Polyester resin remains tacky

[Kez]

I know the difference between laminating resin and finishing resin. I have experience with polyester resins and have been molding my own parts. However, my experience is that finishing resin with wax added will cure tacky if spread to a thin layer. This is especially true if you apply it as the first layer on bare wood.

I am finishing an old new Dumas hull and needed to seal the inside with finishing resin. I did not want to apply a thick layer to fill the weave. I brushed on a layer of finishing resin and used a squeegee to spread the resin. Now it is tacky like laminating resin.

Question: Has anyone tried brushing MEKP (the catalyst) on the tacky resin to force it to cure? Any other tips? I do not want to brush on another layer of resin as it will add weight and there is no guarantee that it will cure properly.

Thanks, k

 

[David Murany]

I would try heating it and letting it cool a couple times. I've found the thin layers don't quite generate the heat a thicker layer does during the chemical reaction. Might just take longer to cure.

 

[Kez]

Good point on heat generation. That makes sense. A thin layer of resin may not generate enough heat. I moved it to the attic and will leave it there for a day. The problem is that the MEKP in the resin may break down after a day or so. I will find out and report on the results

 

[Mark Poole ModVP]

Is this resin fairly fresh? I started writing the date on the can the day I purchase it so I know how old it is. I would mix that same resin again and paint some on a non porous surface to see if it hardens all the way. If it does then I would brush another coat over the tacky one.

 

[HTV Boats]

Polyester resin is not going to seal wood. Moisture wicks through resin. Use Gel Coat or Epoxy to seal water out.
The purpose of wax is to seal air away from curing resin. With heat generated in the curing process the wax rises to the surface. When repairing gel coat that has no wax PVA can be used to seal the surface. (PolyVynilAlcohol)
I have seen layups not cure due to temps (too cold) and insufficient hardener. Sometimes a coat of hot resin will get the job done but heat and time is the cure. Here in Florida you need very little hardener and putting a part in direct sun will generally speed the process.
Mic

 

[Bill Gibson]

2nd that. Polyester resin is not water proof. Epoxy resin is.

 

[Kez]

Thanks Guys for your replies.

Mark, I bought the resin last summer so it is relatively fresh by my standard. The left over resin in the mixing container cured OK. So it is probably not the resin. I am reluctant to brush on another layer of resin because it will add weight. If I was glassing the outside of the hull, I can always brush on another coat to cure and sand it down. But it is not easy to sand the inside of the hull.

Mic, since polyester is not compatible with epoxy, I have always used epoxy to coat the wood rails and the transom doubler. I may decide to brush on a coat of KlassKote clear from now on to waterproof it. I have PVA but never tried to brush it over wet resin. Do you have to wait for the resin to set up before you brush on the PVA? Or do you brush it on while the resin is wet? And how do you remove it later? Does it come off in a sheet?

Bill, do you use epoxy on a polyester hull? Any issues? I understand polyester will not cure over epoxy. So repairing the hull may be an issue if I coated the rails with epoxy.

Has anyone tried brushing MEKP over sticky resin? I am tempted to try it.

Thanks, k

 

[Carl Van Houten]

If it has not cured completely your best bet in my opinion is to generously wet a piece of cloth with acetone and scrub the uncured resin off and start over. Before you try it again do an "off part test" to make sure you have control of your product. I would get it off now while it will be easy enough to do. If you try the MEKP bath or heat, it may not give you what you are expecting.

I have over 40 years experience with poly. Wash it off and start over and this time be sure what the outcome before you start and you will be much happier with the outcome.

Good luck,
-Carl

 

[Daren Worboys]

Hi I built race cars in the 80/90's in winter if the job didn't cure fast enough we put a heater under the job and cured it that way. Daren

 

[Kez]

Update: I can share what did not work. I first tried putting the hull under a 60W light bulb (incandescent) for 12 hours. The wax started to float to the surface in some area but it is still soft. I then tried brushing on some MEKP and then put cellophane on top. Put the boat in the attic and let it bake. It is still tacky after several hours. Put the hull under the sun for a day. Same thing. I think the resin has cured but it is the very top layer that is tacky.

I still have a can of acetone. After reading Carl's suggestion, I decided to wipe it off. It took a lot of acetone to clean up the sticky stuff. And a lint free cloth is a must. It is still a little sticky but after leaving the whole thing to dry, it is now just slightly tacky. If I touched it with my fingers, the resin will not stick to my fingers. Some of the resin has cured and filled the weave somewhat. I think I am going to leave it alone.

Daren, Like I mentioned in the first post, I never had issues with the resin not curing if I brush on a thick coat such as in a layup. This issue only happens when I brush on a thin coat. Next time I am going to try putting the parts under a heat lamp right away. I suspect after a couple of days, applying heat will have little effect as the MEKP may have evaporated or become ineffective.

Thanks all for sharing your experience

 

[Bill Gibson]

Update: I can share what did not work. I first tried putting the hull under a 60W light bulb (incandescent) for 12 hours. The wax started to float to the surface in some area but it is still soft. I then tried brushing on some MEKP and then put cellophane on top. Put the boat in the attic and let it bake. It is still tacky after several hours. Put the hull under the sun for a day. Same thing. I think the resin has cured but it is the very top layer that is tacky.

I still have a can of acetone. After reading Carl's suggestion, I decided to wipe it off. It took a lot of acetone to clean up the sticky stuff. And a lint free cloth is a must. It is still a little sticky but after leaving the whole thing to dry, it is now just slightly tacky. If I touched it with my fingers, the resin will not stick to my fingers. Some of the resin has cured and filled the weave somewhat. I think I am going to leave it alone.

Daren, Like I mentioned in the first post, I never had issues with the resin not curing if I brush on a thick coat such as in a layup. This issue only happens when I brush on a thin coat. Next time I am going to try putting the parts under a heat lamp right away. I suspect after a couple of days, applying heat will have little effect as the MEKP may have evaporated or become ineffective.

Thanks all for sharing your experience

Now you can scratch it up and seal it with epoxy! I like West Systems epoxy resin and very slow set hardener or a Laminating epoxy resin!
You may plug up the sandpaper when you scratch it up so have plenty of sand paper on hand........epoxy over polyester is fine, just be sure to abrade the surface..........NEVER POLYESTER OVER EPOXY! Good luck!

 

[Kez]

Now you can scratch it up and seal it with epoxy! I like West Systems epoxy resin and very slow set hardener or a Laminating epoxy resin!
You may plug up the sandpaper when you scratch it up so have plenty of sand paper on hand........epoxy over polyester is fine, just be sure to abrade the surface..........NEVER POLYESTER OVER EPOXY! Good luck!

I have never tried sealing the inside of a polyester glass hull with epoxy although I know the epoxy will cure properly. My concern is that if I ever need to repair the hull, like glassing in a new stuffing tube, I will have to sand the repair area free of epoxy or the resin will not cure as you have pointed out. Another option is to use epoxy for any repair that I may need to do. k

 

[Mark Poole ModVP]

I would have to say that the year old resin part of the problem. One of the things that will happen to resin over time is the wax 'migration' will not work as well. If I have a can of resin in the shop that is more than several months old, I might use it for 'home' projects but not in my boats.

I respectfully disagree with poly not being waterproof. There can be an issue such as in the bilge of a boat if the surface is left bare and not gel coated. Still, it would have to stay saturated all the time to be an issue. Finishing resin is waterproof. The 3M brand resin that I have always used since the mid 1980's has never failed me. I have 20 year old hulls that are as tight and straight as when they came from the mold.

 

[francois peilleron]

Take care about MEKP it is very dangerous,I read an article about it;one guy unfortunately got some in his eyes he got blind on one
eye right away and lost his second one eight years later and there was no cure to stop this process;this article mentionned you have
4 seconds to remove it with water
Since I read this aeticle I use only epoxy which is toxic too but not
that far
FRANCOIS

 

[Bill Gibson]

I would have to say that the year old resin part of the problem. One of the things that will happen to resin over time is the wax 'migration' will not work as well. If I have a can of resin in the shop that is more than several months old, I might use it for 'home' projects but not in my boats.

I respectfully disagree with poly not being waterproof. There can be an issue such as in the bilge of a boat if the surface is left bare and not gel coated. Still, it would have to stay saturated all the time to be an issue. Finishing resin is waterproof. The 3M brand resin that I have always used since the mid 1980's has never failed me. I have 20 year old hulls that are as tight and straight as when they came from the mold.

Mark, When the ester product in polyester evaporates, it leaves microscopic pores that can pass water thru the part, making it water resistant, but not waterproof.........epoxy resin is waterproof and is superior in strength to polyester resin, followed by vinylester resin which is also waterproof because it carries epoxy molecules in it, and is stronger than polyester resin, but not as strong as epoxy.......boat builders and such use polyester because it is cheap price wise compared to the other 2. Gel coats make the hull more water resistant because of chemicals added to them, but as the gel coat chalks and fades over time it becomes less resistant to water intrusion.

 

[Carl Van Houten]

As mentioned MEKP is very toxic. I keep a small bottle of dish washing soap and water close by so that I get any on my hands while mixing (and eventually it will happen) so I can quickly wash it off. I also advise that you use something like Nitrile gloves while you are doing your layups because it is also not good to continuously wash your hands in Acetone to remove resin. Not everybody will react the same but I had a friend who developed a very painfull nerve condition from not using protective measures while using Poly products and over a period of 45+ years of building parts it eventually killed him so be careful.

 

[Gary Girvin]

Hi Guys, I have used both polyester resin and epoxy over the last 50 yrs. if i am working on a polyester boat. I will most likely use polyester resin. The only time that I have had problems with it not curing was when I used old mek hardener. I have found that the resin has a longer shelf life than the hardener. If my hardener is more than 6 months old, I will discard it and get new. Epoxies have a longer shelf life but, may discolor or thicken up . A little heat will make it thinner to use. I use epoxy for sealing all of my wood boats. Thank you, Gary

 

[Rudy Formanek]

I, too, have had more problems with old hardener than old resin. Hot Sacramento garages seem to age hardened quickly.

 

[Kez]

Thanks Guys for all your replies. Lots of good information here. I would like to share my own experience.

On MEKP...I always wear safety goggles when I mix resin. Furthermore, I put the tube of MEKP in a sandwich bag and open the cap in the bag. It is especially important when I pierce open a new tube of MEKP.

I did notice Bondo (3M) resin for auto repair tends to set up more consistently. However, it is thicker and does not flow very well. I buy laminating resin and finishing resin from West Marine. The finishing resin flows nicely but it is more likely to have curing problem. I shake the can before pouring the resin out just in case the wax will settle out. It did not help in this case.

I agree that epoxy is lighter and stronger than polyester resin. But I try to use the same resin that the hull is made from. Epoxy on epoxy hulls and polyester resin on poly hulls. One issue I noticed with poly is that a large unsupported area like the deck often sag or become wavy over time.

Good point on MEKP turning bad. It may be part of the problem. I normally mix a small batch at the beginning of the summer. If it sets up OK, I will continue to use it. However, as I have learned, just because the resin sets up OK in the container does not mean it cures the same once you applied it. Probably because there is less mass and therefore less heat generated.

Thanks, k

 

[Carl Van Houten]

I purchase MEKP by the quart. Depending on my build schedule a quart may last 6 months but I have kept it for 2 years before and still used it. The trick with poly hardners is to keep them out of any sunlight (even indirect sunlight) The ultra violet rays will kill these types of hardners. Do that and you will avoid these types of problems down the road.
-Carl