Advice on polyester resin

[Synergy]

Can anyone help? I have coated some ply with polyester resin which I intend to paint with a 2 pack poly u. The problem is that when I sand the resin coated ply the paper picks up the coating and redeposits it back onto the sanded surface. It has been about 2 weeks now since the coat went on. I have had them out in the sun to try and completely cure the resin [that is what I thought the problem was].
I have thought of putting another coat of resin on with a bit more hardener or coat it with the etch primer and see what happens.
I have heard about unwaxed and waxed resins, what is the difference?
Any help would be handy

[Kerry]

An unwaxed resin is generally used where several laminates will be applied over the top of each other. With a waxed resin if it is left too long before applying another layer it will need to be sanded back.

It sounds like the resin has not gone off properly, which could be due to incorrect catalyst or temperature/moisture conditions.

Is is a general laminating resin you used or was it gelcoat?

About the only way to solve your problem is to start again as it is a bugga of a job trying to sand/grind uncured resin.

Regards, Kerry.

[Synergy]

Kerry
It was not gelcoat that I used just a normal resin, if I have to start over what do you suggest remove the resin or cut new bits of ply and start from scratch?
Synergy

[Kerry]

If it has been a couple of weeks and still sticky then there's probably no point in going over the top of this with another run?

What % MEKP are you mixing with the resin?

Before doing it again I would try a small trial run just to make sure it will work. If all is well the resin should go off in at least a few hours (generally less depending on % mix) you should be able to sand it as you expect the following day.

I had this happen once and could not explain why but had to in this instance remove it and there is nothing worse for guming up sand disks. The fly off sticks to clothing like glue.

Regards, Kerry.

[Grand_Marlin]

G'day Synergy,

Firstly, try wiping down with a liberal dose of Acetone.

After this, if it is still sticky, go over the top with a "hot" brew of resin.

Mix it at 5% Catalyst (5ml in 100ml or 50ml in a litre) ... this should get the old stuff to set up.

I have had to do both of these things on certain occasions ... sometimes just for no apparent reason you will get a sticky surface.

Cheers

Pete

[Edencraft]

Do not mix 5% MEKP and Polyester resin as any more than 3% does not effect the exothirm. If you are using general laminating resin from Huntsman, Valspa, FGI etc you are probably using 60min resin, as such if you add 2% MEPK (catalyst) at 25 degrees ambient temp you should get 60min working time before the resin gels. If the temp is higher the 25 degrees reduce your catalyst to 1.5% at say 30 degrees and 1.25% at 35-38degrees, over 38 degrees don't laminate if possible, never use less than 1% catalyst. There could be a number of reasons why the resin did not cure, is the resin promoted or unpromoted? Waxed or unwaxed, has the resin had inhibitors added to increase working time, what type of catalyst are you using? How long have you had the resin (resin does go off after about 6 months as does catalyst). Under catalized resin will never truly cure, it will go hard but never as hard as it should and will allways barcole low numbers regardless of how long you leave it in the sun. Under catalized gel coat is one of the bigest causes of osmoasis in production boats.

If you where to put a hot brew over the existing resin you may get a hard sandable finish but the oiginal resin will not be cured and you run a high risk of delamination and poor secondary bonding. I would be throwing away your old resin buy some fresh resin and catalyst and start from scratch again.

[Grand_Marlin]

Edencraft ... just remember he isnt building a boat, he is coating a board prior to painting ....

Cheers

Pete

ps. have you organised any demo days yet?

[Grand_Marlin]

Mr Ausfish ... how can replying to someones name be considered spamming??

[Edencraft]

Grand Marlin I am just real sensitive about ensuring timber is correctly treated before being used in a marine enviroment. You know what they say do the job right the first time.

We should have a demo day on the Gold Goast early in the new year for the 6.0 Offshore.

Todd

[Grand_Marlin]

G'day again Todd,

Yes, I couldn't agree more about doing it right the first time.

I didn't ask what he was doing with the ply, but I should have.

Also, if they were small bits of ply, and he had some more spare, then yes, start again.

If he had to go and buy another sheet of ply then it starts to become an expensive stuffup, especially if he had built a console box or something.

A lot of pepole dont have the spare cash to waste on materials.

It is a bit different to you and I, who are in the trade and buy our materials wholesale.

Now, I am not here to argue with you, as you know all the correct mixing rates, etc etc etc.

The reason I said what isaid was - I had a bloke mix me up some resin ... unfortunately his maths wasn't real good and I ended up with 0.2% instead of 2% Catalyst

This job wasn't structural ... it was covering a 1/2 inch hole from a sounder cord in a dash, prior to re flowcoating.

It had two 100mm square layers of 450.

Well, of course at 0.2% it went tacky, but didn't set.

It was in a pr!ck of a place where you couldnt get at it properly, so I decided to try a 5% brew over the top, instead of starting again.

It set up hard, and sent the existing 0.2% mix off as well.
(you could check this as you could touch it through the front side of the hole.. it went rock hard)

It isnt something I would do everyday, but it did work.

As the resin was just a sealer prior to painting, I would try this before throwing the whole lot away.

If someone had posted that they were doing something structural, well sorry, but you have to stat again.

Please keep me informed re: demo days.

Cheers

Pete

[Sea-Dog]

« Reply #9 - on: Today at 4:16am »
G'day again Todd,

.............

Cheers

Pete

Pete, what the heck are you doing on the computer at that ungodly hour??????

P.S. It looks like I missed out on that Tri-hull - someone picking it up today > >


Cheers, Sea-Dog

[Dignity]

Just a thought but why dont they put a packed date on MEKP as it usually has a limited shelf life and if synergy had some left over from a previous job of 12 months or longer the catalyst would cause his initial problem. Also you don't know how long it has been on the shelf before you bought it. All my resin not going off has generally been to using old MEKP as I hate to see waste but in the end have to do what Pete has done albeit with fresh MEKP although never been game to go quite that high.

sam

[Synergy]

Thanks for the hints.
A few more details.
The resin is Huntsmen and so is the hardner.
I used some older resin first that had been left over and been in the shed for 2 years or more and it was fine, I used it on the small bits first just in case and of course they are all good.
The job is a replacement of the old side pocket covers, with some mods. So they will get wet but not be immersed or sit with water in contact for extended periods.
I had thought of putting a hot mix over the top, will this work on a piece 200mm by 1800 mm?
Synergy

[Synergy]

Thanks for the hints.
A few more details.
The resin is Huntsmen and so is the hardner.
I used some older resin first that had been left over and been in the shed for 2 years or more and it was fine, I used it on the small bits first just in case and of course they are all good.
The job is a replacement of the old side pocket covers, with some mods. So they will get wet but not be immersed or sit with water in contact for extended periods.
I had thought of putting a hot mix over the top, will this work on a piece 200mm by 1800 mm?
Synergy

[Grand_Marlin]

G'day Sea Dog ... couldnt sleep, so I came out to the computer...

I have found that the catalyst is usually the culprit with age, and also if it gets any dirt in it, it will not work properly.

Synergy, it should work ok ... just try it and see what happens.

Todd is completely correct with what he is saying about the catalyst times / dose rates etc, and when doing a structural layup you have to be very fussy.

Cheers

Pete