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Maintenance Masonry and Stone Workshops

Historic Mortar 101

The winter months are a great time to plan outdoor projects and home maintenance. If you’re curious (or terrified) about historic mortar, this post is for you.

I attended the free Historic Mortar workshop offered by Henry Frerk and Sons in mid-January and recently shared a recap of what I learned on Instagram. I didn’t really anticipate that the information would be so valuable to so many other people, but… holy cow! It ended up turning into a three day event and consumed my entire weekend (in a good way).

Because of the overwhelming response I received, I decided to also recap what I learned here on the blog where I can also include links to additional information and instructional videos.

Just a reminder: I am not an expert on this subject, I’m slowly learning all of this stuff myself. If you are serious about learning more about historic mortar and masonry and how to maintain or work on your own home or buildings, I would encourage you to seek out a workshop or course, and, as always support local businesses and crafts/tradespeople.

Note: See the end of this post for hands-on workshop sign-ups!

Mortar is meant to be the sacrificial element of the wall.

You want the mortar to be soft enough for water to pass through it, but not so soft that it washes out of the wall. It’s also meant to last about 70-80 years. That’s a long time! You shouldn’t mess with your mortar until it begins to show signs of deterioration or unless there’s an issue that needs to be addressed.

Water follows the path of least resistance.

Meaning it should be able to exit through the mortar and not the brick. Bricks that are cracked or spalling are an indication that there are water issues somewhere in your wall: whether the bricks are below grade or touching dirt, your mortar is an incorrect mix, or your bricks have been sealed, painted, or sandblasted.

Does everyone in the Midwest have Efflorescence?

Efflorescence, that white powdery substance found on brick, usually suggests a water problem that might not be related to mortar. If you have efflorescence on your brick it’s a good idea to check the grading around your house and to make sure you don’t have any dirt touching your brick (the CBA posted a great article on this subject last year). Painted brick and the wrong kind of mortar can become the perfect storm for efflorescence. The moisture has to go somewhere! Other ways things to consider: getting a dehumidifier to help mitigate humidity during the summer and also keeping the air circulating during the winter months.

Portland cement is a dirty word (in historic masonry).

Portland cement is a modern marvel and dates back to the late 1800s. Of all the mortar mixes, it cures the fastest and is the most hydraulic (it can cure underwater). However, stronger doesn’t equal better when it comes to historic brick. Because of its strength, your bricks will ultimately become the sacrificial element of your wall. Stay away from Portland cement when repointing your historic brick. On the opposite end of the spectrum is lime putty which has no hydraulic properties and instead pulls carbon dioxide from the air to cure. Which can take years. It’s too soft to use in Chicago’s harsh and unpredictable weather. So what is recommended? Hydraulic lime mortar (NHL or PHL). Learn some more mortar basics here, here, and here.

Cement + Lime + Sand = Mortar

These days, every mortar mix includes some amount of Portland cement. For Chicago bungalows, Type N and O mortars are typically used for repointing. If your home is still rocking its original mortar, you can get a sample of it sent to a lab to test its original composition before doing any repointing. If you have questions about mortar mixes or you’re looking for a premix mortar, I highly suggest talking to the experts at Henry Frerk. They carry everything you need to get started (not an ad for them, they are just experts and a great local resource).

Most Chicago bungalows were tuckpointed with a V-shaped mortar joint.

The color of your mortar can change the entire look of your home.

When you work with someone to repoint your face brick, have them do a few large test patches with a couple different mortar colors on different areas of your house before you choose the color of mortar you want. This will give you a good idea of what the end result will be. If you have a choice (meaning you’re not color-matching existing mortar) choose a darker mortar because it blends better than a lighter colored mortar. (Elizabeth at Henry Frerk has a ton of mortar color mixtures and color mixtures that she has saved from the projects they’ve worked on.)

To DIY or not… that is the question.

There are a few reasons to tackle a repointing project yourself, but the main one is typically: cost. (There’s also a reason people pay to have their historic brick repointed with the wrong kind of mortar: Portland cement is cheap and paying someone to repoint your brick with hydraulic lime mortar will cost you more money.) So, whether you’re an adventurous DIY-er or simply can’t afford to hire the work out, sometimes the only option is to learn some basics and do the job yourself with the correct materials. It could be argued, though, that learning basic masonry skills is never a bad thing when you own a brick building. Here are some best practices to keep in mind:
1. Don’t work in cold weather: you don’t want your mortar to freeze.
2. Work with the shade.
3. Your mortar mix should be the consistency of brown sugar.
4. After you’ve removed the old mortar, soak your wall down for at least 20 minutes before repointing (the mortar should suck into the wet wall).
5. Keep your wall hydrated: hang burlap on the wall so that your new mortar doesn’t dry out too quickly.

I’ve included a resources and reading list at the end of this post, as well as a sign-up to receive information about future hands-on workshops.

There’s a special place in hell for people that paint their historic brick and limestone.

Painted brick holds in moisture and doesn’t allow water to properly shed. This creates a perfect storm for things like efflorescence and brick spalling, and eventually your brick walls will crumble to dust. If you really don’t like the color of your brick, or recoloring is your only option, consider a limewash or silicate coating instead.

But seriously, just don’t paint your historic brick. If the color of your brick home is not to your taste… don’t worry! You’ll be dead soon.

Resources and reading list

The CBA’s trusted referrals page:
http://directory.chicagobungalow.org/

National Parks Service briefs (these can take a really long time to load):
https://www.nps.gov/tps/how-to-preserve/briefs.htm
https://www.nps.gov/tps/how-to-preserve/briefs/2-repoint-mortar-joints.htm
https://www.nps.gov/tps/how-to-preserve/briefs/22-stucco.htm

Henry Frerk additional resources:
http://hfsmaterials.com/restoration-preservation/resources/
http://hfsmaterials.com/restoration-preservation/restoration-products2/lime-mortar-tips/
http://www.masonrydesignmagazine.com/understanding-the-basics-of-lime-mortars/

US Heritage Group in Chicago (how-to videos, products, and resources):
https://usheritage.com/how-to-videos/
https://usheritage.com/services/mortar-analysis-and-matching-services/
https://usheritage.com/document-library/
https://usheritage.com/building-owners/
https://usheritage.com/in-house-training-2/

Limeworks.us:
https://limeworks.us/product-category/dvds-and-books/
https://www.youtube.com/playlist?list=PLvwpWxpGHjJcG0aXk6W1VrNJIO1I8V7aD
https://limeworks.us/events/hands-on-workshops/

The Belvedere School for Hands-on Preservation:
Historic masonry preservation: http://bobyapp.com/calendar/2020-09
http://bobyapp.com/blog/2009/09/bricks-re-pointing-french-bread

Lastly, I’ve heard from many homeowners that hands-on education is their preferred method of learning. Not only hands-on, but also taught in a relatively similar context to what they will be working in. I’ve had a difficult time finding hands-on workshops in Chicago (the ones I have found are linked above in the resources list). Because of this, I’ll be organizing at least one workshop this year (Spring 2020) with Simon Leverett of www.masonguru.solutions. If you are interested in participating in a hands-on workshop to learn basic masonry and repointing techniques, please use the form below to add your name to the list. Class size and price will depend on how many people are interested and where we can find an area to work on. Ideally, I would like to accommodate all that are interested and also help someone in the city who may need some repointing work.

As always, this blog remains free of ads and sponsored content. The views expressed in this post are my own.

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