Tag Archives: lumber treatment

Incising Lumber


My former wife (mother of my two youngest children – Allison and Brent), was by training an RDH (Registered Dental Hygienist). In order to keep her registration current, she had to obtain CEUs (Continuing Education Credits). One way to generate CEUs was to attend the annual state dental convention.

One year I went along with her and as we perused the trade show floor, the assumption was somehow made of me being a dentist – so I received lots of attention. Also tons of free stuff – I don’t think I needed to purchase a tooth brush, tooth paste or dental floss for the next decade!

Other than my annual visits to the dentist, about the only thing I remotely knew in regards to teeth were the incisors are the front four teeth on the top and bottom.

With my tremendous knowledge of incisors – I was able to easily translate to incising of lumber.

For those in the east and south – you may have never seen pressure preservative treated lumber which has been incised. Most treated lumber in those regions is Southern Yellow Pine – which is highly treatable (think of it as being a chemical sponge).

Travel west and north, the lumber species of choice for pressure treating is grade stamped as Hem-Fir. Hem-Fir is not a species unto itself, it is a lumber species “group” which includes California Red Fir, Grand Fir, Noble Fir, Pacific Silver Fir, Western Hemlock and White Fir.

Incised LumberDifficult-to-treat (refractory) lumber species, such as Hem-Fir, must be incised prior to preservative treatment to meet minimum penetration requirements for preservative-treated wood. Incising is a pretreatment process in which small incisions or slits are punched into the wood. To me, the resultant product looks as though the lumber has been walked on by someone wearing golf shoes!

Incising increases preservative retention and penetration during the treating process by increasing the amount of exposed, easily penetrated end-grain and by decreasing the side-grain surface area. While incising has been used since the 19th century, the process appears to have developed casually with little consideration given to optimizing the process to maximize preservative treatment and minimize strength loss. While AWPA (American Wood Preservers Association) standards require incising, they do not define or recommend what type, how deep, or how many incisions are required. Generally, it appears the more effective an incising pattern is in achieving preservative penetration, the more it reduces strength.

AF&PA’s National Design Specification® (NDS®) for Wood Construction includes provisions for the downward adjustment of lumber strength characteristics for incised lumber by use of an Incising Factor known as Ci. Referenced design values are multiplied by Ci when dimension lumber is incised parallel to grain a maximum depth of 0.4”, a maximum length of 3/8”, and a density of incisions up to 1100 per square foot.

E values are to be multiplied by 0.95, while other values (with the exception of compression perpendicular to the grain of the wood) are multiplied by 0.80.

Sound engineering design of incised lumber (which includes pole building columns) take into account these strength reductions.

If you see Hem-fir and it has all these little cuts – don’t panic. It just means it’s been incised for adequate infiltration of chemical treatment. This ensures preserving a longer life of whatever you are building, be it a deck, garage or even a new pole building house.

Pressure Treated Lumber: Copper Azole

Most of us – both those who specify wood treating and those who use it, look upon the litany of possible wood treatments like alphabet soup.

Lumber Treatment PlantOr maybe more like Scrabble – where my 19 year old daughter always seems to either draw the right letters, or make otherwise incomprehensible words (to her Dad anyway) out of a total jumble.

Copper azole preservative (denoted as CA-B and CA-C under American Wood Protection Association/AWPA standards) is a major copper based wood preservative which has come into wide use in Canada, the USA, Europe, Japan and Australia following restrictions on CCA (Chromated Copper Arsenate). Its use is governed by national and international standards, which determine the volume of preservative uptake required for a specific timber end use.

Copper azole is similar to ACQ (Alkaline Copper Quaternary – read more at https://www.hansenpolebuildings.com/blog/2012/06/acq-treated-lumber/) with the difference being the dissolved copper preservative is augmented by an azole co-biocide like Tebuconazole instead of the quat biocide used in ACQ. The azole co-biocide yields a copper azole product which is effective at lower retentions than required for equivalent ACQ performance.

Here in North America it is marketed widely under the Wolmanized brand in North America.

The AWPA standard retention for CA-B is 0.10 lb/ft3 for above ground applications (UC-3) and 0.21 lb/ft3 (pounds of pressure treating chemical retained per cubic foot of wood) for ground contact applications (UC-4A). Type C copper azole, denoted as CA-C, has been introduced under the Wolmanized brand. The AWPA standard retention for CA-C is 0.06 lb/ft3 for above ground applications and 0.15 lb/ft3 for ground contact applications. Both CA-B and CA-C require a retention of 0.31 lb/ft3 in order to meet the IBC Code requirement of a UC-4B for structural in ground use in post frame buildings.

For detailed information on pressure treated lumber for structural in ground use: https://www.hansenpolebuildings.com/blog/2012/10/pressure-treated-posts-2/

The copper azole preservative incorporates organic triazoles such as tebuconazole or propiconazole as the co-biocide, which are also used to protect food crops. The general appearance of wood treated with copper azole preservative is similar to CCA with a green coloration.

Every piece of pressure treated lumber will have a tag on it stating what treatment chemical was used and to what level it was treated.  Be sure for look for these tags.  Don’t get fooled by companies stating they use wood treated for in ground use, only to be sent lumber with inadequate treatment.  Your future question to me will be “why did my posts rot?”  With the right chemicals, and the right level of treatment, your letter will have two words, “Thank You.”