Protective Coatings for Wood-Based Materials 

in Wildland-Urban Interface (WUI) Fires

Laura Dubrulle, Mauro Zammarano

Flammability Reduction Group, Engineering Laboratory, National Institute of Standards and Technology

laura.dubrulle@nist.gov

The term ‘Wildland-Urban Interface’ (WUI) refers to the area where homes and secondary structures are built in close proximity of forests,

grasslands or wildland vegetation in general. The number of communities located in WUI areas is constantly expanding and is now more

than 75,000 in the United States. As a result, the risk posed by wildfires to human lives and properties is increasing, and a large effort to limit

the impact of WUI fires on communities is ongoing [1-3]. In WUI fires, building-detached fuels and, in particular, fences can act like “fire lines”

that promote rapid flame spread throughout the community [3]. In this work, commercial fire retardant (FR) coatings are applied to woodbased materials to inhibit the combustion of detached fuels and thereby harden the communities. Preliminary results on the commercial

coatings have been obtained by Micro-Scale Combustion Calorimetry (MCC) and Cone Calorimetry.

Introduction

7 commercial FR coatings:

• 4 film-forming coatings

(3 water-based)

(1 organic solvent-based)

• 3 penetrating coatings (stains)

(water-based)

Market Research According to ASTM D2369, D1475 and D792

Product Name

Solid Content 

(mass %)

Density Matching FR by

Initial Final FTIR spectroscopy

Film-forming

A 62.8 ± 0.1 1.2808 ± 0.0150 1.3184 ± 0.0019 Melamine / Pentaerythritol

C 61.5 ± 0.4 1.3575 ± 0.0062 1.5017 ± 0.0076 Pentaerythritol

F 47.3 ± 0.1 1.2381 ± 0.0090 1.4303 ± 0.0137 Melamine / Pentaerythritol

H 75.1 ± 0.2 1.3755 ± 0.0022 1.6616 ± 0.0180 Melamine

Stain

B 13.9 ± 0.0 1.0650 ± 0.0025 1.2798 ± 0.0012 Pentaerythritol

D 15.3 ± 0.1 1.0815 ± 0.0036 1.4227 ± 0.0056 Ammonium Phosphate

E 28.3 ± 0.1 1.1358 ± 0.0024 1.4835 ± 0.0127 Guanidine Phosphate

Physicochemical properties of commercial products

Experimental

Micro-Scale Combustion Calorimetry

References:

[1] Radeloff, V.C, Ecological Application, 2005.

[2] Stein, S.M. Gen. Tech. Rep, DOA, 2013.

[3] Maranghides, A., NIST report 1909, 2011.

Status – completed:

 Coating of wood samples

 Characterization of coating physicochemical properties

 Micro-scale combustion calorimetry of coatings

75 °C  750 °C

1 °C/s

Heat Release 

Rate (HRR) 

measurement

FilmformingTHRa

(kJ/g)

PHRb

(W/g)

TPHRc

(°C)

Residue

(mass %)

A 6.9 ± 0.2 85.5 ± 1.8 352.5 ± 1.3 45.8 ± 1.0

C 6.2 ± 0.2 62. 9 ± 1.4 349.2 ± 1.1 49.8 ± 0.2

F 7.3 ± 0.2 71.3 ± 0.4 341.2 ± 1.8 39.7 ± 1.8

H 7.7 ± 0.3 48.8 ± 0.9 395.0 ± 2.1 37.4 ± 0.4

Stain

THR 

(kJ/g)

PHR 

(W/g)

TPHR

(°C)

Residue

(mass %)

B 3.9 ± 0.3 79.3 ± 3.9 405.3 ± 1.2 68.5 ± 0.6

D 1.5 ± 0.6 N/A N/A 16.9 ± 0.4

E 4.0 ± 0.3 26.4 ± 0.9 337.5 ± 5.4 35.6 ± 0.5

Stains have 

lower THR 

than filmforming 

coatings

Except for 

stain D, all 

show 

intumescent 

properties

aTotal Heat Release, bPeak Heat Release, cTemperature to Peak Heat Release

0

2 0

4 0

6 0

8 0

100

7 5 175 275 375 475 575 675

HRR (W/g)

Temperature ( C)

Film-forming A

Film-forming C

Film-forming F

Film-forming H

0

2 0

4 0

6 0

8 0

100

7 5 175 275 375 475 575 675

HRR (W/g)

Temperature ( C)

Stain B

Stain D

Stain E

C = lowest THR D = lowest THR

Cone Calorimetry

Lumber THR (kJ/g) PHR (W/g) TPHR (°C) Residue (mass %)

Uncoated 11.6 ± 0.1 140.2 ± 6.5 386.8 ± 4.1 14.4 ± 0.6

Sample Time to ignition 

(s)

Time to flame-out

(s)

THRa

(MJ/m2)

PHRb

(kW/m2)

Mass loss

(g)

Uncoated 18 485 49.8 197.7 32.5

Film-forming

A 26 28 0.6 43.7 4.7

C N/A N/A 0.4 6.4 3.7

F 79 868 47.4 120.1 35.2

H 18 31 1.8 128.4 2.5

Stain

B 30 650 60.6 202.4 41.6

D 18 583 51.5 159.5 33.4

Flaming experiment  50 kW/m2

ASTM E1354, intumescent samples  60 mm between cone and sample

Uncoated lumber Film-forming C

Film-forming C 

 No ignition + char formation

Preliminary results only, replicate tests will be conducted lowest THR/PHHR and mass loss

aTotal Heat Release, bPeak Heat Release

Future work:

 FR pressure treated lumber

 Cone Calorimeter experiments + smoldering tests

 Accelerating weathering of coatings