What overcoating does and when it makes sense
Applying a new layer of finish to an existing coated floor is a quick, cost-efficient way to extend the floor's life and avoid having to sand back to bare timber. It can also add wear resistance, change the sheen level, or give slip-resistant properties to existing or factory prefinished flooring.
Surface preparation is the key to a successful overcoat. The method required depends on the type of surface, its condition, and any previous maintenance of the floor.
When a floor is not suitable for overcoating
The floor must be in sound condition. Deep scratches, very worn areas and physical damage to the surface mean the floor is unlikely to be successfully restored by overcoating alone -- it needs a full sand.
The surface must be free from contamination. Floors previously treated with polish, wax or similar products may not be suitable for overcoating because residual contamination can prevent the new coat from adhering.
Adhesion testing -- do it every time
A trial application and adhesion test should always be carried out before overcoating. Prepare a small area in an inconspicuous spot exactly as you would prepare the full floor -- the test has to be representative of what the adhesion will be on the finished job. For extra safety, do several test patches. This is particularly relevant on large floors.
Apply finish to the test area. After a minimum of 24 hours, firmly scrape the surface with a coin. If the finish stays attached, the adhesion is satisfactory. If the surface dents but does not breach, that is acceptable. Adhesion improves slightly as the finish cures, so if the coin test is repeated after 48 hours a different result may be seen in some cases.
If the adhesion is still not acceptable after 48 hours, the floor cannot be overcoated and must be sanded to bare wood.
Process for existing coated timber floors
1. Clean the floor thoroughly using the Bona PowerScrubber and Bona Deep Clean (10% solution). Other cleaning machines may be suitable, but no residues from the cleaning process can remain on the surface -- they will affect adhesion.
2. Abrade the floor using a Bona FlexiSand with a multi-head attachment or similar. Complete the edges by hand. Select a grit that evens out the surface by removing scratches. Bona Diamond Abrasives 80 grit with Bona intermediate pads is recommended for the best abrasion with minimal visible scratch marks.
3. Clean thoroughly to remove all dust.
4. Cut back using Bona Diamond Abrasives 240 grit. Machine clean with clean water to remove dust, or use the Bona Tampico brush system. Other abrasives may be used but all dust must be removed and no visible scratches should remain.
5. Apply 1 or 2 coats of Bona Traffic HD, Traffic HD Raw, or Traffic HD Anti Slip as required.
Process for prefinished flooring
1. Clean the floor thoroughly using the Bona PowerScrubber or other suitable scrubber/drier and Bona Deep Clean (10% solution). No residues can remain on the surface.
2. Abrade the floor using a Bona FlexiSand with multi-head attachment or similar. Complete edges by hand. Bona Diamond Abrasives 240 grit with intermediate pads is recommended for the best abrasion with minimal visible scratches. Machine clean once more with clean water, or use the Bona Tampico brush system, to remove dust.
3. If the Diamond Abrasives system is not an option, the Bona Scrad system without sanding wings can be used. Move quickly and lightly across the floor to avoid swirl marks while making sure the surface is adequately prepared. The abrasion must be sufficient to achieve good adhesion as demonstrated during the adhesion tests.
4. Apply 1 or 2 coats of Bona Traffic HD, Traffic HD Raw, or Traffic HD Anti Slip as required.
Recommended equipment and product notes
Bona recommends the following equipment for the best adhesion and to reduce the chance of seeing evidence of the prep process: Bona FlexiSand with Quattro or Multi-disc plates, intermediate pads, Bona Diamond Abrasives in 80 and 240 grit, Bona PowerScrubber, and Bona Deep Clean.
Bona Traffic GO should not be used as part of an overcoating specification.
Bona finishes are non-yellowing and do not change colour from UV light. But they cannot prevent the wood itself changing colour due to tannin bleed, the movement of natural oils, or the effects of UV light.
While Bona finishes provide a sealed surface resistant to wear, scuffing and spillage, no surface-applied finish can prevent physical damage to the substrate or make the floor harder. Dents and scratches from furniture, dropped items, dog claws and similar should be managed through preventative measures.