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Author Topic:   Epoxy versus Polyester resin

Roarque posted 11-03-2005 11:34 AM ET (US)
I noted the West System fibreglas repair kits use epoxy resins instead of the traditional polyester. Asking the question, I was told that epoxy "grips" the polyester-based resins of a fibreglas boat hull better than polyester does. This sounded like marketing baloney to me so I thought I'd ask here.
Is the very expensive West System epoxy-based resin really worth $2X the polyester-based resin of the easier-to-find generic fibreglas repair kits?
I've worked with fibreglas for over 35 years off and on to repair everything from rusty running boards to holes punched in Hobie Cats and I've always used the generic ( ie polyester-base resin ) kits. Seemed to work just fine.
However, since reading the CW regularly, I hear people here talking about the West System kits as though they are the gold standard for Whaler repair.
Any experience comparing the two resins?
russellbailey posted 11-03-2005 12:32 PM ET (US)
I raced wildwater canoes for about 10 years. These are decked, tippy, long, narrow, and fragile boats that you race down challenging whitewater (Class 3-4). Patching is frequent, and the hulls are highly stressed. Our tandem 16' racer was about 35 lbs.
In patching these, it made a big difference in using polyester (or its fancier cousin vinylester) versus epoxy. The secondary bond of polyester/vinylester is much weaker than epoxy, and the patch would tend to peel off.
A Whaler hull has nowhere near the stress of those applications, and it may not matter in these cases.
Binkie posted 11-03-2005 12:50 PM ET (US)
Don`t patch a crack or a hole in a glass boat with mat and plyester resin, use epoxy and mat. The polyester resin will not adhere and will always peel off, sometimes on your first fishing trip.
A few years ago, a fellow fishing club member, patched a large crack in the bottom of his no-name glass boat. I told him it wouldn`t work, but he said it LOOKED good. That weekend he had to beach his boat to keep it from sinking. After he repaired it again, using epoxy he had no more trouble.
Binkie posted 11-03-2005 12:53 PM ET (US)
BTW polyester resin is used for boat BUILDING, and epoxy is used for repairs on the hull.
jimh posted 11-03-2005 01:23 PM ET (US)
A thorough reading of this reference ought to provide the answer to your question:
http://www.epoxyworks.com/22/fiberglass.html
The only reason more boats aren't built with epoxy resins is the cost. When making a small repair the cost difference is insignificant. Use the proper materials, even if they are more expensive.
Jerry Townsend posted 11-03-2005 03:12 PM ET (US)
Roarque - having run a few tests years and years ago on fiberglas materials where I found that polyester resin generally does not bond well with epoxy resins - while epoxy will generally bond to polyester or other materials.
Epoxy also provides a stronger material than does polyester resins.
BW boats are made with polyester resin - so basically, you can use either resin.
The one thing to watch is to use a laminating/layup resin instead of a finishing resin - because the finishing resins have a wax blended in. Finishing any fiberglas job simply requires spraying a generous coat of wax over the last application of resin - which completes the cure. ---- Jerry/Idaho
PeteB88 posted 11-03-2005 04:01 PM ET (US)
Quality doesn't cost - it pays!!
Don't even think about anything but epoxy - especially ease of use, extreme versatility, durabilty, and ability to use it on all kinds of projects including over wood. One West Systems gallon kit and you are the Duke of Epoxy in your neighborhood.
NEVER use polyester over wood.
As regards russelbailey's comments about white water canoes - we used epoxy composite construction and finishing techniques for white water river boats (drift boats) including skid shoes on hull bottoms. They take an incredible beating not only on the water but launching and trailering on extreme roads in Pacific NW high desert. NO issues with epoxy joints, laminates and finishes.
HOWEVER russ man, I would never assume that your canoes or our drift boats take more of a beating than any Whaler - you ain't rode with Dale the Whale WOT on Lake Michigan in big chop and waves - while he's gigglin' and everyone is grabbing rails to hang on. Talk about pounding wave top after wave top, big air, entire boat out of the water and boat-slams after boat-slams.
After the first year he "Dale Proofed" (fixed everything that busted) the boat with epoxy and custom fabricated big thick stainless steel brackets and thick wood lams. That was almost 10 years ago - still pounding, slamming, flying that boat and still giggling his ass off!!!
Epoxy!!! Mix it right, read the manuals, you'll use it every where with the pumps. best of lukc.
BobL posted 11-03-2005 07:06 PM ET (US)
Roarque,
Epoxy is the gold standard for any fiberglass repair. The difference is the strength of a secondary bond. Polyester provides a strong primary bond during original construction because all of the fiberglass cures as one piece. A repair is different because you want a strong bond to the existing fiberglass (secondary bond). Epoxy excels at producing a strong secondary bond while polyester does not. When I do a repair I want it to hold the first time and I do not want to fix it a second time. The extra expense of epoxy is worth it for my boats.
BobL
merc125 posted 11-03-2005 10:26 PM ET (US)
Don't feeel obligated to use west system, there are many less expensive alternatives. RAKA seems similar to west, US Composite makes a thick body resin that dosn't sag, gels quickly and seems to wet out cloth better than the thin resins.
Junk boats and beat up corvette bodies have been my hobbies for a long time. Any failures in repairs I have made, were usally at the bond between old and new. The Epoxy bond is much stronger, sometimes even stronger than the original primary polyester material. MartyD
David Livingstone posted 11-04-2005 08:36 AM ET (US)
Roarque, epoxy is worth the extra cost due top it’s mechanical bonding strength and lower working temperature. Polyester-base resin is used in the majority of boat building applications, including Boston Whaler. During the lay-up process, the fibres and resin harden as one unit to form a chemical bond. You’ll probably remember reading that Whaler puts the inside and outside hulls together while the resin is still wet. This results in a strong chemical bond. The two pieces cure (harden) as one unit. Kind of like pouring half a glass of chocolate milk into a half glass of white milk, they form one full glass and can’t be separated. But once everything hardens, it’s a different story. We are now talking about a mechanical bond. All repair work involves mechanical bonds. Back to the milk, but now the half a glass of chocolate milk is frozen rock hard. The white milk can be added to the glass but the bond will be a mechanical one and the two can be separated. It’s important to note that if the white milk is warm and the surface of the chocolate milk is heated a little than the bond will be stronger.
Polyester- base resin can still be used in a repair application as long as the surface is ground down and is clean, dry and warm (70 degrees or above). In the thirty + years that I’ve been using fibreglass, almost all of the failures can be attributed to poor surface prep and glassing over damp and or cold areas. Also polyester- base resin is not water proof. It has to sealed from the water by gelcoat or paint.
Epoxy – based resin has a much stronger mechanical bonding property than polyester. The surface prep is the same is using polyester, but depending on the hardener, it can be applied in cooler temperatures. It still works better if the bonding surface is preheated. Epoxy is water proof but can be broken down by UV and has to be covered with paint.
Some important rules to remember when you are using epoxy:
1. Epoxy can be applied over polyester or epoxy
2. Polyester can not be applied over epoxy. It can only be applied over polyester!
3. Gelcoat is polyester
Good luck with your repairs,
David
jimh posted 11-04-2005 09:04 AM ET (US)
See:
http://www.westsystem.com/webpages/userinfo/manual/
for excellent instructions on the use of Epoxy.
Gelcoat can be used as a top coat to epoxy. Refer to 002-550 Fiberglass Boat Repair and Maintenance, published by Gougeon Brothers, for detailed information on patching gelcoat over an epoxy repair.
http://www.westsystem.com/webpages/productinfo/guide/index.htm#002-550
Roarque posted 11-04-2005 11:09 AM ET (US)
Thanks to binkie, marty, david, jim, bob, russel, pete and jerry for your comments. I went out and bought the West System booklet "Fiberglass Boat Repair and Maintenance" even though a lot of the info is on their website ( cudos to jimh).
I often spend time in the front seat of my truck waiting for the gulf coast islands ferries. I can make use of this time to read a chapter or so in this informative manual. When I glanced at the booklet/manual about 2 weeks ago, all I remembered was their emphasis on the use of epoxy to repair maturely-cured polyester resin.
You guys have re-inforced their point so now when I read the purchased copy of the booklet/manual I find it full of useful tips on techniques for boat repairs.
Please see my additional post on molding of resin as it cures.
Greg
LHG posted 11-04-2005 08:05 PM ET (US)
I don't know what kind of hull repair you are contemplating, but when it comes to epoxies, don't overlook Illinois Tool Work's (ITW) White Marine-Tex. (they also make other epoxy liquids, etc) This white epoxy putty consistency material is super smooth and easy to work with, bonds agressively to wood and polyester glass work, sands easily, plus it cleans up with water. Nothing like it for my money. For drilling out and refilling stripped screw holes in Whalers, with or without underlying backing, there is no equal. Also great for repairing engine bolt holes in transoms. No pumps and misc drug style paraphenalia (as I like to call it) has to be purchased either. These West guys, great product though it may be, have a racket going if you ask me.
Jerry Townsend posted 11-05-2005 12:15 AM ET (US)
Larry - I have not used or even seen the Illinois White Marine-Tex you mentioned - but I question the water solubility of the product in use on a boat. I realize that the water solubility is primarily applicable before the material cures - but??? It may work - but I would want to see some real solid proof.
Another point regarding the use of epoxy or polyester resins - is that epoxy will 'eat' foam - whereas polyester does not affect foam. That is, in all probability, a principal reason for BW boats being made with polyester resins. ---- Jerry/Idaho
Tom W Clark posted 11-05-2005 12:26 AM ET (US)
It is an old wives tale that epoxy will "eat" polyurethane foam.
It is true that polyester resin will dissolve Styrofoam while epoxy will not.
I will agree with most here that epoxy is stronger than polyester resin.
I will disagree with most there that that necessarily means you will be better off using it on your Whaler.
For many repairs, polyester resin will be the material of choice.
As far as epoxy goes, there seems to be this cult of the West Systems around here. West is good but so are many others.
My favorite is System Three Resins, a Washington company.
Industrial Formulators, Inc is also an excellent producer of epoxy resins, and they are in British Columbia!
LHG posted 11-05-2005 01:59 AM ET (US)
Jerry - I'm surprised you haven't seen or heard about Marine-Tex, in either white for boats, or grey for metals. It has been widely used for years, all around the globe. It's a very successful and popular product. Almost everybody carries it.
For larger BW hull repairs, I still think the BW factory directions, using polyester resin, are the preferred method.
jimh posted 11-05-2005 07:11 AM ET (US)
WEST System epoxy was the first to be developed for boat building applications, and they have a very strong distribution network in place. Their products are widely available at marine stores. There are other epoxy formulators and suppliers who also try to cater to marine applications, and these may also be fine products, but often they are harder to source due to limited distribution.
Marine-tex® is simply a two-part epoxy resin which has been pre-mixed with fillers and blended to a particular consistency. If the color and consistency is correct for a particular application, it is probably a fine product. Using WEST System resins, hardeners, and fillers you can create epoxies of various consistencies, colors, and with fillers of different properties, as appropriate for the application.
In the typical quantities that will be used to make minor repairs, the price of one epoxy versus another does not seem to be a great influence. I find it is much handier to get a package of WEST System products from the local boat store when I need to make a repair than it is to send off a check and mail order from other suppliers. If I were planning to build an entire boat or some other large structure with epoxy, the price of the resin would become more of a concern, and it might very well be that alternative suppliers to WEST Systems could become attractive.
The physical properties of epoxy resins appear to be better than polyester resins in most cases. Epoxy has more strength, has better adhesion, and can elongate more without cracking than polyester resin. It forms better secondary bonds. It is more waterproof. Boats are built with epoxy, but, due to the higher cost of the resin, it is often only the more expensive or exotic hull laminates which use epoxy. Competitive sailboat hulls, for example, are usually molded with laminates using epoxy.
When you make a repair to a Boston Whaler with polyester resin there is little chance that you will be using the same resin that was used to produce the laminate. Boston Whaler does not divulge the identity of the resins it uses in making Boston Whaler boats. It is very likely you will be using a different resin than the original laminate.
As I have said before, it seems quite likely that the reason the factory has recommended polyester resin be used to make repairs is because the factory has polyester resin available to it in huge quantities and their experience with making repairs or secondary bonds has been with polyester resins. It also avoids putting them in the somewhat awkward position of making a boat with one material then recommended repairing it with a different material.
Roarque posted 11-05-2005 07:01 PM ET (US)
Found a good source for epoxy resins here in Nanaimo BC.
The sales person noted that epoxy resin does have superior adhesion characteristics to cured polyester BUT polyester resin cannot be then applied over epoxy resins.
Since gelcoat is only sold with a polyester resin base, this poses a problem for surface finishing the epoxy resin repair. The solution proposed by this supplier is to paint the repaired area with epoxy paint.
My plan is to repair with epoxy resin and chopped cloth, then sand smooth and apply a coat of epoxy paint to match the desert tan hull. Fortunately the repair is to the bottom of the boat, visible solely to salmon and cod.
To the best of my knowledge there are no CW correspondents who claim to be of either of these spieces.
PeteB88 posted 11-06-2005 06:52 AM ET (US)
I seem to always gravitate to West Systems but agree System 3 and some of the others are fine products. It is my understanding that the Gougeon Bros and West were first on the market, targeting marine use, like System 3 and that W E S T is an aconym for Wood Epoxy Saturation Treatment but am not certain of that .
There has been plenty said about epoxy for repairs and mods but it is important to remember that marine epoxy is better than anything for bonding or coating to bare wood especially for finish coatings. Epoxy base coats over wood, application and wet out of fiberglass cloth or kevlar or graphite with epoxy resins underscores the extreme vesatility of epoxy.
WHen it gets down to it customer service and ease of use prevail.
Marine Tex gets a nod because it is pigmented and you do not have to coat over it. It is very handy for repairs but kind of messy to work with - - and too expensive as far as I'm concerned.
best

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Author	Topic: Epoxy versus Polyester resin
Roarque	posted 11-03-2005 11:34 AM ET (US) I noted the West System fibreglas repair kits use epoxy resins instead of the traditional polyester. Asking the question, I was told that epoxy "grips" the polyester-based resins of a fibreglas boat hull better than polyester does. This sounded like marketing baloney to me so I thought I'd ask here. Is the very expensive West System epoxy-based resin really worth $2X the polyester-based resin of the easier-to-find generic fibreglas repair kits? I've worked with fibreglas for over 35 years off and on to repair everything from rusty running boards to holes punched in Hobie Cats and I've always used the generic ( ie polyester-base resin ) kits. Seemed to work just fine. However, since reading the CW regularly, I hear people here talking about the West System kits as though they are the gold standard for Whaler repair. Any experience comparing the two resins?
russellbailey	posted 11-03-2005 12:32 PM ET (US) I raced wildwater canoes for about 10 years. These are decked, tippy, long, narrow, and fragile boats that you race down challenging whitewater (Class 3-4). Patching is frequent, and the hulls are highly stressed. Our tandem 16' racer was about 35 lbs. In patching these, it made a big difference in using polyester (or its fancier cousin vinylester) versus epoxy. The secondary bond of polyester/vinylester is much weaker than epoxy, and the patch would tend to peel off. A Whaler hull has nowhere near the stress of those applications, and it may not matter in these cases.
Binkie	posted 11-03-2005 12:50 PM ET (US) Don`t patch a crack or a hole in a glass boat with mat and plyester resin, use epoxy and mat. The polyester resin will not adhere and will always peel off, sometimes on your first fishing trip. A few years ago, a fellow fishing club member, patched a large crack in the bottom of his no-name glass boat. I told him it wouldn`t work, but he said it LOOKED good. That weekend he had to beach his boat to keep it from sinking. After he repaired it again, using epoxy he had no more trouble.
Binkie	posted 11-03-2005 12:53 PM ET (US) BTW polyester resin is used for boat BUILDING, and epoxy is used for repairs on the hull.
jimh	posted 11-03-2005 01:23 PM ET (US) A thorough reading of this reference ought to provide the answer to your question: http://www.epoxyworks.com/22/fiberglass.html The only reason more boats aren't built with epoxy resins is the cost. When making a small repair the cost difference is insignificant. Use the proper materials, even if they are more expensive.
Jerry Townsend	posted 11-03-2005 03:12 PM ET (US) Roarque - having run a few tests years and years ago on fiberglas materials where I found that polyester resin generally does not bond well with epoxy resins - while epoxy will generally bond to polyester or other materials. Epoxy also provides a stronger material than does polyester resins. BW boats are made with polyester resin - so basically, you can use either resin. The one thing to watch is to use a laminating/layup resin instead of a finishing resin - because the finishing resins have a wax blended in. Finishing any fiberglas job simply requires spraying a generous coat of wax over the last application of resin - which completes the cure. ---- Jerry/Idaho
PeteB88	posted 11-03-2005 04:01 PM ET (US) Quality doesn't cost - it pays!! Don't even think about anything but epoxy - especially ease of use, extreme versatility, durabilty, and ability to use it on all kinds of projects including over wood. One West Systems gallon kit and you are the Duke of Epoxy in your neighborhood. NEVER use polyester over wood. As regards russelbailey's comments about white water canoes - we used epoxy composite construction and finishing techniques for white water river boats (drift boats) including skid shoes on hull bottoms. They take an incredible beating not only on the water but launching and trailering on extreme roads in Pacific NW high desert. NO issues with epoxy joints, laminates and finishes. HOWEVER russ man, I would never assume that your canoes or our drift boats take more of a beating than any Whaler - you ain't rode with Dale the Whale WOT on Lake Michigan in big chop and waves - while he's gigglin' and everyone is grabbing rails to hang on. Talk about pounding wave top after wave top, big air, entire boat out of the water and boat-slams after boat-slams. After the first year he "Dale Proofed" (fixed everything that busted) the boat with epoxy and custom fabricated big thick stainless steel brackets and thick wood lams. That was almost 10 years ago - still pounding, slamming, flying that boat and still giggling his ass off!!! Epoxy!!! Mix it right, read the manuals, you'll use it every where with the pumps. best of lukc.
BobL	posted 11-03-2005 07:06 PM ET (US) Roarque, Epoxy is the gold standard for any fiberglass repair. The difference is the strength of a secondary bond. Polyester provides a strong primary bond during original construction because all of the fiberglass cures as one piece. A repair is different because you want a strong bond to the existing fiberglass (secondary bond). Epoxy excels at producing a strong secondary bond while polyester does not. When I do a repair I want it to hold the first time and I do not want to fix it a second time. The extra expense of epoxy is worth it for my boats. BobL
merc125	posted 11-03-2005 10:26 PM ET (US) Don't feeel obligated to use west system, there are many less expensive alternatives. RAKA seems similar to west, US Composite makes a thick body resin that dosn't sag, gels quickly and seems to wet out cloth better than the thin resins. Junk boats and beat up corvette bodies have been my hobbies for a long time. Any failures in repairs I have made, were usally at the bond between old and new. The Epoxy bond is much stronger, sometimes even stronger than the original primary polyester material. MartyD
David Livingstone	posted 11-04-2005 08:36 AM ET (US) Roarque, epoxy is worth the extra cost due top it’s mechanical bonding strength and lower working temperature. Polyester-base resin is used in the majority of boat building applications, including Boston Whaler. During the lay-up process, the fibres and resin harden as one unit to form a chemical bond. You’ll probably remember reading that Whaler puts the inside and outside hulls together while the resin is still wet. This results in a strong chemical bond. The two pieces cure (harden) as one unit. Kind of like pouring half a glass of chocolate milk into a half glass of white milk, they form one full glass and can’t be separated. But once everything hardens, it’s a different story. We are now talking about a mechanical bond. All repair work involves mechanical bonds. Back to the milk, but now the half a glass of chocolate milk is frozen rock hard. The white milk can be added to the glass but the bond will be a mechanical one and the two can be separated. It’s important to note that if the white milk is warm and the surface of the chocolate milk is heated a little than the bond will be stronger. Polyester- base resin can still be used in a repair application as long as the surface is ground down and is clean, dry and warm (70 degrees or above). In the thirty + years that I’ve been using fibreglass, almost all of the failures can be attributed to poor surface prep and glassing over damp and or cold areas. Also polyester- base resin is not water proof. It has to sealed from the water by gelcoat or paint. Epoxy – based resin has a much stronger mechanical bonding property than polyester. The surface prep is the same is using polyester, but depending on the hardener, it can be applied in cooler temperatures. It still works better if the bonding surface is preheated. Epoxy is water proof but can be broken down by UV and has to be covered with paint. Some important rules to remember when you are using epoxy: 1. Epoxy can be applied over polyester or epoxy 2. Polyester can not be applied over epoxy. It can only be applied over polyester! 3. Gelcoat is polyester Good luck with your repairs, David
jimh	posted 11-04-2005 09:04 AM ET (US) See: http://www.westsystem.com/webpages/userinfo/manual/ for excellent instructions on the use of Epoxy. Gelcoat can be used as a top coat to epoxy. Refer to 002-550 Fiberglass Boat Repair and Maintenance, published by Gougeon Brothers, for detailed information on patching gelcoat over an epoxy repair. http://www.westsystem.com/webpages/productinfo/guide/index.htm#002-550
Roarque	posted 11-04-2005 11:09 AM ET (US) Thanks to binkie, marty, david, jim, bob, russel, pete and jerry for your comments. I went out and bought the West System booklet "Fiberglass Boat Repair and Maintenance" even though a lot of the info is on their website ( cudos to jimh). I often spend time in the front seat of my truck waiting for the gulf coast islands ferries. I can make use of this time to read a chapter or so in this informative manual. When I glanced at the booklet/manual about 2 weeks ago, all I remembered was their emphasis on the use of epoxy to repair maturely-cured polyester resin. You guys have re-inforced their point so now when I read the purchased copy of the booklet/manual I find it full of useful tips on techniques for boat repairs. Please see my additional post on molding of resin as it cures. Greg
LHG	posted 11-04-2005 08:05 PM ET (US) I don't know what kind of hull repair you are contemplating, but when it comes to epoxies, don't overlook Illinois Tool Work's (ITW) White Marine-Tex. (they also make other epoxy liquids, etc) This white epoxy putty consistency material is super smooth and easy to work with, bonds agressively to wood and polyester glass work, sands easily, plus it cleans up with water. Nothing like it for my money. For drilling out and refilling stripped screw holes in Whalers, with or without underlying backing, there is no equal. Also great for repairing engine bolt holes in transoms. No pumps and misc drug style paraphenalia (as I like to call it) has to be purchased either. These West guys, great product though it may be, have a racket going if you ask me.
Jerry Townsend	posted 11-05-2005 12:15 AM ET (US) Larry - I have not used or even seen the Illinois White Marine-Tex you mentioned - but I question the water solubility of the product in use on a boat. I realize that the water solubility is primarily applicable before the material cures - but??? It may work - but I would want to see some real solid proof. Another point regarding the use of epoxy or polyester resins - is that epoxy will 'eat' foam - whereas polyester does not affect foam. That is, in all probability, a principal reason for BW boats being made with polyester resins. ---- Jerry/Idaho
Tom W Clark	posted 11-05-2005 12:26 AM ET (US) It is an old wives tale that epoxy will "eat" polyurethane foam. It is true that polyester resin will dissolve Styrofoam while epoxy will not. I will agree with most here that epoxy is stronger than polyester resin. I will disagree with most there that that necessarily means you will be better off using it on your Whaler. For many repairs, polyester resin will be the material of choice. As far as epoxy goes, there seems to be this cult of the West Systems around here. West is good but so are many others. My favorite is System Three Resins, a Washington company. Industrial Formulators, Inc is also an excellent producer of epoxy resins, and they are in British Columbia!
LHG	posted 11-05-2005 01:59 AM ET (US) Jerry - I'm surprised you haven't seen or heard about Marine-Tex, in either white for boats, or grey for metals. It has been widely used for years, all around the globe. It's a very successful and popular product. Almost everybody carries it. For larger BW hull repairs, I still think the BW factory directions, using polyester resin, are the preferred method.
jimh	posted 11-05-2005 07:11 AM ET (US) WEST System epoxy was the first to be developed for boat building applications, and they have a very strong distribution network in place. Their products are widely available at marine stores. There are other epoxy formulators and suppliers who also try to cater to marine applications, and these may also be fine products, but often they are harder to source due to limited distribution. Marine-tex® is simply a two-part epoxy resin which has been pre-mixed with fillers and blended to a particular consistency. If the color and consistency is correct for a particular application, it is probably a fine product. Using WEST System resins, hardeners, and fillers you can create epoxies of various consistencies, colors, and with fillers of different properties, as appropriate for the application. In the typical quantities that will be used to make minor repairs, the price of one epoxy versus another does not seem to be a great influence. I find it is much handier to get a package of WEST System products from the local boat store when I need to make a repair than it is to send off a check and mail order from other suppliers. If I were planning to build an entire boat or some other large structure with epoxy, the price of the resin would become more of a concern, and it might very well be that alternative suppliers to WEST Systems could become attractive. The physical properties of epoxy resins appear to be better than polyester resins in most cases. Epoxy has more strength, has better adhesion, and can elongate more without cracking than polyester resin. It forms better secondary bonds. It is more waterproof. Boats are built with epoxy, but, due to the higher cost of the resin, it is often only the more expensive or exotic hull laminates which use epoxy. Competitive sailboat hulls, for example, are usually molded with laminates using epoxy. When you make a repair to a Boston Whaler with polyester resin there is little chance that you will be using the same resin that was used to produce the laminate. Boston Whaler does not divulge the identity of the resins it uses in making Boston Whaler boats. It is very likely you will be using a different resin than the original laminate. As I have said before, it seems quite likely that the reason the factory has recommended polyester resin be used to make repairs is because the factory has polyester resin available to it in huge quantities and their experience with making repairs or secondary bonds has been with polyester resins. It also avoids putting them in the somewhat awkward position of making a boat with one material then recommended repairing it with a different material.
Roarque	posted 11-05-2005 07:01 PM ET (US) Found a good source for epoxy resins here in Nanaimo BC. The sales person noted that epoxy resin does have superior adhesion characteristics to cured polyester BUT polyester resin cannot be then applied over epoxy resins. Since gelcoat is only sold with a polyester resin base, this poses a problem for surface finishing the epoxy resin repair. The solution proposed by this supplier is to paint the repaired area with epoxy paint. My plan is to repair with epoxy resin and chopped cloth, then sand smooth and apply a coat of epoxy paint to match the desert tan hull. Fortunately the repair is to the bottom of the boat, visible solely to salmon and cod. To the best of my knowledge there are no CW correspondents who claim to be of either of these spieces.
PeteB88	posted 11-06-2005 06:52 AM ET (US) I seem to always gravitate to West Systems but agree System 3 and some of the others are fine products. It is my understanding that the Gougeon Bros and West were first on the market, targeting marine use, like System 3 and that W E S T is an aconym for Wood Epoxy Saturation Treatment but am not certain of that . There has been plenty said about epoxy for repairs and mods but it is important to remember that marine epoxy is better than anything for bonding or coating to bare wood especially for finish coatings. Epoxy base coats over wood, application and wet out of fiberglass cloth or kevlar or graphite with epoxy resins underscores the extreme vesatility of epoxy. WHen it gets down to it customer service and ease of use prevail. Marine Tex gets a nod because it is pigmented and you do not have to coat over it. It is very handy for repairs but kind of messy to work with - - and too expensive as far as I'm concerned. best