Portland Cement vs Lime Mortar

akira181

My mother stays in an old Grade II / Grade C (we're in Scotland) listed building with 2 other flats above hers. The gable wall is needing repointed and the top floor flat has found a tradesman to do the job.

I asked about his quote as it was very vague in detail and he's provided a good response. However, I was under the impression that old buildings should be repointed with lime mortar and Portland Cement should be avoided.

The contractor's response was that there are many products for repointing and he'll use the best, long-lasting one called "Portland Cement" or "Lime Mortar". 

That to me reads that he is calling Portland Cement a Lime Mortar, which I think is wrong but I'm not 100%. Can someone clarify so I can get back to the contractor?

Thanks!

stuart45

Should be a similar mix to the original. If it's a lime mortar, then the repointing should be done with a lime mortar, not containing at Portland cement.

akira181

The building is pre 1900 so it's definitely a lime based mortar. However, as with most old buildings, it has been patched with cement at some point in the last 30-50 years and needs redone.

That reads to me as the contractor is calling Portland cement a lime mortar. Am I right in saying the two are not the same or does all lime mortar mixes comprise some percentage of portland cement?

FreeBear

He could mean a cement mortar with added hydrated lime - Still just as problematic as regular (Portland) cement. You need to find someone that will use NHL3.5 and zero cement.

It is getting a bit late in the year to be doing pointing, especially up in Scotland - If you are getting frosts already, the work needs to be delayed until the spring when things start to warm up. If the mortar gets frosted before it has a chance to dry out fully, it will crumble & fall out within a few years.

stuart45

Nowadays a lime mortar should contain no Portland. Tests done on it have shown that even a small amount can clog up the pores, although the more added makes things worse. Years ago a 1/2/9  Portland/lime/sand was an acceptable mix for older brickwork, but things have changed since the Smeaton project.