GRP, Epoxy or Poly...?

Hi
I have one (maybe stupid) question. Have a keelboat, info says it is GRP, built in 1990. There is a need to fix/reinforce some areas, and I am unsure about what resin should I use.
I know there is epoxy, polyester(?) and probably some more, and I had an experience it should be applied one some kind on the special kind, and not this or that. Do you track what I mean? Should epoxy work with said GRP? Are there any tricks or "no-ways"? Of course I am going to use some woven (cloth) as well, but how to choose the resin?
Thanks for cooperation.

 

epoxy or polyester

Hi you can not use epoxy if the the boat is built with polyester

 

you can use epoxy over polyester, you can't use polyester over epoxy. polyester has a very poor secondary bond when it comes to adhering to epoxy. epoxy on the other hand will pretty much stick to anything.

you must remember at this point you're not going to get a chemical bond. IF the boat was made using polyester (as it probably was being a high volume manufacture) using polyester will save you some money. the epoxy has a much superior secondary bond than the esters do as well as other physical properties. vinylester comes close to all the properties of epoxy at slightly less the cost.

most use epoxy for repairs and esters for making new parts. i buy 5 gallon epoxy kits from us composites for a little over 200. their 5 gallon vinylester kits are 160. so cheap, good quality epoxies can be found. $50 is cheap insurance when not having to worry about the secondary bond of a repair, the there are many boats out there still running around repaired years ago with polyester resins.

if you're going to to with polyester, stay away from the casting resins. they're the cheapest of the resins for a reason. isopolyester is an excellent resin to use as well as the vinylester. mostly it's a matter of choice.

 

Stick tp GRP.

 

GRP or glass reinforced plastic (or FRP, fibreglass reinforced plastic) is a composite of glass fiber and a plastic binder. the plastic binder can be either polyester based resin, epoxy based resin or any kind of thermosetting plastic. without know exactly which 'plastic' was used it's it hard to tell what the boat was made of without contacting the manufacturer directly. safest, cleanest and less smelliest way to go would be epoxy.

 

I agree with Grantn too - trying to match Poly to existing hull/deck is a lottery. You may get satisfactory performance, or you may not. Epoxy will be your best sure bet.
Now if you are just going to tart up prior to sale .....

 

Not knowing exactly what boat you have makes it a little difficult, only because if your boat is made of wood and then covered in "GRP", then it's epoxy, if it's just "GRP" then it's most likely polyester. Very few production boats are made with epoxy, some very high end boats use it, but the vast majority are made with polyester resin. Epoxy is needed over wood because it will bond much better to it. If the boat is made from polyester resin, then using polyester resin to repair it is fine, there's no real need to go with epoxy for normal repairs.

Before people start screaming that epoxy is the only good way to do a repair and that polyester won't hold up, a few things need to be explained. Epoxy does bond better to most things than ployester, it's a much better glue and as a resin is much stronger. But most boats have many secondary mechanical bonds in them and the larger the boat (Yacht), the more mechanical bonds there are. Some of these large hulls are lengthend during production or at a later date and polyester resin is normally used to do these modifications with no issues.
The main reason for the "polyester doesn't bond well" line of thought is mostly due to the poor methods used to do repairs by inexperianced people. Many people do a very poor job on the prep work, with little or no sanding and not even cleaning the dirt off the surface before slapping on some cloth and then flooding the area with resin. This type of repair is doomed and will fail very soon, then the resin is blamed, epoxy will hold up better in this situation.

With polyester the surface needs to sanded well, 36 grit on a grinder works well and it needs to be clean, with all the wax, oil, dirt, moss, old paint, gloss and anything else on the surface removed, this is important for epoxy also. Mat needs to be used as the first layer, cloth or roving will peel off easily if used alone, or as the first layer. Everybody knows that epoxy needs to be mixed accurately, but they feel it's not as important with polyester, the short answer is, "yes it is". Stay between 1 and 2% with catalyst, mix it very well and you should be safe, using more or less can lead to an undercured laminate that will never achieve the physical properties it should have. If it's cold out you need to heat the area you're working on, when it's hot out mix less resin at a time, don't go with too little or too much catalyst, it may still get hard, but that doesn't mean it's properly cured.

When done with even some attempt at doing a good job, polyester on polyester repairs hold up with few problems.

 

"Before people start screaming that epoxy is the only good way "
I think I said ' trying to match Poly to existing hull/deck is a lottery' in a very well modulated typing style.

"no real need to go with epoxy for normal repairs"
What is this NORMAL repair? The repair can be cosmetic, structural, water facing, deck facing, internal, non structural etc etc etc.

"Epoxy does bond better to most things than ployester"
Epoxy bonds to EVERYTHING better than Polyester!

The question is why would you NOT use epoxy ???
Is it the few cents extra you will pay for the superior *guaranteed* result.
Is it the joy of being able to say "'There, that Polyester fix on your thru-hull fitting *should* be all right " ?
The fact that you hate the local Epoxy Distributor?

" polyester doesn't bond well line of thought is mostly due to the poor methods "
.... and the fact that to get a chemical bond in Poly you not only need to prepare well, you also have to match the chemical composition down to the percent of catalyst - or temperature, moisture, mechanical strain MAY work the repair and cause separation, and I dont know of ANY repair where that is desirable. What is the point of doing something that MAY work???

 

Sorry if you thought this was pointed at you, it wasn't, it's to ward off the line of thought that "only" epoxy will work.

Rarely is epoxy needed to do a good repair, there are times when it is, but for the most part it's not. Matching the exact chemistry or catalyst percent of the part being repaired is not needed and I see very few repairs fail for reasons other than poor workmanship.

I have no problems with the local epoxy reps, we see each other at shows and seminars, plus we really don't sell to the same markets.

If you wish to use epoxy on every repair, then that's up to you.

 

Most know my views on epoxy, but for the majority of repairs on production boats polyester is fine and in fact is the material of choice for marinas, yards and shops.

 

Thanks guys!
I had a deal with the builder, and waiting for the answer. But I think there is never too much info if you are able to kind of sort it out
And even more, I appreciate the opinion of people who do the job - I mean, if you are repairing your boats, it might be worth listen to you, and then to the company that are building boats every day.
The mixture will be hull (GRP, I guess no wood here), stainless steel stiffeners and wooden side panels; biggest surface of GRP, wood is smallest.
Does it change the case?

 

Buy the Gougeon Brothers book. http://www.westsystem.com/

Pericles

 

i always say "stay with what your boat was made with" but,,,shhhhhh epoxy dudes ,,,if you dont know what it was made with, epoxy is your best bet ( i hate epoxy) but theres time i have to sercome to "the other side"
chemical bonds in poly can ONLY happen if what your putting on today is against something made YESTERDAY. poly only chemically bonds to itself within 24 hours,,,after that its a mechanical bond. I use poly on everything i can,,and its how you prep that counts,,,but that also goes with epoxy