This is part of a series of blog entries that will feature mason, Randy Ruth.
Randy was the former lab technician at LimeWorks.us and received lots of questions on masonry and the use of our materials. We post some of these questions on our blog. Look for “FAQ” in other titles of our blog.
Q: I have an old stone basement foundation (house was built in 1900) and need to “re-point” or fill in holes in the basement walls. Would your Ecologic mortar work? I am not sure that lime based mortar was used originally; would this still be OK or how can I tell if lime was used?
A: “cement” was not produced in the United States until 1870 in Coplay, PA, only up until around 1910 was Portland cement starting to find its place in society as a masonry binder. Prior to 1910, most mortars used were based on either lime putty, Natural hydraulic quicklime, or natural cement. Regardless of what the exact mix design was used to build your basement foundation, Ecologic™ Mortar would most likely be suitable for repointing your old stone basement foundation walls as it would be sympathetic to the adjacent mortar mix by maintaining good vapor permeability. An easy way to determine if you have a lime based mortar, especially in stone construction, is to break a piece from the wall and visually inspect for any white nodules or specks. The white nodules are an indicator of what is called a “hot lime” mix and commonly found in stonework. Any presence of those nodules or specks suggests a high lime content mortar, and should thus be repaired with a comparable material.
Of course following the Lithomex technical data sheet is important to ensure a quality application, but what about the little things that can’t fit on one sheet of paper? The small details that help make good finish “POP” into a quality indistinguishable patch. There are many things that are far to subtitle to translate onto paper from experience and feel of mortar and trowel. So practice, timing and tools are critical overview subjects to be discussed here.
Practicing patching old single salmon bricks not in a wall is a cheap and technically challenging exercise. The porosity of salmon bricks demonstrates the importance of controlling suction. If suction is not controlled, bond failure can occur while detailing outside corners. It’s these corners that give rise to the technical challenge. By coating multiple sides of a brick, it helps create focus on multiple surface planes. The initial reshaping step doesn’t have to be perfect. It just has to have about 1/8 inch extra material beyond the desired finish. Once Lithomex is well bonded to three sides of a brick, wait for the material to stiffen to thumbprint hard.
Re-troweling the surface will compact the patch to compensate for any slight shrinkage. While using trowels, squares, straight edges, miter rods and improvised tools to shave back and cut away undesired material to the finished profile will create the rough finish. When finishing a masonry unit in a wall, long metal straight edges are great to use as a profiling tool. With the edges exposed over to adjacent units or edges, they act as a guide to bring the finish to proper plane. Typically much of this profiling can be done in the first day of patching; however 12-24 hours later more intricate detailing and carving can be done. Tooth chisels can be used during this time frame to scratch in tooth marks or crandled finishes.
As more time is allowed to let the patch “firm up” stone masons chisels can be used in a traditional method to give more authentic characteristics. Sanders and rubbing block are also useful for honing the surface to a more polished or pristine finish.
Following these tips and practicing will build upon previous experiences for the craftsman or aspiring novice, facilitating a better rounded approach to brick, stone and terracotta patching.
Often when applying Lime Paint the surface texture may be rough, such as that of a brick, stone or stucco. A good brush for Lime Paint should be made of a high quality, durable natural bristle. What would be the most distinctive difference is the size. The wider thicker ferrule allows for more bristles and allows for a greater painting efficiency, due to its greater capacity to carry the thin paint.
Q: Could I perhaps use cement and sand? What is the advantage of using lime on old stone structures
A: You should not use only cement and sand for a variety of reasons, the first being that in today’s mortars, lime adds workability and plasticity to the Portland cement mortars. Without lime in the mix or proprietary additives, the cement and sand mortar will have extremely poor workability. Secondly, modern-day cement is much different than early cement or lime, it is very hard, dense, vapor impermeable, and brittle. Cement can trap moisture inside the wall and erode the mortar behind the repair mortar, this can cause further unseen deterioration and masonry unit (stone, brick, terracotta) deterioration, thus resulting in a delayed and much larger/costly masonry repair.
The advantage of using an appropriate lime mortar on old stone structures deals with compatibility. There is a rule of thumb when approaching a restoration project and that is to repair in kind with like materials. By following this approach an individual can avoid unforeseen problems associated with trying something “new and improved” when there is such a well over 2,000 years of lime building history. There have been a number of studies done around the world on historic structures that conclude that even a small amount of Portland cement added to a lime mortar mix, can cause detrimental damage to the adjacent masonry and historic bedding mortar.