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Posted to uk.d-i-y
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Damp treatment for *severe* penetrating damp
wrote:
Or can we just repoint, knock off and replaster with waterproofer added
to the plaster mix?
Is it an old house (how old?) or new?
Victorian terrace
Make sure that whoever re-points uses either lime mortar
(unlikely for most builders as it's a PITA for them) or
1:1:6, which is much more likely and OK for builders -
not straight cement:sand, even "with a plasticiser, mate,
so it's OK" (because it's not OK). Just a small point 
Whats the 1:1:6 mix of? Also what would be the implication of using
normal sand/cement mix (with plasticiser)?
1:1:6 is cement:lime:sand by volume. It's not as hard as cement
mortar. If you use cement:sand, it's effing hard. The mortar
used originally was soft lime mortar. Plasticiser in cement
mortar is for workability, it doesn't change the hardness. Under
some circumstances, if you use a hard mortar, it can lead to the
stuff being slowly ejected, or, much worse, damaging the brick
faces:
@@@@@@@@@
@@@@@@@@@ Brick
X- @@@@@@@@@
Y- ##::::::: ## = hard mortar, ::: = soft mortar (original lime).
X- @@@@@@@@@
@@@@@@@@@ Brick
@@@@@@@@@
Large force transmitted at X possibly leading to flaking. The
hard mortar at Y may be ejected due to small movements of the
structure, potential water ingress and frost damage.
1:1:6 will also match in much better with the rest of the
buildings. You can use white cement, the results can be a bit
too white though! It's worth being a little careful with mortar
colour, to avoid eyesores.
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