working on an old brick church [ built around 1832 ] the mortar between the bricks is in rough shape and in places cracks run for a few feet. I have read before someplace that soft mortar should be used. What is soft mortar and what other tips can you offer me to aid in the repair of this church.
Thanks
Replies
there are book on this subject... and everyone has an opinion... it's not a fun job... but just some points
you have old wood fired brick thats not very hard that must breath so you don't want to seal it or use mortar thats harder than the brick
what was used was "lime mortar" no portland about 1200 psi and self sealing
you want to match that psi if you can
p
First off, clean out all the loose morter, using a joint raker. You can also drive a 16 penny nail about 1/2 way into a foot long piece of 2x2 and use the nail head to rake them out. Anywhere that the morter is cracked, take a grinder and grind the morter back as far as you can.
I have filled and struck millions of joints (literally) and here is how I do it.
If at all possible start at the top and strike downward. If you must go upward, you will need to rebrush the entire face every few hours.
Do not give in to the temptation to fill and strike the joints with your fingers, you will be really sorry - you will sand your finger tips down to the meat before you know it. It takes bit of practice, but make the trowel and flat jointer work for you.
Doing this for a number of years for our family business is what drove me to go to college...
Good luck.
TTF
Edited 1/8/2006 10:18 pm ET by TTF
Edited 1/8/2006 10:19 pm ET by TTF
In the premixed mortar mix, do you ever use Type 0, as opposed to the more common type N?********************************************************
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John Wooden 1910-
No, I dont think so. Main premix type in N for stone. Under normal circumstances, I wouldn't use premix - 1/2 a bag of cement, 1 bag of lime, fill the mixer with sand.
Like the first reply - don't use portland cement in the mix for historical restoration work
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John, We use 8 parts sand, 3 parts masons lime, and 1 part portland cemnt. This mix will take a long time to set up but is pretty durable and compatible with the soft brick and existing mortar. I am not a mason but this is the mix that I was taught by a historic preservation mason. If you want to get really technical disolve a sample of the existing mortar in acid and screen out the sand and try and match the sand with a local variant. For high end work you might try and color the mortar to match the existing. The mix above will be very light in color depending on your sand. When I was getting my historic preservation degree we would do mortar analsis in a lab and determine composition by weight and volume. Depending on your geographical location there may be burnt and ground oyster shell in the mix as the lime component. We also see bits of charcoal in historic mortar for some reason. The most important thing is to NOT use a hard portland mix with old brick or the faces of your brick will spall and fall off. I hope this helps. Jay
"We also see bits of charcoal in historic mortar for some reason."This is because back then, much of the lime came from burning limestone with charcoal
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You can try getting in touch with the international masonry institute in washington d.c. sorry don't have the web address in front of me, just google it. They will have hundreds on articles to view on restoration work.
Piffin is right in that an historic mortar prior to the 1850's , or there abouts, was nothing more than lime and sand, and maybe hair or straw for a binder. Portland Cement was invented mid to late 19th century I believe. However, the difference in the lime from then as to today is the hydration process. Back then, they baked lime to high degrees driving out all the water, this is called 'calcining'. The result would be a product called "quick lime" which when reintroduced to water, would have an almost violent bioling effect, and would get very hot because of the water quickly changing the lime's crystaline structure. This would be mixed with sand and applied giving you a softer morter than todays Portland. I don't believe that quicklime is available anymore because of the dangers of working with it. It would often splash up and hit a mason or plasterer in the eye and they often would lose the eye as a result.
Today's lime is what we know as 'hydrated lime'. It is still baked and made the same way but it contains a certain percentage of waternow and can be introduced as part of a mix along with sand and cement to make the mortar more cream-like and workable. It is not as voilitile when introduced to water. You still should take care not to get it on your skin or hands as it still will cause burns
Just hydrated lime and sand is not quite as durable or strong as the old quick lime and sand...I have tried it.
That said...Jay is right too. A little bit of Portland mixed in with the sand-lime ratio given is what I have worked with and I have seen used in the historic preservation projects that I have been involved with. It makes a good "soft mortar".
thank you very much for ypur reply, it is mist helpful