Resins and MEKP

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RESIN

The three most common resins used are Polyester (almost clear when cured), Vinyl Ester (slight brown tinge when cured) and Epoxy (usually, perfectly clear). As far as cost go, polyester is the cheapest, with Vinyl Ester being about twice polyesters price. Both Polyester and Vinyl Ester use MEKP as a Catalyst or hardener. Epoxy resin by contrast is about four times the price of polyester, it uses its own hardener specific to its resin and the hardener ratio cannot vary or be changed to effect a cure. With both polyester and Vinyl Ester, it is possible to add or reduce the amount of MEKP, so as to give a longer or shorter working time. Epoxies MUST use the correct ratio of resin to hardener so as to complete the chemical composition of the mixed product. So Epoxy resins are not as 'user' friendly, or tolerant to user error as the Polyester or Vinyl Ester resins but have other properties (such as used for sheathing or gluing) that make them superior in every respect.

As a very rough guide when using polyester / vinyl ester resins, if the temperature increases by as little as 5 deg C during the day, then the usual working time will be halved using the same amount of MEKP. So a rise of 5 deg will halve the working time, also, a drop of 5 deg will double the working time. Similarly, by doubling the amount of MEKP used will halve the gel time of the resin or halving the amount of MEKP will double the gel time or working time.

Vinyl Ester is more chemically resistant than Polyester resin. While Epoxy, has the best chemical resistance.

MEKP - Catalyst

MEKP is the hardener for both Polyester and Vinyl Ester resins. As a starting point for most resins, MEKP is added at a ratio of about 1.5% (2.5% for Flowcoats and Gelcoats). Obviously the amount will need to be adjusted depending on working time required, temperature of the day and humidity. MEKP is a clear liquid and is most dangerous to use. Please adhere to any instructions placed on the label.


POLYESTER RESIN  
Q. I was wondering what the difference is between waxed and un-waxed polyester resin? And what is LSE?  
A. Polyester resin from us can be supplied as waxed (when it dry's and goes hard, it has a waxy feel to the surface and needs to be sanded to laminate the next layer over the top) OR Unwaxed (when it dry's and goes hard, it has a sticky feel to the surface and is ready to laminate directly over the cured resin) OR LSE (low styrene emission) (when it dry's and goes hard, it has a waxy feel to the surface and can be laminated without sanding for up to about 4 days after the previous laminate has cured)
   
Q. What is the gel time on the Polyester resin?  
A. Usually 35 to 45 minutes depending on temperature and humidity  
   
Q. Is this Polyester a clear resin? Is it clear in colour when you pour it?  
A. This resin has a small honey colour. You will need clear casting resin if you want perfectly clear  


EPOXIES  
Q. What is the difference between your 2:1 epoxy & your 5:1 epoxy?  
A. same result but the 2:1 ratio does not develop 'amine blush' as all 5:1 ratio's do. So it stays clear even around moisture!  
   
Q. What sort of coverage will I get with the 2:1?  
A. coverage is about 300 grams per sq mtr on glass  
A. coverage depends on the surface you are applying it too, roughly 6 sqm /Lt  
   
Q. What is the pot life of this resin (2:1)?  
A. Pot life depends on temperature, size of mix, shape of vessel used for mixing epoxy & humidity - say average day, mixed in a flat tray for longer life, one should get about 35 to 45 min working time.  
   
Q. What is the working time for the 2:1 epoxy? 
A. Pot Life 150 gms - 45 minutes @ 25° C 
Gel Time Thin Film 120 minutes @ 25 °C 
Full Cure Time 7days @ 25°C
 


 

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