The first thing you need to do when you arrive on the jobsite is to assess the condition of the subfloor.

We've talked a lot about subfloor assessment in other units from the Flooring Technology series, including each of the units relating to particular floor coverings, plus the following units concerning subfloor preparation:

• Inspecting and testing subfloors
  
  
• Concrete grinding
  
  
• Subfloor coatings and toppings

You'll also find technical information relating to acceptable subfloor specifications in the three Australian Standards listed below:

• AS 1884-2012 Floor coverings - Resilient sheet and tiles - Installation practices
  
  
• AS 2455.1: 2019 Textile floor coverings - Installation practice Part 1: General
  
  
• AS 2455.2: 2019 Textile floor coverings - Installation practice Part 2: Carpet Tiles

Below is a summary of the main things you should consider when you're assessing the subfloor prior to the installation of hard underlays.

Always keep in mind that as the installer, it's your responsibility to decide whether the subfloor is suitable and has been adequately prepared.

If you're worried that the substrate isn't suitable, or that there is an underlying problem that might cause trouble later on, don't ignore it.

Check with your supervisor or manager before going ahead.

Questions to ask yourself

General issues

• Is the substrate generally smooth and flat?
  
  Make sure that any variations in 'planeness' are within the tolerances set by the underlay manufacturer.
  
  Although hard underlays are able to bridge small irregularities in the subfloor, they are not designed to span across high spots.
  
  If the substrate is degraded due to exposure to the weather, you may need to sand the entire surface.

• Is the surface free from dirt, oil, adhesive residues and all other contaminants?
  
  Dust and other substances on the surface will interfere with the strength of adhesive bonds.
  
  Some contaminants may also degrade the underlay over time.

Concrete subfloors

• Are the relative humidity (RH) and alkalinity (pH) levels within the allowable limits?
  
  Excessive moisture in the concrete subfloor can allow fungal spores or mould to develop.
  
  There are limits set for RH and pH, both in the Australian Standards and in the underlay manufacturers' own installation instructions.
  
  The only time you should over-ride these specifications is when an approved moisture barrier is being installed.

• Is the substrate sound and free from loose, powdery or scaly material?
  
  If the substrate is concrete and you are planning to use adhesives, the surface must be sound and sufficiently porous to allow the adhesive to bond properly.
  
  If it's not in good condition, the affected layer may need to be removed and resurfaced.

• Are there expansion joints in the floor?
  
  Expansion joints need to be in good condition and free from dirt or obstructions.
  
  You'll need to keep them clear and finish them off with approved cover strips in the finished floor.
  
  Don't get mixed up with relief cuts that have been put into the concrete to stop it from cracking during the curing process. These will be a 5 mm wide saw cut.

• Have heating elements been installed in the floor?
  
  Floor covering manufacturers provide recommended limits for the temperature of the subfloor.
  
  Make sure the heating elements will not exceed this temperature, and follow the specific instructions relating to substrate preparation for heated floors.

Wooden subfloors

• Is the existing floor properly supported and well secured?
  
  Any structural problems or loose boards should be fixed before the installation begins, especially squeaky floorboards or springiness in the floor surface.

• Are there protruding nail heads or other surface defects?
  
  Twisted or cupped boards should be sanded or planed back before the hard underlay is put down.
  
  Protruding nails should be re-punched.

• Is the subfloor ventilation adequate and in compliance with the relevant standards?
  
  Check that the air vents provide sufficient ventilation.
  
  Also make sure that the subfloor cavity meets the minimum requirements for clearance between the floor and the ground.

• Has the moisture content (MC) been checked and is it within the allowable limits?
  
  The moisture content of structural members and floor boards or sheets must all be within the allowable MC range.
  
  There must also be no evidence of plumbing or stormwater leaks that might have a long-term effect on the MC.