Plaster Blown? Here’s Why

Today we’re going to be talking about everyone’s favourite topic – plaster. I know, we’re getting crazy over here at DreamyHome, but tell me, do you know why plaster might blow? If not, you came to the right place. We’re going to talk about the conditions that can cause it, what it even is, and what to do if you have plaster blown in your home.

Has your plaster blown? It’s likely caused by moisture in your home, improper installation, or poor drying.

Let’s talk a bit more about this, shall we?

Spotting and Fixing Blown Plaster

Let’s start with the easy stuff, shall we? We need to know what blown plaster actually is before we can address what causes it, right? Well, without further ado, it’s time to talk about blown plaster.

What Is It & Why Does It Happen?

Long story short, blown plaster happens when (for one of many reasons) your plaster doesn’t adhere properly to the substrate it’s attached to. Beyond clear damage, a good sign of blown plaster is if you knock along your wall. You’ll notice that healthy plaster will sound solid, while blown plaster will sound solid. Here are some common issues:

  1. Porous Surface – A porous surface, by nature, has a lot of little bubbles of air along its surface. This isn’t necessarily bad, but when used as a surface for plaster, it can get… less than ideal. This is because the surface you place the plaster on can actually dry out the plaster. While it’s designed to dry, plaster isn’t meant to dry quickly; it needs time to do its thing. A porous surface can also prevent the plaster from properly gripping, leading to blowing.
  2. Moisture – Along the same note, plaster doesn’t really like moisture. It uses a chemical reaction to bond to a surface, and dampness interferes with that process. When applying plaster, you need a clean, dry surface, or you risk cracking and blowing. It’s actually also easier for moisture to interfere with porous surfaces because of the added texture.
  3. Dirt & Grime – Like I said, cleaning the surface you put plaster on is vital. Any leftover oils or grease, along with dirt and dust can interfere in plaster binding to its surface.
  4. Other Wrong Surface – If you’ve been reading DreamyHome religiously, you’ll know that we recently talked about plastering over tile. In short, it’s a bad idea for the same reason as a porous surface – it’s not designed to hold plaster. You’ll have a hard time getting the plaster to stick without some sketchy workarounds, and even then, there’s a big issue. Tile isn’t meant to hold plaster – that means you risk it all coming down at once. That is (surprise) not ideal!

Repairing Blown Plaster

I’ve got bad news for you. If your plaster has severely blown, you can’t do anything to fix it. If you’ve got a small section that’s blown out, however, you can tear it out and reapply plaster – though that’s far from ideal.

Using PVA applied directly to the substrate and the bit between plaster and wall should allow you to replaster right up to the damage, which can be painted over. Some people recommend drilling holes into the wall and physically anchoring the plaster to the substrate, though that’s not really good advice, for one main reason.

You plaster to make a smooth surface for paint or wallpaper. If you’re placing screws and washers into the wall to anchor it, you’re going to have screw heads clear as day underneath the paint. And we’re not talking about a handful of screws, no. You would need dozens, even hundreds (depending on the size of the damage) of screws to properly do the job, which won’t be pretty.

In short, once the plaster has blown, it can’t be fixed or touched up. Your best bet will always be to entirely tear it out and reinstall your new plaster properly.

If you find that plaster in your home is blowing or already has, the best option is to contact a professional. It will cost money, and it won’t be an easy process, but you’ll have a fixed wall. And honestly, it’s better to pay and fix it than to wait for the blowout to get even worse.

Final Thoughts

Blown plaster is a major pain in the butt. It looks… not great, and it’s easy for moisture to grow in the blown area, leading to more failure in the future. You can’t really fix blown plaster, either. Blown plaster is often caused by excess moisture or application to an improper substrate – both things that you can’t really solve. The only real way to fix a section of blown plaster is by entirely tearing out your wall and replacing it. Sure, you can try to mechanically anchor the blown section to the wood beneath, but that’s not going to look good and is pretty time-consuming.

While I know that nobody likes to hear it, if you have blown plaster, it’s likely time for you to call a professional. They exist solely to make your life easier, and will do a drastically better job at finding the issue than you likely could. So call a pro, sit back, make a drink, and let them do what they do best.

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About the Author Harry Thompson

Involved in home renovations throughout his life, Harry is an expert in everything to do with home and garden DIY. In his spare time, he enjoys cooking and tending to his garden.