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Written by Sean Mulligan M23 "Dauntless"
Epoxy resin is the best choice for maintenance and modifications of marine components as well as previously laid-up polyester resin (what your boat is likely made of). It is stronger and sticks better to cured polyester resin than trying to apply a polyester resin repair. I have used West System epoxy resins and their related products for years now. The product is outstanding as is the technical support. They publish multiple small booklets that guide the do-it-yourself boatwright though any number of situations.
The entire system is based around their 105 Resin. They make numerous hardeners that can be used with this base resin. Most of the hardeners differ in their respective curing speeds and assist with working with the epoxy in varying conditions and temperatures. With polyester resin you can vary the amount of hardener to get varying rates of cure, but epoxy resin is different. It is imperative that the ratio be exact for the resin / hardener mixture. Most of the West System hardeners are 5:1 while some special hardeners are 3:1. West System sells a set of cheap plastic pumps that fit right into the cans and give you exact pre-measured amounts of resin and hardener, removing the guesswork. As far as the hardener, you buy either Fast #205, Slow#206, or Extra Slow #209 hardener (there is also a special Clear Coat hardener #207).
Each hardener has a temperature range that it is designed to work in. Use the correct hardener for the conditions! Too cold and it will never set, too hot and it will set so fast you cannot do anything with it (to say nothing of the fact that it can generate so much heat it will start smoking!) I used fast hardener #205 on my rudder project for the fiberglass application since the temps were in the 50-60 degree range and it worked great. For clear coating the topsides of the rudder I used the 105 resin with 207 clear coat hardener prior to application of the varnish.
In addition to the basic 105 Resin and hardeners they have a line of fillers that can be added to the resin to change properties to suit your particular needs. Fillers are available from high strength that is tough as nails to easily sandable fairing fillers for finish work. Some fillers are just to make the epoxy resin thicker so you can get it to hold a shape or fill a gap. Other fillers are specialized for bonding hardware, laminating, fairing, etc. You can mix the fillers with the resin in varying amounts to form different consistencies that are described in the booklets in food terms we can all understand such as catsup, mayonnaise, and peanut butter. Each can of filler is provided with a graphic chart to show you what that particular filler's abilities and applications are.
Epoxy resin is the best choice for maintenance and modifications of marine components as well as previously laid-up polyester resin (what your boat is likely made of). It is stronger and sticks better to cured polyester resin than trying to apply a polyester resin repair. I have used West System epoxy resins and their related products for years now. The product is outstanding as is the technical support. They publish multiple small booklets that guide the do-it-yourself boatwright though any number of situations.
The entire system is based around their 105 Resin. They make numerous hardeners that can be used with this base resin. Most of the hardeners differ in their respective curing speeds and assist with working with the epoxy in varying conditions and temperatures. With polyester resin you can vary the amount of hardener to get varying rates of cure, but epoxy resin is different. It is imperative that the ratio be exact for the resin / hardener mixture. Most of the West System hardeners are 5:1 while some special hardeners are 3:1. West System sells a set of cheap plastic pumps that fit right into the cans and give you exact pre-measured amounts of resin and hardener, removing the guesswork. As far as the hardener, you buy either Fast #205, Slow#206, or Extra Slow #209 hardener (there is also a special Clear Coat hardener #207).
Each hardener has a temperature range that it is designed to work in. Use the correct hardener for the conditions! Too cold and it will never set, too hot and it will set so fast you cannot do anything with it (to say nothing of the fact that it can generate so much heat it will start smoking!) I used fast hardener #205 on my rudder project for the fiberglass application since the temps were in the 50-60 degree range and it worked great. For clear coating the topsides of the rudder I used the 105 resin with 207 clear coat hardener prior to application of the varnish.
In addition to the basic 105 Resin and hardeners they have a line of fillers that can be added to the resin to change properties to suit your particular needs. Fillers are available from high strength that is tough as nails to easily sandable fairing fillers for finish work. Some fillers are just to make the epoxy resin thicker so you can get it to hold a shape or fill a gap. Other fillers are specialized for bonding hardware, laminating, fairing, etc. You can mix the fillers with the resin in varying amounts to form different consistencies that are described in the booklets in food terms we can all understand such as catsup, mayonnaise, and peanut butter. Each can of filler is provided with a graphic chart to show you what that particular filler's abilities and applications are.
The one area where I choose to stray from West System was the selection of fiberglass cloth and tape. West System suggests that you use their Episize brand cloth and tape. Since epoxy resin is typically thicker than its polyester cousin, it is slightly harder to get epoxy resin to wet-out regular fiberglass cloth completely as opposed to polyester resin. Episize brand fiberglass cloth accepts the epoxy resin more readily. If you are fiberglassing a structural component Episize brand would be best, but just to enhance the watertight integrity of the rudder blade or similar project, regular fiberglass cloth works fine. It just takes a little more work to wet-out. One of the biggest reasons I used the regular fiberglass is simply availability.
Regular fiberglass cloth and tape is available in bulk at West Marine (or online at: http://www.westmarine.com) and available by the yard. Episize fiberglass cloth from West Marine has to be ordered in 10 yard increments with 10 yards of 6oz Episize roughly $150.00 vs. a little under $20.00 per yard for regular 6oz cloth from a 60 inch wide roll with no minimums.
Remember, your goal when wetting out the cloth / tape is to get the fabric completely wet-out but not to use too much resin. Resin in and of itself does not have a lot of strength. Therefore a thick layer of resin just lying on top of already saturated cloth is doing you no favors (and in epoxy resin, costing you money!). The trick is this: Wet the cloth out until all of the fibers become translucent. If it still shows the white color of the cloth, it needs more resin. Then squeegee off the excess resin until you can see the weave of the cloth. If it looks like there is a smooth layer of glass on top of the cloth there is still too much resin on there, squeegee more off.
You can lay an additional layers of glass on top of the last layer as long as the resin below has not gone past the gel state. (The resin is still in the gel state if you can dent it with your thumbnail). If you do, the new layer will chemically bond to the old layer. Once the resin gets past the gel state you need to let it cure fully and then remove the amine blush from the surface before adding more layers. Amine blush is a waxy film produced by the resin as it cures. If you try to apply additional resin on top of this it will not bond. Let the resin fully cure. Wash it thoroughly with a stiff brush, soap and water, and then sand to provide a tooth for the next layer to bite on. Laying a second layer of cloth on after the first layer has cured works just fine but uses a different process to bond it. Whereas the second layer chemically bonds to the first when laid down during the first layers gel state, laying the second layer on after the first layer has cured makes it dependant on a mechanical secondary bond. This is why removing the waxy amine blush and sanding the surface is so important. Make sure you wash before you sand. If you do not you will force the entire waxy amine blush right into all the scratches that are caused by the sandpaper. Wash before and after sanding.
Cost is a factor while using Epoxy; a gallon of polyester resin including hardener will run under $40.00 at West Marine, a gallon of West System (not related to West Marine) Epoxy Resin and hardener will cost you well over $100.00. Do yourself a favor and bite the bullet. It's worth it to do the job right the first time and be done with it!
It is preferred to use Epoxy Resin over existing Polyester - however, it is not okay to put polyester resin on top of cured epoxy. This also holds true for some paints and gel-coats. You may have to use an epoxy barrier coat or primer to seal the epoxy if you want to paint or gel-coat over it. Read and follow the manufacturers instructions and recommendations closely.
My experience has been that once you have used the epoxy resin and see how adaptable the entire system of fillers and hardeners really is, you will never want to go back to polyester.
Remember, your goal when wetting out the cloth / tape is to get the fabric completely wet-out but not to use too much resin. Resin in and of itself does not have a lot of strength. Therefore a thick layer of resin just lying on top of already saturated cloth is doing you no favors (and in epoxy resin, costing you money!). The trick is this: Wet the cloth out until all of the fibers become translucent. If it still shows the white color of the cloth, it needs more resin. Then squeegee off the excess resin until you can see the weave of the cloth. If it looks like there is a smooth layer of glass on top of the cloth there is still too much resin on there, squeegee more off.
You can lay an additional layers of glass on top of the last layer as long as the resin below has not gone past the gel state. (The resin is still in the gel state if you can dent it with your thumbnail). If you do, the new layer will chemically bond to the old layer. Once the resin gets past the gel state you need to let it cure fully and then remove the amine blush from the surface before adding more layers. Amine blush is a waxy film produced by the resin as it cures. If you try to apply additional resin on top of this it will not bond. Let the resin fully cure. Wash it thoroughly with a stiff brush, soap and water, and then sand to provide a tooth for the next layer to bite on. Laying a second layer of cloth on after the first layer has cured works just fine but uses a different process to bond it. Whereas the second layer chemically bonds to the first when laid down during the first layers gel state, laying the second layer on after the first layer has cured makes it dependant on a mechanical secondary bond. This is why removing the waxy amine blush and sanding the surface is so important. Make sure you wash before you sand. If you do not you will force the entire waxy amine blush right into all the scratches that are caused by the sandpaper. Wash before and after sanding.
Cost is a factor while using Epoxy; a gallon of polyester resin including hardener will run under $40.00 at West Marine, a gallon of West System (not related to West Marine) Epoxy Resin and hardener will cost you well over $100.00. Do yourself a favor and bite the bullet. It's worth it to do the job right the first time and be done with it!
It is preferred to use Epoxy Resin over existing Polyester - however, it is not okay to put polyester resin on top of cured epoxy. This also holds true for some paints and gel-coats. You may have to use an epoxy barrier coat or primer to seal the epoxy if you want to paint or gel-coat over it. Read and follow the manufacturers instructions and recommendations closely.
My experience has been that once you have used the epoxy resin and see how adaptable the entire system of fillers and hardeners really is, you will never want to go back to polyester.
Working With Epoxy
The repair, modification and/or maintenance projects on this page are provided to show how one person accomplished a given task. Some projects are hazardous, dangerous and expensive and should be attempted only by professionals.. No warranty of success is included nor implied with any of these projects. The Webmaster, contributors and authors, will not accept, nor be held responsible as a result of any use of the material presented.
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