Duratec Clear Hi-Gloss Top Coat questions

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#1

So I just got this in the mail Friday evening. I ordered it because I was told that this is what I should use to coat my molds with before laying up the carbon fiber for infusion.

I have a few questions since Michigan Fiberglass does not offer data sheets and I can’t seem to find the right places to find answers.

I don’t have a tool to measure thickness. So would you say two medium coats and two - three flow coats would be enough? Flow coats meaning just enough so that way its an even glossy wet coat. I have to get something to measure thickness but for now I need to do it by feel haha.

If I have to reduce it, whats the safe amount? I have a 2.0mm full size HVLP and a 1.0mm mini HVLP. Is 1/5th too much? I need it to be strong enough to withstand the minor impact and temperatures car body panels deal with from cold Canadian winters to hot Arizona summers. I also make a few engine parts so the top coat has to be able to take some heat. Before I tried using Silmar249 surfboard resin reduced at 1/5th with lacquer thinner. Now I’ll be using MEK solvent. I was told the MEK solvent is several times better than lacquer thinner, acetone, and styrene.

How long should I wait before I lay the carbon fiber? Just until its tacky but not soft? Or until full cure. A problem I had with the silmar 249 is if I waited till full cure it would delaminate sometimes.

Does it matter what I harden it with? Before I tried mixing regular MEKP with the infusion grade vinylester resin from Michigan Fiberglass and it started foaming when I infused it. I then tried this yellow MEKP blend I guess it is. That worked.

My last question… Is this just a thinner polyester / vinyelster resin or is this specially formulated for this? I plan to infuse over this with vinylester resin but I was wondering if this is suitable for infusion or too weak. I switched to VE because I learned that PE resin just does not saturate CF as well as VE.

Lastly will light amounts of super77 destroy the bond? Or will it be dissolved? I was going to get airtack 2 but I didnt want to buy a full gallon. If anybody knows a place to get smaller quantities let me know :D.

Sorry for asking so much!

#2

you can spray it pretty thin and have no problems. it cures good at just 10mils, 1 mist coat then one decent coat is the minimum(for epoxy parts). you would want to go a little thicker on VE or PE parts(atleast 15-20mils). Use MEKP-925 to catalyze. Duratec has both VE and PE version of the topcoat, it is formulated for use as a topcoat or can be used in mold. You can let it tack and take advantage of the sticky surface, or wait a day and have no tack, depends what you are doing. Scotch brite the surface if its been more than a day.

#3

Thanks! Whats the diff between MEKP and MEKP-925?

#4

Im not a chemist so I cant tell you exactly, im sure someone here can, but its just formulated differently. There are many different catalyst available. As far as I know all duratec products use MEKP-925 if im not mistaken. In reality you can use just about any mekp catalyst and be fine, but some work better than others, so always best to use the recommended one to get the best results.

#5

^^ Hojo, that could be the reason why my duratec mix feels tacky when cured. I use Duratec high gloss addative in all my gel coating. It just makes the gel coat so much nicer and helps to thin it for spraying.

I always use acetone to reduce gel coat and duratec… call me crazy but i reduce 5 parts gel : to 1 part acetone and have not had issues with finish.

I would get that MEKP they recomend. 2 ounces will do 1 gallon of duratec.

That ve top coat is good to 325F degrees. It’s not uv protected however. What you said on the spraying sounds good but you may want to lay down 3 full wet coats… overlap by 40 to 50%.

I run my hvlp pressure at max rating for my gun.

p.s. VER is way better than PER. good choice to switch to all VER from polyester.

Here is all i found on what makes 925 different:
“Norox® MEKP-925 is a methyl ethyl ketone peroxide composition formulated to be an excellent cure initiator for both unsaturated polyester resins and vinyl ester resins. With most unsaturated polyesters it gives longer gel and gel to cure times but with a higher peak exotherm than Norox® MEKP-9, particularly in thick sections.”

#6

Over the past few days I’ve made a few parts using the VE top coat and infusing with the VER michigan fiberglass sells. Right away I was not impressed with the VER because it does not look like its thin enough to infuse it well. I was told to buy MEK solvent and I’ve been using that to reduce it. I reduce it around 1/10th in volume and end up with soft parts.

I also notice a boat load of pin holes in the VE top coat. I sprayed on several thick coats and let it fully cure. I then infuse and its like the VER resin eats the top coat and fuses with it instead of bonding. Before I was using surfboard resin (silmar 249) for the top coat and a polyester infusion resin to infuse the parts with and got waaay better results. Stronger results. And it dried in 1/3rd the time. Can somebody see what I’m doing wrong or are these just the wrong materials for the job? I’m very upset because I right now feel that I wasted money.

Also is the top coat supposed to be rock hard or some what soft when hardened? I tested the parts and a big chunk of it and they are both soft like a Urethane clear coat.

BTW Its not the mold release or the PVA because I never had problems like these. The pin holes are everywhere and are also in the intersection of the carbon fiber. I did get air in the prt, but even with air it shouldn’t have come out that bad.

#7

Also, if what I was doing before (PE gel coat and PE infusion resin) was working well should I just stick with what I was doing? I got great results, I was just worried about the parts having print through issues because of the heat distortion temp being 186. I mainly switched to VER because of a higher heat distortion but not only does it seem like the infusion VER is not good for infusion due to its thick viscosity, but its just becoming a pain now.

I also think of switching to epoxy because when Ifirst started I used epoxy and it worked great. Until I put the part in the sun… And right now I don’t have the capabilities of post curing at anything higher than 150… I just moved into a new shop and I’ll be able to now build a room but I don’t think I’d risk making it hotter than 100 because since I have a low budget, I need to use dry wall and ply wood.

BTW when I make my parts I use 5 + layers of carbon fiber and 1.5 oz fiberglass in corners and rounder areas for reinforcement. I make interior and exterior parts for exotic cars.

#8

is the VER a infusion resin? you shouldnt need to thin out a infusion resin. as for the topcoat, either you didnt let it cure enough before starting or it was too thin for VER. As for spraying to avoid fisheyes, spray 1-2 mist coats before doing full coats, let those mist coats sit for a few minutes to tack. How long did you let the part cure? it might need to sit longer, post curing will help greatly aswell. Though without seeing exactly what you are doing its hard to answer all your questions.

#9

The Duratec 925 mekp is a slower cure I believe. The have 3 available to modify pot life.

Do not thin the resin! For sure this will deteriorate the properties of the matrix. Tensile strength and interlaminar shear will go downhill.