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Matching 1908 Period Mortar... Black Flecks In Mortar


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#1 Langy3366

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Posted 08 August 2012 - 01:47 PM

Hi,
Anyone know how to create the mortar for a 1908 North Wiltshire based house that has black flecks of stone in the mortar? Picture attached.

Best Regards

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#2 joiner

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Posted 08 August 2012 - 01:53 PM

Very common. Add anything to give the flecks, here it was coal dust because this place used to be the offices to the colliery on the site (here with the addition of bits of crushed ash from the boilers)...

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Edited by joiner, 08 August 2012 - 01:54 PM.


#3 temp

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Posted 08 August 2012 - 03:22 PM

Google found..
http://www.periodliv...king-good-match

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"We tried adding crushed barbecue charcoal to introduce ‘black bits’ but this tended to make the mortar go rather grey. Finally, after calling every lime supplier in the country, Karen tracked down a supplier of ‘black bits’ and we had a match."

Perhaps worth sending them an email?

#4 temp

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Posted 08 August 2012 - 03:26 PM

I suspect you may have to follow the proceedure they used on the link above to find the right sand. But seems some companies sell mortar wit black bits!

http://www.tradition...l-lime-products

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BM3
A pointing lime mortar. Cures to a white colour with black flecks.
Supplied in 25kg bags, 15 litre tubs and one tonne bags.

Perhaps too white? See if they can send sample?

Edited by temp, 08 August 2012 - 03:27 PM.


#5 joiner

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Posted 08 August 2012 - 04:06 PM

Interesting links, Temp.

The reason charcoal gives a grey finish is because it crushes down too fine and the resulting dust mixes too completely with the lime mortar. Crushed coal, washed, gives you the flecks.

All the lime plaster on the walls here was mixed with coal dust resulting in a grey plaster an inch thick. Chasing it out for the electrics made a hell of a mess because the lack of the reaction that would have occurred with sand didn't happen and it made the stuff as powdery as hell.

#6 Simon28

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Posted 05 March 2013 - 02:23 PM

Generally when you are mixing a mortar it is the larger heavy aggregate that will produce the overall appearance of the mortar from arms length distance viewing.

The black fleck that you are looking for can be achieved with crushed flint, large aggregate charcoal or a pozzolanic material like fly potash or similar. This can be added to the mortar mix to suit but you should be aware that the more pozzolanic material that is added the harder it will set. A consideration for use against soft stones and other softer building materials.

Charcoal will indeed make the mortar greyer and that should be considered when you are mixing finer particle sizes. This can be counterbalanced with whiter sands as the finer aggregates.