Mortar type

[cbasson]

Hello,

I am about to repoint my house but am unsure about the type of mortar to use.

House was built c. 1900, so from what I have read lime mortar seems like the likely choice.

From reading other posts on here, 3.5 NHL could be the one..

It has been suggested to me that a 1:1:4 mix (lime + O.P.C + sand) can also be used (or maybe 1:1:5 - checking). Does that still constitute a lime mortar? As it has concrete added does that not let the mortar breathe and will therefore affect the (soft) bricks?

Here are a couple of pictures of the pointing. You can see the original pointing has been touched up by covering it with some new pointing which is flaking off.

Untitled

• cbasson
• 9 Jun 2015
• 1

This second one shoes the underlying pointing better

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• cbasson
• 9 Jun 2015
• 1

Thanks for help

Charlie

 

[cbasson]

First thing is, what is the exsisting mortar made of? and how old is your house? Using any amount of cement with lime mortar is a bad idea. . The repointing may not last as long without it, but it is always easier to repoint than to replace damaged bricks.

Guess this still stands..

 

[cbasson]

Anyone help please?

 

[^woody^]

If the original is lime then you should not use any cement in any repointing. Cement does not prevent breathing, but it is less flexible.

It looks like that repointing is falling off because its too thin and the joints have not been raked out sufficiently

 

[cbasson]

Thanks Woody

Would the 3.5 NHL be the mortar to use if is lime mortar?

 

[theprinceofdarkness]

yes, 3.5 or 5, mix with 2 1/2 part sharp sand. If you go to a lime or restoration specialist you can get sands of different colours. If you are rich St Astier make a ready mixed lime pointing mortar in a multitude of shades. this is really designed for repair work in traditional buildings.
Frank

 

[cbasson]

Thanks Frank

I guess the photos dont show that much of the underlying mortar but i guess its fairly safe to assume the orignal mortar used was lime given the build date?

 

[theprinceofdarkness]

I would have thought so.
Frank

 

[cbasson]

Cheers Frank

I know there is multiple threads on this but always reassuring to post your own details (houses, bit like kids but more expensive..). Appreciate the help.

 

[Joe Malone]

In all likelihood for a property built circa 1900 then it is probably cement. The problem is that the only way to prove this is by laboratory analysis. My labs do a check on the mortar constituents for around £85.00

However, if you don't have a test done then you are always best to err on the side of caution by choosing lime mortar. If its cementitious mortar then you won't do any harm by pointing with NHL 3.5, or NHL 5 for severe exposures (Roof work etc.). However if it is lime mortar and you choose cement then you will concentrate moisture and salt action into the masonry units rather than the mortar joints and expedite spalling of the masonry due to hydraulic first action. What you have to understand in that lime is breathable and as such serves a key role in moisture evaporation and salt migration to the surface; effectively the lime mortar is sacrificial to protect the masonry units. Incorrectly point up with OPC mortar at your peril.