Shortcuts Are Often The Longer Routes
A lack of basic knowledge on adhesive properties and the intricacies of floor construction sometimes produces disastrous results, especially when dealing with wooden floors, says Alec Stacey, technical manager at Bona:
A COMMON scenario is where unsuitable substrates are considered sound enough to bond flooring to. These can be wide ranging, but bitumen coated subfloors often cause problems. Some adhesives bond well to layers of bitumen which may have been used as the adhesive for a former floor installation, such as polyurethane or solvent-based ones.
However, always consider the age and physical condition of this layer. Bitumen as it ages becomes increasingly brittle so bonding timber to it is not the best option, especially as timber exerts great stresses as it expands and contracts as part of the normal seasonal cycle of humidity. Remember also that the bitumen may have served as the damp proof membrane (DPM), which may have been breached in the past.
Problems can also occur, even if the bitumen is intact and physically sound, due to the composition of the adhesive used on top of it.
Some adhesives (particularly silane-based ones) contain plasticizers (softeners) which can react with bitumen, causing bond failure between adhesive and bitumen.
Similar issues can arise with a substrate where flooring is already present, such as ceramic tiles, stone, or Marley tiles. It may be tempting to bond directly to such a subfloor, but you must determine the compatibility of the adhesive along with the soundness of the surface you are sticking to. In the case of Marley tiles; these may have been installed using a similar adhesive to the bitumen described above with similar issues.
Also relevant are any treatments the surface may have received during its life. Wax-based polishes or other surface dressings may have been applied along with various possible contaminants such as grease or oils which could reduce an adhesive’s bond strength. Stone floors may have been treated with impregnating resins or oils for easier cleaning. Moisture protection is also relevant with stone floors in older properties where there is no a DPM.
As a rule of thumb, I never recommend bonding timber to a substrate where it is difficult to gauge its physical integrity. This includes Marley tiles and other relatively ‘soft’ floorcoverings. Remove these and make an assessment of the subfloor. Remove bitumen where present. If well-bonded traces remain, these can be isolated by using a suitable primer, such as a two pack epoxy product.
If a moisture barrier is absent, two coats may be applied. Timber can then be bonded to this using a suitable reactive adhesive, such as silane-based or polyurethane. Modern adhesives are useful for this type of task compared to previous solvent-based systems. I have seen several failures where a contractor attempted to adhere timber to a liquid DPM or glazed ceramic tiles using a solvent-based or water-based adhesive. Once the timber exerts any stress onto the subfloor the bond fails and the timber lifts.
Even if the correct adhesive is used, preparation of the substrate is essential. When bonding to ceramic tiles or metal, a clean surface is key. The surface should be cleaned, cleaned, and cleaned again, preferably using detergents and degreasers and then abraded slightly for additional peace of mind.
Always consider the consequences of omitting an essential part of the floor’s specification. If a floor lifts due the problems described here, expensive and time-consuming remedial work will be difficult to avoid.
This article has been reproduced from the Contract Flooring Journal website. You can find them at www.contractflooringjournal.co.uk.