replying to Poster, fcbolton wrote:
going back many years...... mastic could be bought in bags as dry sand
together with a powdered red dye. for red accringtons rake out the joints as
depth of about6mm (the original mortar is likely to be "clog iron
mortar".which is based on ground ashes .buildings built late 19th century
before cement was widely available. mix the mastic powder with BOILED
linseed oil (some say double boiled linseed oil) paint the raked out
joint with a primer of boiled linseed oil. point the joint with the mixed
mortar. the mix should be fairly stiff but well mixed . do the vertical
sections first try and do about 1m sq at a time.. the boiled oil acts as a
drying agent and will take days to set (compare with cement mortar which sets
within 3hours.. when the who wall is complete paint the whole wall surface
brick face and new joints with one coat boiled linseed oil. allow to set(set
not dry). i have made small samples of boiled oil based mortars and they
set to a vey hard mass. only do this type of pointing to accrington hor
semi engineering brick. the normal modern brick requires a weak cement lime
sand mortar water mixed this allows any dampness to evaporate through the
joints NOT through though the face of the brick normal recc is 1 1 6
cement lime sand mix. many 19th cent buildings may not have been built
with a cavity thus rain kept out with the boiled linseed.

p

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