Wet Basement Room in Birkenhead: Walls, Floor and Junction Sealed from the Inside

This basement room in Birkenhead had a problem a lot of North Shore homeowners will recognise. Water was seeping through the base of the concrete block wall and spreading across the floor. Here’s what we found and how we sealed the room from the inside. If you want the wider picture, our basement waterproofing Auckland page explains how we approach these jobs.

The problem: water coming in at the base of the block wall

When we arrived, there was water sitting on the floor and the bottom of the block wall was wet and stained. The worst of it was right along the line where the wall meets the floor. The old vinyl sheet flooring had lifted, and underneath it the concrete was damp, with powdery deposits left behind as the water dried.

That junction is a common weak point in basements. The block wall and the floor slab are two separate pieces of concrete, so water under pressure from the ground outside often finds its way through the joint first. Covering it with new flooring would only hide it for a while.

What we did, step by step

1. Stripped the old flooring

The wet vinyl came up first. You can’t seal over old flooring, and we needed to see the bare concrete to know what we were dealing with.

2. Ground back the floor and walls

We ground the floor slab and the lower block walls back to clean, sound concrete. A coating is only as good as what it sticks to, so this step matters. If your problem is mainly damp coming up through the slab rather than in at the wall, a rising damp slab case study on the North Shore shows that kind of job.

3. Patched and coved the wall base

Next we repaired the wall base, filling the joint where the wall meets the floor and forming a cove, which is a smooth curved fillet instead of a sharp corner. We also patched around the corners and the block pier. A coved junction lets the membrane run in one continuous sheet from wall to floor, with no sharp edge where it could crack or thin out.

4. Applied ARDEX WPM 300 HydrEpoxy over the walls and floor

Finally, we applied ARDEX WPM 300 HydrEpoxy over the walls and the floor, around 20 m² in all. It’s a moisture barrier made for applying from the inside, on the side of the wall you can actually reach, so there was no digging outside the house. The finished coat is light grey and runs unbroken across the wall and floor junction, which is exactly where the water had been getting in.

Why we sealed it from the inside

The usual way to waterproof a below-ground wall is from the outside, but that means digging down the full height of the wall. On a lot of North Shore sections that isn’t practical. Neighbouring houses, paths, driveways or a steep slope get in the way. Treating walls, floor and junction as one continuous system from inside the room deals with the water where it shows up, without the excavation.

Is your basement showing the same signs?

Look for these:

• Water or damp patches where the wall meets the floor
• Staining or a tide line along the bottom of a block wall
• Flooring that lifts, bubbles or feels damp underneath
• Powdery or crusty deposits on bare concrete

Every basement is different, so the first step is always a proper look on site. For another job like this one, see how we dealt with a leaking basement wall in Parnell.

Basement waterproofing in Birkenhead and the North Shore

If water is seeping into your basement in Birkenhead, we’re happy to come and take a look. Basement waterproofing in Birkenhead often comes down to the same weak point we found here: the joint between the block wall and the slab.

You can also read our waterproofing FAQs.