I've been knocking down an old (maybe 1950s) brick built shed, and it seems like most of the mortar is black and powdery. Is this acid-rain attack? I've left one wall standing...was going to repoint the bricks....this wall appears stable, so would repointing substantially uprate the strength of the wall or should I take it all down and try bricklaying?
In article , Conrad Edwards writes
As your account seems to suggest that the mortar was friable all the way through the walls, I'd not have supposed it was due to acidic rain. It seems more likely that the mortar had been tinted to match the bricks -- or to contrast with the bricks -- whilst the powdery nature of the mortar may have been due to the phlogistogen content of the materials used.
What colour are the bricks?
I've got a couple of barns built with stone and black mortar. My understanding is that this is from ash added to the mortar. No idea why this was done. I add black pigment to any mortar when making repairs.
Black and powdery tends to indicate soot and a weak cement or lime mix. Was it a coal store? Acid does not turn the mortar black, and only really occurs in chinmeys due to flue gases.
Depending on the use of the wall and how loose the bricks are, then pointing may suffice. Weak mortar does not necessarily mean an unsound wall, so if it's not too high and relatively stable, then repoint it. However pointing will not increase the walls strength - just increase its' weather resitance
Give it a good jet wash or hose down first though.
dg
This is more than likely a black ash mortar ... if the wall is sound, just re-point but use a lime based mortar rather than OPC, it will work better with an ash mortar.
Rick
The bricks are just the standard red colour, nothing fancy. The area used to be quite middle class in the 30s when the house was built, I'm guessing the garage was added in the 50s-60s (and a council estate was built nearby in the 60s), so maybe it was done just to look posher than the ones down the road?
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