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Finishes for external timber surfaces

May 11, 2015

While internal timber surfaces are able to be readily & satisfactorily coated with a wide variety of paints, stains & oils, the performance of exterior finishes, particularly on timber surfaces exposed to the elements of UV light, heat, cold, water, dust & grit, is an entirely different matter.

Dark vs Light

External dark coloured timber projects that are subjected to full sun exposure during Queensland's hot summer months can lead to shrinkage & distortion issues. This can occur to either naturally dark timber (oiled or clear finished) or dark coloured stained or painted timber.

If you are painting timber cladding, fences, decks or furniture that are fully exposed to outdoor weather conditions go lighter instead of darker. Dark coloured surfaces in hot sun exposure can reach temperatures of exceeding 70 Degrees Celsius. This will result in the timber 'cooking' & drying out to under 8% moisture content. Shrinkage & shrinkage distortion can result, and even correctly seasoned timber, may end up with unacceptable appearances.

Darker colours absorbing more solar radiation than light colours will also deteriorate the finish of the timber rapidly. Light colours, particularly white, reflect the maximum amount of UV light possible & provide the best protection to both the timber & paint film.

Fig: Distortion in dark coloured timber exposed to full sun

These types of performance issues can be minimised by following Timber Queensland's recommendations, including the use of appropriate robust fixings, & light or pale coloured stains or paints

Resource: Timber Queensland

Find Out More Below:

Finishes For Exterior Timber 

Finishing Timber Externally 

Outdoor Timber Performance 

Resin or tannin bleed from pine

May 6, 2015

Whilst recently performing a six month inspection, a client of ours noticed the knots in his timber were leaching out. To assist in determining the ultimate cause of this situation, 5 Star Timbers worked with a Timber Queensland Technical Consultant & one of Taubmans paint experts to solve the case & assist in finding a solution.

So what is Resin / Knot Bleed?

All timber species contain naturally occurring extractives of one type or another. These include resins, gum & tannins. It is not uncommon for some of these extractives to 'bleed' through paint finishes, particularly where initial moisture levels in the timber may be high, where high temperatures mobilise the extractives & / or where timber has not been 'sealed' with a quality oil-based primer.

'Knotty' softwoods including hoop, cypress & other pinus species can have high levels of resins associated with the knots, particularly knots that are dark coloured.

Fig. An example of knot bleed in LVL

To minimise the potential for resin bleed from knots, Timber Queensland's technical information recommends knots be sealed with a two pack polyurethane prior to application of an oil based primer. Sealing knots with a silver frost paint or shellac has also been found to have some benefits, although not as effective as polyurethane.

Where knot bleed has occurred such as above, scrape off any excess resin, clean with white spirits, lightly sand, apply a knot sealer, prime spots with an oil based primer & apply top coats. There is, however, no guarantee it may not reappear.

Source: Timber Queensland Technical Update - April 2015

Grab more information from the following links:

Timber Queensland Finishes For Exterior Timber 

Timber Queensland Treated Pine Cladding 

Taubmans D682 Prep Right Traditional Undercoat 

Treated LVL External Guidelines 

Do you have timber questions that you would like help with?

Check out the Technical Data Sheets available on the 5 Star Timbers website
or give us a call on 07 3386 0595 or 07 3386 1055 & we'll happily help you out.