Is the steel inside the cast concrete or cast stone corroded?
Crumbling cast stone and/or visible signs of rust are clear indicators of internal corroding steel. When cast concrete de-alkalizes, it can cause steel rebar inside to oxidize, which in-turn expands and cracks the stone. Evidence of this unique problem should prompt quick action. What are your choices and how can you prevent it from happening? What are the consequences of doing nothing?
Should we patch, repair, or our re-point our masonry?
Patching is an economic solution provided there is suitable material remaining to hold the new patch and provided proper testing is done so the new patching material is compatible. Replacement brick or stone can often be salvaged from demolished buildings or quarried from areas where original material was mined. But, testing is imperative. Replacements should always exhibit similar tensile and compressive strength and suitable salt transference and porosity. Contrarily, applying dissimilar material can cause the surrounding substrate to expand, contract, or crumble. Mortar is subject to, and reacts differently to varying types of brick, stone, and composite chemical compounds such as patching agents. In short, replacement mortar, brick, and stone are only appropriate when laboratory tested to be characteristically similar and compatible with the original material.
Is appearance important?
While aesthetics is important, performance should be regarded first. It is nearly impossible to match exactly the color and texture of original historic substrate. The bulk of historic building ingredients are sourced directly from the ground. And unlike today’s modern manufacturing elements and processes, colors and shades cannot be minutely controlled and therefore matched to the degree of contemporary synthetic material. Furthermore, environmental conditions can change the appearance of a patch months after completion. Penetrating moisture and environmental deposits affect new patches differently than the original surrounding masonry. However, experience dictates that after a few years, the patina of environmental stains will change the entire area, creating greater uniformity of color and feel over time.
Waters Craftsmen is unequaled in the business when it comes to matching historic fabric. We can sometimes find the same mine or aggregate source that was originally used. But more important, we use extensive laboratory analysis to determine the best replacement composition for performance and color matching, subject to the particular environment.
Is there a problem with using cement to patch our masonry? Should we match our historic mortar the same?
Normally, yes. The most important factor when considering cement is testing. There are four critical characteristics that must be considered to ensure quality, endurance, and compatibility; 1) compressive strength, 2) salt transference, 3) porosity, and 4) tensile bending strength. By testing these aspects, Waters Craftsmen can design the most correct mortar to patch or re-point the original masonry. Contrarily, to create a mortar without first examining the substrate is foolhardy at best. Use too much, or a mismatched composite and it will crack…too little and it may crumble. Also, a wrong blend can trap moisture, leading to the aforementioned infiltration problems.
IS THE MASONRY ON YOUR HISTORIC BUILDING FALLING APART?
Centuries ago, expert masons made mortar using lime, aggregate and pozzolana (drying material). They understood where to obtain each ingredient and how to mix it. For ages, these techniques were passed down for generations and good masons literally learned to “feel” a superior mortar…but those days are long gone. Now we’re lucky if the modern mason knows which end of a bag to open. Current opinions about mortars vary among companies, architects, and contractors. However, one fact is beyond debate…after thirty five years, Waters Craftsmen has a perfect record. We have never suffered a failure, because we leave nothing to chance. Using thorough testing to custom design mortar to match the original substrate, every project is assured the very best quality and sustainability.
Some years ago Waters Craftsmen was tasked to replace the facade of a historic house, located in an upscale old district. Upon our advice, the owner opted for a less costly laboratory designed patching material, rather than using original expensive serpentine stone, which is infamous for spalling within forty to fifty years. Our replacement custom design retained the aesthetic character, dramatically reduced the price, and will outlast the original material.
The high costs of amateurs…
On many occasions, I have seen the depletion of limited client resources, because owners were persuaded to replace historic material with a supposed “exact match” that eventually exceeded the customer’s ability to pay. Sadly, such projects end up incomplete and in some cases bankrupt the institution. Inner-city churches seem particularly susceptible, and have suffered this demise due to plastic salesmen, stained glass re-leaders, cement masons, and shingle roofers. All possibly capable in their respective fields, but none with the holistic historic restoration approach and project planning experience of Waters Craftsmen.