Epoxy Why Do You Pour Into Another Cup Mix Again

I've started working with epoxy resin and have put quite a few pages of useful information under casting in the Materials section, together with the write-up of a contempo exam. I've copied them hither in full..

Definition and general properties

Epoxies tend to exist stronger than other resins, certainly much less brittle on their own than polyester .. in other words, they have very good flexural strength! They come every bit two parts which are commonly mixed in ratios ranging 2:ane-4:1 resin to hardener by weight. Also compared to others, epoxy resin generally has a very long pot-life (working time) i.e. even a 'fast' epoxy resin will still give c.15mins working fourth dimension before it starts gelling whereas a regular/slow tin accept 100mins or more (the average would seem to be 40mins). A 'fast' epoxy may be demouldable in 8hrs and sandable later on 12-18 hrs whereas a 'slow' may need 30hrs before it can be removed from the mould. Full cure by and large takes five-vii days.

The density is on average like polyester resin SG one.1 (the weight in grams of 1 cubic centimetre of mixed resin). Viscosity is generally higher than other resins (i.east. its commonly a thicker liquid) with an mPas of one thousand-1400 being considered 'medium' for epoxy. The thinnest I've meet then far has a viscosity of 600 mPas .. compare this with polyurethane resins which can be as little as 50 mPas.

They are as well much more adhesive (hence their modification every bit epoxy glues). They are ordinarily more transparent and cleaner looking than many general-purpose polyesters. All the same, water-clear epoxies specifically for solid casting are not mutual, presumably due to the high hazard of excessive oestrus build-up .. the water-articulate epoxies commonly bachelor are well-nigh always merely for laminating or blanket. There are a swell many varieties, but most share a relatively long pot-life and cure time compared to other resins. Epoxy resin is simply as commonly used equally polyester for the binding resin in fiberglass piece of work only considering epoxy is more expensive this applies more to industrial applications.

'The chemistry of epoxies and the range of commercially available variations allows cure polymers to be produced with a very broad range of properties. In general, epoxies are known for their fantabulous adhesion, chemic and heat resistance, good-to-first-class mechanical backdrop and very good electrical insulating properties.' Wiki 'Epoxy'

In terms of working conditions, epoxy is almost odourless compared to polyester resins.. though this shouldn't fool anyone into thinking that expert ventilation is non as important!

Oftentimes resins marketed for sculpture purposes are tagged every bit 'not Lloyds canonical' meaning they may not have the structural integrity or moisture resistance necessary for boat-building only are fine for sculpture. This works to reward considering they are often cheaper.

Uncured epoxy can be cleaned upwards with acetone, cellulose thinners or methylated spirit.

You may see the term 'infusion resin' applied to standard laminating resin. This just means that the resin is of a suitably low viscosity to be used for vacuum infusion .. which is a process whereby instead of being brushed on resin is sucked into the reinforcement textile under pressure. This eliminates the air pockets which may occur using brush-on methods and ensures stronger fibreglass.

Advantages of using it

Because of its flexural strength information technology is ideal for the laminating or casting of load-bearing forms or those which volition be subjected to stress. Many epoxies also accept enhanced wet or chemic resistance making them preferable for exterior sculpture (but run across below re. UV exposure).

Because of epoxy's adhesive qualities, good 'wetting' properties, the relatively long pot-life before it starts gelling and its toughness.. it is considered ideal for blanket or laminating. Information technology is a common constituent in special paint finishes; for the home-practitioner the longer working time makes information technology platonic if you desire to mix your ain resin paints.

Re. the above qualities, the resin can just be used every bit an adhesive and information technology has very proficient gap-filling properties when combined with fillers. About epoxies will bond wood, metal and fifty-fifty quite a few plastics. For example it will usually bond with any plastic affected by acetone. Epoxy will bail well to cured polyester fiberglass only polyester won't return the favour on epoxy. As with anything, if you're serious, and y'all want to learn properly for yourself ..practise a test get-go. Epoxy is more adhesive than polyester or polyurethane considering it is able to form bonds with the substrate (the cloth being glued) at atomic level whereas other resins can only bond mechanically i.e. past gripping tightly.

Epoxies do not attack polystyrene, and so may be an platonic choice for blanket polystyrene or styrofoam forms.

Epoxy will have a diverseness of fillers, basically anything inert and costless of moisture.. talc, Fillite, marble dust, metal powders etc. I've read that powdered/stale 'ball clay' mixed into epoxy volition even make a good, clay-like putty. Because of the generous working-time it's practical to mix resin with hardener start before calculation filler .. this is usually advised with epoxy. This has an advantage considering it means that the consistency can be judged as one's calculation.

Like both polyester or polyurethane resin, near of the epoxy resins available for home utilize demand no special pre-warming in club to cure when mixed and will do and then at normal room temperature i.due east. c. 20C. Most however allow 'post curing', that is, accelerating the cure by heating at a moderate temperature for a number of hours.

The resin component has a much longer shelf life compared to other resins .. sometimes up to three years, although the manufacturers are usually bound to define it every bit ane yr. This is partly because the hardener role is more active, with a shorter shelf life. Plainly though, there are stories of unopened epoxies being discovered after decades and working ok!

Fully cured epoxy tin can be softened by heating to a temperature over 200F i.e. with a estrus gun, merely this should but be done in a well ventilated room.

Drawbacks

As i should expect, one pays for the advantage of a long pot-life by having to wait much longer for the cure and, every bit mentioned, with some it could be a couple of days before the bandage can be safely demoulded. Information technology also means that epoxy is not and so suitable for 'slush' or 'rotocasting' methods especially by hand, unless you want to sit at that place doing it for more than an 60 minutes!

The resin itself doesn't present quite the same health & prophylactic issues as polyester and is considered picayune more than than a possible irritant to eyes and peel. However, the hardener part is a different thing! It is classed as 'corrosive' and could be very unpleasant if information technology gets on the peel. It is also harmful by inhalation. Precautions need to exist taken against skin contact and, as with all resins, good ventilation is essential!

In price epoxy resins average a picayune more expensive than polyurethanes, merely a lot more the cheapest polyesters (see instance prices beneath).

Epoxy resins are pretty unforgiving when the mix is even a little bit out, for example the Technical Information Canvass for DX020 from Tomps states 'The components should be measured to an accuracy of ii% or better' .. in other words, more than 98% accurate! This tin merely exist done past weight .. not recommended past volume! It too means that it's not a skilful idea to measure out portions in separate cups and and so decant one into the other when ready, because fifty-fifty the slight amount adhering to the loving cup could make a difference. Mixing needs to be obsessively thorough! .. not forgetting the sides or the bottom of the mixing vessel. When mixing silicone rubber thoroughly I usually recommend spending at to the lowest degree 3mins to be certain, and I would say the aforementioned for epoxy. Oftentimes it's wise to transfer a thoroughly mixed batch into another vessel and mix once again to avoid unmixed residues on the sides or bottom of the cup.

There are often warnings accompanying epoxy resins that thick layers .. especially massed volumes.. will become very hot during cure, causing increased shrinkage. Many epoxies are labelled as 'laminating resin' which often (though not always) means that they are not suitable for cast volumes. I've read the advice that, if fume starts ascent from curing epoxy 'information technology's likely that the epoxy is damaged and should be replaced' .. and I would add that it should be swiftly but calmly taken outside! To avoid this happening, large and solid castings therefore need to exist done in stages which, because of the long pot-life, tin can go a lengthy process! Although ane presumably doesn't have to expect each time until the layer is cured, I'm bold it makes sense to wait until information technology's at to the lowest degree cooled down merely fifty-fifty this can take a while! W Organisation recommends layers of not more than 12mm when working with their epoxies. At that place is normally no danger of excessive heat build-upward or shrinkage when laminating thin layers with a reinforcement in the standard style.

Even the low viscosity epoxy types are considerably thicker than some polyurethane casting resins, then they are not a skillful option for intricate castings. On the other hand, if the moulds are 1-piece and open the long pot-life gives a lot of time to pour and coax the resin to fill an involved shape. Only partly equally a result of higher viscosity, many minor air bubbles are generated while mixing and these are persistent! Usually the extended pot-life allows taking the time to deal with these i.e. by skimming abroad, or passing a hair-dryer or heat gun over the summit surface which will eliminate many. Bear in mind though that any heat applied will reduce the pot-life, though this volition not be a dramatic reduction. Pouring the resin into an enclosed mould needs to be done very slowly and carefully!

Another problem involving bubbles occurs when using epoxy for coating a porous surface such as foam or wood. As the epoxy heats itself while curing this will aggrandize the air underneath it, forcing it out to form bubbles in the resin. The only solution is to make sure that the original surface is completely sealed showtime. I way is to prime number the surface first with a very sparse coat of resin and let this ready firm before applying a thicker glaze.

Epoxies are particularly susceptible to prolonged UV exposure. For this reason when used in boat-building they are more often employed for the inner construction rather than the outer surface. Sunlight doesn't simply discolour epoxy, it degrades it. Deterioration due to UV is known equally 'chalk out' in the example of epoxy paints or coatings. The usual gear up is to coat with a '2k' UV resistant varnish although I've read that this doesn't solve the trouble completely.

Although epoxy is ideal for fibreglassing in that location are some notable differences in method compared to polyester work. The major one is .. with the polyester resin I use for fibreglassing work (Tiranti's GP) it doesn't matter if one layer has been left to go fully hard before the next is applied. The 2nd layer volition bond firmly to the kickoff, and I've certainly never experienced any instances of layers 'delaminating', that is, coming apart because of time intervals. Well-nigh of the guidance when using epoxy suggests the reverse. Layers should be practical while the start layer is still in the so-called 'green stage', meaning that although it may feel touch-dry it should still be possible to make an impression with the fingernail. Any after and the fresh epoxy will no longer be able to chemically link with it. In this event the difficult epoxy surface needs to be sanded so dusted/cleaned, to at least ensure a good mechanical bail. Some other difference is that whereas with polyester resin one can compensate for certain weather condition but by varying the catalyst dosage i.e. according to the volume of resin existence used, the improver of fillers or the ambient workplace temperature .. with epoxy this is non possible because resin and hardener must always be mixed according to the ready ratio. The only ways to compensate are either to accept the option of either a slower or faster hardener on hand to use, or to apply external heat while mixing or curing.

Working life

Here are my exam notes from 25/5/2015, testing Polyfibre'south EL68 resin with EHA57 hardener (non the one imaged above). The mix ratio was an like shooting fish in a barrel one.. 2:1 resin/hardener.

The product is +14 months erstwhile (bought March 2014 and unopened). A little, approx. 1g, poured in plastic loving cup then tiny amount of greenish pulverization pigment mixed in.. appearing to mix well. Topped upwards to 20g resin, then colour thoroughly mixed in again. Profuse creation of air bubbles! 10g hardener added and mixed together. Material is colourless compared to my usual GP polyester resin.. clear, though not quite h2o-clear. No noticeable smell. I left about of the resin left in the loving cup simply I trickled some onto a polypropylene sail to see how the resin would cure in small-scale/thin amounts and to examination whether polypropylene would exist a good 'releasing' base of operations.

Surprisingly, no testify of heat reaction for a long time, very mild heat felt from the lesser of the loving cup at 35mins. After 45mins mix is much thicker but may withal be spreadable .. stronger heat from cup but by no means excessive. After 60mins firm gel in loving cup but the thin 'spills' on polypropylene sheet are still gummy like clear 'beloved'. Later 90mins virtually fingernail hard at cup middle only notwithstanding soft at edges and flat spills are notwithstanding unchanged.

Returned to at 7.30 a.m. the next morning (16hrs). Both pot and pools touch-dry and difficult, no surface tackiness even on thin residuum lining the mixing cup. On demoulding the cup contents the resin parted easily and cleanly, with complete surface reproduction, though it gripped noticeably more than polyurethane or polyester. There was a small area of tackiness around the rim of the cast piece (lesser of the cup) which could exist due to not mixing 100% thoroughly .. fifty-fifty though I was consciously much more than thorough than I commonly am when mixing PU or polyester! The thin residuum lining the cup above the mass came abroad intact with the casting and was potent but very flexible, no brittleness. The pigment color was completely even with no grain.

The 'spills' on the polypropylene canvas were affect-hard and firm, with a beautifully shine, polished-look surface showing no sign of pitting or clouding. Merely they would not detach fifty-fifty on extreme flexing of the sheet, remaining flexible. An endeavour to prise up a minor area with the tip of a scalpel blade merely curled and damaged the resin though it did disassemble. For the moment the resin is effectively stuck fast and I will have to expect longer earlier I try over again.

After some other day the resin 'spills' were no easier to disassemble. By getting a bract underneath the pieces could be popped off, but not easily. It shows the adhesive forcefulness of epoxy because even superglue fails to cling besides to polypropylene! Epoxy is supposed not to be able to establish a bond though with plastics which are impervious to acetone, of which polypropylene is ane. If I ever use polypropylene equally a 'releasing' base for epoxy work I will take to remember to spray with a release agent i.due east. pva (polyvinyl alcohol) or possibly hairspray (as I've heard).

Apart from this the two other most significant results were the lack of expected rut from the resin mass .. although pocket-sized the piece is 2cm thick and av. four.7cm across .. and the bubbles! I purposely left them unattended to in the loving cup to come across whether they would pop of their ain accord, which they didn't. On the plus side though, they all rose to the surface. There were bubbles initially in the 'spills' but nearly of these could be forced out by 'tamping' i.e. jolting or shaking the sheet. I had to pop the remaining few with a cocktail stick.

As for the lack of estrus, it may be due to the hardener part being a niggling past its shelf-life although the resin part is relatively inert and should be fine. Unfortunately I tin't check the results against technical guidance or MSDS since Polyfibre doesn't provide either!

A little bit of history

'Credit for the first synthesis of bisphenol-A-based epoxy resins is shared by Dr. Pierre Castan of Switzerland and Dr. S.O. Greenlee of the United States in 1936' Wiki 'Epoxy'

What was information technology about 1936? This was the same yr that the kickoff proper patents for both glass fibre and polyester resin were independently recorded!

Additional info

Colouring epoxy resin

Like other resins the full general dominion is that one tin can add upward to x% by weight if using a powder pigment, upwardly to 5% if using any other liquid colourant. Similarly, water-based colourants are out .. but normally oil or spirit-based are ok, plus of course peculiarly formulated resin colourants which are usually pre-mixed with a small corporeality of resin. In the test detailed above the resin 'wetted' standard powder paint very well .. all of information technology dissolved very easily, at that place was no frothing of the resin, no graininess and no sinking of the pigment. For more info see this article;

http://www.westsystem.com/ss/adding-pigments-to-epoxy/

Dealing with the bubbles

Careful heating with hair-dryer or heat gun over the open surface of the mixed or curing resin. The oestrus source should not be too shut, in the example of a estrus gun almost 30cm away. Some other method is to put some methylated spirit in a small 'mistifier' bottle and spray a fine mist on the surface. The booze doesn't adversely affect the resin and evaporates quickly, simply acts long enough to reduce the surface tension and pop the air bubbles.

Methods of thinning

Thinning the resin itself could help a lot in the elimination of air bubbles when mixing. Information technology can also help the resin to improve impregnate a surface if the resin is being used as a coating, or to brand it flow better into a complicated form. Apparently there are a number of ways of doing information technology, though I tin can't vouch for them considering I haven't tried them myself. Ane method is to oestrus the resin! Epoxy changes viscosity, becoming thinner when it's warmed. The recommended method is to estrus up the two parts separately (whichever way yous adopt .. just continuing the cups in hot h2o would probably be best) and and so mix them. As always, comport in mind that heating will reduce the working fourth dimension and advance the cure. Note also that if using ii cups for dosing the resin initially, once warmed both should be decanted into a 3rd cup for mixing together to maintain the ratio. I noted from 1 info source that the temp should non exceed 115F (46C). I wouldn't imagine that it'due south a very good idea to estrus it if you're pouring a massed book anyway though, because it increases the adventure of the resin overheating with its ain exotherm .. if one really does have to exist equally careful as they say!

Apparently another method is either to add acetone (not more than ten% by volume) or methylated spirits (U.s.a. 'denatured alcohol') at xv-20%. Adding solvent will touch the forcefulness of the cured resin, but this may not thing besides much with small castings. See this article for more informed advice:

http://world wide web.westsystem.com/ss/thinning-west-organization-epoxy/

Cold casting with metal powder

Works well with epoxy and the surface is not as well hard to be successfully 'cut back' or buffed with steel wool. Apparently olive oil tin exist used to give an even patina.

What it costs and where to get it

Prices are dated, and adjusted to include VAT

EL68 resin/EHA57 hardener £26.04 per 1.5kg (1kg resin, 500g hardener. Specialplasters 5/2015) Specialplasters describes this as 'a low viscosity epoxy resin for laminating and casting'. Mix ratio ii:one resin/hardener past weight. Manufactured by Polyfibre. The hardener is described as 'fast curing'; EL68 is a Bisphenol F type epoxy (Bisphenol F epoxies more often than not have a lower viscosity and greater chemical resistance once cured). Polyfibre exercise not currently offer an MSDS or further tech data on their website!

http://www.polyfibre.co.britain/index.php?sec=prod&prod=83

EL2 Laminating Epoxy £20.ten per 1kg (770g resin, 230g hardener), £65.93 per 5kg (Easycomposites 5/2015). A choice of hardener is offered; fast (12-17mins pot-life) or slow (95-115mins). Mix ratio 100:thirty resin/hardener; medium viscosity when combined one thousand-1400 mpas; clear; SG when combined i.05-1.15. Easycomposites advises that applying information technology over 1mm thick in one cascade could result in besides much oestrus build-up unless the slow hardener is used in which instance 5mm should exist possible.

http://www.easycomposites.co.britain/products/epoxy-resin/EL2-epoxy-laminating-resin.aspx

DX020 £29.x per 1.5kg (1kg resin, 500g hardener.Tomps v/2015) Also described as a low viscosity laminating and casting resin. Pot-life 75-90mins; demould time 2hrs; Shore D 80-ninety hardness afterwards 5days cure. Manufactured by Atlas Polymers.

Epovoss Glosscoat £35.86 per 1kg (Tiranti 5/2015) from the website page: 'A full general purpose clear epoxy resin for casting, embedding, cold enameling and coating. The resin is very slightly straw coloured, merely this is virtually unnoticeable in coating applications. Epoxy resin cures with a nontacky surface, is self levelling, nonshrinking and will adhere to most surfaces. Polyester Pigments may exist used with this resin (five% maximum), and too a whole range of fillers.' Mixing ratio 100:twoscore resin/hardener; pot-life 30mins; SG c.one.1; demould 12hrs.

Further info sources

http://world wide web.westsystem.com

A leading supplier of high-class marine epoxies. At that place is a lot of technical information and guidance on the site, most all of it dealing with boat-edifice work, but even some of that is useful, i.e. if you want some proficient communication on methods of coating with epoxy and getting a shine, bubble-free surface have a look at this

http://www.westsystem.com/ss/bubble-complimentary-coating/

berrymakince.blogspot.com

Source: https://davidneat.wordpress.com/tag/uv-effect-on-epoxy/

Share this post