Why getting the quantity right matters
On every job, sufficient product must be applied to ensure the finishes behave properly during the levelling and drying phase, the appearance meets expectations, and the system performs well over the following years. The amount of product used on a floor directly impacts the performance of the coating system.
Each quantity in the table below includes an additional 0.5 litres of product. This accounts for the material that stays in the roller when it comes off the floor and the small amount left in containers and trays. The roller must come off the floor wet -- that is how you know the coverage rate is being met.
Primers are calculated at 8 m2/Lt, Prime White at 11 m2/Lt, and all other finishes at the middle of the coverage range (so 8-10 m2/Lt is calculated as 9 m2/Lt).
The maths on a 50 m2 floor
It seems logical that 5 litres of finish is enough for a final coat if you assume a coverage rate of 10 m2/Lt. 50 divided by 5 equals 10 m2/Lt. But the roller must come off the floor containing product, and there will be other wastage in the tray and containers. This usually accounts for about 0.5 litres.
With only 4.5 litres actually on the floor, the calculation becomes 50 divided by 4.5 = 11.1 m2/Lt. The product is now covering 11% more area than the highest suggested coverage rate. This means a higher chance of applicator marks, inconsistent sheen, and poor performance -- particularly if the coverage is stretched for every coat in the specification. With all application methods, regular checks and calculations should be made to monitor coverage rates.
Site factors that affect how much product you use
These figures are a guide. Assess the site and adjust up or down. Are there large gaps between boards where finish will fall through? Is the floor dry or softwood that will absorb more primer? Did the sanding leave a coarse surface that will soak up more product? Or does the wood have a tight grain sanded finely that will use less? All these factors change the quantity needed.
Use a Bona roller when applying Bona finishes. If using other rollers, they should be synthetic with a minimum 10-12mm nap. Wash rollers thoroughly before use to avoid shed fibres ending up in the finish.
When using rollers or bar applicators, hold the extension pole lightly, avoid pressing down hard, and monitor coverage as you go. When coating floor edges, stairs, or areas where a roller cannot reach, apply the finish generously with a brush rather than brushing too thinly, and roll the join between brush and roller work immediately.