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Gluing plastic dimensional lumber
By Patrick Ropp
More people are using recycled plastic/wood composite lumber for decks and other
various projects. Although each manufacturer of recycled plastic lumber has his
own blend, we found that most are using very similar ingredients: an equal
amount of melted recycled plastic mixed with recycled wood chips or sawdust and
then extruded in the form of dimensional lumber. Since the wood is encased in
plastic, the plastic/wood composite boards are supposed to last longer than
traditional decking materials and carry a good warranty. Many of these boards
are not intended for use as structural members, but they work great for decking
and other lower load projects.
Recently, a customer called us asking if WEST SYSTEM® epoxy will glue a
particular type of recycled plastic lumber. Since we only had older data on a
different brand, we conducted PATTI™ adhesion tests on two new brands: Trex™
Brand and SmartDeck™. The adhesion results are shown in the following chart.
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| Trex |
|
|
|
|
| Surface Prep |
Adhesive |
Cure |
Adhesion |
Failure Mode |
| No Prep |
105/205 |
Overnight |
586 psi |
100% Substrate |
| No Prep |
105/205 |
2 Week |
586 psi |
100% Substrate |
| Sanded 80 Grit |
105/205 |
Overnight |
739 psi |
98% Substrate |
| Sanded 80 Grit |
105/205 |
2 Week |
668 psi |
96% Substrate |
| Flame Treatment |
105/205 |
Overnight |
617 psi |
100% Substrate |
| Flame Treatment |
105/205 |
2 Week |
617 psi |
100% Substrate |
| |
| SmartDeck |
|
|
|
|
| Surface Prep |
Adhesive |
Cure |
Adhesion |
Failure Mode |
| No Prep |
105/205 |
Overnight |
607 psi |
10% Substrate |
| No Prep |
105/205 |
2 Week |
674 psi |
2% Substrate |
| Sanded 80 Grit |
105/205 |
Overnight |
810 psi |
100% Substrate |
| Sanded 80 Grit |
105/205 |
2 Week |
783 psi |
100% Substrate |
| Flame Treatment |
105/205 |
Overnight |
770 psi |
100% Substrate |
| Flame Treatment |
105/205 |
2 Week |
841 psi |
100% Substrate |
Different methods of surface preparation are the variables for this test. With the Trex
Decking, any surface preparation (including none at all) results in substrate
failure, an indication the adhesive and adhesion are adequate for the material.
Even with no surface preparation, the surface seems to be rough enough to
provide a good grip for the epoxy. With
the SmartDeck, we found that without surface preparation, the epoxy adhesion
failed (at the interface), not the substrate. The surface was fairly smooth and
just didn’t have enough “tooth” for the epoxy to grab on to. When the
surface was sanded or flame treated (see below), the adhesion increased as much
as 25%.
I also glued two pieces of each brand of the plastic/wood composite face to face
using two step bonding and cycled them in the hot/humid hut, the cool/dry hut,
the hot/dry hut, and the freezer. In the 6" x 8" samples, I have not
seen any delamination or failure of either substrate. In
conclusion, sanded and flame treated TREX and SmartDeck produced the best
adhesion. In both cases, a builder should see favorable results bonding TREX and
SmartDeck (with some surface preparation) plastic/wood decking with WEST SYSTEM
epoxy.
Flame treating a plastic surface for bonding
To flame treat a plastic surface, hold a propane torch flame about 4" to
6" from the plastic (with the tip of the flame just above the surface) and
move it across the surface at a rate of 2 or 3 inches per second overlapping the
previous pass slightly. Keep the torch moving and only allow the exhaust gases
to hit the surface. If done correctly, the surface will not discolor or burn in
any obvious way. This technique oxidizes the surface and improves adhesion. For
best adhesion, bond to the surface within 30 minutes of treatment.
Sources
Trex Wood-Polymer Lumber Products
Trex Company, LLC
20 S Cameron St
Winchester, VA 22601
(540) 678-4070
www.trex.com
SmartDeck
U.S.Plastic Lumber
2300 Glades Road
Boca Raton, FL 33431
888-733-2546
www.usplasticlumber.com
Epoxyworks 16 / Fall 2000
Copyright © 2002, Gougeon Brothers, Inc. All rights reserved.
This page is maintained by Gougeon Brothers, Inc. Last Modified on 10/28/02.
Reproduction in any form, in whole or in part, is expressly forbidden without the consent of the publisher. EPOXYWORKS, Gougeon Brothers, WEST SYSTEM, Episize, Scarffer and Microlight as used throughout this publication, are trademarks of Gougeon Brothers, Inc., Bay City, Michigan, USA.
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