In article ,
"mark" writes:
I am going to put a brick porch on an old house.
I want the mortar to blend in with the lime mortar of the house.

I don't want to use the real M'Coy, just something that looks a similar
colour.

I propose to use white cement/lime/sand and am seeking advice on the ratios.

Do you need lime at all? Hopefully you aren't expecting your
new structure to move. If you do, the cement:lime ratio should
be 1:1 - many other ratios don't work.

The other thing is the sand - most builder's sand has loads of
iron oxide in it (which is what makes it yellow/orange) and it
will end up looking bright yellow through to dull orange regardless
of any white cement/line you use. You can get better washed sand
which is lighter in colour (silver sand), and you should look for
that. Don't use sandpit sand - it can be too rounded off to bind
well (to reduce scratching in eyes).

The sand originally used with lime mortar will not have been
graded as accurately as sand is today. To match it, you should
mix sharp sand with some finer sand (such as silver sand) to get
a broader particle size and shape. Sharp sand also tends to have
less iron oxide than builders sand, which will help avoid it being
yellow/orange.

The typical soft ratio for using with a lime mortar building
is 1:1:6 cement/lime/sand, but that is soft enough to eventually
allow things like moss growth. As this isn't repairing a lime
mortar building, I would go for something like 1:1:3 to 1:1:4, or
a no lime mix 1:0:4+plasticiser.

--
Andrew Gabriel
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