Polyester resin set time

[Kez]

We all know the setting time of polyester resin can be controlled by the amount of catalyst (MEK peroxide). The more catalyst the faster the setting time.

It's been quite warm and while trying to extend the working time of the resin, I keep reducing the amount of catalyst. Problem is below certain amount (I would say about 2 drops per ounce of resin) the resin just would not cure properly. So the longest working time I can get for a batch of resin is about 1/2 hour. This is OK to do a small part like a fuel tray or a hatch but it is too short for a boat hull or a complex part. Other than waiting for a cooler day, is there anything else I can do?

Epoxy is defintely easier to work with.

Thanks,

kez

 

[My Gypsy]

I feel your pain. I shot a gallon of gelcoat and started applying CSM to a new safety cell mold for my 2.5L hydro yesterday. It was 84 degrees in the shop. The gelcoat started to kick in 6 minutes. I was shooting 24 ounces in 3 minutes and then had to disassemble the gun and get it rinsed in acetone before it started to gel. I was using vinyl esther resin for the glass and was doing good to use 4 ounces at time before it started to gel.

Your resin manufacturer can recommend the lowest amount of MEKP. Beyond that, everyone I have talked to on this subject just says to work faster.

 

[Ted buckley]

We all know the setting time of polyester resin can be controlled by the amount of catalyst (MEK peroxide). The more catalyst the faster the setting time.

It's been quite warm and while trying to extend the working time of the resin, I keep reducing the amount of catalyst. Problem is below certain amount (I would say about 2 drops per ounce of resin) the resin just would not cure properly. So the longest working time I can get for a batch of resin is about 1/2 hour. This is OK to do a small part like a fuel tray or a hatch but it is too short for a boat hull or a complex part. Other than waiting for a cooler day, is there anything else I can do?

Epoxy is defintely easier to work with.

Thanks,

kez

Kez, I just finished-up on a SAW Hydro that I've been putting together and had the same results when trying to be cheap on the hardener. The sides of the boat turned-out sticky to the touch, but there are a couple things to try. I've been working with Poly. resin a long time. Try either wet sanding the sticky and let it dry. Try using some of the hardener on a soft cloth and wiping over the sticky. What happens it that the resin is dried underneath - but the surface seems to be sweating out - leaving the sticky. Kinda like working with Bondo. The surface feels kinda wet to the touch - but when sanded below the sticky gets drier underneath. Does this make sense?? :huh: Otherwise - eventually the surface Will dry out.

 

[Mark Poole ModVP]

If you are working in a shop in this heat it can be tough. What works for me is to have EVERYTHING else ready to go before I mix. I cut and prefit all the glass, have a cup of acetone ready and anything else that would need to be in place for building. If you are getting a half hour of working time while working at 90 plus I would say you must be very lean on the hardner. Even when my work area is 80 degrees I mix to only get about 10 to 15 min of work time. What I do on a hull is lay up half of it then flip the mold around, mix another batch of resin and do the other half. This way I am not rushing to get glass mopped out while racing against gelling resin.

 

[Dan Hutchinson]

Cobra Tunnel Boats

I had this same problem and i build lots of parts the key is just like john said have everything layed out and ready to go. this is how i do things. have my fiberglass mat already cut (i have patterns ) then measure out my resin i use 6 to 8 ozs of resin for a top or bottom. and 3.5 cc of hardener. (mek) then i stop and make sure i have all my pieces ready, my roller is free, and i have extra pieces pulled apart and ready in case i need a patch. then i make a last minite check then add the MEK and go, go, go !!! using this method usually gives me ample time to roll out all air pocket( usually ) Now in cases where its real hot i use a tub of ice to soround my resin cup. make sure you get the resin real cold. pour you resin first and let it chill this will give you a extra 15 minites of working time.

P/S im no expert by no means!

I do layup parts almost everyday, and after alot of trial and error. ive learned many new tricks. and i hope this helps you out. if you want you can call me and ill try to help out further (863)858-0536 Dan

 

[dwilfong]

One of my first jobs was in a fiber glass fab shop. Made all kinds of stuff. We used Copper naphthenate in the 55 gal drum mix to control the heat and set up time of resin.

I would do all the mixing first the cobalt then the copper naph. the kicker was hydrogen peroxide 50% solution. Back then we used asbestos for filler to make puddly.

Also would mix talcum power to make the gel coat.

Any horse store will have the copper naph. thy use it for hoof rot.

David

 

[Kez]

I feel your pain. I shot a gallon of gelcoat and started applying CSM to a new safety cell mold for my 2.5L hydro yesterday. It was 84 degrees in the shop. The gelcoat started to kick in 6 minutes. I was shooting 24 ounces in 3 minutes and then had to disassemble the gun and get it rinsed in acetone before it started to gel. I was using vinyl esther resin for the glass and was doing good to use 4 ounces at time before it started to gel.

Your resin manufacturer can recommend the lowest amount of MEKP. Beyond that, everyone I have talked to on this subject just says to work faster.

I usually use laminating resin for the layup but for this job I am using the 3M resin for autobody repair. It is a finishing resin and thicker than laminating resin. They did not recommend the lowest amount of MEKP. I found out 2 drops is just about the minimum.

 

[Kez]

We all know the setting time of polyester resin can be controlled by the amount of catalyst (MEK peroxide). The more catalyst the faster the setting time.

It's been quite warm and while trying to extend the working time of the resin, I keep reducing the amount of catalyst. Problem is below certain amount (I would say about 2 drops per ounce of resin) the resin just would not cure properly. So the longest working time I can get for a batch of resin is about 1/2 hour. This is OK to do a small part like a fuel tray or a hatch but it is too short for a boat hull or a complex part. Other than waiting for a cooler day, is there anything else I can do?

Epoxy is defintely easier to work with.

Thanks,

kez

Kez, I just finished-up on a SAW Hydro that I've been putting together and had the same results when trying to be cheap on the hardener. The sides of the boat turned-out sticky to the touch, but there are a couple things to try. I've been working with Poly. resin a long time. Try either wet sanding the sticky and let it dry. Try using some of the hardener on a soft cloth and wiping over the sticky. What happens it that the resin is dried underneath - but the surface seems to be sweating out - leaving the sticky. Kinda like working with Bondo. The surface feels kinda wet to the touch - but when sanded below the sticky gets drier underneath. Does this make sense?? :huh: Otherwise - eventually the surface Will dry out.

Ted,

I have the same issue. The surface remains tacky if I used too little MEKP. Finishing resin has wax added to it so that it floats to the surface during cure. The wax seals the surface and stops the MEKP from evaporating. Laminating resin without the wax will cure tacky. I do not understand why adding too little MEKP will result in a tacky surface. This is not really a problem for me if I want to add more layers of glass. But the part seems not to cure as hard as if I added more MEKP.

I will try your trick of wiping the sticky surface with MEKP. In the past, I have found that mixing a batch of resin with a lot of MEKP and brush a thin coat over the part will cause the resin to cure.

Thanks,

kez

 

[Kez]

If you are working in a shop in this heat it can be tough. What works for me is to have EVERYTHING else ready to go before I mix. I cut and prefit all the glass, have a cup of acetone ready and anything else that would need to be in place for building. If you are getting a half hour of working time while working at 90 plus I would say you must be very lean on the hardner. Even when my work area is 80 degrees I mix to only get about 10 to 15 min of work time. What I do on a hull is lay up half of it then flip the mold around, mix another batch of resin and do the other half. This way I am not rushing to get glass mopped out while racing against gelling resin.

Mark,

When it is cool, I like to do like what you described. Layout and prefit the cloth in the mould and the brush resin onto the cloth. However, using this method, it takes longer to wet out the cloth leaving me not enough time to work out the air pockets. I think it will work well if I do half the hull at a time like you described.

kez

 

[Kez]

Cobra Tunnel Boats

I had this same problem and i build lots of parts the key is just like john said have everything layed out and ready to go. this is how i do things. have my fiberglass mat already cut (i have patterns ) then measure out my resin i use 6 to 8 ozs of resin for a top or bottom. and 3.5 cc of hardener. (mek) then i stop and make sure i have all my pieces ready, my roller is free, and i have extra pieces pulled apart and ready in case i need a patch. then i make a last minite check then add the MEK and go, go, go !!! using this method usually gives me ample time to roll out all air pocket( usually ) Now in cases where its real hot i use a tub of ice to soround my resin cup. make sure you get the resin real cold. pour you resin first and let it chill this will give you a extra 15 minites of working time.

P/S im no expert by no means!

I do layup parts almost everyday, and after alot of trial and error. ive learned many new tricks. and i hope this helps you out. if you want you can call me and ill try to help out further (863)858-0536 Dan

Dan,

Do you layup your hulls by brushing resin over the cloth and mat? Or do you brush on the resin then lay the cloth in the mould?

I have found that resin sets up faster if you leave it in the cup. I guess it generates heat and it accelerates the curing process. So my new approach is to spread out the resin quickly in the mould then lay up the cloth. However the risk is that if it starts to set up before I can get all the pockets worked out, it will ruin the part.

Can you post a photo of the roller you use? I use only brushes for the layup and use a stabbing motion to work out the bubbles. On stubborn corners, it can be a problem.

Thanks,

kez

 

[dwilfong]

here is some good info.

http://www.omgi.com/product-adv-resin.html

 

[tnrcboatracer]

We all know the setting time of polyester resin can be controlled by the amount of catalyst (MEK peroxide). The more catalyst the faster the setting time.

It's been quite warm and while trying to extend the working time of the resin, I keep reducing the amount of catalyst. Problem is below certain amount (I would say about 2 drops per ounce of resin) the resin just would not cure properly. So the longest working time I can get for a batch of resin is about 1/2 hour. This is OK to do a small part like a fuel tray or a hatch but it is too short for a boat hull or a complex part. Other than waiting for a cooler day, is there anything else I can do?

Epoxy is defintely easier to work with.

Thanks,

kez

Kez, I just finished-up on a SAW Hydro that I've been putting together and had the same results when trying to be cheap on the hardener. The sides of the boat turned-out sticky to the touch, but there are a couple things to try. I've been working with Poly. resin a long time. Try either wet sanding the sticky and let it dry. Try using some of the hardener on a soft cloth and wiping over the sticky. What happens it that the resin is dried underneath - but the surface seems to be sweating out - leaving the sticky. Kinda like working with Bondo. The surface feels kinda wet to the touch - but when sanded below the sticky gets drier underneath. Does this make sense?? :huh: Otherwise - eventually the surface Will dry out.

Polyester resin is oxygen inhibited, meaning that oxygen causes it not to cure. The same with gel coat. When exposed to air, the surface stays tacky. Adding a little paraffin to the resin solves the problem. The air inhibited property is good if you are laying up several layers over time, as it ensures a better bond between layers.

But it is bad if you want the surface to cure out. The parafin migrated to the surface and seals out the air. That is one reason that you need to wipe down with solvent, lightly sand, and wipe down again before bonding; the wax needs to be removed. Similarly, when repairing gel coat, you add a little parafin which again migrates to the surface and allows the gel coat to fully harden. You can watch the parafin pop up out of the gell by applying gentle heat after application.

OOPS, posted before I finished reading the thread. I see that you know about the parafin in laminating resin. But I think it is more about oxygen inhibition, than MEKP evaporation.

 

[Dan Hutchinson]

kez

hows it going!! sorry i didnt get back sooner i had to take my mother to the emergency room last night.

Heres how i do my layup. i brush resin into my piece then lay the mat on top and finish brushing more resin all over the dry spots. so its completely wet . (some builders dont do it this way because of the extra weight of all the resin.) then when the whole piece is wetted out. i take my super small metal roller and roll out all of the air pockets. in the corners this roller comes in handy . because the roller is so small it pushes resin in the tight spaces to fill any corners.and it also works well for pushing down the mat as well. i hope this helps. Dan

p/s you can still call me to pick my ideas if you want (863) 858 0536

 

[Mark Poole ModVP]

I always brush resin in the mold before putting the glass in. This way resin comes up through the glass and is quicker and eaiser to wet out. Reduces air bubbles too. If there ends up being too much resin in the glass simply mop it out with several dry brushes.

 

[Dan Hutchinson]

thats exactly what i said. wet the part then lay your mat on it and brush it all in until its wet. then roll out the air bubbles and roll the corners to get it to lay down.

 

[Kez]

here is some good info.

http://www.omgi.com/product-adv-resin.html

Thanks David for the information. I thought MEKP was the only catalyst for polyester resin. I wonder if full size boat manufacturers use these to control the curing rate.

 

[Charles Perdue]

Cool the mold and the resin before you lay it up......this makes the cure time longer.

 

[dwilfong]

here is some good info.

http://www.omgi.com/...-adv-resin.html

Thanks David for the information. I thought MEKP was the only catalyst for polyester resin. I wonder if full size boat manufacturers use these to control the curing rate.

In the shop I worked in we made some very large pieces the bigger the piece the more copper was put in the mix.

Peroxide was the only kicker we used. much easer to control. It also made for a better piece. the strength of the piece is all about the reaction and how much heat is in the final kick off.

To hot and it is brittle. to slow and it is soft.

Depend on what you are making some things need the hardness some need flex.

If it is soft to the touch you need more kicker. If it sets to soon add copper.

Get some unscented baby power it makes a great gel coat. IT also takes color real nice.

There are many resins. GP blue will do most thing. but the green stuff is the shizzle.

Loved working with the stuff just hated the Itch.

David

 

[Kez]

kez

hows it going!! sorry i didnt get back sooner i had to take my mother to the emergency room last night.

Heres how i do my layup. i brush resin into my piece then lay the mat on top and finish brushing more resin all over the dry spots. so its completely wet . (some builders dont do it this way because of the extra weight of all the resin.) then when the whole piece is wetted out. i take my super small metal roller and roll out all of the air pockets. in the corners this roller comes in handy . because the roller is so small it pushes resin in the tight spaces to fill any corners.and it also works well for pushing down the mat as well. i hope this helps. Dan

p/s you can still call me to pick my ideas if you want (863) 858 0536

Dan,

Hope your mother is doing OK.

I saw similar rollers at a local marine supply store although never thought about using one other than my brushes. I can see it is faster to roll the cloth/mat into the mold rather than using a brush and try to stiple and wet the cloth. I will pick one up this weekend and give it a try.

kez