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hi

this is about a 1920s brick-built flat with slate roof. the whole
building comprises 4 flats, (two ground floor, two upper). the slate
roof is divided (above the party wall) by a small wall with coping
stones, sealed along the sides with cement "skews".

recently rainwater has been leaking into both upper flats, affecting
the corresponding rooms on either side of the party wall.

this has been diagnosed by quotes from two different roofers as being
a problem with the skews (i think the diagnosis was based on their
sounding a bit hollow when tapped). the solution is to remove the old
skews cementing, replace any slates that get broken along the way, and
build it back up again.

but one roofer has suggested a cheaper alternative would be to paint
two or three coats of flexacryl.

i'm worried in case this might be a false or short-term economy:
what's the expert opinion about using flexacryl for this...?

many thanks for your help!

Can you define what are "cement skews".

Using any type of brush on sealer is only a short term solution