Interior mortar question


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Old 11-28-08, 10:23 AM
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Interior mortar question

Hi all,
150 year old brick farmhouse with plaster interior walls...I had to pull down a section of plaster upstairs (second floor bedroom) about 4ft x 6ft which was pulling away from the brick wall and quite soft. We thought momentarily about removing the entire wall of plaster and leaving the brick, but I think that's out at this point. Anyway, there are several places on this wall where the mortar has fallen out and even the old bricks are broken and falling out. Seems to me I need to replace some mortar before I smooth up the wall again! Is there any difference between exterior brick mortar work and interior? What about a spot where there is about half a brick missing (can't find the brick anywhere)? Can I clean that out and try to fit in part of a brick somehow? Since I will be covering this back over, I'm not concerned about matching colors, so I'm looking for the best combination of easiest and best mortar to use...

Thanks everyone!

Kathy
 
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Old 11-28-08, 10:33 AM
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If your house is 150 years old, the bricks are probably not fired(hard). That makes them soft and easy to break/chip. As far as the mortar, I don't think there is a difference. I would clean them well and let dry and maybe add some kind of screen (lathe) for the plaster to bond to. You could dig out the broken brick and replace it, however I would probably just add extra morter to fill. There may be a problem with the new mortar adhearing to the old mortar. Be prepared! Old houses are great, but present different problems because of materials at that time. Good luck!
 
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Old 11-28-08, 11:36 AM
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There is no difference in the mortar because of where it is placed, there IS however a difference because of it's age. DO NOT use portland cement mortar to repair the wall, or you will destroy it.

You obviously have a water issue on the exterior of the wall, or above the area where the old plaster sloughed off. Fix that first, then use a lime mortar to repair the brick, then a gypsum plaster to restore the wall finish.
 
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Old 11-28-08, 12:25 PM
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We put in a new roof in September (we bought in March) and are now going through fixing interior problems. There were significant water problems along the north and east sides of the house - this room is on the east side. Our last house was built in 1913 and a much more "modern" house. This one is 1861 and has presented some new and interesting problems. The bricks are extremely soft and the outside is painted white, which I wish it wasn't, but I don't want to scour away the entire house trying to get the paint off. That's for another day! I had a house in Vermont older than this one, but it was frame. Anyway, thank you for the information and any more is welcome!

Kathy
 
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Old 11-30-08, 01:21 PM
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Originally Posted by Tscarborough View Post
There is no difference in the mortar because of where it is placed, there IS however a difference because of it's age. DO NOT use portland cement mortar to repair the wall, or you will destroy it.

You obviously have a water issue on the exterior of the wall, or above the area where the old plaster sloughed off. Fix that first, then use a lime mortar to repair the brick, then a gypsum plaster to restore the wall finish.
Please explain the difference in portland/lime mortar and when and where to use lime mortar. I'm not familiar with the lime mortar, but then I am not a mason. Thanks!
 
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Old 11-30-08, 01:49 PM
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Portland cement was developed and became available in the early part of the last century. It is pretty safe to say that anything built before 1900 will use a lime mortar or plaster.

Portland cement mortars are hydraulic, that is, will set under water. The chemical reaction that makes it get hard is independent of external requirements (but environmental factors can affect it, like cold temps.); everything needed is in the mortar.

Lime mortar, on the other hand, relies on atmospheric gases to harden. It will not set under water, and will, in fact remain usable for a very long time so long as it is kept covered with water.

The issue is one of permeability. Lime mortar walls breathe, portland mortar walls do not. When you patch a breathing wall with portland mortar, you will trap moisture in the wall, and this will cause the lime mortar to deteriorate at a very rapid pace.



This is what happens when you patch lime mortar with portland mortar. It was "repaired" in the late 1970's in an attempt to save it. Ironically, the structure is a lime kiln dating from the 1880s.

Here is another section that was NOT repaired (because it didn't need it). As you can see, the mortar has eroded a little but the structure is still sound, unlike the "repaired" area.

 
 

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