There are major changes happening with the supply of H3 rougher header (unprimed) treated pine.
Traditionally in Australia most H3 treated pine has had a CCA preservative treatment and been structurally rated F7 (or F5 in some wider sections).
Now Australian manufacturers are only producing H3 treated pine that has a LOSP treatment and is structurally rated MGP10.
In the December 2015 edition of the Easy Times we advised that NHS would start moving from a F7 structural rating to a MGP10 structural rating for H3 rougher header treated pine up to 190 x 45mm section sizes.
The next phase of that transition is about to commence. From 1 March 2016, NHS Cardiff will start selling H3 rougher header treated pine with a LOSP treatment and a MPG10 structural rating. NHS Lambton will transition to the same as it sells out of CCA treated timber.
What is the difference between F7 and MGP10 structural rating?
F7 is a visual stress grading system and MGP10 is a machine stress grading system. There are no hard and fast rules as to what is superior to the other in terms of spans. Refer to the current Australian Standard AS1684 span tables for each structural rating. NHS staff in-store may also be able to assist with span information.
Each length of timber has its structural rating stamped on it. The wider sections (240mm and wider) that are currently F5 are expected to remain F5. Treated pine posts are expected to remain F7. H2F framing pine (blue pine) is already MGP10 graded.
What is the difference between CCA and LOSP preservative treatments?
Both will be treated to H3 hazard level which is suitable for outside, above ground exposure. Both will be a green colour, though there may be some colour variation between the two.
Both have relative strengths to the other. For example, LOSP (Light Organic Solvent-borne Preservative) treated timber is less likely to swell or distort than CCA (Copper Chrome Arsenate) treated timber due its different treatment process. On the other hand with LOSP it is more essential that all exposed surfaces resulting from cutting, notching or drilling of the timber during installation are resealed on-site with some form of preservative, such as Enseal. Furthermore, as with any treated timber product used in weather-exposed applications, a post-treatment protective coat must be applied, such as paint or a similar film-forming finish. Some primers/surface coatings are not compatible with LOSP. NHS has suitable LOSP-compatible primers available, ask our staff for assistance.
Treated pine decking is usually ACQ treated and this will continue, though it is also available with LOSP treatment. H4 rougher header treated pine posts (90 x 90mm & 90 x 70mm) which are suitable for in-ground use, will remain CCA treated. Treated pine sleepers (H4) will continue to be CCA treated, though ACQ treated sleepers are available as a special order.
A NHS staff member will be happy to assist if you are unsure of the preservative treatment of a length of timber.
Current SDS for TREATED PINE H3 F7/MGP10 products is available on the NHS online store.