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ContinuousWave: Whaler Repairs/Mods
MEKP (Methyl Ethyl Ketone Peroxide) Gelcoat
|Author||Topic: MEKP (Methyl Ethyl Ketone Peroxide) Gelcoat|
posted 10-02-2001 09:30 AM ET (US)
I just read that MEKP will speed the process of gelcoat harding. Does anyone use this product? I don't recall see it mentioned. Is it a must or optional? Thanks
posted 10-02-2001 10:23 AM ET (US)
That is the "hardener" that you see in a typical fiberglass repair kit.
posted 10-02-2001 10:36 AM ET (US)
We used to use Methyl Ethyl Keytone (MEK) at work. Now it is banned. Is this the same product?
I am told to make sure and use rubber gloves when using MEK. It is absorbed though your skin and attacks your liver.
|Tom W Clark||
posted 10-02-2001 10:17 PM ET (US)
As Peter points out, MEKP (methyl ethyl keytone peroxide) is the catalyst in the gelcoat (and lay up fiberglass). Without it, the gelcoat will not cure. Not an option, but a part of the gelcoat.
MEK is used as a "thinner" for spraying gelcoat.
posted 10-03-2001 07:06 PM ET (US)
MEK is a thinner, similar in use to acetone, but much more potent. It's not yet banned in California, but I'm sure it will be...it will dissolve grease, uncured resin, paint. I use it all the time and will probably eventually have to pay the price. M-E-K Peroxide is a polyesther resin hardener, not the same as MEK.
posted 10-03-2001 11:12 PM ET (US)
I have a question about about a product that uses M-E-K Peroxide. I had a few chips along the bow near the top and a couple on the chime. Boat US recommended EVERCOAT Gel coat scratch patch as a repair. Its already colored and ready to go. It seemed to work well, except it never got rock hard. It sticks well and I have had it out bay long enough now to know it sticks. But I can still put a impression in it using a fingernail. Boat US now says I should try Polyester Gel-paste (also by Evercoat) Before I remove all the existing repairs and start over can someone tell me if this will get rock hard like the orignal gelcoat?
It came with a small tube of M-E-K Peroxide so I am guessing this is a good sign but would like to hear from anyone that has used this product.
posted 10-03-2001 11:58 PM ET (US)
Reading some of the gelcoat repair threads, I get the impression that gelcoat will not cure properly when exposed to air. Perhaps that is the reason for the softness of your repair, WantaWhale.
PS I finally got my Whaler running two weekends ago. It was great to spend an afternoon out on the water, even if the fish weren't biting.
posted 10-04-2001 12:09 AM ET (US)
Gelcoat resin will not cure to a hard finish if exposed to air. To cure to a hard finish you should either cover it with polyvinyl-alcohol (PVA) or SaranWrap.
PVA is now available through supply catalogues like WEST MARINE. You can apply the PVA with a spray bottle, like those used for spray cleaners like "409".
I have even heard that hair spray will work, too. I haven't tried that, myself, though.
posted 10-04-2001 12:24 AM ET (US)
A little chemistry lesson.
Gelcoat (and other polyester resins) are cured or hardened by addition of a catalyst. The catalyst increases the speed of a chemical reaction that causes the molecules in the resin compound to link up and change from a liquid to a solid. The catalyst is not part of the chemical reaction, but its presence accelerates the speed of the reaction. When mixing resin with catalyst, you just have to add enough catalyst to get the reaction rate to speed up to a reasonable cure.
With epoxy the situation is different. The chemistry that occurs depends on a chemical reaction taking place between the "resin" and the hardener. The two ingredients must be mixed in the proper proportions, determined by the stoichiometry of the chemical reaction. If there is an excess amount of either reagent, that reagnet material remains "uncooked" in the final mixture.
For this reason it is extremely important to add very accurate amounts of hardener to the resin, always in the proportions specified. In some epoxies this ratio is 1:1, while in other epoxies it is 3:1 or 5:1. Whatever ratio the formulator specifies, it should be followed as accurately as possible. Extra resin or hardener will be left over after the reaction has "kicked" and will dilute the resultant material properties, particularly its strength.
In either case, polyester resins or epoxies, it is possible to produce batches which do not cure entirely. Such uncured resins will lead to later difficulties, and are often associated with problems like osomotic blistering where the presence of water causes the formation of acid compounds from the uncured resins.
When mixing resins, the ambient temperature also affects the reaction rate. At higher temperatures the reaction rate will be faster. Thus, if you are mixing a batch of gelcoat and using it on a warm summer day, it will harden faster than it would on a cold winter afternoon. I also believe that the more hardener added, the faster the reaction rate up to a point.
With epoxy, adding more hardener than called for by the proportions of the mix will not increase the cure rate, but it will result in an undesireable mount of uncured material left over in the mixture.
posted 10-04-2001 06:27 PM ET (US)
Ok I will try PVA and see what happens. Already tried the wrap and it didn't work.
If the PVA doesn't work I will remove repairs and try the second product with MEKP .
Thanks for the advice...
posted 10-04-2001 08:12 PM ET (US)
Jim's right. Generally, the amount of catalyst ("hardner") added will affect the reaction rate at a given temperature.
A little polymer chemistry lesson. The reactions we are talking about here are polymeric reactions which produce long chain molecules (polymers). If I recall my polymer chemistry correctly, MEKP provides free radicals to initiate the reaction between the chemical units (monomers and/or oligomers) that are ultimately linked together to make up the polymer chains.
So the more you put in the mixture the more free radicals you have. The more free radicals you have, the greater the reaction rate is going to be because you have more reactions started and going on simultaneously using up the starting monomeric or oligomeric material faster.
There is a trade off between the reaction rate and the physical properties of the polymer reaction product. Generally, the higher the rate, the shorter the resulting polymer chains will be when the reaction is over. The shorter chains yield a product with lesser physical strength properties than one with generally longer chains. So, on the one hand, you want the rate to be fast enough so that it will cure in a reasonable amount of time at a given temperature, but on the other hand, not too fast such that the resulting chains are not within a desired length range, statistically speaking.
Fortunately, the manufacturers have long ago figured all of this out and have provided us with the right recipe.
posted 10-04-2001 08:29 PM ET (US)
WantaWhale (and jimh and others)-
While it is true that gelcoat normally needs a barrier or release agent like saran wrap or PVA in order to cure properly (and *all* gelcoats I've come across need the addition of a catalyst, specifically mekp), be aware that at least Spectrum gelcoat *paste* does *not* need to be protected from ambient air in order to cure. I have done a lot of little putzing around with Spectrum's paste (factory color-matched), probably on the order of 50 or more disparate patches for screw holes, scratches, etc., and I've never used any release agent at all. And for what it's worth, I have not had good luck with Evercoat curing well. Not saying it wasn't something I did wrong with the Evercoat, but the Spectrum paste has simply worked well for me every time.
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