Best Prep For Re-gel Coating?

[Darkhorse1201]

Hello to all - I am going to re- gelcoat my boat (I know, I know - paint is easirer but I have my reasons) and want to know any suggestions for preping the fiberglass hull other than just sanding the bejebus out of it. Thanks!

 

[Chris1956]

Re: Best Prep For Re-gel Coating?

Yoy should check the direction on the gel coat. I would think that a 400 grit wet/dry sanding of the surface is what you want. Then wipe everything with acetone.

Are you going to need to cover the wet gel coat with plastic to help it cure?

 

[ondarvr]

Re: Best Prep For Re-gel Coating?

Use 80 grit to prep the surface for a good bond. Any small stress cracks need to be sanded out and filled with glass or they will return, don't just leave them or use use body filler. Gel coat won't stick well to epoxy so don't use it to do any repairs. Don't worry about very small imperfections in the current surface, gel coat goes on fairly thick, and you will be doing lots of sanding after it's sprayed, so they'll get filled and hidden.

Don't thin the gel coat more than needed, it will lessen it's ability to hold up to water and UV rays and use a product designed to thin it, styrene and acetone aren't the best products to use, but can work if used in very small amounts (less than 5%).

Make sure you catalyze the gel coat at 2% and mix it very well.

Make a test panel before you spray the boat to make sure everything is working as planned, sand the test panel to make sure there's no porosity.

You will need to put on at least 20 mils to have enough to sand on, so put on that much or more, 25 to 30 would be better.

You didn't say how big the boat is, but if you can turn it over it will be much easier to do a good job.

 

[Darkhorse1201]

Re: Best Prep For Re-gel Coating?

Use 80 grit to prep the surface for a good bond. Any small stress cracks need to be sanded out and filled with glass or they will return, don't just leave them or use use body filler. Gel coat won't stick well to epoxy so don't use it to do any repairs. Don't worry about very small imperfections in the current surface, gel coat goes on fairly thick, and you will be doing lots of sanding after it's sprayed, so they'll get filled and hidden.

Don't thin the gel coat more than needed, it will lessen it's ability to hold up to water and UV rays and use a product designed to thin it, styrene and acetone aren't the best products to use, but can work if used in very small amounts (less than 5%).

Make sure you catalyze the gel coat at 2% and mix it very well.

Make a test panel before you spray the boat to make sure everything is working as planned, sand the test panel to make sure there's no porosity.

You will need to put on at least 20 mils to have enough to sand on, so put on that much or more, 25 to 30 would be better.

You didn't say how big the boat is, but if you can turn it over it will be much easier to do a good job.

Thanks for the headsup on the 80 grit. Its kinda what I figured as gelcoat is thick and I figured it needed to "grab" the underlaying surface.
You say to fill all the stress cracks which I plan on doing. I was going to use Formula 27 fairing compound - is this not a good idea?
I will be putting on about 30 mils to allow for wetsanding afterwards.
The boat is 18' and still together (I/O motor, etc.) so turning it over is a no go.
Thanks.

 

[BillP]

Re: Best Prep For Re-gel Coating?

Sand like hexx at 45 degree angles from sheer to chine...and do a final wipe down with styrene before spraying. Styrene will help chemically link the old to new surfaces. Most boat factories strive for a finished thickness of 35-40 mils. The better ones have a device that measures it. Too thin cracks and too thick cracks. Less than 30 is pushing into the too thin category...over 40 is too thick. You're sanding down to get the finished product so I'd try to get at least 40 mils as a starting place. When mixing it do it easily to avoid entrapped air and apply in several passes instead of one.

About the thinning. Gel cote and poly resin is made with styrene. I've used styrene with stellar results on boat plugs, molds and finished products. All I've known to be correct is styrene for thinning and gelcote mfgs still spec it. I suspect special gelcote thinners are really relabled styrene with additives but don't know that for sure. Acetone isn't made for thinning poly resin and not anywhere close to styrene...but it works. Acetone evaporates too quickly and removes styrene already in the gelcote...which makes it pourous. Those swirl mark areas you see in the gelcote on boat hulls, thats usually from thinning with acetone or using way too much styrene.

bp

 

[Darkhorse1201]

Re: Best Prep For Re-gel Coating?

Thaks for the info. I am planning on using Styrene anywyas as thats what the maker of the gelcoat I bought recommends.

 

[ondarvr]

Re: Best Prep For Re-gel Coating?

The small stress cracks are from that portion of the boat flexing, it may be flexing most of the time, or it may have only been flexed once from an impact, it's hard to tell without seeing them. Gel coat has no strength and is somewhat brittle and the fillers (fairing compounds) have little or no strength also, so you are removing the cracked material and replacing it with something that's no stronger than what cracked before, plus some cracks go deeper into the laminate and will return very soon even without any stress or flexing.
Reglassing them is the only way to help ensure they don't return and if that area continues to flex they can still come back.

There are many misconceptions about gel coat and I want to clear some up.

Styrene is a very important component of gel coat and resin and they are formulated to have a certain % for best performance. If more is added there are many negative results, as the styrene becomes the weak "link" in the crosslinking process. Styrene yellows and degrades in sunlight, it is also less water resistant than the base resin in the gel coat, plus it's not as strong or flexible, so you end up with a product that is less water, weather and crack resistant. Not exactly the qualities you're looking for in a gel coat.

Styrene will clean the surface, but it does not promote a chemical bond to the old gel coat, some call it reactivating the gel coat or resin, but it doesn't happen.

The recommended gel coat thickness is 18 to 20 mils wet, on hulls you can go a little thicker, but if you apply too much (30+) cracking can become an issue. Also thick gel coat tends to yellow sooner than thinner gel coat.
Thinner gel coat is less blister resistant, but more crack resistant and has less yellowing. You can get a mil gauge designed to check the thickness, they're small and cheap (a couple of bucks) but can be hard to find in the retail market.

Patchaid type products that are designed for thinning gel coat may, or may not contain styrene, but also have other ingredients like the same quality base resins (only unthixed) that are already in the gel coat to help reduce the viscosity, instead of just styrene. They also contain extra promoters that help the gel coat cure in a thin film, some also have wax so the surface will cure tack free.

There are only a few companies that make gel coat and even fewer that also make the base resins that go into them. So if you're buying gel coat retail, it's normally not from the manufacturer and there is no real way to tell who made it, as many of the retail companies change suppliers frequently looking for a better price.

I do have another question though. You said you have reasons for wanting to re-gel coat and not paint, and there are good ones, what's yours?

 

[Darkhorse1201]

Re: Best Prep For Re-gel Coating?

The small stress cracks are from that portion of the boat flexing, it may be flexing most of the time, or it may have only been flexed once from an impact, it's hard to tell without seeing them. Gel coat has no strength and is somewhat brittle and the fillers (fairing compounds) have little or no strength also, so you are removing the cracked material and replacing it with something that's no stronger than what cracked before, plus some cracks go deeper into the laminate and will return very soon even without any stress or flexing.
Reglassing them is the only way to help ensure they don't return and if that area continues to flex they can still come back.

There are many misconceptions about gel coat and I want to clear some up.

Styrene is a very important component of gel coat and resin and they are formulated to have a certain % for best performance. If more is added there are many negative results, as the styrene becomes the weak "link" in the crosslinking process. Styrene yellows and degrades in sunlight, it is also less water resistant than the base resin in the gel coat, plus it's not as strong or flexible, so you end up with a product that is less water, weather and crack resistant. Not exactly the qualities you're looking for in a gel coat.

Styrene will clean the surface, but it does not promote a chemical bond to the old gel coat, some call it reactivating the gel coat or resin, but it doesn't happen.

The recommended gel coat thickness is 18 to 20 mils wet, on hulls you can go a little thicker, but if you apply too much (30+) cracking can become an issue. Also thick gel coat tends to yellow sooner than thinner gel coat.
Thinner gel coat is less blister resistant, but more crack resistant and has less yellowing. You can get a mil gauge designed to check the thickness, they're small and cheap (a couple of bucks) but can be hard to find in the retail market.

Patchaid type products that are designed for thinning gel coat may, or may not contain styrene, but also have other ingredients like the same quality base resins (only unthixed) that are already in the gel coat to help reduce the viscosity, instead of just styrene. They also contain extra promoters that help the gel coat cure in a thin film, some also have wax so the surface will cure tack free.

There are only a few companies that make gel coat and even fewer that also make the base resins that go into them. So if you're buying gel coat retail, it's normally not from the manufacturer and there is no real way to tell who made it, as many of the retail companies change suppliers frequently looking for a better price.

I do have another question though. You said you have reasons for wanting to re-gel coat and not paint, and there are good ones, what's yours?

Thanks for all the info. First I buy my gelcoat stuff from U. S. Composites - whether or not they are the manufactuer I have know way of knowing but they are a reputable company and very helpful.
My reason for re-gelcoating the boat is twofold: 1) My boat sits in the lake from June 1 to late Sept with occasional haulouts for cleaning. I have read many threads here about performance of paints being submerged for long periods of time and the paint bubbling up from such and the additional cost of paint over gelcoat and while I realize gelcoat takes more labor - I dont mind. 2) My boat is an unusual color scheme (teal) and almost impossible to find in paint. I am slowing restoring this boat and I prefer to keep things as factory like as possible plus I dont wish to spend the huge $$$ it takes to custom mix the factory color as well as the danger that it might lift below the waterline.
But thanks again for the info as theres no such thing as too much information!!!

 

[ondarvr]

Re: Best Prep For Re-gel Coating?

Is the current gel coat bad enough that sanding and buffing can't bring back the finish? Since you are planning on redoing it any way, have at it with a sander and buffer to see if the color and gloss will come back, if it does you just saved a month or two of work.

Make sure you get a gel coat designed for marine type use, not all gel coats are formulated to be under water for long periods of time either.
Does US Composites have the teal color, or are you mixing it? The reason I ask is there are places that will sell you gel coat that's already color matched to your boat. It can be very difficult to do it yourself.

 

[Darkhorse1201]

Re: Best Prep For Re-gel Coating?

Probably could have saved it except for the hole in the side from the previous owner! Figured to do it all right the first time - my wife says Im kind anal like that - no such animal as good enough!!!
As to the gel coat - it is a marine version and yes the color is premixed in the exact shade of the original color.

 

[BillP]

Re: Best Prep For Re-gel Coating?

I don't know about misconceptions but do know this...Resin mfgs still spec styrene for thinning and zero spec acetone. Boat factories still use styrene for thinning...big expensive high end boat mfgs use it. Surfboard mfgs still use styrene. Gelcote mfgs still publish in their specs that too thin or too thick will crack and they speak of 40 mils. The differences I see from working on old boats is thin makes a million tiny cracks over the entire surface that can hardly be seen or felt and too thick makes large cracks that show more in stress areas...empiracle evidence but my conclusions reflect what mfgs say. I also know from visiting large high end boat factories within the last few yrs that 30-40 mils is spoken on everything from molds to finished products.

On the styrene deal...Using styrene to prep a previous glass surface definitey does something to make a stronger bond between old and new... much better than acetone. Anyone who wants to see it up close and personal can do simple testing of their own. I did R&D in a glass shop making rc boat hulls. We were laminating hulls/decks and trying to find the best way to glue or glass in solid fiberglass stringer/motor mounts for .60 glow engines. For experimenting I took several hulls, wiped the work surface with acetone (some WERE sanded and others NOT sanded) and used regular polyester laminating resin as a glue to bond the glass stringers on. The ones that weren't sanded and wiped down with ACETONE broke off easily by hand. The sanded ones broke off with more difficulty but not a great deal more difficulty. Next I did the same process but used STYRENE to wipe down with. There was a huge increase in bonding strength and it took a hammer to bust the sanded ones loose...this was with straight poly resin as a glue...which isn't even supposed to be used as a glue (like I said this was R&D to see bonding strength between different processes). I even walked on the hulls to break them loose and the hulls cracked before the stringers busted loose. There was NO contest in strength between those prepped with acetone and those prepped with styrene. I've always been told by factory resin reps that styrene cross links and gives better bonding...in my mind they were proven 100% correct and I've used styrene for prepping before glassing ever since.

Whether someone uses too much styrene for thinning and causes problems is another topic but I believe it takes more to do damage than most would ever use.

OK, I'm off the soapbox. bye.

bp

 

[ondarvr]

Re: Best Prep For Re-gel Coating?

BillP

My intent is not to create an argument with you, only to give accurate information, and I know that many of the things people believe about gel coat and resin have a grain of truth, but are not exactly correct.

If you read any information on applying gel coat (from the manufacturer) it will say 18 to 20 (or very close to that) mils and only slightly more on hulls to help prevent blistering. Anything over 30 is in the danger zone for cracking, less is not an issue for cracking if it's cured well. The thicker amounts you talk about can be used in tooling, one reason is molds are supposed to be made more ridgid than a part, so they should see less flexing, which means less cracking, so the gel coat can be thicker. Another reason is that many molds get sanded after they're made, so there needs to enough gel coat to sand and buff it a few times during it's lifetime. Thicker gel coat can also help keep the glass from printing through to the surface, but the thicker gel coat is made possible by having less flex in the mold.

In lab testing it's been proven time after time that thicker gel coat tends to yellow sooner than thinner gel coat.

I know of no high end boat builders that thin their resin with styrene, we sell them the resin at the correct viscosity for them to use in there plant. Nor do I know of any resin manfacturer that says to thin it with styrene.
Adding more stryrene doe's not improve resin, as I said before it degrades it, adding more than just a few percent can weaken and lessen it's water resistance. If a lower viscosity resin is needed, then it's always best to have the resin manufacturer sell you one formulated how you need it.
At one time resin was typically from around 40% to as high as almost 50%
styrene, now the majority of it is 35%, this is due to federal regulations. The % is not important part though, it's that it was formulated to have that % for best performance, not more or less. Small shops and most retail outlets can still use the higher styrene resins in most areas of the country, so if you start with 40 to 50% styrene and then start adding more, you end up with very little actual resin in the mix and the resin is where the strength is.

We do find that many shops, or at least some of the people in their repair departments, like to concoct methods of thinning the gel coat to spray it for doing repairs, that's noramlly why we're called in to do a repair class.
If there are 10 people doing repairs, we typically find 3 of them have very few problems and their repairs turn out well almost all of the time. 4 or 5 will have more problems, but still not bad, the remaining few have problems all the time, with very inconsistent results. These last few rarely follow the recommended methods or measure anything, they use the glug glug method, just pour it in until it looks right, then sort of mix it. Adding styrene and acetone are 2 of the things that create those problems and it takes less of them than you might think. If you follow the recommeneded methods of using the correct products you will get much more consistent and long lasting results.


The styrene helping the bond opinion has more merrit. Styrene can start to break down resin that is not thoroughly cured (it can damage cured resin also, but takes much longer) and depending on the type of resin may have more or less of an affect. But it doe's not reactivate the resin, I know you didn't say this, but that's a term many people use. Styrene can do a very good job of cleaning the surface, and like Tail Gunner found out when painting his boat, acetone evaporates very fast and may not clean the surface adequately. Styrene does not evaporate as quickly and can do a better job of cleaning the surface. If you were sanding the parts correctly, then you should have been getting a very good bond. When bonding with ployester resin the bond may be very good, the problem is the resin is brittle and weak compared to the glass fibers it's designed to be used with. So when it's used without glass, what normally fails is the resin layer between the two parts being glued, not the bond, the surface of each part will typically still have resin stuck to it after it's been broken apart. There is also a huge difference in the strength of different types of polyester resins, so depending on the resin used the results may very.



These are not just my opinions, they are also from the chemists in our lab that formulate and test the products we make.
I must say that a few years ago I did ask them to test the styrene helping the bond issue again, but I don't think they did. I just wanted more testing done in this area. I do feel that if styrene is used, then at least whatever amount of it is left on the surface will not be as much of a contaminate as other products might be.

 

[ondarvr]

Re: Best Prep For Re-gel Coating?

If anyone would like a copy of our book on composites and their use, send me a PM and I will try to email you a copy at N/C. You will need a high speed connection and it doesn't always work though.
This is a manual on how to use resin and gel coat, it is "not" a catolog and we do "not" sell to the retail market.

 

[Tail_Gunner]

Re: Best Prep For Re-gel Coating?

:redface: Indeed that was a lesson, i had wiped down the boat twice maybe three time's with acetone both before and after scuffing the surface with sand paper. Made my first shot of Perfection paint and there were a million pin hole's in some area's while other area's were perfect, I no longer use acetone when prepping paint, i wipe it down with styrene only and have never had the issue since.

 

[BillP]

Re: Best Prep For Re-gel Coating?

Couple of random comments...and any arguments can taken up with the majority of resin mfgs who post their specs online. Googling still shows them specing styrene for thinning. Gelcote is the same and they still say too thin or too thick is prone to cracking. Looking at product labels (as mentioned by swsidlo about the gelcote he has) at retail level (where I live too) still shows styrene speced for thinning. "Scientifically" speaking they still say styrene chemically links. This isn't saying mfgs don't spec other "stuff" but it isn't dominate.

From my own experience and practical application...most every tradesman who pro glasses for a living knows too much styrene for thinning breaks the resin down. They know the amount normally used for thinning doesn't come close to giving a problem with yellowing or anything else. So while it's technically (and politically?) correct that too much styrene is harmful...raw "scientific" data has to be put in perspective.

I suppose (just guessing) the main reason resin contains less styrene now than yrs earlier is more likely caused from the EPA tightening down on the chemical industry by taking harmful hazmat out of products. Rarely does it make the product higher quality or longer lasting.

Regardless of all the bs and back to the root of the original post. Prepping or thinning with styrene gives a better job 99% of the time. Use it (as directed by the majority of mfgs) and get better bonding or thinning than if using acetone. It doesn't matter how or why.

bp

 

[ondarvr]

Re: Best Prep For Re-gel Coating?

The people advising the use of styrene to thin resins and gel coats are not the manufacturers of the products, they are the people I (we) sell them to. The reason they (the retailers) say to use styrene is because most of the time the affects aren't noticed immediately and people with less experiance won't know or notice the difference. If you make a repair and it fades or fails in some way in a year or two, typically they think either the product was supposed to do that (as in low quality product), or that they did something wrong. Plus styrene is easier to find and and keep in stock because it has a long shelf life. The retailers also want to buy as few types or formulations of resin as possible and for the least amount of money, so if they can tell the consumer to just add styrene if needed, then it makes it much easier on them.

The general idea in the market place is that polyesters do not stick well, are not that water proof (resistant), not very strong and will fail and cause the wood to rot, and that epoxy is the only way to go. Not using the products correctly is what leads people to these conclusions.

As even I said in my first response, although not recommended, acetone and styrene can be used in small amounts (less than 5%) without too many side affects. What I see recommended by many people is thinning resin by 25 to 50% with styrene to help it soak into wood, it may soak in better, but you just killed the rest of it's good properties. What we see in the field being done by people in the industry is similar, they tend to add far more than what's what OK, in the "if a little is good, then more must be better" state of mind.

If I'm doing a repair or building something like I am now, in doing a major remodel on my house, I find that many of the ways even craftsman in the industry recommend doing things are not correct, or don't yield the best results. I get the best and most reliable information from the people that make, design and test the products I plan to use, that way I know if what I have in mind will work. I don't rely on the guy at Home Depot to get me the right information.

Much of the blame for the misinformation out there is on us as manufacturers, we do a poor job of getting this information to the users of the products, we sell it and if nobody has any questions, then we say nothing. Even most boat builders don't use the products as designed to get the best results.

The other problem with polyesters is that the chemistry is so forgiving, you can do many things wrong and still get a part or repair that appears to be very good, at least for a while. That's why there are so many misconceptions about how to use them.

 

[BillP]

Re: Best Prep For Re-gel Coating?

Yep, even resin reps have misconceptions. Several mfg web sites say use styrene. If a person can believe what DOW Chemical puts in writing...they invented and patented the styrene replacement for thinning polyester because the EPA started making companies reports usage of styrene over a measured amount per yr. Low styrene resin is made for that reason alone...they don't mention low styrene resin being better except for the hazmat issues. Dow also says styrene is used for the manufacturing of poly resin as THE thinner...and if they didn't use it the resin would be too thick for regular consumption. Their patented replacement thinner is added to resin with styrene. There's more but I'm not going there. Anyone can find the same info and make their own mind up.

 

[ondarvr]

Re: Best Prep For Re-gel Coating?

BillP

If you read what I said before it addresses this. I said new resins typically have 35% or less HAP (hazardous air polutants), this is due to federal regulations and the main HAP is normally styrene, the older formulas and some of the ones that can be used by retailers are much higher in styrene. I never said low styrene resins are better in any way than high styrene resins, I said that the actual % is not that important, what's important is that it was formulated to have a specific %, not more or less than that amount. If the resin is formulated to have 35% styrene and you add a bunch more, it will not perform as designed, this will happen whether it was formulated for 35, 40 or 50% styrene. I also said styrene is a very important component in resin, but if a little (correct amount) is good, it doesn't mean that more is better.

I did go the DOW website, it may not have been the one you visited though. They did talk about low styrene resin, but I saw nowhere were it said we (DOW) recommend you add styrene to our resin before use.

When resin is made, the main components are put in a kettle and heated or cooked and the cook is monitored until it reaches a certain point, this point can be different for different resins. When it reaches the correct point it is very thick and at room temperature would be considered almost a solid, at this time normally styrene (other monomers can be used also) is added until it is at a more usable viscosity for it's intended use. The ratio can be from 75/25 to 50/50 (resin/styrene), but is determined by what it will be used for and the type of resin it is. Other things are also added at this time, like inhibitors to keep the resin from reacting with the styrene. When catalyst is added, it breaks down the inhibitors and allows the reaction to continue until the resin becomes a solid.

The only thing I've been saying is that adding just about anything in large amounts to resin or gel coat will have side affects that may undermine what you are trying to do.

 

[BillP]

Re: Best Prep For Re-gel Coating?

The Dow site I read had a long list of products with pdf files on each to read specs. I read one that was about styrene as a thinner. Others I read were about DOW's different type of resins. Another site (patents) showed DOW's letter of request for a patent which explained the reason (to lower styrene emissions) for the proposed thinner.

All the misconceptions? This string started as asking for info to prep for gelcoat. Nobody suggested anything about using excessive styrene for thinning or that resin needed (or always needed) thinning before use. It is NO misconception (if a person wants to inquire about it), that gelcoat mfgs (not retailers) STILL spec in writing to thin gelcoat with styrene (of course it means IF the user desires thinner viscosity).

The end.