CEN/TC193/SC1/WG14
Date: 2025-06
Secretariat: DIN
Adhesives for load-bearing timber structures made of hardwoods — Classification and performance requirements — Part 1: Adhesives for the bonding of selected hardwood species (group A), with no specific high shear strength classification
Klebstoffe für tragende Holzbauteile aus Laubholz — Klassifizierung und Leistungsanforderungen — Teil 1: Klebstoffe für bestimmte Laubholzarten (Gruppe A) ohne besondere hohe Scherfestigkeitsklassifizierung
Adhésifs pour structures portantes en bois feuillus — Classification et exigences de performances — Partie 1: Adhésifs destinés au collage de structures portantes en bois feuillus sélectionnés (groupe A), sans classification spécifique pour la résistance au cisaillement élevée
CCMC will prepare and attach the official title page.
Contents Page
5.2.2 Aminoplastic and phenolic adhesives sub-type GP 0.3 s 11
5.2.3 One component polyurethane adhesives sub-type GP 0.3 12
5.2.4 One component polyurethane adhesives sub-type FJ 0.1 12
5.2.5 Emulsion polymer isocyanates adhesives sub-type FJ 0.1 12
This document (prEN 18307-1:2026) has been prepared by Technical Committee CEN/TC 193 “Adhesives”, the secretariat of which is held by UNE.
This document is currently submitted to the CEN Enquiry.
This document is one of a series of standards dealing with adhesives for use with timber structures and is published in support of product standards for load-bearing timber structures in connection with EN 1995‑1‑1 Eurocode 5: Design of timber structures - Part 1-1: General – Common rules and rules for buildings.
The series consists of:
• three standards for classification and performance requirements for adhesives for load-bearing timber structures (EN 301 for phenolic and aminoplastic adhesives, EN 15425 for one component polyurethane adhesives and EN 16254 for emulsion polymer isocyanate adhesives),
• one standard for classification and performance requirements for adhesives for load-bearing hardwood timber structures (prEN 18307-1), made of selected hardwood species (group A), with no specific high shear strength classification,
• one standard for the definition of groups of selected hardwood species (A and B) and sampling specifications for testing according to FprCEN/TS XXX[1],
• seven test methods (EN 302‑1, EN 302‑2, EN 302‑3, EN 302‑4, EN 302‑8 and EN 15416‑1, EN 15416‑3) used to assess the performance of adhesives after specified heat and humidity treatments, and
• five test methods (EN 302‑5, EN 302‑6, EN 302‑7 and EN 15416‑4, EN 15416‑5) to characterize the working properties of the adhesive.
NOTE prEN 18307-1 is part of a sub-series of three standards for classification and performance requirements for adhesives for load-bearing hardwood timber structures; prEN 18307-2 and prEN 18307-3 are not published yet:
Part 1: Adhesives for the bonding of selected hardwood species (group A), with no specific high shear strength classification.
[Part 2: Adhesives for the bonding of selected hardwood species (group B), with no specific high shear strength classification].
[Part 3: Adhesives for the bonding of selected hardwood species (group A and B), with specific high shear strength classification].
SAFETY STATEMENT
Persons using this document should be familiar with the normal laboratory practice, if applicable. This document cannot address all of the safety problems, if any, associated with its use. It is the responsibility of the user to establish appropriate safety and health practices and to ensure compliance with any regulatory conditions.
ENVIRONMENTAL STATEMENT
It is understood that some of the material permitted in this document may have a negative environmental impact. As technological advantages lead to acceptable alternatives for these materials, they will be eliminated from this document to the greatest extent possible.
At the end of the test, the user of the document should take care to carry out an appropriate disposal of the wastes.
NOTE Local regulations can apply.
1.0 Scope
This document establishes a classification for phenolic and aminoplastic polycondensation adhesives classified according to EN 301, one component polyurethane adhesives classified according to EN 15425 and emulsion polymer isocyanate adhesives classified according to EN 16254, according to their suitability for use for load-bearing timber structures made of selected hardwood species (group A) in defined climatic exposure conditions; it specifies performance requirements for such adhesives for the factory manufacture or factory-like manufacturing conditions of load-bearing timber structures made of selected hardwood species only, with no specific high shear strength classification.
NOTE An adhesive with high shear strength classification is needed when the declared characteristic shear strength of the glued laminated product is above 3,5 N/mm2, which is the declared characteristic shear strength of glulam made of softwoods according to EN 14080:2013 Table 4. See prEN 18307-3 requirements in this case.
It also classifies aminoplastic adhesive systems being used with a range of hardener dosage, and one component polyurethane adhesive product lines where all the products within the line have the same chemical composition except for a different amount of catalyst.
This document only specifies the performance of an adhesive for use in an environment corresponding to the defined conditions.
The performance requirements of this document are applicable to the adhesive only, not to the manufacturing timber products. This document does not cover the performance of adhesives for on-site gluing (except for factory-like conditions) nor the production of wood-based panels, except solid wood panels, or modified and stabilized wood with considerably reduced swelling and shrinkage properties, e.g. such as acetylated wood, heat treated wood and polymer impregnated wood. It also does not cover preservative treated wood.
This document is primarily intended for use by adhesive manufacturers and for use in timber products made of selected hardwood species bonded with adhesives, to assess or control the quality of adhesives. The requirements apply to the type testing of the adhesives. Production control activities are outside the scope of this document.
Adhesives meeting the requirements of this document are adequate for use in a load-bearing timber products made of selected hardwood species, provided that the bonding process has been carried out according to an appropriate product standard.
Selected hardwood species covered by this document are listed in FprCEN/TS XXX[2], group A. FprCEN/TS XXX[3] also specifies nominal physical properties of the mentioned species that are used for testing according to this document.
2.0 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
EN 301, Adhesives, phenolic and aminoplastic, for load-bearing timber structures - Classification and performance requirements
EN 302‑1, Adhesives for load-bearing timber structures - Test methods - Part 1: Determination of longitudinal tensile shear strength
EN 302‑2, Adhesives for load-bearing timber structures - Test methods - Part 2: Determination of resistance to delamination
EN 923, Adhesives - Terms and definitions
EN 13556, Round and sawn timber - Nomenclature of timbers used in Europe
EN 15425, Adhesives - One component polyurethane (PUR) for load-bearing timber structures - Classification and performance requirements
EN 16254, Adhesives - Emulsion polymer isocyanate (EPI) for load-bearing timber structures - Classification and performance requirements
3.0 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 923 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp/
— IEC Electropedia: available at https://www.electropedia.org/
3.1
aminoplastic resin
thermosetting synthetic resin derived from a condensation reaction of the –NH groups or –NH2 groups of amines or amides with aldehydes
3.2
phenolic resin
thermosetting synthetic resin derived from a condensation reaction of a phenol with an aldehyde
3.3
polycondensation adhesive
adhesive mixture made from a resin formed by a polymerisation reaction involving the elimination of water, usually with a hardener
Note 1 to entry: Such adhesives usually also contain extenders and/or fillers.
3.4
one component polyurethane (PUR) adhesive
isocyanate containing urethane polymers, which are cross-linked by reaction with water
3.5
emulsion polymer isocyanate (EPI) adhesive
water based emulsion polymer or a mixture of water based emulsion polymers cross-linked with an isocyanate as hardener
3.6
service class 1
climatic conditions characterised by a relative humidity of surrounding air of 65% (upper limit) and 50% (yearly average) at a temperature of 20°C
[SOURCE: prEN 1995‑1‑1:2024/10 Table 4.2]
Note 1 to entry: In service class 1, which comprises typical indoor conditions, the average moisture content in most softwoods will not exceed 12 %.
3.7
service class 2
climatic conditions characterised by a relative humidity of surrounding air of 85% (maximum) and 75% (yearly average) at a temperature of 20°C
[SOURCE: prEN 1995‑1‑1:2024/10 Table 4.2]
Note 1 to entry: In service class 2, to which most covered exterior conditions belong, the average moisture content in most softwoods will not exceed 20 %.
3.8
service class 3
climatic conditions characterized by a relative humidity of surrounding air of 95% (maximum) and 85% (yearly average) at a temperature of 20°C
[SOURCE: prEN 1995‑1‑1:2024/10 Table 4.2]
Note 1 to entry: Exterior conditions typically belong to service class 3.
3.9
glue line
adhesive layer between the wood members
3.10
thick glue line
glue line of nominal thickness in the range of 0,3 mm to 2,0 mm at the time of bonding
Note 1 to entry: Thick glue lines are achieved by using spacers, grooves or similar devices when two plain members are glued together.
3.11
close contact glue line
glue line of thickness maximum 0,1 mm
Note 1 to entry: Close contact glue line is achieved by pressing together two plane wood members with a clamping pressure of (0,8 ± 0,1) N/mm2 without additional grooves, spacers or similar devices.
3.12
adhesive product line
series of products, all with the same chemical composition except for a different amount of catalyst
Note 1 to entry: Only for this reason the products have different reactivity.
3.13
primer treatment
application of a coating (primer) substance to both adherend surfaces, prior to the application of an adhesive to improve adhesion and/or durability of the bond
Note 1 to entry: This does not include application of pure water.
4.0 Classification
4.1 General
Adhesives for the bonding of timber structures shall produce joints of such strength and durability that the integrity of the bond is maintained in the assigned service class throughout the expected life of the structure.
EN 301, EN 15425 and EN 16254 introduce two types of adhesives, I and II, for the bonding of timber structures made of softwood species according to their suitability for use in different climatic conditions:
— Type Ι to be used in service classes 1, 2 and 3 (prEN 1995‑1‑1:2024/10 Table 4.2), except for emulsion polymer isocyanates: adhesives to be used in service classes 1, 2;
— Type ΙΙ to be used in service class 1 only (prEN 1995‑1‑1:2024/10 Table 4.2).
These two types of adhesives are further divided into five application area according to the end use:
— General purpose adhesive (GP) for aminoplastic and phenolic adhesives, one component polyurethane adhesives, and emulsion polymer isocyanates adhesives to be used for glue lines between laminations, for finger joints in laminations and structural timber, and for large finger joints.
— Finger jointing adhesive (FJ) for aminoplastic and phenolic adhesives, one component polyurethane adhesives, and emulsion polymer isocyanates adhesives to be used for finger jointing of laminations and structural timber only.
— Gap filling adhesive (GF) for aminoplastic and phenolic adhesives to be used for fibre parallel gluing, e.g. glue lines between glulam components of block-glued glulam and for large finger joints.
— Special purpose adhesives (SP) for one component polyurethane adhesives to be used for glue lines between laminations with thicker glue lines (maximum glue line thickness 0,5 mm) and for finger joints in laminations.
— Small dimension adhesives (SD) for emulsion polymer isocyanates adhesives to be used in beams with a maximum cross section 45 000 mm2 (maximum glue line thickness 0,2 mm) and for finger joints in laminations and structural timber. The beam width shall not exceed 180 mm and the beam height shall not exceed 300 mm.
Combined to type and application area, the adhesive classification finally refers to:
— The maximum test temperature according to EN 302‑8 for aminoplastic and phenolic adhesives, one component polyurethane adhesives, and emulsion polymer isocyanates adhesives, and EN 302‑1 after treatments designation A6, A7 or A8 for one component polyurethane adhesives and emulsion polymer isocyanates adhesives: 50, 70 or 90, in degrees Celsius.
— The maximum glue line thickness in use for aminoplastic and phenolic adhesives, one component polyurethane adhesives, and emulsion polymer isocyanates adhesives: 0.1, 0.2, 0.3, 0.5, 0.6 or 1.5, in millimetres.
— The application mode for aminoplastic and phenolic adhesives: M for mixed application and S for separate application of adhesive and hardener.
4.1.1 Classification
Adhesives for the bonding of timber structures made of selected hardwood species (group A) addressed by this document shall first be classified as Type I according to the relevant standard for the bonding of timber structures made of softwoods species, i.e. EN 301 for aminoplastic and phenolic adhesives, EN 15425 for one component polyurethane adhesives, and EN 16254 for emulsion polymer isocyanates adhesives. This classification further includes the use in different climate conditions and applications areas.
In addition, they shall be submitted to an extension of classification for the bonding of the selected hardwood species intended to be used according to the procedure defined in paragraph 5.
Table 1 specifies the different adhesive classes for which this document applies and their designations. The designations consist of:
— European Standard reference: prEN 18307-1.
— Type: Ι.
— Application: GP, FJ, GF, SP and SD.
— Maximum test temperature in degrees Celsius: 70 or 90 (for Type Ι).
— Application mode for aminoplastic and phenolic adhesives: M for mix-in application, and S for separate application of adhesive and hardener.
— Adhesives tested for working properties are specified by the letter “w” at the end of the designation code.
Each application area and use shall be part of the designation.
EXAMPLE prEN 18307-1 I 90 GP 0,6 M w and prEN 18307-1 I 90 FJ 0,1 S for a MUF adhesive classified as general purpose adhesive with mixed application of resin and hardener and working properties and also classified as finger joint adhesive with separate application.
Table 1 — Adhesive classes
Adhesive class (Designation code) | Application area | Max. test temp.b °C | Max. glue line thickness (mm) | Service classesa | |
Test | Use | ||||
| General use Face lamination and finger jointing |
|
|
|
|
prEN XXX.1 I 70 GP 0,6M prEN XXX.1 I 70 GP 0,3S prEN XXX.1 I 70 GP 0,3 prEN XXX.1 I 70 GP 0,3 | General purpose General purpose General purpose General purpose | 70 70 70 70 | 1,0 1,0 0,5 0,5 | 0,6 0,3 0,3 0,3 | 1,2,3 1,2,3 1,2,3 1,2 |
| Special use Face lamination and finger jointing |
|
|
|
|
prEN XXX.1 I 90 GP 0,6M prEN XXX.1 I 90 GP 0,3S prEN XXX.1 I 90 GF 1,5M prEN XXX.1 I 90 GP 0,3 prEN XXX.1 I 90 SP 0,5 prEN XXX.1 I 90 SP 0,5 prEN XXX.1 I 90 GP 0,3 prEN XXX.1 I 70 SD 0,2 prEN XXX.1 I 90 SD 0,2 | General purpose General purpose Gap filling General purpose Special purpose Special purpose General purpose Small dimension Small dimension | 90 90 90 90 70 90 90 70 90 | 1,0 1,0 2,0 0,5 1.0 1.0 0,5 0,3 0,3 | 0,6 0,3 1,5 0,3 0.5 0.5 0,3 0,2 0,2 | 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1,2 1,2 1,2 |
| Special use Finger jointing |
|
|
|
|
prEN XXX.1 I 70 FJ 0,1M prEN XXX.1 I 90 FJ 0,1M prEN XXX.1 I 70 FJ 0,1S prEN XXX.1 I 90 FJ 0,1S prEN XXX.1 I 70 FJ 0,1 prEN XXX.1 I 90 FJ 0,1 prEN XXX.1 I 70 FJ 0,1 prEN XXX.1 I 90 FJ 0,1 | Finger joint Finger joint Finger joint Finger joint Finger joint Finger joint Finger joint Finger joint | 70 90 70 90 70 90 70 90 | 0,3 0,3 0,3 0,3 0,3 0,3 0,3 0,3 | 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 | 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3 1, 2 1, 2 |
a According to prEN 1995‑1‑1: 2024/10; refers to the initial classification code for the bonding of softwoods for the use of the glued products in the different service classes. b According to EN 302‑8 for aminoplastic and phenolic adhesives, one component polyurethane adhesives, and emulsion polymer isocyanates adhesives, and EN 302‑1 after treatments designation A6, A7 or A8 for one component polyurethane adhesives and emulsion polymer isocyanates adhesives. | |||||
5.0 Requirements
5.1 General
Adhesives for the bonding of timber structures made of selected hardwood species (group A) addressed by this document shall meet the performance requirements for Type I classification according to the relevant standard for the bonding of timber structures made of softwoods species, i.e. EN 301 for aminoplastic and phenolic adhesives, EN 15425 for one component polyurethane adhesives, and EN 16254 for emulsion polymer isocyanates adhesives, with respect to their suitability for use in different climatic conditions and the application area.
In addition, they shall be tested according to EN 302‑2 and paragraph 6.1 with every selected hardwood species intended to be used, and meet the requirements specified in 5.2.
5.1.1 Delamination test
5.1.2 General
When tested according to EN 302‑2 and paragraph 6.1, the tested adhesives shall meet the requirements below:
Db ≤ 5.0%
With Db: total delamination of each test piece prepared with the hardwood species intended to be used.
In the case of Gap Filling (GF) aminoplastic and phenolic adhesives and Special Purpose (SP) one component polyurethane adhesives previously tested with thick glue lines with the reference softwood species (Spruce), the delamination test according to EN 302‑2 with the selected hardwood species may be performed with close contact glue lines only.
By deviation to EN 302‑2, if requested by the applicant, the test may be performed with the lamination and glulam cross-section, and sawing patterns of the laminations conforming to the maximum sizes and the laminations sawing patterns used in the respective product. In this case the use of the adhesive is limited to the tested conditions.
In the case of Oak (Quercus robur, Quercus petrea, Quercus alba) with a mean density of less than 830 kg/m3 the following provision apply:
— the maximum delamination shall be less than or equal to 8 %.
5.1.3 Aminoplastic and phenolic adhesives sub-type GP 0.3 s
Provided that the adhesive has been tested according to EN 302‑2 with separate application of resin and hardener with the reference softwood species spruce (Picea abies L.), the additional delamination test according to EN 302‑2 shall be conducted with every selected hardwood species intended to be used with separate application of resin and hardener only. The test pieces may be produced under industrial conditions. The conditions of production shall be given in the test report. This test covers the use of the adhesive system with mixed and with separate application of resin and hardener.
Aminoplastic adhesives being used with a range of hardener dosage shall be tested with the lowest and the highest mixing ratio.
5.1.4 One component polyurethane adhesives sub-type GP 0.3
If the adhesive is to be used with a primer, provided that the adhesive has been tested with the primer according to EN 302‑2 with the reference softwood species spruce (Picea abies L.) and EN 302‑1 after treatments designation A1, A4 and A5 with the reference hardwood species beech (Fagus sylvatica L.), the additional delamination test according to EN 302‑2 shall be conducted with every selected hardwood species intended to be used treated with the primer. The following provisions apply: the two laminated members with the same closed assembly time (short or long) shall be prepared with two different waiting times between primer application and spreading of the adhesive. These two waiting times shall be the minimum evaporation time and the maximum evaporation time of the primer as recommended by the adhesive manufacturer.
In case of an adhesive line, the test shall be performed with the fastest and the slowest product.
5.1.5 One component polyurethane adhesives sub-type FJ 0.1
When testing an adhesive within application area finger-jointing (FJ) only, the additional delamination test according to EN 302‑2 may be replaced by the delamination test specified in EN 15425 Annex B with every selected hardwood species intended to be used.
In the case of an adhesive line, the test shall be performed with the fastest product.
5.1.6 Emulsion polymer isocyanates adhesives sub-type FJ 0.1
When testing an adhesive within application area finger-jointing (FJ) only, the additional delamination test according to EN 302‑2 may be replaced by the delamination test specified in EN 16254 Annex A with every selected hardwood species intended to be used.
6.0 Test methods
6.1 Delamination test
The test shall be made in accordance with EN 302‑2 with the high temperature procedure (for Type I adhesives) on specimen prepared with the hardwood species intended to be used. Select wood with nominal physical characteristics required for the test (see FprCEN/TS XXX[4]). Species shall be nominated in accordance to EN 13556 in the test report. In addition to the nomenclature code, latin name, origin and mean density shall be indicated, with the standard deviation for the mean density.
By deviation to EN 302‑2, if requested by the applicant, the test may be performed with the lamination and glulam cross-section, and sawing patterns of the laminations conforming to the maximum sizes and the laminations sawing patterns used in the respective product. In this case the use of the adhesive is limited to the tested conditions.
By deviation to EN 302‑2, for the preparation of the laminated members, bond the laminations in accordance with Table 2.
Table 2 — Preparation of the laminated members with close contact glue line
Parameters | Members 1, 2 | Members 3, 4 |
Adhesive spread Single sided c Mixed and/or separate application b | As recommended by the adhesive manufacturer | As recommended by the adhesive manufacturer |
Air temperature | (20 ± 2) °C | (20 ± 2) °C |
Open assembly time | Maximum 5 min a | Maximum 5 min a |
Closed assembly time | Minimum | Maximum |
Pressure | As recommended by the adhesive manufacturer | As recommended by the adhesive manufacturer |
Pressure time | As recommended by the adhesive manufacturer | As recommended by the adhesive manufacturer |
a Or as recommended by the adhesive manufacturer. b If only delamination test with separate application of resin and hardener is required, the test pieces may be produced under industrial conditions. The conditions of production have to be given in the test report. This test also covers the use of the adhesive system with mix-in application of adhesive and hardener. c By derogation, for specific hardwood species considered difficult to bond, double side application can be used; single side application also cover double side; the opposite is not valid resulting in the limitation of the classification area to double side application of the glue mix and shall be indicated in the approval report and the Technical Data Sheet. | ||
In the case of one component polyurethane adhesives used with a primer, the two laminated members with the same closed assembly time (minimum or maximum) shall be prepared with two different waiting times between primer application and spreading of the adhesive. These two waiting times shall be the minimum evaporation time and the maximum evaporation time of the primer as recommended by the adhesive manufacturer.
EXAMPLE The adhesive manufacturer recommends a minimum evaporation time between the primer treatment and the bonding operation of 10 min and a maximum evaporation time of 4 h. Based on this, one laminated member with short closed assembly time is produced with an evaporation time of the primer of 10 min and the other laminated member with short closed assembly is produced with an evaporation time of the primer of 4 h. For the laminated members produced with long closed assembly time, the same procedure is followed.
The additional tests for primer treatment cover the requested application rate (±2,5 g/m2), a relative tolerance of the content of the active component of ± 10 % and a minimum and maximum evaporation time between primer application and adhesive application as recommended by the adhesive manufacturer.
EXAMPLE The additional test for the primer treatment was performed with an application rate of the primer of 10 g/m2. The primer was used with a concentration (= active component) of 5 % (95 g water was mixed with 5 g of primer). Based on this, the primer may be used in a range of the application rate between 7,5 g/m2 and 12,5 g/m2. The concentration of the primer may be between 4,5 % and 5,5 %. The minimum and maximum evaporation time is set by the requirements given in EN 15425.
The end of an impregnating-drying cycle for any given specimen shall only be considered when the mass of the specimen is between 102 % and 108 % of its original mass. Should the mass of any given specimen exceed its original mass by more than 8 % after 18 h drying, it shall be placed in the drying duct once again, and subject to further identical drying conditions, removed and re-weighed after 1 h until the specimen is within the required mass range. Some hardwood species may need longer drying time than 18 h (but the drying time shall not exceed 30 h).
Experience has shown that the drying time for poplar can sometimes exceed 30 h. Nevertheless, it shall not exceed 32 h.
Repeat the entire impregnating-drying cycle twice to achieve three cycles, comprising a total test period of just over three days. Interruption after each cycle (for several days) is allowed.
At the end of the procedure, measure the total delamination Db. The delaminated glue lines shall be systematically opened in case of negative results for a more careful examination.
By deviation to EN 302‑2 a failure in the latewood area of an annual ring, which is adjacent and parallel to the glue line, shall be considered as a valid delamination
7.0 Marking and labelling
Each adhesive trade unit shall be labelled. The labelling shall at least include the trade name of the product, the batch number and the shelf life. Adhesive type according to prEN 18307-1 and approved hardwood species shall be included either on the label or in the technical data sheet.
EN 302‑8, Adhesives for load-bearing timber structures - Test methods - Part 8: Static load test of multiple bond line specimens in compression shear
prEN 1995‑1‑1:2024/10, Eurocode 5, Design of timber structures — Part 1-1: General - Common rules and rules for buildings
