Typical Problems of Historic Masonry

What is Mortar

Mon, 8 Dec 2008 08:41:25 -0500

Mortar is made from three components, aggregate, binder and water. Aggregate is usually sand but sometimes pebble, rocks, shells, coal, mica. Binder is usually lime in older buildings but also sometimes hydraulic lime, clay, natural cement or Portland cement or any number of combinations of materials depending on the year of construction, geographic location and any number of unknown decisions made by the mason.

Properly formulated, mortar is designed to deteriorate slowly over many years or even centuries. It protects the masonry that it surrounds by pulling water away from the masonry units and by supporting the masonry during environmental changes over time.

What is Wrong With Water Sealants

Sun, 23 Nov 2008 09:49:21 -0500

Water repellants are chemicals that are applied to a masonry building to keep water from penetrating the masonry. Early commercial versions of these treatments tended to penetrate only the very surface of the masonry. Used in combination with inappropriate Portland cement on a building designed for lime mortar, these materials cause severe and rapid damage to masonry. Water finds its way past the thin veneer of repellant and into the substrata of the masonry wall. Water trapped inside the wall dissolves salts in the masonry and causes crystallization of salts in masonry below the surface of the brick or stone. This is called Sub-Efflorescence... It is one of the two causes of rapid damage. The second major cause is freeze thaw cycles. Again, if water is trapped in the masonry behind the water repellant, the masonry stays wet and freeze thaw causes the water to expand in the brick or stone causing spauling.

Recently, new water repellants using chemicals called Silanes and Siloxanes, have come on the market. These chemicals absorb more deeply into the masonry and chemically bond to the masonry in a more long lasting way. These materials are considered breathable in the sense that they allow a percentage of the water vapor in air to pass through.

However, there are some problems with modern water repellant materials. The first problem is that even the best water repellants need to be reapplied by a skilled and experienced company about once every 10 years. I have yet to work on a building whose owner has shown me a log of all the things that have happened to the building before they owned it. Even a good steward of a historic building can not guarantee the good sense of those who come after them. The second problem is that it is imperative that the masonry wall will not have any mortar or masonry cracks. Even a recently repointed masonry wall can develop problems without the knowledge of the owner.

I am not a purist preservationist, I do realize the need for modern technologies under certain circumstances. I would recommend using these products under limited circumstances such as on horizontal masonry surfaces where copper or aluminum caps or flashing are aesthetically unappealing. But generally, mechanical solutions like flashing last for a 100 years or more, they are both visible and inspect-able and can be replaced by anyone.

What To Know Before Your Repoint

Wed, 12 Nov 2008 21:20:15 -0500

In many places in the United State, masonry buildings built through 1900 and as late at the 1930s were built with a lime based mortar not a Portland cement based mortar which is used almost exclusively now.

There were many variations on the tradition of lime mortar but generally, the masons knew what they were doing and they mixed a mortar in a 1:3 ration of lime to sand. A mix that was softer than the masonry units and one that was intended to make sure the building would last 350 years or more.

Masonry damage

Tue, 23 Sep 2008 21:17:35 -0400

Few repairs are as simple or inexpensive as the maintenance of rain gutters. If you have limited access to the roof or are at any risk of falling, seriously consider calling a professional. Wherever a rain gutter has been clogged or removed, water damage is sure to follow.

Ivy Vines and creeping Trees

Fri, 8 Feb 2008 09:32:05 -0500

Although some vines do not leave marks on masonry, trees or vines on or around a building should be removed. Trees offer many environmental benefits to masonry buildings... particularly there ability to shade a building in the summer and reduce heat gain. However, tree roots will damage foundation walls and vines will grow into mortar joints in search of water. Paint, vinyl siding or any other material that obstructs ones ability to visually inspect a building for cracks or animal nests should be avoided. Plus, bricks are beautiful in and of themselves. If you must have vines over a brick wall, one solution is to build movable trellis panels that can by pulled away from the brick wall periodically.

When is it time to replace Mortar?

Wed, 19 Dec 2007 09:35:06 -0500

The periodic replacement of mortar insures the future health of masonry. This process generally needs to be completed about once every 100 years. If mortar is cracked or powdering, water is likely to penetrate the wall. In lime mortar buildings, when the mortar has turned to dust it has come to the end of its useful life and needs to be replaced. If your mortar is worn out of the joints, substantially cracked, or if you see damage to the masonry, replacement of the mortar is required.

What is wrong with painting brick

Mon, 19 Nov 2007 09:41:41 -0500

If your contractor is suggesting that you paint your old brick, seriously consider getting a second opinion. Historically, many masonry buildings were painted with whitewash or with a tinted lime render. But this material is highly vapor permeable, natural and healthy and will wear off the building over the course of time... In contrast, modern paints are designed to seal our water and water vapor... This is a problem...

Painting brick will tend to trap water in the masonry causing rapid deterioration during freeze thaw cycles. Additionally, water flows in the path of least resistance. If your brick is sealed with paint, the water in the masonry will migrate towards the inside of the house ruining plaster, rotting wood and causing mold.

Old paint contains lead and often asbestos too. It is important to find a qualified contractor to remove paint. Old paint must not be washed down the street towards a rain drain- this is both immoral as the paint and paint stripper will pollute local rivers and it is also illegal. Contractors need to collect the waste water from the cleaning process and have it treated. Paint removal is dangerous and expensive. It is best to avoid it.

Moss Suggests Moisture Problems

Sat, 21 Apr 2007 09:33:34 -0400

In an inspection of your property look for evidence of water being held in the masonry. Prolonged exposure to water will cause plant growth on masonry. While moss can be attractive and desirable on a dry stone wall, the walls of a building need to be dry. Consistently wet walls can become health problems and will encourage mold growth in the cavity behind the wall. Look to the roof line above the moss for deteriorated or missing gutter systems that might allow rain water to splash back up onto the building.

Repairs made with Portland Cement can also cause plant growth. Lime mortar is highly vapor permeably allowing for easy evaporation of water droplets in both the mortar and the brick it supports. In contrast, Portland cement is waterproof. In older load-bearing brick buildings repaired with Portland cement mortar, rather than lime mortar, moss growing on the repair is common. If your building is showing evidence of moss from Portland cement mortar it should be removed and replaced.