Bumps in internal walls, is this from damp?

[Woodpecker2]

Recently purchased a cottage, original part mid to late 1800s, newer extension to the rear. We knew there were damp issues but am curious about the bumps on the wall as in the photo. They are only on the internal walls marked red on the floor plan. Assume it’s gypsum plaster internally? Exterior is stone, I believe some old lime mortar and some patched repairs in cement. High external ground level at the front. Smells very musty in kitchen cabinets that sit against the red wall, but rest of the kitchen is fine.
When purchasing we planned to complete repairs to the chimney (completed - not near to these walls though), and in time re-do the like mortar to the front of the house.

What should we be doing internally? Are the bumps related to damp? The wall doesn’t feel damp to touch and the bumps are hard. Should we be looking to like plaster internally, at least in the hallway and kitchen?

Thanks in advance!

 

[aockenden]

Its worth exploring what’s underneath those bumps to gather more info. Take a small screwdriver and dig into one of them. Is it hollow underneath? Is it a pocket full of salty white deposits? It it some actual lump of something hard under there?

Regardless of what you find, these sorts of effects are virtually unheard of when permeable, vapour-open, capillary active materials (paints, plasters and mortars) are used instead of layers of impermeable modern gunk.

 

[Woodpecker2]

Thank you for replying. Just took a screwdriver to two bumps, appears to be something much harder and solid beneath!

 

[Cubist]

You'll find it was a little piece of grit lifted from the base coat by the plasterers float when he was applying the final skim coat. That speck of grit aided the formation of a small bubble in the skim coat plaster. Bad workmanship but very easy to remedy and nothing to do with damp.

 

[Lacan07]

You'll find it was a little piece of grit lifted from the base coat by the plasterers float when he was applying the final skim coat. That speck of grit aided the formation of a small bubble in the skim coat plaster. Bad workmanship but very easy to remedy and nothing to do with damp.

This is what I was thinking, it looks rather large to be that close to the surface though, I wonder if the plasterer skipped the float coat and just applied a base and skim coat? There's no way something like that could move through the wall of its own volition after the plaster has set.

 

[Woodpecker2]

Thanks both. It’s odd though as it’s only on two of the four walls in that room, and then on the other side of the kitchen wall but none of the other kitchen walls. I would have thought it was done room by room, possibly more than room at once but who knows - I don’t suspect any work has been done in the past 12 years at least.

What would be the solution or best place to start? If it smells damp, regardless of the hard lumps, I’m guessing it’s wise to look to have the plaster removed and redone with lime (I’m not quite sure of the process or how much would need to come off though)

 

[Woodpecker2]

There are lots of the bumps too, more so towards the lower half of the wall and less right at the top

 

[aockenden]

Idk, there’s some clues here that make me think it IS damp related, not just some plastering defect. More prevalence lower down on the walls, musty smell, plus in the first pic in the opening post there’s a section in the bottom right that looks properly blown.

 

[Cubist]

Thanks both. It’s odd though as it’s only on two of the four walls in that room, and then on the other side of the kitchen wall but none of the other kitchen walls. I would have thought it was done room by room, possibly more than room at once but who knows - I don’t suspect any work has been done in the past 12 years at least.

You have remember that there is always the senior craftsman mate or apprentice. Most of these were/are required to help with the work under the craftsman's guidance but sadly some of of those learners could not tell you which is the business end of a hammer, if you catch my drift.

Idk, there’s some clues here that make me think it IS damp related, not just some plastering defect. More prevalence lower down on the walls, musty smell, plus in the first pic in the opening post there’s a section in the bottom right that looks properly blown.

That's a fair point. There may be something else going on here besides poor workmanship. If you can check the other side of that wall and what the room is used for further clues may arise.

In terms of how to proceed - it should be easy enough to either scrape or chip off any high spots and fill any cavities before a skim coat to finish. I don't think it would be necessary to strip all the existing plaster though.