Curious, what causes skim coat to fall off ?

[SimonH2]

1060s ex-council house. On some of the walls, the skim coat has de-bonded from the base coat - and in places the base coat has de-bonded from the bricks. But it's not everywhere.
For example, I've just started stripping the wallpaper in the front bedroom, and this is the result. This is the side wall of the house (party wall with the neighbour), and chimney where it passes through the upstairs room. On the wall itself, just about all the skim coat has come off - except for a few inches near the ceiling that's firm. The side of the chimney is all firm, and the face of the chimney is "patchy".

I assume there's something in either the mix or the technique that causes it - given how some walls are OK, some are completely bad (except near the ceiling, and some are patchy.

Just curiosity really - knowing why won't change the fact that it'll need redoing !

 

[stevethespreader]

Lots of things bad prep mostly also age if lime aaaaaand wallpaper strippers

 

[SimonH2]

I was thinking ...
On the large areas, they've probably thrown on a coat and used a large float with little pressure, except at the ceiling when they'll have worked it a bit more to get the join right. On the small area, probably used a bit more pressure with a smaller float and/or worked it a bit more given the two corners in close proximity. Hence a difference in how well the skim coat has mechanically keys with the base layer.

Same again for the base layer - another wall has that loose (like we had in the back bedroom).

Does that make sense ?

Also, how do we determine what material the base coat is ? It's light grey and very dusty - but that doesn't really narrow it down much !

 

[chappers]

Stop complaining, it's done well to last since the 1060's. Skim coat is just one of the things the Normans brought with them on their conquest.

 

[SimonH2]

Eh ? I'm not complaining, trying to understand.

 

[chappers]

sorry was my attempt at humour re the date you gave. As Steve said probably just age and repeated rounds of re-decorating over the years

 

[SimonH2]

Fair enough. It's not done too badly, but "interesting" that some walls are fine while others are completely crap.

 

[noseall]

My guess is that it will have suffered as a result of drying too quickly when applied and the reason that the perimeters survived is because they would have 'borrowed' moisture from the adjacent walls or ceiling, prolonging the cure in these locations.

 

[SimonH2]

That's interesting.
When we had one of the walls back top bare brick in the back room, the plaster said he'd never seen anything like it in his 30+ years experience. Even though he watered the wall first, the amount of suction in the brick took him by surprise and he reckons he used several buckets of water keeping the base coat moist wet while it set.
'kin hard red brick, says Claughton on them - I've just taken some out to make a cupboard over the stairs.

 

[stevethespreader]

That's interesting.
When we had one of the walls back top bare brick in the back room, the plaster said he'd never seen anything like it in his 30+ years experience. Even though he watered the wall first, the amount of suction in the brick took him by surprise and he reckons he used several buckets of water keeping the base coat moist wet while it set.
'kin hard red brick, says Claughton on them - I've just taken some out to make a cupboard over the stairs.

Red brick is classed as medium suction old mortar can make suction worse and accelerate the suction, obviously he did not apply enough water to the brick before putting the base coat on , if you apply enough water you can virtually kill the suction