Kawa poplar timber - properties and market opportunities

 

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Results

Trees and logs

Heartwood content

As height in tree increased, percentage of heartwood decreased (Figure 1).

Figure 1: Heartwood percentage according to tree height for 16 trees.

Typically low heartwood content for 28-year-old Kawa poplar headlogs

Sawn timber testing

Sawn timber recovery

The 43 logs that were processed had a total volume of 14.2 m³. These logs were processed into 7.6 m³ of nominal sized sawn boards, yielding 53% conversion to sawn timber.

There was a statistically significant (P= 0.00015) trend for increased sawn timber recovery as log diameters increased (Figure 2).

Figure 2: Sawn timber recovery according to diameter

Grade recoveries

Recovery of graded timber was 93.9% based on the “best grade” method (Table 2), with graded board length averaging 2.6m (Table 4). End splits and knot/pruning defects were the most significant cause of degrade. Under the “long-length” grading method, recovery of graded timber increased to 94.7% due to a reduction in degrade due to knots and pruning wounds (Table 2), with graded board length averaging 2.8m (Table 4).

Table 2: Recoveries of graded timber and defects as percentages of sawn timber volume for the two grading methods.

Outturn category	Percentage of sawn timber in category by grading method
	"Best"	"Long length"
Graded timber	93.9	94.7
Defect - End splits	2.4	2.4
Defect - Knots and pruning wounds	3.2	2.4
Defect - Crook and bow	0.5	0.5
Defect - Pith	<0.1	<0.01
Total	100	100

The volume docked due to knots and pruning wounds was broken down into different categories, which showed that the most common downgrade was due to large spike knots, followed by large knots and then pruning wounds (Table 3).

Table 3: Frequency of different categories of knot and pruning wound defect/degrade

Knot/pruning wound defect category	Percent total volume
Large knot defect	20%
Large spike knot defect	33%
Knot degrade	12%
Spike knot degrade	3%
Large pruning wound defect	12%
Pruning wound degrade	19%
Total	100%

Most of the recovered timber volume was assigned to the “clears” grade (Table 4). Under the “best grade” method, 74% of the recovered volume was assigned to the “clears” grade with the average length of clear sections being 2.5 m (range 0.7-4.0 m). 

The proportion of recovered volume assigned to the clears grade decreased from 74% for the "best grade" method to 64% for the "long length" grading method, but the average length of clear sections increased from 2.52m for "best grade" method to 2.6m for "long length" grade method. The "long length" method resulted in greater proportions of recovered volume being assigned to the cladding and structural grades, and the average board lengths for these grades being 0.3 m and 0.5 m longer, respectively, than under the “best” grading method (Table 4).

Table 4: Overall recovery of different timber grades and the average board length from application of the two different grading methods.

Grade	"Best" grading method		"Long length" grading method
	Grade recovery (%)	Average board length (m)	Grade recovery (%)	Average board length (m)
Clears	74	2.52	64	2.6
Cladding	17	2.96	23	3.3
Structural	9	2.71	13	3.2
Overall	100	2.6	100	2.8

Strength and stiffness

Characteristic values - Ingrade solid timber Kawa

The characteristic values of modulus of elasticity and modulus of rupture were 10.58 GPa and 45.90 MPa, respectively (Table 5), which were sufficient for the timber to be assigned to the SG10 strength class. The bending strength exceeded the requirement for higher strength classes, with the assignment to SG10 determined by bending stiffness (modulus of elasticity). Scion's report is available here »

Table 5: Kawa Poplar Characteristic Bending Strength/Stiffness & Density Properties (90 x 45)

	Bending Stiffness MoEj (GPa)	Bending Strength MoRj (MPa)	Density at Test kg/m3	Nominal Density kg/m3
Mean	10.76	59.13	475.93	429.73
Minimum	6.88	33.37	395.15	358.13
Maximum	13.04	74.34	566.88	511.2
Range	6.16	40.97	171.74	153.08
Standard Deviation	1.33	11.25	35.96	32.36
Coefficient of Variation	12.38%	19.02%	7.56%	7.53%
Count	31	31	31	31
Characteristic Strength (MPa)		45.09
Characteristic Stiffness (GPa)	10.58
Characteristic Density at Test (kg/m3)			471.2
Characteristic Nominal Density (kg/m3)				425.7
Assigned Grade	SG10	SG10

 

Table 6: Statistical Summary of Density and Moisture content results (90 x 45)

	Moisture Content %	Density at Test kg/m3	Nominal Density kg/m3
Mean	10.75	475.93	429.73
Minimum	8.73	395.15	358.13
Maximum	12.13	566.88	511.20
Range	3.40	171.74	153.08
Standard Deviation	0.65	35.96	32.36
Coefficient of Variation	6.04%	7.56%	7.53%
Count	31	31	31

Figure 3: Modulus if elasticity vs modulus of rupture, No. 1 framing solid timber 90mm x 45mm.

Figure 4: Modulus if elasticity vs density, No. 1 framing solid timber 90mm x 45mm

Figure 5: Modulus of rupture vs density, No. 1 framing solid timber 90mm x 45mm

Characteristic values - Clears glulam Kawa

The characteristic values for modulus of elasticity and modulus of rupture were 11.0 GPa and 32.6 MPa, respectively, which were sufficient for the timber to be assigned to the SG10 strength class. The bending strength exceeded the requirement for higher strength classes, with the assignment to SG10 determined by bending stiffness (modulus of elasticity). Scion's report is available here »

Kawa poplar glulam being tested, showing the four laminates making up the beam.

Table 7: Kawa Poplar Glulam Characteristic Properties (80 x 45)

	Bending Stiffness MoEj (GPa)	Bending Strength MoRj (MPa)	Density at test (kg/m3)
Mean	11.03	60.71	494.77
Minimum	9.71	21.27	443.77
Maximum	12.24	80.35	551.96
Range	2.53	59.08	108.19
Standard Deviation	0.60	15.01	24.72
Coefficient of Variation	5.47%	24.72%	5.00%
Count	32	32	32
Characteristic Strength (MPa)		32.6
Characteristic Stiffness (GPa)	11.0
Characteristic Density at Test (kg/m3)			491.7
Assigned Grade	GL10	GL12

 

Table 8: Statistical Summary of Density and Moisture content results

	Moisture Content %	Density at Test kg/m3	Nominal Density kg/m3
Mean	12.73	494.77	438.91
Minimum	11.56	443.77	392.77
Maximum	17.37	551.96	490.43
Range	5.81	108.19	97.66
Standard Deviation	0.95	24.72	21.43
Coefficient of Variation	7.47%	5.00%	4.88%
Count	32	32	32

Typical failure starting with Finger-joint failure on tension edge then progressing through the inner finger-joints. This beam had a MoE of 10.86 GPa and MoR of 71.46 MPa.

Failure starting with Finger-joint failure on tension edge. This beam had a MoE of 10.78 GPa and MoR of 31.92 MPa.

Typical Tension failure in Clearwood also with compression wrinkle in Clearwood. This beam had a MoE of 11.25 GPa and MoR of 76.81 MPa.

Characteristic values - Ingrade thermally modified Kawa

The characteristic values of modulus of elasticity and modulus of rupture were 9.23 GPa and 9.33 MPa, respectively. Although characteristic stiffness (9.23 GPa) was sufficient for a grade of SG8, characteristic bending strength of 9.33 MPa was not sufficient for a grade of SG 6 (a requirement of 10 MPa). No. 1 framing grade Thermowood 230 poplar did not have sufficient strength to be assigned to a SG strength class. Scion's report is available here »

Thermally modified Kawa poplar samples after testing.

Table 9: Thermally modified Kawa Poplar Characteristic Properties (90 x 45)

	Bending Stiffness MoEj (GPa)	Bending Strength MoRj (MPa)	Density at test (kg/m3)
Mean	9.35	26.67
Minimum	6.89	10.18
Maximum	10.60	58.08
Range	3.71	47.90
Standard Deviation	0.89	11.77
Coefficient of Variation	9.51%	44.13%
Count	29	30
Characteristic Strength (MPa)		9.33
Characteristic Stiffness (GPa)	9.23
Characteristic Density at Test (kg/m3)			386.8
Assigned Grade	SG8	Reject

 

Table 10: Statistical Summary of Density and Moisture content results

	Moisture Content %	Density at Test kg/m3	Nominal Density kg/m3
Mean	5.70	389.19	368.19
Minimum	5.24	343.60	325.20
Maximum	6.32	437.42	412.57
Range	1.09	93.82	87.37
Standard Deviation	0.22	26.14	24.68
Coefficient of Variation	3.80%	6.72%	6.70%
Count	30	30	30

Small clears testing

Modulus of elasticity of the 140 small, defect-free specimens tested ranged from 5.65 GPa up to 11.17 GPa, with a mean of 9.02 GPa. Modulus of elasticity was significantly higher in specimens cut from the outer position in a log and increased with log position up the stem, with the difference in modulus of elasticity between specimens cut from the inner and outer positions greatest in the butt log. Modulus of rupture and nominal density also exhibited similar within-tree patterns of radial and longitudinal variation.

H1.2 Boron preservative trials

Retention and penetration - water-based diffusion

Boric acid equivalent (BAE) test results ranged from 0.60% (m/m) up to 1.98%, with a mean of 1.03%. These values all exceeded the threshold of 0.40%, which meant that all sixteen samples passed the H1.2 boron retention requirements as per NZS 3640:2003. The samples tested achieved full cross section retention of the preservative, not just retention in the sapwood zone. All samples also passed the penetration spot test as per NZS 3640:2003.

Table 11: Kawa H1.2 boron penetration and retention test results, water-based diffusion

Sample	Penetration spot test	Retention analysis BAE %m/m (critical level 0.4000)	Retention analysis outcome
7-1-1	Pass	1.03	Pass
7-1-2	Pass	1.15	Pass
13-2-1	Pass	0.87	Pass
16-1-1	Pass	0.72	Pass
17-1-1	Pass	1.12	Pass
7-1-1	Pass	0.88	Pass
7-1-2	Pass	0.95	Pass
9-1-1	Pass	0.76	Pass
9-1-2	Pass	0.60	Pass
11-2-1	Pass	0.91	Pass
11-2-2	Pass	1.10	Pass
4-1-1	Pass	0.93	Pass
14-1-1	Pass	1.98	Pass
4-3-1	Pass	0.85	Pass
17-1-2	Pass	1.65	Pass
15-2-1	Pass	0.97	Pass

Retention and penetration - Monoethanolamine-based diffusion

Boric acid equivalent (BAE) test results ranged from 0.37% (m/m) up to 0.65%, from this small sample size. 

Table 12: Kawa H1.2 boron penetration and retention test results, monoethanolamine-based diffusion

Sample	Penetration spot test	Retention analysis BAE %m/m (critical level 0.40)	Retention analysis outcome
BAX 9-1-1 dressed 90x45	Pass	0.41	Pass
BAX 9-1-2 dressed 90x45	Pass	0.37	Fail
BAX 9-1-3 not dressed 100x50	Pass	0.54	Pass
BAX 17-1-2 not dressed 100x50	Pass	0.65	Pass

Durability performance - Scion Framing Trial

Scion produced a 12-month durability performance exposure report: The decay resistance of Poplar in an accelerated framing test: The condition of samples after 12 months exposure.

Table 13a: Summary of assessment results after twelve months exposure

Group and treatment	Mycelium (Lower rating is better)		Decay - Surface (Higher rating is better)		Decay - Joint (Higher rating is better)		Mould (Lower rating is better)
		Op1	Ax1	Op	Ax	Op	Ax	Op	Ax
Poplar, untreated	2.9	3.3	8.6	6.2	8.7	6.8	3.1	2.9
Poplar, boron treated	1.0	1.0	10.0	10.0	10.0	10.0	1.7	1.7
Radiata pine, untreated - Supplied from Northland	4.7	4.5	9.2	6.0	8.9	5.4	2.5	2.7
Radiata pine, untreated - Sourced from Central North Island	4.1	3.4	7.9	7.7	8.2	7.6	3.2	3.0
Radiata pine, boron treated	1.0	1.0	10.0	10.0	10.0	10.0	2.0	2.1

¹ Op and Ax represent different ends of the “I-frame” samples with feeder blocks inoculated with Oligoporous placenta and Antrodia xantha.

Scion produced a 24-month durability performance exposure report: The decay resistance of Poplar in an accelerated framing test: The condition of samples after 24 months exposure.

Table 13b: Summary of assessment results after twenty-four months exposure

Group and treatment	Mycelium (Lower rating is better)		Decay - Surface (Higher rating is better)		Decay - Joint (Higher rating is better)		Mould (Lower rating is better)
		Op1	Ax1	Op	Ax	Op	Ax	Op	Ax
Poplar, untreated	4.4	4.5	1.2	0.6	0.8	0.4	4.6	4.1
Poplar, boron treated	1.1	1.1	10.0	10.0	10.0	10.0	1.6	2.0
Radiata pine, untreated - Supplied from Northland	5.7	5.0	0.4	0.4	0.4	0.6	2.4	3.1
Radiata pine, untreated - Sourced from Central North Island	5.6	3.9	1.3	3.2	0.6	2.6	4.3	4.3
Radiata pine, boron treated	1.3	1.0	10.0	10.0	10.0	10.0	2.6	3.0

¹ Op and Ax represent different ends of the “I-frame” samples with feeder blocks inoculated with Oligoporous placenta and Antrodia xantha.

Thermal modification

Some distortion resulted from the thermal modification process. Crook and cupping were evident in some boards, especially in the 200mm wide boards. The 200 mm width boards cupped more than the 150mm width boards, sometimes as deep as 4-5mm from edge to edge. Distortion was severe around large knots, which required docking, that distortion often extending away from the knots and into the residual board. Knots tended to check severely, and these checks usually extended through the wood from one surface to the other.

Shrinkage was high, nominally sized 200mm x 50mm boards shrunk to 45-48mm x 180-190mm.

See photographs of the thermally modified timber in this study here »

DMDHEU modification

Cross section Nitrogen results for DMDHEU-modified Kawa poplar

Board	Sample #	Nitrogen % - Heartwood	Nitrogen % - Sapwood
P1	1	5.8	3.9
P1	2	4.9	3.9
P1	3	5.1	3.9
P2	1	5.8	-
P2	2	5.6	-
P2	3	5.5	-
P3	1	-	4.4
P4	1	-	3.6
P5	1	-	3.9

Test results are available in the Scion report.

Appearance products

The sawn poplar timber from this study was used to create a range of appearance products.

Poplar table

Kawa poplar table produced from research timber.

Kawa poplar table showing attractive timber patterning.

Poplar door

Exterior door made with thermally modified Kawa poplar (inlay panels are elm).

Poplar test cabin

The poplar test cabin was transported to the NRC Mata nursery site in August 2022.

Thermally modified uncoated Kawa poplar weatherboards, corner boxes, fascia, window/door joinery and window surrounds. The light-coloured weatherboards in the fifth row from the bottom is H3.2 micronised copper azoles (MCA) treated Kawa poplar control.

Kawa poplar glulam beam and solid timber rafters, with 200mm TG&V sarking

See photographs of the poplar test cabin being constructed here »

Poplar floor

The coating with non-yellowing epoxy followed by water-based polyurethane was very successful, both in terms of application and appearance. The floor appeared to be significantly harder than if only coated with polyurethane, but hardness was not tested.

Poplar floor in the test cabin. The surface of this floor was successfully hardened using epoxy. Moisture level was too high at the time of laying and the floor "opened up" with slight gaps between the boards. This should be easily remedied.

Structural poplar

Framing and joists nailed well and were much like radiata pine to handle. Some boards had bow or crook which the builder rejected, then used for nogs and short lengths. Joists were stiff and rafters were attractive, complementing the poplar sarking. The laminated clearwood beam became a feature and joins between laminates were barely noticeable because of the indistinct latewood.

Poplar sarking

The sarking remained stable in service and didn't shrink noticeably. The water-based satin polyurethane didn't yellow the attractive pale colour and timber grain, but also didn't bring out much lustre in the grain.

Poplar weatherboards

During the first summer the micronized copper azoles (MCA) H3.2 treated weatherboards experienced some cupping, whereas the thermally modified weatherboards remained very stable and without any noticeable cupping or movement in service. Because the cladding was not coated, during the first summer the surface began to silver. The thermally modified cladding silvered faster than the MCA treated cladding into the classical silver colour seen in cedar weatherboards.

Thermally modified poplar window and door joinery

The thermally modified window and door joinery began silvering at the same rate as the thermally modified cladding. No movement was observed during the first summer.

Preservative treatment

A range of timber preservative treatment tests were undertaken. These included chrome copper arsenic (CCA) H4 treated posts, CCA H3.2 treated sawn timber, and MCA H3.2 treated weatherboards.

CCA H4 treated Kawa posts

Four quarter round posts, four round posts and two round strainers were tested for retention and penetration as per NZS 3640:2003.

Table 14: H4 CCA treated Kawa posts and strainers

Sample name	Description	Sapwood %	Penetration spot test	Arsenic %m/m	Chromium %m/m	Copper %m/m	Total Active Elements (TAE) %m/m (Critical level 0.72)	Retention Analysis Outcome
1	Round post, radiata control	90	Pass	0.479	0.548	0.297	1.32	Pass
2	Round post, radiata control	90	Pass	0.461	0.526	0.282	1.27	Pass
3	Round post, Kawa	90	Fail	0.226	0.227	0.126	0.58	Fail
4	Round post, Kawa	90	Fail	0.215	0.211	0.116	0.54	Fail
5	Round strainer, Kawa	85	Fail	0.313	0.319	0.178	0.81	Pass
6	Round strainer, Kawa	75	Fail	0.258	0.265	0.149	0.67	Fail
7	Quarter round post, Kawa	90	Pass	0.224	0.231	0.126	0.58	Fail
8	Quarter round post, Kawa	90	Fail	0.258	0.264	0.151	0.71	Fail
9	Quarter round post, Kawa	100	Pass	0.270	0.279	0.159	0.71	Fail
10	Quarter round post, Kawa	90	Fail	0.258	0.263	0.141	0.66	Fail

Test outcome: Samples 1 and 2 (radiata controls) met the requirements of the specifications for H4 CCA treated roundwood as per NZS 3640:2003. Samples 3-10 (Kawa poplar) did not meet the requirements of the specifications for H4 CCA treated roundwood as per NZS 3640:2003.

Figure 6: The VBRT test with ammonia buffer (heartwood/sapwood colour test) shows heartwood as red in the radiata samples (1 and 2) but did not determine the poplar heartwood boundary, which was guessed based on general colour of the samples. 

Figure 7: The penetration test shows the presence of preservative, which is only required in sapwood.

H4 CCA treated square poplar posts

Samples of sawn poplar posts (air dried prior to treatment) supplied by Ian Wilson all passed the required CCA retention as per NZS 3640:2003 based on full cross section analysis (Table 15).

Table 15: H4 treated square sawn poplar posts

Sample	Retention Analysis Arsenic %m/m	Retention Analysis Chromium %m/m	Retention Analysis Copper %m/m	Retention Analysis TAE %m/m (Critical Level 0.72)	Retention Analysis Outcome
1	0.265	0.308	0.174	0.75	Pass
2	0.587	0.635	0.383	1.61	Pass
3	0.399	0.402	0.266	1.07	Pass
4	0.593	0.626	0.367	1.59	Pass
5	0.297	0.332	0.215	0.84	Pass
6	0.329	0.356	0.225	0.91	Pass
7	0.601	0.637	0.382	1.62	Pass
8	0.272	0.319	0.177	0.77	Pass
9	0.275	0.301	0.184	0.76	Pass
10	0.406	0.406	0.230	1.04	Pass
11	0.335	0.362	0.200	0.90	Pass
12	0.308	0.350	0.206	0.86	Pass
13	0.602	0.602	0.371	1.57	Pass
14	0.303	0.315	0.179	0.80	Pass
15	0.311	0.324	0.196	0.83	Pass

No analysis of penetration was provided but it is assumed all samples passed this test based on the photo provided by IVS labs:

Figure 8: Evident from this photograph is that some of these posts (e.g., sample 13) contained heartwood, which was penetrated by the preservative.

H3.2 preservative treated sawn poplar

H3.2 CCA preservative treated 30mm poplar

Identifying poplar sapwood using the VBRT colour test method was largely unsuccessful. However, an attempt was made to mark the heartwood/sapwood boundary (Figure 9).

Figure 9: Assumed heartwood (marked "x") and sapwood.

Sapwood percentage was then estimated. Where no sapwood was present the Penetration spot test was automatically passed. Where sapwood was present, only this was assessed for evidence of penetration based on the colour of the penetration test (Figure 10).

Figure 10: Penetration test

Where sapwood was present, only this was then also analysed for retention (Table 16).

Table 16: H3.2 30mm poplar decking retention analysis of "sapwood"

Sample	Test number	Sapwood %	Penetration spot test	Retention analysis Arsenic %m/m	Retention analysis Chromium %m/m	Retention analysis Copper %m/m	Retention analysis TAE %m/m (Critical level 0.37)	Retention analysis Outcome
1a	1	40	Pass	0.211	0.233	0.117	0.56	Pass
1b	2	50	Pass	0.223	0.229	0.125	0.58	Pass
1c	3	50	Pass	0.222	0.230	0.122	0.57	Pass
1d	4	30	Pass	0.215	0.252	0.116	0.58	Pass
1e	5	80	Pass	0.256	0.285	0.136	0.68	Pass
1f	6	25	Pass	0.247	0.258	0.140	0.64	Pass
1g	7	30	Pass	0.222	0.227	0.129	0.58	Pass
1h	8	25	Pass	0.218	0.254	0.115	0.59	Pass
2a	9	40	Pass	0.238	0.255	0.134	0.63	Pass
2b	10	40	Pass	0.230	0.235	0.131	0.60	Pass
2c	11	40	Pass	0.258	0.274	0.150	0.68	Pass
2d	12	20	Pass	0.202	0.223	0.111	0.54	Pass
2e	13	45	Pass	0.179	0.202	0.091	0.47	Pass
2f	14	30	Pass	0.183	0.191	0.102	0.48	Pass
2g	15	20	Pass	0.182	0.184	0.101	0.47	Pass
2h	16	15	Pass	0.187	0.194	0.104	0.48	Pass
3a	17	0	Pass	N/A	N/A	N/A	N/A	Pass
3b	18	0	Pass	N/A	N/A	N/A	N/A	Pass
3c	19	0	Pass	N/A	N/A	N/A	N/A	Pass
3d	20	100	Fail	0.130	0.141	0.068	0.34	Fail
3e	21	25	Fail	0.214	0.229	0.129	0.57	Pass
3f	22	40	Fail	0.187	0.194	0.112	0.49	Pass
3g	23	25	Fail	0.151	0.160	0.085	0.40	Pass
3h	24	25	Fail	0.135	0.147	0.071	0.35	Fail

Because the VBRT colour test was unable to accurately determine the heartwood sapwood boundary, retention analysis was repeated, assuming the full cross section of every sample was 100% sapwood (Table 17).

Table 17: H3.2 30mm poplar decking full cross section retention analysis

Sample	Test number	Retention analysis Arsenic %m/m	Retention analysis Chromium %m/m	Retention analysis Copper %m/m	Retention analysis TAE %m/m (Critical level 0.37)	Retention analysis Outcome
1a	1	0.193	0.219	0.105	0.52	Pass
1b	2	0.206	0.217	0.114	0.54	Pass
1c	3	0.202	0.215	0.111	0.53	Pass
1d	4	0.202	0.229	0.109	0.54	Pass
1e	5	0.216	0.247	0.117	0.58	Pass
1f	6	0.231	0.239	0.132	0.60	Pass
1g	7	0.205	0.212	0.113	0.53	Pass
1h	8	0.197	0.224	0.107	0.53	Pass
2a	9	0.254	0.273	0.150	0.68	Pass
2b	10	0.239	0.245	0.138	0.62	Pass
2c	11	0.294	0.289	0.176	0.76	Pass
2d	12	0.270	0.291	0.162	0.72	Pass
2e	13	0.215	0.234	0.123	0.57	Pass
2f	14	0.238	0.253	0.136	0.63	Pass
2g	15	0.255	0.260	0.145	0.66	Pass
2h	16	0.264	0.263	0.153	0.68	Pass
3a	17	0.023	0.028	0.010	0.06	Fail
3b	18	0.090	0.096	0.045	0.23	Fail
3c	19	0.116	0.122	0.064	0.30	Fail
3d	20	0.127	0.143	0.070	0.34	Fail
3e	21	0.135	0.142	0.080	0.36	Fail
3f	22	0.121	0.127	0.072	0.32	Fail
3g	23	0.088	0.094	0.050	0.23	Fail
3h	24	0.085	0.092	0.047	0.22	Fail

H3.2 CCA preservative treated 20mm Kawa poplar decking

Samples 10 and 11 were two samples from the one radiata control board from the same batch. Samples 10 and 11 passed the penetration test but the poplar samples failed because of patchy penetration of the preservative (Figure 11).

Figure 11: Penetration test.

Table 17: H3.2 20mm Kawa poplar decking full cross section retention analysis

Sample	Penetration spot test	Retention analysis Arsenic %m/m	Retention analysis Arsenic %m/m	Retention analysis Chromium %m/m	Retention analysis Copper %m/m	Retention Analysis Outcome
1	Fail	0.185	0.168	0.081	0.43	Pass
2	Fail	0.195	0.177	0.086	0.46	Pass
3	Fail	0.271	0.244	0.133	0.65	Pass
4	Fail	0.160	0.142	0.072	0.37	Pass
5	Fail	0.221	0.202	0.099	0.52	Pass
6	Pass	0.236	0.221	0.104	0.56	Pass
7	Fail	0.236	0.215	0.105	0.56	Pass
8	Fail	0.195	0.178	0.084	0.46	Pass
9	Fail	0.203	0.189	0.091	0.48	Pass
10	Fail	0.175	0.165	0.075	0.42	Pass
11	Pass	0.147	0.161	0.092	0.40	Pass
12	Pass	0.162	0.177	0.103	0.44	Pass

Micronised Copper Azole (MCA) H3.2 treated weatherboards

Samples 1 and 2 were two samples from the one radiata control board from the same batch. Samples 1 and 2 passed the penetration test but the poplar samples failed because of patchy penetration of the preservative (Figure 12).

Figure 12: Penetration test.

Table 18: Retention and Penetration, MCA-treated Kawa poplar cladding

Sample	Sapwood %	Penetration Spot Test	Retention Analysis Copper %m/m
1		Pass	0.150
2		Pass	0.157
3		Pass	0.069
4		Fail	0.084
5		Fail	0.156
6		Fail	0.210
7		Fail	0.164
8		Fail	0.177
9		Fail	0.179
10		Fail	0.083
11		Fail	0.117
12		Fail	0.202
13		Pass	0.220

Full cross section retention of copper preservative was similar to the radiata control for most Kawa poplar samples, but were quite variable, ranging from 0.069 % to 0.220% m/m.

Next: Discussion »

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