Learn More about Floor Preparation
Subfloor Preparation - Flatness, Moisture & Level
It is critically important to have a suitable subfloor for any floor installation. All floors (except solid hardwood timber) are decorative surface floors and need a subfloor that's:
- Flat - typically within 2 - 3mm variance per sqm i.e. anywhere within one metre should not have a dip or hump of greater than 2 - 3mm. Uneveness can put undue pressure and damage to locking systems, cause creaking noises and cause the floor to break apart. For vinyl floors, it can also "telescope" all the imperfections, showcasing the ripples, dips, and unevenness on top of the floor.
- Stable - the subfloor should not be moving e.g. older timber plank subfloors sometimes move up and down with weight and can cause damage to flooring or "telescoping" where the issues with the subfloor are reflected above the floor.
- Dry - moisture typically needs to be within 12% Moisture Content (MC) for timber substrates and 2.5% for cement-substrates. Moisture-issues can cause a variety of latent issues, including warping, expansion, gapping and bulging.
Additionally, an unsuitable subfloor also makes it difficult to install over - locking systems may not engage easily or the glue may not sufficiently transfer to the back of the planks.
How to Check the Subfloor for Suitability
Checking for Flatness
You can use a 2m straight edge or spirit level. Lay it across the entire floor area and see if there is any movement or any gaps underneath the straight edge - any uneveness will show if you press down one end and the other end comes off the group, or if you notice any gaps within the 2m straight edge.
Remember: Most floors only tolerate 2mm over 1m, which is at most 4mm over 2m - any gap you can visibly see is going to likely be 2mm or greater!
For the pros that have a laser level, you can also use it to check for higher and lower spots on the subfloor.
Checking for Stability
The floor may be flat right now, but is it stable and will it continue to be stable years into the future? As concrete is very stable, this typically only applies to timber-based substrates such as plywood, yellow-tongue, particleboards or plank subfloors.
You can do a rough check by walking over the floor - do you notice any movement, bouncing, vibration or creaking noises? Any creaking noises may signal the subfloor has some "give" in it and perhaps you may need to stabilise it.
With timber substrates, it is sometimes possible to add additional screws to tighten them against the battens or joists.
Checking for Moisture
Firstly, check for visible signs of moisture e.g. darker spots, previous moisture ingress You can use a digital moisture meter - a cheap option for $20 - 30 should suffice from any hardware store or online. There will be two settings - one to check timber-based substrates and another to check cement-based substrates. Ensure that timber moisture content is not above 12% and cement moisture content is not above 2.5%.
If all this is too overwhelming, you can typically install a preventative moisture barrier - this is extremely helpful if you are concerned about potential future elevated moisture levels e.g. underfloor moisture.
- 200um Plastic Moisture Barrier - this is suitable under floating floors and can be rolled down below the underlay. You simply roll it out and sticky tape the joins.
- Roll-on Polyurethane Moisture Barrier - suitable for glue down floors such as solid timber or engineered timber, and is applied with a paint-roller to the substrate before glue is trowed and timber is stuck down.
How to Flatten / Level the Subfloor
Pour Self Levelling Compound
Pouring self-levelling compound is the most common approach. As self-levelling compound is a high-flow liquid based cement, it automatically flows out and fills the low spots. Once it has been poured across the room, the lower spots are automatically brought up and high slows are generally left untouched or covered with a thin coat.
This is the step by step process:
- Prime the subfloor - you must first prime the subfloor so the self-leveller can grip to the substrate. In the same way you use a paint roller, you roll the primer all over the substrate and wait for it to dry (typically half to one hour to dry). There are different primers for porous substrates e.g. concrete or non-porous substrates such as timber flooring or tiles.
- Mix and pour the self levelling compound - with a mixing paddle and bucket, mix the self-levelling compound and pour it as you go, using a trowel or rake to spread the levelling compound into each other. Choose the correct levelling compound:
- Concrete Substrates - if using it for residential or light commercial use under floating or direct-stick floors, use our standard Self Levelling Compound.
- Timber Substrates - if pouring over a timber or any substrate that may be subject to movement (even minor vibrations), then use our Timber & Industrial Levelling Compound. This leveller is stronger and more "flexible" and is also recommended for heavier-duty and industrial applications.
- Check the outcome - follow the steps previously to ensure you've brought the floor to a suitable flatness.
Tips for Pouring Levelling Compound:
- Have two or more people - you have a limited working time to pour each bag, so it's best to have two or more people when pouring - one person mixing and the other pouring the levelling compound into the water. You want to quickly pouring onto the floor, rake it out and then repeat quickly.
- Always order more bags than you expect - you can only pour everything in one setting and if you were to pour again, you will have to start again with priming and it is difficult to achieve complete flatness. In a single sitting, if you have enough bags for the area, it will find it's own level.
- Never mix too much water - the most common issue arise when too much water is mixed in e.g. dust on surface, cracks in the levelling compound due to shrinkage, weaker or softer surface. If you mix 5 litres of water - this is too much! Most bags only allow between 4.4 - 4.8L of water, so please order enough bags to complete your area without adding additional water.
How to Use Rapid-Setting Feather Cement
A complement and sometimes alternative to levelling compound is our Rapid Feather. It's a quick and simple DIY mixture that is troweled onto the floor and sets around 10 minutes. It doesn't require primer, so it's quick and easy to apply.
Our Rapid Feather Edge is great for:
- Filling and repairing cracks or joins:
- Filling cracks before pouring levelling compounds to prevent leaking through
- Smoothing joins between particle boards or plywood
- Smoothing tiles and building out grout lines
- Smoothing off minor unevenness:
- If the subfloor is uneven e.g. concrete is rough, it can be troweled with a thin layer to smooth off the uneveness.
- Patching dips or holes:
- It can be trowed into holes and bring them up to the same level as the rest of the floor.
- Building ramps:
- As a thick non-flowing mixture, it can be used to ramp up to meet other floors
Your Turn to Prepare the Subfloor
We've given a brief overview on the most common subfloor preparation methods, but please do read the detailed notes on each product page and especially the installation instructions on the actual bags or buckets! If you need further assistance, feel free to ring Flooring Works on 1800 312 848.