How to control rising damp in walls?

Nobby

I have been trying help with my mother's old house.

It is a two bedroom cottage style home from the early 1900s. It is a brick house with what appears to be render on the inside walls.

The paint is peeling and blistering on the interior of the house, not just the inner surrounding ones. Although they are the worst.

It looks like there may have been floorboards in the house, but where removed and then concrete was poured into it as there are vents in the lower sections of the walls.

I scraped off the paint blistering and a lot of damp render came with it.

I then put a waterproof membrane over it. And later painted it. The paint hasn't dried on the wall and there is fresh blistering. 

I don't believe that would be a DPC between the bottom bricks due to the age of the building.

How can I put a DPC into the walls?

MitchellMc

Welcome to the Bunnings Workshop community @Nobby. It's terrific to have you join us, and many thanks for your question about rising damp.

It sounds like there might be two issues at play here: damp coming through the wall and an incompatibility between the products you’ve used.

If the paint is blistering on top of a waterproof membrane, it may not be due to moisture coming through from behind. Instead, it could be that the paint isn’t bonding properly to the waterproofing layer. Many waterproofing products aren’t designed to be painted over, they’re meant to have tiles or another surface applied on top. I’d start by checking the manufacturer’s instructions to confirm whether your paint and membrane are compatible.

Regarding the damp issue itself, you’re right that a home from the early 1900s probably doesn’t have a proper damp-proof course (DPC). Unfortunately, this can’t really be installed in the traditional sense after construction. However, there are specialised companies that inject a chemical DPC into the bottom course of bricks to create a moisture barrier.

Before going that route, it’s worth investigating where the moisture is actually coming from. Rising damp often happens because water is pooling against the external walls or the ground level has built up over time, allowing moisture to wick up through the bricks. Start by examining the outside of the most affected walls. Check whether garden beds, paths or soil are sitting too high against the brickwork, or if there’s poor drainage that lets water collect near the base of the walls.

If you find damp soil sitting against the brickwork, it might be more effective to lower the ground level slightly or install a waterproof membrane on the outside of the wall instead of just treating the inside. That helps stop the problem at the source rather than just masking the symptoms inside the house.

Please let me know if you have any questions.

Mitchell