Masonry Magazine January 2006 Page. 24
LIME MORTAR
The longer lime is left as putty, the more workable it will be in the end. Over time, the lime putty undergoes a process whereby the lime crystals reduce in size upon aging and transform into small plates that slide when rubbing against each other. This action allows more water to be absorbed, giving lime the property of being highly workable, or having "plasticity."
While Portland cement hardens due to the chemical reaction with the water, if stored in a sealed container, lime putty will remain workable and soft indefinitely. Lime will harden over time only when it comes in contact with carbon dioxide and moisture.
Once a lime-sand mortar is mixed and placed in the wall, the water will begin to absorb or evaporate and the mortar will appear to set after several hours. However, the lime then begins to react with the carbon dioxide present in the air and harden, a process that actually will take years to complete. A simplified explanation is that, chemically, the lime is returning to its former state of being a stone.
A more complex explanation is that the carbon dioxide and moisture convert the lime on the surface of the joint back to calcium carbonate. The open pore structure of the lime-based mortar allows the carbonation process to take place deeper in the joint over time.
GIBCO'S MRF
ICC REPORT #3212
ADMIXTURES THAT ENHANCE THE PERFORMANCE OF MASONRY MORTAR
* Replaces Lime
* Greater resistance to Freeze & Thaw
* Lower Batch cost
* Reduced Shrinkage
* Less Storage & Handling
* Avoids Waste less calls backs
* Non-toxic
GIBCO INDUSTRIES. INC.
PO BOX 880, LANGLEY, OK 74350-0880
1-800-822-0802
www.gibco-usa.com
CIRCLE 313 ON READER SERVICE CARD
MASONRY RESTORATION SET
OUR MORTAR REMOVAL SET INCLUDES:
* Trow & Holden "Type B short stroke air hammer with 1" piston
* 10' air hose assembly with all hardware installed, including Staubli push-button Quick-Connect
* Mortar removal chisels (4)- 1/8" and 1/4" carbide cape chisels, 4-tooth carbide ripper, 1/4" steel swept cape chisel (chisels also avail. in thicknesses starting at 1/32"
* Tool pouch & literature on tool use
EVERYTHING YOU NEED TO GET STARTED FOR A SPECIAL PRICE $469
"Use with 5 HP compressor
MADE TO LAST IN BARRE, VERMONT
TROW & HOLDEN COMPANY
45 South Main Street, Barre, Vermont 05641
Toll Free 1-800-451-4349 In Vermont call 476-7221
www.trowandholden.com
CIRCLE 167 ON READER SERVICE CARD
Why Lime Mortars are Used
ANY RENOVATIONS to structures built with a lime-sand mortar should be completed with a similar lime-sand mix. Unlike today's cement-based mortars, lime mortars are flexible and will take slight movement and settlement in the brick wall.
The mortar joint to the right of the green tape represents a sample produced using a straight lime and sand mix on this 19th century gothic revival house. The third one was adequate for use.
Also, unlike the modern-day cavity wall, moisture movement in and out of the wall is very much part of the system. Modern brick is harder, more vitreous and impervious to water penetration, while old brick is soft and porous. While brick walls of today are made to shed water like a raincoat, old brick walls are much like wearing an overcoat - they get wet, but then dry out by evaporation. Older brick benefits from the use of permeable lime mortar because it allows the moisture that has penetrated the brickwork to escape through the joint and not through the brick.