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Adhesion and Delamination in Timber Floor Repair and Restoration

From time to time, the topic of adhesion and delamination arises as an interesting point of discussion in timber floor repair and timber floor restoration. Several factors can influence and contribute to poor adhesion and/or delamination of many coatings, including Timberseal and Tungseal.

As detailed on the Timberseal label and documented in Urethane Coatings literature, Timberseal is a fast-drying sealer for cork, particle board and all timber species. Its primary function is to seal timber cells and thereby ensure that the subsequent coat/s of polyurethane or oil-based finish remains laminated to the timber surface. Timberseal bonds to ALL timber species, even oily timbers such as Brush Box, Back Butt, Tallowwood and Spotted Gum; however, adhesion will be compromised if natural contaminants (resins/oil/wax) accumulate on the surface.

Understanding the Causes of Poor Adhesion

Ageing or acclimatisation of timber flooring

Sap is the blood or juice of timber, which contains a broad mixture of chemicals as detailed above as natural contaminants. Regardless of the time from felling the tree to coating the subsequent timber, some residual sap will always remain in the timber. Accordingly, over time a portion of this sap will migrate.

Atmospheric conditions

Relative humidity and moisture in the air relative to temperature – constantly change. Timber expands and contracts in cycles of taking up and releasing moisture. After each cycle, contaminants from residual sap condense on the timber surface.

Temperature and Climate

Temperature and climate influence the time and the rate at that residual sap continues to migrate from within timber to the surface. During summer, higher temperatures force timber cells to expand, assisting sap to migrate. Direct sunlight warms the surface it is shining onto, further expanding cells and slightly reducing pressure. Sap moves from the cooler high pressure within the timber to the warmer lower pressure on the timber surface.

Natural contamination

Most timber types have the potential to leave natural contaminants (resins/oils/waxes) on the surface to be coated. Oily timbers, notably Brush Box, Black Butt, Tallowwood and Spotted gum, are more prone to these contaminants and have acquired a reputation as ‘difficult’.

Surface preparation

Overly fine sanding hardwoods will polish or burnish the surface and close the grain (cells on the timber’s surface), preventing the penetration of the first coat.

Artificial contamination thinning

Timberseal should not be thinned - thinners compromise the physical properties (reduces flexibility = greater edge bonding) and assists oil migration from within the timber to its surface. Thinners should only be used if the timber seal has thickened.

Solutions to Improve Adhesion

Removal of Natural Contaminants

Generally, removal is best completed by dampening a rag with a cleaning solvent (dampen with mineral turpentine when coating with Tungseal or modified oils) and wiping down the surface. Ensure the rag is thoroughly rinsed or replaced with a clean rag every 4 – 6 months. In this scenario, removal should be repeated between the first and second coats and the second and third coats. Furthermore, this procedure must be followed when re-coating oily timbers (re-coating means additional coats onto timber that has been coated previously – regardless of how much time elapsed since the last coat.) Timber, particularly oily hardwoods, should be sanded with nothing finer than 120 grit paper or equivalent and not burnished. The grain must be left sufficiently open to allow penetration of the first coat.

Artificial contaminants

Thinners should only be used if timber seal has thickened. Furthermore, this procedure must be followed when re-coating oily timbers. High natural oil and wax (antioxidant) levels in some timbers will prolong the curing process. This is particularly applicable to oil-based finishes that cure by the process of ‘autoxidation’ as the oils and antioxidants significantly slow the process of oxygen absorption, inhibiting curing.

In circumstances of slow curing, natural oil has time to accumulate on the surface. Oil between coats can significantly reduce adhesion and contribute to delaminating when the subsequent coat is applied. When re-coating high traffic and/or high-stress (e.g. surfaces subjected to dragging furniture) oily timbers, extra attention should be given to identify adhesion/lamination damage, and if present, repair damage by sanding before re-coating.

Timber Vision Concept is equipped with the proper knowledge, expertise, tools and techniques to provide quality timber floor repair. Contact us today for all your timber flooring Gold Coast needs!


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