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Schoolmarm
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Can you tell us why that is preferable to nhl 5 Middi? As I have pretty much insisted on everyone using it on my roof.
Any mortar mix, be it lime based or cement based and in various strenghts, has to be chosen according to type of masonary and situation for these to perform at their best.Schoolmarm said:
Most of the time is a question of choise. NHL 5 is a type of mortar that is mainly used in conjunction with non permeable ( or breatheable ) masonary, especially in permanently wet situation. It makes an extremely strong bond, especially under compression. From my point of view it would be the wrong choise for traditional clay ridge tiles but may be acceptable for the modern or glazed ridge tiles.
If NHL is chosen to " BED IN " traditional clay ridges then nhl 3.5 would be a better choise, especially on old buildings, as this mix is a bit more forgiving from an impermeable or high rigidity point of view. Traditional clay ridge tiles ( or any " soft" clay tiles) do not need to be associated with rigidity or impermeability, especially on an old building.
One of the main reason for using my suggested mix is that it easily available from any builders merchant, it is of similar strenth to a traditional clay tile and similar element of breatheabily , and most important reason of all, I can re-point,brush or rake the mortar joints at different stages of application ( up to 24 hours later) to match any existing ridge tile mortar already in position, or, any soft red brick masonary on the building ( ie, chimney stacks)
It is my personal choise made after a trial and error process. "Period house" architects and co's have been extremely pleased at the end results, albeit the inclusion of cement did raise one or two eyebrows, but did agree that when used in certain situations and in limited quantities there would be no problem.
Middi
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Thankyou. 
angrybird
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this isnt about ridge tiles but i'm hoping middi might pick up on this topic
the driveway to my house has 6 foot high limestone walls on either side ,the mortar has all but gone!apart from what looks like mud and a few ferns growing out of it.What should mix should I repoint the walls with please ?
kind regards
Jacqueline x
the driveway to my house has 6 foot high limestone walls on either side ,the mortar has all but gone!apart from what looks like mud and a few ferns growing out of it.What should mix should I repoint the walls with please ?
kind regards
Jacqueline x
The strength of this mix is as close as one can get to the strength and porousity of a hand made clay tile or ridge tile. The rule of " building mortar " thumb is that the mortar strength and porousity should not exceed the strength and porousity of the masonary that it is supposed to bind. If the tiles, or ridges, in question were of a modern construction, ie- usually glazed and impermeable, then a modern 4 : 1 sharp sand and cement mix would be more appropriate.dans said:
If a very strong mortar mix is used on "breatheable" masonary ( ie- soft red bricks, tiles, etc..), especially in externally exposed situations, frost damage will be inevitable at the mortar joint. The damage will occur to the " softer" constructed masonary due to the inability to naturally dissipate moisture and water retained within as it is prevented to do so ( at the joint !!) by the very dense and strong mortar mix. This moisture will freeze and expand against the " solid" and " impermeable" mortar resulting in the " softer" material to give way.
Strong mortar mixes is one of the reason why " spalled " soft red bricks occur when used to repoint these.
The rule of construction:- " always match the strength and porousiry of mortar to the masonary"
I hope it makes sense
Middi
Lime rich mortarangrybird said:this isnt about ridge tiles but i'm hoping middi might pick up on this topic
the driveway to my house has 6 foot high limestone walls on either side ,the mortar has all but gone!apart from what looks like mud and a few ferns growing out of it.What should mix should I repoint the walls with please ?
kind regards
Jacqueline x
it is very porous and will complement the porousity of the limestone.
angrybird
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Thanks middi,thats a great help x
middi said:The strength of this mix is as close as one can get to the strength and porousity of a hand made clay tile or ridge tile. The rule of " building mortar " thumb is that the mortar strength and porousity should not exceed the strength and porousity of the masonary that it is supposed to bind. If the tiles, or ridges, in question were of a modern construction, ie- usually glazed and impermeable, then a modern 4 : 1 sharp sand and cement mix would be more appropriate.dans said:
If a very strong mortar mix is used on "breatheable" masonary ( ie- soft red bricks, tiles, etc..), especially in externally exposed situations, frost damage will be inevitable at the mortar joint. The damage will occur to the " softer" constructed masonary due to the inability to naturally dissipate moisture and water retained within as it is prevented to do so ( at the joint !!) by the very dense and strong mortar mix. This moisture will freeze and expand against the " solid" and " impermeable" mortar resulting in the " softer" material to give way.
Strong mortar mixes is one of the reason why " spalled " soft red bricks occur when used to repoint these.
The rule of construction:- " always match the strength and porousiry of mortar to the masonary"
I hope it makes sense
Middi
A thorough and well explained explanation as always! Thank you again!!