before applying the cleaner. If you don’t pre-wet, you’re more likely to cause staining and excessive erosion of the mortar joints. Some staining can be corrected – for a price. Damage the mortar joints, however, and you’ve reduced the weather resistance of the entire wall. Short of re-pointing, that kind of damage is irreversible. Make sure your contractor uses plenty of water to rinse the spent cleaner and dissolved soiling from the surface. Six to eight gallons per minute is ideal.
- 400-1,000 psi is the safest, most-effective pressure for rinsing dissolved soiling and spent cleaner from cleaned masonry. Higher psi risks wand marks and eroded mortar joints.
- Follow all safety information on the product label. It’s there to protect YOU!
- Never go it alone. Questions or problems? Call your distributor, masonry producer, cleaner manufacturer, or the manufacturer’s local field rep. Your success is their success.
David W. Boyer is president of PROSOCO, a national manufacturer of products that clean, protect and maintain masonry, concrete and stone architecture. For more information, contact Gary Henry at 785.830.7343, or e-mail firstname.lastname@example.org.