Resins & MEKP

29 Likes Comments Comment
Like if this Guide is helpful


Visit our eBay store to see our range of resins!

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

Polyester resin is the cheapest form of resin available currently to the industry and gives the poorest adhesion (as compared to Vinyl Ester and Epoxy resins). Polyester resin possesses the highest water absorption with also the highest shrinkage when laminating.  Polyester resin is generally only suitable with fibreglass fibres and is best suited to building items that are not weight sensitive. Polyester resins  suffer from osmotic blistering when untreated by an epoxy resin barrier to water for boats immersed permanently.
Surfboard resin is from the polyester family, but is very clear to view (almost as clear as water) when compared to GP resin (which has a blue or pink colour initially that disappears when MEKP hardener is added and cured to form a slightly honey colour) and has higher UV stabilisation qualities than normal Polyester resin.

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)

Coverage depends on the material that it is being saturated. As a general rule, Chopped Strand Mat (CSM) requires, in theory twice its own weight in resin to saturate it (for practical purpose when laminating by hand, then a factor of two and a half times the CSM weight is what maybe needed in the resin required). Woven cloth by contrast uses its own weight in resin and Stitched knitted fabric requires only 90% of the glass weight in resin to saturate the cloth. Example: Using 450gram per of CSM will use 450gram  x 2 = 900 gram in theory. For practical purpose and for estimating, use 1 Kg per sq. mtr. for this 450gr. CSM.

Vinyl Ester

Vinyl ester resins are stronger than polyester resins and cheaper than epoxy resins. Vinyl ester resins utilize a polyester resin type of cross-linking molecules in the bonding process.  Vinyl ester is a hybrid form of polyester resin which has been toughened with epoxy molecules within the main molecular structure.  Vinyl ester resins offer better resistance to moisture absorption than polyester resins but it's downside is in the use of liquid styrene to thin it out and its sensitivity to atmospheric moisture and temperature.  Sometimes it won't cure if the atmospheric conditions are not right.  It also has difficulty in bonding dissimilar and already-cured materials.  It is not unusual for repair patches on vinyl ester resin canoes to delaminate or peel off.   As vinyl ester resin ages, it becomes a different resin (due to it's continual curing as it ages) so new vinyl ester resin sometimes resists bonding to your older canoe, or will bond and then later peel off at a bad time. It is also known that vinyl ester resins bond very well to fibreglass, but offer a poor bond to Kevlar and carbon fibres due to the nature of those two more exotic fibres.  Due to the touchy nature of vinyl ester resin, careful surface preparation is necessary if reasonable adhesion is desired for any repair work.  We supply only one type of Vinyl Ester resin.

Coverage depends on the material that it is being saturated. As a general rule, Vinyl Ester resin will use the same amount of resin to saturate the Fibreglass as will the Polyester resin

Epoxy resin

Epoxy resin is known in the marine industry for its incredible toughness and bonding strength.  Our quality epoxy resins stick to other materials with 2,000-p.s.i. vs. only 500-p.s.i. for vinyl ester resins and even less for polyesters.  In areas that must be able to flex and strain WITH the fibres  without micro-fracturing, epoxy resins offer much greater capability. Cured epoxy tends to be very resistant to moisture absorption.  Epoxy resin will bond dissimilar or already-cured materials which makes repair work that is  very reliable and strong.  Epoxy actually bonds to all sorts of fibres very well and also offers excellent results in repair-ability when it is used to bond two different materials together. Initially, epoxy resin is much more difficult to work with and requires additional skill by the technicians who handle it.

Coverage depends on the material that it is being saturated. As a general rule, Chopped Strand Mat (CSM) is not a preferred material to use with Epoxy resin. If one has to use CSM, then a special 'powder bond' type needs to be used instead of the normal emulsion bond type that is used with both Polyester and Vinyl Ester resins. Woven cloth uses its own weight in resin and Stitched knitted fabric requires only 90% of the glass weight in resin to saturate the cloth. Example: Using 198 gram per of woven cloth will use 198 gram  x 1 = 198 gram in theory. For practical purpose in brushing on a single coat, the resin usage will be 250 grams per sq. mtr. (on glass and up to twice as much on timber)

Epoxy resins available from us include:

521 Marine resin - a low viscosity, general purpose resin mixed in the ratio of 5 parts resin to 1 part hardener. All 5:1 ratio resins get an 'amine blush' - a sort of milky finish when exposed to water even after curing

2 to 1 clear resin - a low viscosity, high quality clear resin mixed in the ratio of 2 parts resin and 1 part hardener. This resin does not get 'Amine Blush' and remains clear (ideal for epoxy surfboards, boat building etc).

Clear Coat is our 1:1 ratio resin that is suitable for coating jewellery and the like.

Epoxy Coating is a 3:1 ratio resin, it is a rock hard surface, set up to apply on factory and garage floors. Most times available in white or grey.

Epoxy Glue is our 1:1 ratio glue for structural gluing in most conditions to a whole variety of materials.

Explore more Guides