521 Marine Epoxy Dispensing and Mixing Instructions

First-time users

First time using our product? Please do a small test batch to get a feel for the mixing and curing process, before applying the mixture to your project. This will help build confidence handling and working with our product.

WARNING! Curing epoxy generates heat. When contained, a large mass of curing epoxy has a very short pot life and can create enough heat to melt plastic and foam and burn your skin. For this reason, do not use foam or glass mixing containers. If a pot of mixed epoxy begins to exotherm (heat up), quickly move it outdoors. Avoid breathing the fumes. Do not dispose of the mixture until the reaction is complete and has cooled. Do not fill or cast layers of epoxy thicker than 1/2″-thinner if enclosed by foam or other insulating material. Do not pour into confined spaces.*

* * DO NOT attempt to adjust the epoxy cure time by altering the mix ratio. An accurate ratio is essential for a proper cure and full development of physical properties **

Dispensing Instructions 

Dispense proper proportions of resin and hardener into a clean plastic, metal or wax-free paper container.

Dispensing with pumps 

Most problems related to curing can be traced to the wrong ratio of resin and hardener. We recommend using calibrated Pro Marine Supplies Pumps (included in your kit) to dispense the resin and hardener.

Please note: Pumps are calibrated to deliver the proper working ratio of resin to hardener.

Pump 1 full pump stroke of resin for each, 1 full pump stroke of hardener. Depress each pump head fully and allow the head to come completely back to the top before beginning the next stroke. Partial strokes will give the wrong ratio.

Verify the proper ratio before you use the first mixture on a project. A good idea is to re-check the ratio anytime you experience problems with curing.

Dispensing without Pumps (Volume measure)

To measure 521 Resin and 521 Slow or 521 Fast Hardener by volume, combine five parts resin with one part hardener. 


To assure thorough mixing, be sure to scrape the sides and bottom of your mixing container as you mix. Use the flat end of the mixing stick to reach the inside corner of the pot. Stir the two ingredients together thoroughly at least 1 minute-longer in cooler temperatures