How to deal with damp marks on bagged brick?

renosouth1234

 

Hi guys, I’m doing a bagged brick effect on the exterior of our brick veneer house. I’ve done a test and there’s brown damp lines sitting above the damp course for about 4 days with no sign of it going away. Any idea what this would be about and I’m assuming will damage the render over time? I used an acrylic render from Dunlop for this test but am switching to lime mortar for the rest so it’s more breathable. Will be painting over in white outdoor paint. No primer applied just cleaned and applied with a mit. 
we do get damp under our house as we live on a high water table but I don’t know why it would be showing so damp above the course line. Is this normal for bricks? 
Any advise really appreciated thank you! 

MitchellMc

Welcome to the Bunnings Workshop community @renosouth1234. It's amazing to have you join us, and many thanks for your question about applying render.

Thanks for sharing your situation — the photos definitely help highlight what you're dealing with. Before jumping to any conclusions, I’d first ask what the weather has been like in your area lately. If you haven’t had a few solid days of sun and it’s been rainy or humid recently, that could easily explain what you’re seeing. The brown damp lines above the damp course may simply be moisture that hasn’t had a chance to evaporate yet. It’s quite common for brickwork to hold onto moisture, especially if the wall was damp when you applied the render. That moisture may now be trying to work its way out through the render layer. Since you didn’t use a primer and applied the acrylic render directly with a mitt, the wall may be drying unevenly, particularly if the bricks had any residual moisture in them or the weather has prevented proper curing.

It’s worth noting that acrylic renders are less breathable than lime-based ones, which could be slowing down the drying process. The fact that you’re planning to switch to lime mortar for the rest of the work is a good move — lime is far more breathable and better suited to homes that are prone to dampness. Given your high water table and known underfloor damp issues, the bricks may be holding onto groundwater or moisture from humid conditions, and it's just now showing up through the render. I’d suggest giving it a few more days of dry weather to see if the damp patches begin to fade. If they persist, then it could indicate that moisture is somehow rising above the damp course — possibly through bridged mortar joints or internal moisture pressure from behind the wall.

If you can, take a look at the other side of that wall (from the inside) and check whether there’s any visible water sitting against it or signs of moisture. That could help confirm whether the issue is just external and cosmetic or something deeper. At this stage, I wouldn’t be too alarmed, but I would let it dry a bit longer before continuing. If the damp doesn't recede, it may be worth further investigating whether the damp course has been compromised or if other waterproofing measures are needed before proceeding with paint or additional render.

Please let me know if you have any questions.

Mitchell