Can hardwood floorboards be installed onto STRUCTAflor flooring panels?

[Khogg]

I am an owner/builder and have a home where we have installed 19mm H2 STRUCTAflor particle boards subfloor. They are on joists and stumps and have plenty of ventilation under the house. (https://www.bunnings.com.au/3600-x-800mm-19mm-flooring-h2-particleboard-green-tongue_p0460006?store=...).

We have 250sq mtrs of 19mm thick x 90mm wide solid Karri wood tongue and groove floorboards that we want to install onto the subfloor and are unsure if the panels will be strong enough to staple into and hold the staples over time (https://www.bunnings.com.au/titan-15g-x-38mm-electro-galvanised-collated-flooring-staples-pack-of-20...).

Do we have to glue it as well? Do we have to add a plywood first? There are a lot of google chats that mention particle board and how you can't do it and I am wondering if they are talking about the cheap particle board and a concrete sub floor???

Any advice would be great. 

[EricL]

Hello @Khogg 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your hardwood flooring.

Since you are installing solid Karri timber over a particleboard subfloor, there are a few important considerations to ensure the floor performs well and avoids future issues.

First, your choice of 19mm H2 STRUCTAflor particleboard is actually a purpose-made structural flooring product. It is not the same as the low-density chipboard that people often warn against. STRUCTAflor is engineered to be a structural subfloor and is commonly used under both carpet and timber flooring. It is moisture resistant (H2 treated), tongue-and-groove jointed, and designed to carry loads over joists. So, it is much more suitable than the “cheap particle board” you may have seen warnings about.

Where the issue arises is with fastener retention. Particleboard does not hold nails or staples as firmly as plywood because its particle structure does not have the long grain to grip fasteners. Over time, staples may loosen with seasonal timber movement. That is why most flooring installers recommend either using a combination of mechanical fixing and adhesive, or laying a plywood underlay first for better holding power.

If you want to staple directly into the STRUCTAflor, you should definitely use flooring adhesive as well. The adhesive provides most of the long-term holding power, while the staples or nails act to clamp the boards in place until the glue cures. A full trowel-spread polyurethane flooring adhesive is commonly used between solid timber flooring and subfloors. This combination helps minimise squeaks, movement, and staple pull-out.

Adding a 12–15mm plywood underlay is the premium approach. Plywood gives much stronger staple retention and allows you to staple without as much reliance on adhesive. It also adds a stable layer that helps spread loads and allows you to sand the timber floor more in the future. The downside is the additional cost and extra height added to your floor system.

So, you have two main options. If you want to avoid the cost and height of adding plywood, you can staple and glue directly to the STRUCTAflor, provided you use a high-quality flooring adhesive and ensure good coverage. If you want the most secure and long-lasting installation, particularly given Karri is a dense hardwood that moves with humidity changes, then laying plywood over the STRUCTAflor before fixing the boards is the best practice.

Let me call on our experienced members @DIY4Knuckleheds, @Noyade, @Remarka6le and @ProjectPete for their recommendations.

If you need further assistance, please let us know.

Eric