The Mystery of Why Some Sengkang & Punggol HDB Flats Have Mould-Stained Walls is Finally Solved

Remember last year when news broke that some flats in Sengkang and Punggol looked “haunted” because of mouldy walls?

Well, the mystery has finally been solved.

It turns out it’s actually due to Trentepohlia odorata, and here’s the surprising twist: it’s not mould at all.

The Mystery of Why Some Sengkang & Punggol HDB Flats Have Mould-Stained Walls is Finally Solved

Early last year, there were reports that Anchorvale Parkview in Sengkang and Matilda Court in Punggol, both near Punggol Waterway, showed wall discoloration after only five years. Some residents said the problem spread to interior walls.

HDB then launched an independent technical study.

Experts conducted site visits, sampling, lab analysis, and literature reviews to understand why some flats were prone to mold growth and how to prevent similar incidents.

Responding to Lianhe Zaobao, HDB said the orange-brown substance on affected walls wasn’t mould, but a common local algae.

It thrives in sunlight and moisture but doesn’t harm residents’ health.

The expert team noted that algae grew along wall cracks, indicating rain had seeped in, creating a damp environment perfect for algae growth.

HDB mandates that only weather-resistant paint be used on external walls due to its higher algae resistance.

The contractors used non-compliant paint with less polymer content, making it less resistant to weathering and less durable.

Paint thickness was also uneven, with thinner areas less resistant to algae growth and prone to moisture accumulation.

HDB has warned the contractors for the two HDB estates. Both have taken remedial action.

Other projects by these contractors include Tampines GreenBloom, Woodlands Vista, Vista Spring@Yishun, and Boon Lay Grove.

HDB reported that Matilda Court and Anchorvale Parkview completed cleaning in May last year and January this year, with no algae complaints since.

Both areas are undergoing repairs and repainting.

Some Anchorvale Parkview blocks still show discoloration, which HDB says is residual staining from the first cleaning, not algae regrowth. These blocks will undergo another cleaning round.

Since 2022, HDB has clarified in all tender specifications that algae-resistant paint must be used in all public areas of flats. They’ve also increased audits during painting and extended the external wall paint warranty from six to seven years.