There's a variety of subfloors you're likely to encounter when installing resilient floor coverings.

We discussed the main subfloor types and typical preparations in the following two units:

• Inspecting and testing subfloors
  
  
• Subfloor coatings and toppings.

So in this lesson we'll summarise these issues by putting them into a set of questions that you should ask yourself before laying the floor covering.

Remember, as the flooring 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.

Everyone will be thankful in the long run, even if it means that there'll be a delay while the problem is fixed.

Questions to ask yourself

General issues

Is the substrate smooth and flat?

AS 1884-2012 states that the planeness tolerance is 4 mm over a 2 metre length, and the smoothness tolerance is 1 mm over a 150 mm length.

Is the surface free from dirt, oil, adhesive residues and all other contaminants?

Certain substances can interfere with the strength of the adhesive bond, and in some cases also discolour the vinyl surface.

Concrete subfloors

Are the relative humidity (RH) and alkalinity (pH) levels within the allowable limits?

There are strict limits set for RH and pH, both in the Australian Standards and in the flooring 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?

The concrete or underlayment surface must be sound and sufficiently porous to allow the adhesive to bond properly.

If it's not in good condition, the affected layer will need to be removed and replaced with a new underlayment.

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.

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, and can be filled with a suitable compound.

Have heating elements been installed in the floor?

Flooring 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 gaps between boards, protruding nail heads or other surface defects?

Gaps, ridges, cupped boards, protruding nails, and other defects will 'telegraph' through to the surface of the floor covering.

In general, structural floors made from plywood and strip flooring need to have a hard underlay placed on top to provide a flat smooth surface.

Is the subfloor ventilation adequate and in compliance with the relevant standards?

Check that the air vents provide sufficient ventilation and 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.

Old resilient floor coverings

Some flooring installers lay new vinyl on top of old resilient coverings if they're well bonded to the subfloor.

However, AS 1884 does not allow this practice because of the risks involved.

It's also likely that you'll void the warranty on any new materials laid if you leave an existing covering underneath.

One of the main reasons for not putting new coverings on top of old is that you can never be sure the bond will stay sound.

Sometimes it's the old adhesive that breaks down and causes a separation with the subfloor.

At other times it can be the new adhesive that doesn't bond well to the old floor covering, often because of old polish or other ingrained contaminants on the surface.

There are also potential problems with different shrinkage rates between the two coverings, which may result in blistering, cracking or other surface defects.

You can also end up with indentation problems in the new covering, because the old flooring has too much cushioning to provide adequate support or has existing grooves in the surface.