Tuckpointing with Lime Mortar - NO PORTLAND CEMENT
Posted in the Rebersburg Forum
Since: Aug 09
#1 Jun 29, 2010
As it turns out and according to research on the old hydraulic lime mortar, using Portland may be a strategic error. At least, as far as longevity is concerned.
It all boils down to the way we think about buildings and how they weather. Everyone knows that the point of a building is to keep out water, right? In recent decades research on building materials and techniques has gone farther and farther down the road of keeping out 100% of all moisture and all air. Now we are combating mold, air quality, and condensation problems.
In the longevity department: no contest. Hydraulic lime wins. Hands down. Why?
Yes, Portland cement seals out water. Hydraulic lime allows water to penetrate. The problem is that most masonry units (like brick, stone, and block) absorb small amounts of moisture from the air and rain. Hydraulic lime acts like a wick to get that water back out-- FAST!! Portland won't let the water pass, trapping it in the wall where it does damage-cracking the joints and even the faces of the bricks or stones. That's why you see the faces of old brick buildings popping off. Repointing with Portland destroys the building-FAST!! Repointing an older building using portland cement starts the countdown to it's demise.
Yes, Portland cement is harder. But harder is also more brittle. Portland is fired at about 2,600 degrees Fahrenheit, as compared to hydraulic lime's 1,800 degrees. When you look at the two under a microscope, hydraulic lime particles are like plates that interlock; Portland's are like needles. Any movement in the building is going to make Portland crack all over the place, while the more flexible lime mortar can move with the building without cracking.
It gets better.
When you get down to the microscopic level, Portland cement has salts in it that actually degrade the mortar from the inside out. This stuff starts decomposing as soon as it gets hard!
You guessed it: hydraulic lime has a little secret of its own, and its not the kind that brings the wall down. Hydraulic lime has small amounts of free lime-lime that never reacted with the water in the beginning, after it was burned. This free lime actually dissolves in the water that is escaping out of the wall, and in the process it fills any cracks that may have formed. The experts call it "autogenous healing." Like a lobster growing back its claw, I guess.
No wonder they used it for 7,000 years, Plus.
No wonder the historic restoration movement is switching from Portland-and-lime mortars to historic, hydraulic-lime mortars.
Hydraulic lime is still a bit hard to find in this country. To my knowledge it's not produced in the U.S. yet. What we use is imported from France. Different grades can be used to make plaster, stucco, lime paint, mortar, and even concrete.
So next time you're wanting you're chimney repointed, a stone or brick historic building restored, find a historic restorations contractor who knows about hydraulic lime. As a mason, the choice is clear to me. What's the point of building new or restoring the old, if our work is not going to stand the test of time?
Jonathan Owens owner of Brookline Builders Inc in Lancaster County Pa, is a Lancaster County native, started Brookline Builders in 1988 when he was 19. Although Brookline Builders will complete all your residential and commercial construction needs in Lancaster County and throughout southeastern Pennsylvania. Jonathan personally enjoys all types of historic restoration. Check out the website of Brookline Builders here http://www.brooklinebuilder.com/
Since: Aug 09
#4 Jan 7, 2014
Brookline Builders is now using Lancaster Lime Works for all their lime mortar. Below is a description of this new Lancaster Pa based company.
Located in Lancaster, Pa., Lancaster Lime Works is a manufacturer of lime putty and lime putty mortars for repointing and historic masonry preservation of all types. Lime putty is the binder for all of our products. Lime putty can be made into mortar, stucco, plaster, and limewash (whitewash), and is also a key ingredient in historic paints.
Lancaster Lime Works is also a reliable source of information and training related to the installation of lime putty, lime mortar, limewash, and all questions relating to historic masonry restoration and historic preservation in general. Lime putty mortar is very different from hydraulic lime mortar and Portland cement mortar, mainly because it is made from pure calcium carbonate with no clays, silica, or other impurities that give them the ability to “set” under water.
Lime putty mortar is much more flexible and long lasting than hydraulic lime mortar or Portland cement. It is the ideal choice for repointing brick and stone because it is softer than the masonry units that it is bedding. Therefore it can flex with building movement, and can even heal itself (called “autogenous healing”). Because of the flexibility and breathability, Lancaster Lime Works highly recommends its products for stucco applications.
Lime putty stucco can be direct applied to brick or masonry substrates, as well as wood lath and straw bales. It can also be used successfully in interior applications, especially where moisture may be present in small amounts. It is breathable, so it does not trap moisture in walls and other structures, eliminating mold and mildew problems that are often associated with modern repointing and modern plasters/drywall.
Lancaster Lime Works takes pride in producing and selling truly historic products for masonry restoration nationwide, and providing training in the proper installation methods for all of our products. Installation of lime putty products is not difficult; rather it is a very workable and forgiving material. Lime putty installation is very different in every way from conventional masonry materials, and knowing how to install it is critical to a successful installation.
Lancaster Lime Works is the source for retail and wholesale lime putty and lime putty mortar, stucco, plaster, limewash, and historic paints. Lancaster Lime Works can assist specifiers with specifications for historic building and restoration projects.
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