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Is N type mortar a good substitute for lime based mortar?

Hello,
I have an old brick house built in 1915. In some places the bricks are so water damaged that they are deteriorating and turn to sand when touched. I'm about to get a lot of brick work done to the house.

1- I'm getting the front wall pointed--these bricks are actually in okay condition but they absorb water which is ruining the interior plaster walls.

2- I'm getting the bricks under the font porch parged. Only about two feet of the bricks are above grade and they are badly deteriorating and crumble away to the touch. They'll dig to the foundation, parge the bricks, then put a rubber barrier before they back-fill.

3- I'm also having the parapet parged. The bricks are also very crumbling and take in water badly during storms. I attempted to parge this myself with a lime based mortar, but did terrible job.

The mason is going to use N type mortar, which is for old soft bricks, right? Is that okay or will it make my bricks worse in the long run because it does have some cement in it? Will it adhere to my sub-par parging job on the parapet using lime based mortar? Also, will the temperature affect the work? It's about 55-34 degrees around here. Please help!

Many Thanks,
Mary

Asked by Mary Farrah
Posted Sat, 11/17/2012 - 13:44
Edited Sat, 11/17/2012 - 13:44

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Mary,
You have more questions than I can answer briefly. But I'll get you started, and then perhaps others can chime in.

Type N mortar is not a lime mortar -- if by lime mortar you mean a traditional mix of sand, lime, and water. Type N mortar includes portland cement -- typically 1 part portland cement, 1 part hydrated lime, and 6 parts sand. More information here: Repointing.

Portland cement adds strength to mortars, but limits flexibility. Mortars containing portland cement are not appropriate for repairs to historic buildings with pure lime mortars; however, you can't be sure of the composition of a historical mortar unless you have tested it.

The type of parging you are talking about is sacrifical parging. To read more about the theory behind sacrificial parging, see Efflorescence = Water Damage.

Answered by Martin Holladay, GBA Advisor
Posted Sun, 11/18/2012 - 07:10
Edited Sun, 11/18/2012 - 07:12.

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