Questions about lime mortars and white portland
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robselina



Joined: 14 Jan 2010
Posts: 24

PostPosted: Tue Aug 03, 2010 10:25 pm    Post subject: Questions about lime mortars and white portland Reply with quote

Hi,

Sorry if this has been addressed before (I did search), but I have a couple of lime mortar and white portland questions.

1) What is typical strength for a lime mortar after curing for 24-48hrs? Should I be able to break up samples with my hands? I gather the carbonation process is a long one, but I don't know what might be 'typical'.

My 1:3 lime:sand samples are quite soft/fragile by my standards. I can break them rather easily by hand.

Some older samples I made with poor quality sand (too much clay) and with a very high lime content (40+%) are still breakable by hand after about a week, though they've definitely got stronger with time.

I'm mostly wondering if I need to improve my curing process or if this is normal. I'm generally trying to make most of my mistakes in testing rather than on the wall. ...

2) When was white portland introduced in the USA? The mortar in my foundation definitely has a white binder, not grey Portland. I'm curious if that pretty much settles that it's a lime mortar or if there's a chance it may have white portland in it. The house was built in 1907.

3) I could use some help between selecting a lime mortar vs a type K portland/lime mortar or other ratio. Here's a little background:

My home is made of adobe block on a rock foundation. The adobe has been stucco'd, the foundation was left exposed (thankfully). The mortar in the rock foundation is badly weathered and I need to repoint it. Here are a few photos of its general condition:









I would say that in general the mortar mix appears to have a white binder, not grey Portland. It's quite chalky and fragile.

I've tried a couple of different mortar mixes to see what best approximates the existing mortar. In the photo below I have two different sand mixes used for both a 1:3 lime:sand mortar (Type L) and a 1:3:10 portland:lime:sand mortar (Type K). Lime used is a Hydrated Lime Type S. Portland is typical grey portland.

From left to right: Type K with Plaster Sand, Type K with State Spec Sand, Type L with Plaster Sand, Type L with State Spec Sand. Chips at the bottom right are mortar from the house. I believe the Type K with Plaster sand best approximates the current mortar:



What worries me is that after a couple of days the lime mortar samples I have made are very weak. I can break them with my hands:



The Type K mortars are quite durable by comparison, but the grey portland binder clearly doesn't match the existing mortar.

I'm debating using the straight lime:sand mortar or getting a sack of white portland and trying a type K mix.

Would you do a straight lime mortar on this foundation? I'm leaning this way since I do not want to trap moisture within the foundation by using a less porous mortar in repointing, but I'm interested in your opinions.

Thanks,

Rob


PS - I found the following page on the NPS website to be very informative about historic mortars:
http://www.nps.gov/history/hps/tps/briefs/brief02.htm
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Andy in NH



Joined: 01 Mar 2006
Posts: 92
Location: Lyndeborough, NH

PostPosted: Wed Aug 04, 2010 5:22 am    Post subject: lime mortar Reply with quote

Rob,

Try contacting Andy degruchy at www.limeworks.us or Virginia Limeworks for more info on the lime mortars. I am still learning about them myself. One key component is to avoid agricultural limes as they have been fired at too high a temperature, rending them useless for building material. Also, how long has you lime putty been together before you mixed your mortar? Definitely a case of fresher is not better (in Roman days there were severe penalties for using lime that had not been slaking for several months). My own interest was piqued when we found chunks of the lime mortar in the basement dirt while excavating for an internal perimeter drain. Most likely seashell based (oldest section of this building goes to 1750) but still wiating for me to get it analyzed.

Correctly prepared lime mortar has felt quite strong in my experieince. Best of luck with your project.
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johnleeke
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Joined: 20 Aug 2004
Posts: 3009
Location: Portland, Maine, USA

PostPosted: Wed Aug 04, 2010 7:45 am    Post subject: Reply with quote

Lime mortars set and cure by chemical reaction with air and water. It takes time for the air and water to penetrate from the exposed surface to the inner volume of the mortar. Check your samples after several weeks or a few months and you will see an outer shell has formed. It can take years and decades for the cure to penetrate three and four inches to the full depth of a joint.

I once did a lime-mortar/cement-mortar comparison test. I placed each recipe mix between two bricks and stacked them up out back of the barn. After 10 years I knocked them apart to examine the mortar. With the straight lime samples the mortars had cured hard for about 1.5" depth from the outer surface of the joint. There was an inner patch that was still soft and crumbly. After 15 years the cure was progressing from out to in, and there was a smaller inner patch that was still soft. But, all around the edge the mortar was nice and hard.

This is one of the great benefits of straight lime mortars. Some of the lime remains unreacted so when there is movement and cured lime cracks a little, the un-reacted lime will react with exposure to the air and water and "heal" itself--something typical cement mortars cannot do.

For best set and cure keep the exposed surface of the mortar damp by misting daily or covering with burlap and wet spray every other day. The water helps the chemical reactions along.

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robselina



Joined: 14 Jan 2010
Posts: 24

PostPosted: Wed Aug 04, 2010 9:44 am    Post subject: Re: lime mortar Reply with quote

Andy in NH wrote:
Rob,

Try contacting Andy degruchy at www.limeworks.us or Virginia Limeworks for more info on the lime mortars. I am still learning about them myself. One key component is to avoid agricultural limes as they have been fired at too high a temperature, rending them useless for building material. Also, how long has you lime putty been together before you mixed your mortar? Definitely a case of fresher is not better (in Roman days there were severe penalties for using lime that had not been slaking for several months). .


Thanks, I'll check out Andy Degrouchy's site.

As for the lime, I'm using a Type S hydrated builders lime, so it is the correct type (I think). It's a powdered lime and is already slacked, so I gather it should be mixed with the sand and water and placed within an hour or so. I mixed it and then immediately formed it into samples and buttered it onto my test rock.

I believe the process of making quicklime putty and then leaving it in the water is meant to turn calcium oxide into calcium hydroxide. In this case, I'm starting with the calcium hydroxide.
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robselina



Joined: 14 Jan 2010
Posts: 24

PostPosted: Wed Aug 04, 2010 9:58 am    Post subject: Reply with quote

@ John Leeke - thanks for the feedback. It sounds like I shouldn't judge the long-term strength based on what I'm seeing today since the chemical reaction to calcium carbonate can be a long one. I didn't have a good feel for how long this should take. Your brick wall is a good example.

I'm thinking about how the older samples are breaking and indeed they have a hard outer shell now but are still very soft in their interior which is why they break. This bodes well for it's long term performance.

I've been misting my samples in the morning before work and then twice in the evening after work. I'll have to think about a good cover when doing the foundations because we generally have such low air humidity around here things dry out rather quickly....

I see the following benefits to using the straight lime mortar:
- Lower risk of trapping moisture within the historic mortar and causing foundation failure by using a less porous mortar for repointing.
- Lower risk of cracking and failure due to freeze/thaw since the lime mortar can 'heal' around these stress cracks.
- Longer working time so i can clean up the rock and have a decent finished look.
- It's worked for 103 years, why screw it up now ;)

Possible downside - short term durability and difficulty in controlling the moisture content after placement.

I think I'm convinced, I'm going to do a test section with the lime mortar (no portland) and see how it comes out.

Thanks,

Rob
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Mike-in-Maine



Joined: 08 Nov 2008
Posts: 145
Location: Fort Kent, ME

PostPosted: Wed Aug 04, 2010 10:42 pm    Post subject: Reply with quote

I'll just paste what ive posted elsewhere on these forums... if youve already read it, I apologize:
___________________________

Please do not use Portland Cement for your historic mortar work!

You need to use NHL (Natural Hydraulic Limestone) Mortar!

There is a HUGE difference and Portland Cement will NOT last the test of time with the freeze thaw cycle and old masonry. (edit to clarify: the actual portland cement will last forever, its the bricks that are in between them that will self-destruct as a result!)

Ive got my NHL mortar from www.palimeworks.com/

Go to their site, and take some time to read about why you need to be using the correct mortar!

(no, im not affiliated with them, but i have first hand experience of dealing with "portland cement repointed" masonry on 19th century homes and the catastophic effects it has... )

ive also done masonry repointing myself using NHL. Its more eco-friendly than Portland cement also, and is historically correct. It will "breathe" properly unlike Portland Cement. (however, it is extremely alkaline, and therefore extreme care MUST be used when mixing and working with it.

limeworks.us has a great sample kit you can order that gives you a bunch of NHL mortar samples to choose from.. you can match your existing historic mortar almost if not exactly in this way. They also do custom matching if for some reason you cant find a match with their pre-mixed offerings.

Removing old portland cement is near impossible without damaging bricks. Unfortunately, these mistakes are common. Word is getting out about the horror of portland cement mortars used on old masonry, and hopefully we will be seeing less and less of these atrocities.

After repointing areas of my foundation, and recreating an original brick porch support column that had been replaced (it was still there under grade!) I would never DARE even think about letting portland cement based mortar touch an historic home. No Way. And any mason who would suggest doing so, should find another field of work.

Natural Hydraulic Lime mortar isnt terribly expensive, but shipping it to you can be. Thats the only downside. expect to pay as much or more for shipping than you do for the mortar itself!
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JLee



Joined: 06 Nov 2006
Posts: 79

PostPosted: Thu Aug 05, 2010 9:16 pm    Post subject: Reply with quote

Mike is right, check out NHL. I used Virginia Lime Works. You can get it with sand already in the bag, or get it pure and add your own sand as I did.
Add water slowly, and mix it longer than you would portland mortars.
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robselina



Joined: 14 Jan 2010
Posts: 24

PostPosted: Mon Aug 23, 2010 3:45 pm    Post subject: Reply with quote

Thought I'd add a little update to this one.

My final samples using Type S builder's lime and plaster sand from the local quarry hardened nicely once given enough time (weeks). I decided to go ahead with this mix (3:1 sand:lime).

We repointed the worst section of the foundation last Saturday. The mortar appears to be setting up well and so far I'm happy with the results.

A few observations from my experience:

1 - Mix your sand and lime DRY first. Then slowly add water. Give your mix a little before adding your last few ounces as the consistency seems to change quickly as you approach optimal moisture content. Mixing dry really helped me have a consistent mortar.

2 - Use a stiff mix (low water) for your coarse build up. In my case I had significant, deep voids to fill. I could really pack it in to these voids with a stiff mix and a wooden rod.

3 - Keep the wall damp for the first few days or you will get cracking. I have a little bit of flaking on a thinner sectios of mortar in a spot that I let dry out a little too much between misting. Use the most gentle mist possible because it's easy to erode the soft mortar.

4 - Don't rush your final cleanup. Even today (third day), the mortar is soft enough on the rocks that I can clean/polish them up with a medium bristle brush.

I'll try to post up some photos at some point.
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MarissaJude



Joined: 14 Mar 2008
Posts: 14

PostPosted: Fri Apr 22, 2011 2:25 pm    Post subject: Reply with quote

Just my two cents from talking to lime mortar and plaster professionals and contacting Virgina Limeworks:

When making your own mix, you should always make your lime putty first(mix dry type s hydrated lime and water until it reaches the consistency of something between sour cream and cream cheese), let it age for at least a few weeks, and THEN mix it with sand (or whatever aggregate is appropriate) to make your mortar mix.

Hope this helps...I realize this topic is months old...
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robselina



Joined: 14 Jan 2010
Posts: 24

PostPosted: Sat Apr 23, 2011 2:44 pm    Post subject: Reply with quote

MarissaJude wrote:

When making your own mix, you should always make your lime putty first(mix dry type s hydrated lime and water until it reaches the consistency of something between sour cream and cream cheese), let it age for at least a few weeks, and THEN mix it with sand (or whatever aggregate is appropriate) to make your mortar mix.


My memory is dusty on this topic but I think it depends on the type of lime you have.

If you start with quicklime ("standard" lime, calcium oxide) you need to make the putty and let it age. This causes an oxidation process which gives you slaked lime, which is calcium hydroxide.

"Hydrated Lime" like I used is already calcium hydroxide when you buy it in powder form, so there's no need to slake it with water.

Hopefully one of the gurus will correct me if I'm wrong on this topic.
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HB



Joined: 23 Feb 2007
Posts: 22
Location: SEPA

PostPosted: Mon Apr 25, 2011 8:41 am    Post subject: Reply with quote

Actually, the type s hydrated lime is only partially slaked. 9like 20 percent or so)

The mix as you've done it shoiuld work out, but a better mortar can be had by slaking the hydrated lime for a few months as was said.

I used to mix mine in 5 gallon pails until it was somewhere between sour cream and toothpaste in consistency, then put a lid on it and let it sit for a couple of months.

Pour the water off the top when you open the container (set it aside for use later to mist your work) and then mix the putty with sand.

It's important to really mix the putty with sand for an extended period of time because the more energy that is imparted into the mix, the more "plastic" it becomes (more sticky, better adhesion and more workable, and less prone to cracking as it dries)

I've since gone the route of using natural hydraulic limes as available from PA lime works or VA lime works because it's a bit easier to use, takes less planning ahead, and still offeres the moisture permeability that I need to correctly maintain and rehabilitate my 18th century stone home.

The NHL limes cure on their own as well as by carbonation using atmospherc CO2, so you get the workability of a portland mix with the benefit of a lime only mortar.

Most of these types of mortars will reach their full strength in a few months instead of a few years.

Good luck.

HB

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MarissaJude



Joined: 14 Mar 2008
Posts: 14

PostPosted: Mon Apr 25, 2011 10:08 am    Post subject: Reply with quote

Thanks for the clarification HB!

It's always good to hear from you!
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robselina



Joined: 14 Jan 2010
Posts: 24

PostPosted: Mon Apr 25, 2011 10:36 am    Post subject: Reply with quote

Cool, thank you for the clarification. So far so good on my foundation repair, but I'll keep this info in mind for when I get around to repairing my front garden wall.
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