How Plaster Gets Blown and How to Tell
Posted on 10th April 2025 at 11:29
Plastering offers a number of advantages, including durability, superior sound insulation, fire resistance, and promotes better air quality in the home. It is no wonder that people often opt to plaster their walls. But sometimes plaster becomes blown.
This can cause ugly stains on your wall, structural damage, and looks unappealing. So how does plaster get blown?
Damp is the most common culprit
Penetrating damp, rising damp, or black mould have waged war on plaster for decades. Moisture trapped within the plaster can cause it to expand, especially when there are temperature fluctuations. Damp and mould interrupt the bonding process that is necessary to stay connected to the wall.
If you have blown plaster, it is most likely that damp is the reason.
Poor surface preparation
Sometimes the error isn’t bacterial or fungal, in fact it can be entirely human. It is quite common for a poorly prepared surface area to be the reason behind your blown plaster:
• Dust and Grime: dirty or dusty surfaces prevents plaster from bonding properly to the wall.
• Loose or Flaking Paint: Plaster applied over a poorly painted surface can cause the plaster to detach with the paint.
• Porous Surfaces Drying Quickly: Very porous surfaces can suck moisture out of the plaster too fast.
• Incorrect or no Priming: Some surfaces require specific primers to ensure proper adhesion. Not using the correct primer may lead to blow out.
• Incompatible Materials: Plaster doesn’t adhere very well to smooth surfaces like ceramic tiles unless they are properly prepared.
Poor plaster application
Surface preparation isn’t all that can go wrong in the plastering process. The actual plasterer themselves might have made some serious missteps when applying it.
For instance, if the plaster has been applied too thick, or the plasterer has terrible trowelling technique, your plaster could start to show signs of blow out. If the plaster dries unevenly, or the trowelling leaves weak parts in the plaster then you could find yourself with a problem.
Also, if the plaster mixture is wrong, or the new plaster reacts poorly to the old plaster you could experience blow out.
The house got up and walked (honest)
Sometimes, there’s been absolutely no problem with the plastering job itself. However, the house might have moved. Natural settling or other structural shifts can cause stress to the plaster and cause delamination.
This might happen in a new build, or somewhere there is extreme thermal expansion and contraction.
How to tell if your plaster has blown
It’s not always easy to tell at first glance, at least to the untrained eye. There are some simple tests you can do to find out:
• Hollow Sound: Tapping on blown plaster makes a hollow sound. Solid plaster doesn’t.
• Loose Patches: Pushing the plaster might feel loose or springy.
• Bulges or Bubbles: Areas where the plaster has come away from the wall might bulge outwards.
• Cracks: Whilst not always indicative of a blow out, extreme spiderweb-like cracking often precedes it.
• Damp Patches and Stains: These are often a sign that damp or mould has caused a problem with the plasters bond.
Don’t leave it to chance
If you want a good plastering job that lasts for a long time, then you need a professional to do it. It’s that simple. It’s also best to call in your local builder to have a look at the plaster in your house to find out whether or not your current plastering is blown.
To discuss your plastering with an expert, call us on 01604 380 930, or email info@srgillbuilders.co.uk with your enquiry.
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