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.