UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of

the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) May 29, 2015

RPM INTERNATIONAL INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (330) 273-5090

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

On May 29, 2015, RPM International Inc. (the “Company”) closed its offering of $250 million aggregate principal amount of 5.250% Notes due 2045 (the “Notes”) pursuant to an Underwriting Agreement (the “Underwriting Agreement”) with Merrill Lynch, Pierce, Fenner & Smith Incorporated and Santander Investment Securities Inc., as representatives of the several underwriters named therein (collectively, the “Underwriters”).

In connection with the closing, on May 29, 2015, the Company issued and sold to the Underwriters the Notes pursuant to the Underwriting Agreement.

The Notes are governed by the Indenture, dated as of April 8, 2014 (the “Base Indenture”), between the Company and Wells Fargo Bank, National Association, as supplemented by the Officers’ Certificate and Authentication Order, dated as of May 29, 2015 (the “Officers’ Certificate,” and together with the Base Indenture, the “Indenture”). Interest on the Notes will accrue from May 29, 2015 and will be payable semiannually in arrears on June 1st and December 1st of each year, beginning December 1, 2015, at a rate of 5.250% per year. The Notes mature on June 1, 2045.

The Indenture provides that an Event of Default (as defined in the Indenture) will occur if the Company defaults in any payment of interest on any Note when due and payable and the default continues for a period of 30 days, defaults in payment of any principal of any Note when due and payable at its stated maturity, upon optional redemption, or upon any required repurchase or upon declaration of acceleration or otherwise (subject to applicable notice and/or grace periods). Other Events of Default under the Indenture include: the Company’s failure to comply with certain corporate restrictions in the Officers’ Certificate, the Company’s failure to comply (subject to applicable notice and/or grace periods) with any of its other agreements contained in the Notes or the Indenture, the default under other indebtedness of the Company in an amount equal to or greater than the greater of $50 million or 10% of Consolidated Stockholders’ Equity (as defined in the Indenture), any final judgment (subject to certain rights of appeal and other limitations) against the Company or any of its subsidiaries in an amount equal to or greater than the greater of $50 million or 7% of Consolidated Stockholders’ Equity (as defined in the Indenture) remains unpaid or discharged for 60 days, and certain events of bankruptcy, insolvency or reorganization.

In certain Event of Defaults, the Trustee by notice to the Company, or the holders of at least 25% in principal amount of then outstanding Notes by notice to the Company and to the Trustee, may declare 100% of the principal of, and accrued and unpaid interest, if any, on, all then outstanding Notes to be due and payable. Upon such a declaration, such principal and accrued and unpaid interest, if any, will be due and payable immediately.

The foregoing description of the material terms of the Officers’ Certificate is qualified in its entirety by reference to the Officers’ Certificate which is filed herewith as Exhibit 4.1 and is incorporated herein by reference.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Exhibit Index