polyester resin

These page entries are meant to be added to and usually start with general outline information, price guidance, suppliers and useful links followed by my worklog where I can put further info and photos as they come. Details of suppliers are listed in the Suppliers section.


An inexpensive 2-part resin which is usually either translucent or clear, and which readily accepts appropriate colourants or fillers. When cured it is hard, though brittle compared to epoxy or polyurethane unless reinforced.

Polyester resin is available in a number of different forms, the principal being the ‘GP’ (general purpose) resin commonly used for fibreglass work in conjunction with glass matting. GP resin is translucent with a slightly beige/brown tint. The next most familiar is the ‘clear casting’ version which cures glass-clear and colourless and is often used for the embedding of objects in clear blocks. There is also ‘gel coat’ resin which is pre-thickened, and opaque white resins (pre-pigmented) are also common. All are catalysed by mixing a measured amount of the same hardener (containing MEKP methyl ethyl ketone peroxide) ranging from c. 1-4% by weight.

GP polyester resin is often referred to as a ‘laminating’ resin ( i.e. specially for fibreglass work) and the ‘clear’ often referred to as a ‘casting’ resin. Although GP can be used for casting, it is not common to use the clear polyester for laminating partly because it is more expensive.

Advantages of using it

It is very economical compared to other resins (esp. 5kg amounts upwards) /- widely available .. many suppliers and extensive literature/info on the web /-  versatile (different types e.g. general purpose, gelcoat and clear casting, can be made thixotropic) /- very strong (esp. with fibreglass reinforcement .. its most familiar use); UV blocker available (to counteract colour change due to UV light); longer pot-life gives more time for mould-filling or coating (excellent choice for PU foam coating, see ‘Polyester coating’ below); takes powder pigment and oil paint well with good, controllable colour achievable due to transparency; similarly fillers, when used for surface qualities i.e. metal powders, will give full effect; choice of catalyst percentage (standard 1% but more can be added for small volumes); some ‘GP’ versions (such as Tiranti’s) have less styrene emission for better working conditions; uncured resin and work tools easily cleaned up with acetone.

Because it is transparent it is the perfect resin for so-called ‘cold metal casting’ which is the technique of imitating metal by filling resin with finely-ground metal powder and abrading the cast surface to expose the metal particles and buff the surface.

Cold metal casting metal powder 2017 prices: £12 per 500g average (Tiranti); £20 per 500g (Tomps).  Up to 4:1 metal powder to resin (by weight) can be mixed to make surfacing layer with either MP or clear casting resin, catalysed 2% (always add catalyst to resin in this case before mixing in metal. If proper gelcoat resin is used less metal can be added, c.2-3 parts metal by weight. Less than 2:1 is ineffective. Wait until rubber-hard, then fill rest with normal resin catalysed 2% for small forms (1% for larger). This can either be unfilled or if preferred, dark pigmented. Wait at least 72 hrs before ‘cutting back’ and buffing ( cutting back is abrading the surface i.e. with steel wool to expose the metal particles properly). Note: Tiranti’s ‘rule of thumb’ is same volume of metal powder to resin plus ‘a little more’ metal powder, and they advise that if measuring by weight the content of metal powder to 1 part resin is; Aluminium 1.25, bronze 6-7, brass 5-6, copper 4-5, iron 6-7


Polyester resin cannot be used indoors without regulation extractor fans and breathing protection because the styrene emissions are harmful, as is the MEKP catalyst. Some polyesters are formulated to have low styrene emission, which may promote a ‘better working environment’ but it doesn’t mean that the same precautions can be ignored!

Strong exothermic reaction may cause cracking in larger volumes (add minimum of catalyst) /- some types e.g. clear casting more prone to surface tackiness (oxidisation) /- brittle if used unsupported for larger forms i.e. without glass matting etc. and smaller solid-cast forms liable to chip if dropped.

Vaseline should not be used as barrier, and polyesters are affected by contact with moisture/water in the atmosphere

Whereas polyurethane resins are more suitable for delicate castings and there are extra-thin versions to assist intricate pouring, polyester resins tend to have standard viscosities and it can be more difficult to eliminate air bubbles. For example Tiranti’s general purpose polyester resin has a viscosity of 900-1100 mPas, compared to the thinner polyurethane resins at 50-70 mPas.

Working life

Always mark newly-bought resin clearly with the date and make a note of the manufacturer’s recommended shelf life (this is a guide only, see the start of the ‘quick view’ comparisons page for more advice on this). Exposure to air, especially moisture in the air, is something that severely shortens shelf life when it comes to any form of resin. Replacing caps straight after working .. and as often as possible while working .. will help to extend the shelf life way beyond the manufacturer’s guidelines! The containers that resin comes in are not designed for easy pouring of small amounts! In practice one will have to decant a certain amount first into another vessel i.e. a disposable plastic cup (which can be pinched at the side to make a handier pouring point). Whenever possible the decanted resin should be used rather than poured back into the main container.

Pot-life c. 20mins. At 2% catalyst Tiranti’s MP ( multi-purpose ) can be safely demoulded in less than 2 hrs but allow 72hrs-1week for full setting. As an average (this will vary according to type/brand and conditions such as room temperature) there will be 15-20mins working time once mixed; touch-hardening in 25-30mins; demoulding and some mechanical work after a few hours, but full curing can take at least a few days.

Standard addition of catalyst is only 1% by weight but to make portioning easier the catalyst is often supplied in dropper bottles with directions for ‘number of drops per 100ml’ of resin.

When mixing large amounts .. i.e. numbers of litres .. the heat from the exothermic reaction assists proper curing so only 1% catalyst is necessary, whereas when mixing very small amounts .. i.e. under 100ml .. this heat is reduced, so to ensure curing up to 4% of catalyst can be safely added. Adding this amount of catalyst to a large volume of resin would most likely cause cracking due to excessive heat.  ‘Gel coat’ can normally be catalysed adding 2%.

Storing polyester resin A place should be chosen for storing polyester resin which is as cold as possible .. certainly never above 20 degrees C. There may be a problem when storing the resin indoors, particularly if anyone is unusually sensitive to the smell because I’ve noticed that however tightly containers are sealed a trace smell will persist. The only options then are either to wrap the containers within many layers of clingfilm etc. or to store in a secured and sheltered place outside. This can certainly be of benefit during cold weather because there’s no lower temperature limit as far as I know, and the shelf life is improved by cold storage. The resin should be brought back to normal temperature before use because it thickens up when cold.

Additional technical info

If barrier/release is needed (not normally necessary with silicone or vinyl) use polyvinyl alcohol or rape seed oil. There is a special release method for building laminated castings in plaster moulds involving a parting wax and polyvinyl alcohol (see Tiranti website for info).

Polyester resins can be easily coloured with small amounts of standard oil paint without affecting cure. Dry powder pigments can also be used, but the powder should be wetted and thoroughly mixed first with a small amount of uncatalysed resin before mixing it with the main batch. There are commercial polyester colourants available, which are strong, but tend to be expensive.

Resins generally yellow a little after long-term exposure to UV light but a ‘UV stabilizer’ is available for use with polyester resins (added 1% to mix). This used to be available from Tiranti, but not currently (2015).

Thixotropic paste (Tiranti) not a separate chemical agent but a gelled form of polyester resin which is ‘100% thixotropic’ and which can be added to other polyester resins to thicken them. Can be used as a resin by itself if catalysed. £12.30 per 1kg inc. VAT, 2017.

Clear casting resin is often very pale blue in appearance but gradually loses this while curing. Some clear casting resins can be very ‘air inhibited’ that is any surface exposed to the air during curing will remain tacky .. may not harden completely and needs to be scraped and sanded off once the rest is fully cured.

What it costs and where to get it

Prices will vary considerably according to where you choose to get it. For example if you find versions of polyester resins in craft/hobby shops the price is likely to be unreasonably high! The following is a guide to more responsible prices .. which can be as little as £3.70 per kg for general purpose resin from a specialist supplier such as CFS.

Tiranti prices (2017, inc. VAT) multi-purpose £9.66 per 1kg, general purpose £9.78 per 1kg, gel coat £11.70 per 1kg, clear casting AM £14.16 per 1kg. Buying 5kg amounts will commonly work out 25-30% cheaper. All Tiranti resins (gelcoat, multi-purpose, general-purpose and clear casting) use the same MEKP catalyst (M50) which is supplied in a dropper bottle. For 2% catalyst addition by volume, 100ml of resin would need 50 drops, by weight 100g would need 40 drops. Catalyst sold separately  £2.42 per 50g bottle. Tiranti’s gel coat can be catalysed adding 2% whereas MP, GP and clear should use just 1% for large solid castings (but up to 4% can be used to accelerate small castings). At 2% catalyst MP can be safely demoulded in less than 2 hrs but allow 72hrs-1week for full setting.


CFS prices (2017, inc. VAT) General purpose £7.57 per 1kg inc. catalyst, £21.48 per 5kg inc. catalyst; Easylam (not approved for marine) £21.29 per 5kg inc. catalyst


Specialplasters.co.uk prices (2017, inc. VAT) Clear casting 1kg £9.12 inc. catalyst; SP100 general-purpose ‘laminating resin’ 1kg £8.28, 5kg £22.20 not inc. catalyst

Further info sources

http://www.cfsnet.co.uk The CFS website contains a lot of technical advice and ‘how to’ articles



‘Fibreglass’ is the common name for the strong, lightweight material made by layering pieces of glass-fibre matting generously filled with polyester resin. Another term you might come across a lot is ‘glass-reinforced plastic’ shortened to GRP. The glass matting is designed to soften considerably once the resin infiltrates it (binders are dissolved) so that it will lie properly over contours. The resin needs to be brushed on and worked in with a stiff painting brush.

Chopped strand mat (2017, inc. VAT) standard 300gsm £1.62 sq metre (specialplasters.co.uk) £2.94 sq metre (Tiranti). Matting used in conjunction with MP or GP polyester resin (do not use clear casting resin) for fibreglass lamination.

Just 1 soaked layer of 300gsm matting may be more than strong enough for a small form i.e. up to 20cm; larger than that 2 layers up to 40cm, and larger than that 3 layers. This is a very rough estimation, and it depends of course on whether the object will be load-bearing or not. It will also depend just as much on shape .. concaved or ribbed forms being generally stronger than flat ones.

For a detailed account of how to make a fibreglass cast from a large silicone rubber mould see the later parts of Making a supported silicone mould for a life-size head and casting in fibreglass which you will find in the Methods section under Mouldmaking and casting.

Polyester coating

Because the foam inside Kapa-line foamboard is polyurethane it will accept resins like polyester (whereas styrofoam is dissolved by it). GP (general purpose) polyester resin from Tiranti £9.78 per 1kg, catalyst £2.42 per 50g. Mix in very small (10g) amounts and catalyse at 2% (i.e. 4-5 drops per 10g of resin). Coat using soft brush, careful re. hair loss. Working time is c.14mins in warm room, to 18mins in cooler room.  Average setting time 20mins, ready for light sanding after a few hours. Forms are better left outside to set if conditions are relatively dry. When brushed on foam surface it will partially soak in which means that one coating will produce a reasonably thick, strong shell when the resin is fully cured. Another coating can be added for greater strength but this may start to fill in detail and show brush build-up.

One way of maintaining more control over the smoothness of the coat is to colour the resin so that the build-up can be better seen. This will also assist later painting. I would recommend using dry powder pigment because this will also act partially as a filler and make the cured resin easier to sand. Polyester resin can take up to 10% powder pigment by weight without affecting proper curing.

76 thoughts on “polyester resin

  1. Hello.
    Basically we applied polyester resin with paraffin wax to the hull of our boat. (flow coat)
    And as it was our first time we made basic errors. like not making it smooth when applying.

    We are now sanding it all down as we are aware that nothing will bond to it properly.
    But my question is, how much of the wax rises to the surface.
    Does all of it rise/bloom or is some left through out the layer.
    Just wondering if we have to sand every last little bit back off, in order to get a proper bond.
    Or will it bond with the last little bit, as no wax is in the bottom part

  2. Thank you for all the help David. I used gelcoat on the back of a piece not having the right flocoat, It remained tacky so I smoothed clingfilm down over it as you suggested, and after 2 days it cured to a hard surface. Very grateful.

    I want to do some layups using linen to make acoustic horns. I ordered some clear gel coat and some clear casting resin. Do you think this will work? I tried with epoxy but cant find an epoxy gel coat and I got holes (bubbles) on the surface. Would epoxy work on top of polyester clear gel coat?

    thank you again, martin

  3. Hi David,

    Your website has been an invaluable source over the last few months on getting up to speed on all things casting and moulding so thank-you for sharing your knowledge.

    I am struggling with bubbles in deep angular undercuts which I had been warned against at the carving stage! I’m mixing multi purpose polyester with bronze filer 1:3 (I do a little dusting with bronze) but it still seems to be too thick to slush cast effectively with bubbles forming at the bottom of the crevices. Brushing it has been marginally better. Would styrene be the solution to make it runny enough to slush cast the first coat like a polyurethane or will this compromise the surface finish? My last options appear to be either having less bronze filler or using a stiff yet fine brush to brush into the crevices on the first coat and then slush cast subsequent coats for the rest of the details. Your thoughts would be very much appreciated as my sculpure graveyard is getting bigger by the day!

    Many thanks,

    • Hi David,

      I’m afraid all I can say is my feeling is that the last option sounds the best one .. to put on a thin coat with a high proportion of bronze filler, covering all. Let that set and then fill the rest with no filler, only perhaps some dark pigment. I’ve never tried adding styrene to thin, so I don’t know how it behaves. Sorry I can’t help more.

      • I used to make these sort of sculpture casts for a living, we accepted that no cast was going to be perfect out of the mould. You can use the same bronze mix, add some colloidal or wood powder to thicken (not too much) and you can just fill up the air holes, then sand down. you can also try the same trick when putting on the first coat, fill all the tricky bits with thickened mix, then cover with the normal coat. Good luck!

  4. Hi David, thank you so much for the valuable information!

    I wanted to further ask about styrene emissions. I am using water extended polyester to cast planters (plant pots) and wish to sell them for indoor use. I was wondering if the cured product also has styrene emissions and whether or not it’s appropriate for indoor use?

    Would I need to attach a proposition 65 warning to my products?

    Thanks for the information. I was not even aware that working with WEP was hazardous.

    Just for the record, I mix the WEP with water and talcum during casting. Thanks again for your generosity.

    • Hello Ifat, I hadn’t heard of ‘water extended polyester’ at all, and an internet search showed me why .. just 7 references for it worldwide .. just 7! So from one of those it appears to be marketed by ‘Silpak’. Is that where you got it? I’m afraid you’ll have to get written proof from Silpak that it’s safe for your purposes along with the official MSDS (Materials Safety Data Sheet). I don’t think any polyester resin (including this one) should be worked with without either extractor-fan ventilation, proper respirators or completely outdoors. Once fully cured, that’s a somewhat different matter, though it’s a fact that regular polyester after curing will continue emitting very low amounts of styrene .. I think, forever! If you can’t get the proper guarantees from Silpak .. isn’t it possible that some form of durable plaster or cement would be so much easier, safer and cheaper?

      • Yes, I did buy it from Silpak. They have a store in Pomona, CA. The WEP is a wonderful material to work with, in terms of the texture, durability, ease of painting, water resistance properties and cure time. When cured it has a texture like a natural rock or a piece of wood, because of the large amount of Talcum in it, it absorbs pigment very easily and produces a natural look. That’s why I love it and would hate to replace it with Cement. Though that is an option I would try.

        It’s good to know that the Styrene emissions are very low after it cures. Perhaps with some sealer it can be reduced even further.

        I talked to Silpak about it, but I don’t think they are willing to commit to it being safe for use for my purpose. They directed me to do my own research. I will ask them for the MSDS sheet.
        So unfortunately, this is a bit of a dead end to me. But I am glad to know that Styrene emissions are very low once it’s cured. Thanks very much for your safety suggestions. I’m glad I now have awareness of this before it causes any nerve damage.

        Thanks for your useful suggestions and for taking the time to look it up!

  5. Hello David,
    Thanks so much for these resources, you are incredibly kind with your time !
    I was wondering whether Polyester resin is fine to use in a gelflex mould ? Will I need to use a mould release ? sorry if these questions are silly, I’m very new to the world of resin
    Thanks !!

    • Hi Eve, No they’re not silly at all .. most people aren’t sure. Yes re-meltable vinyl (such as Gelflex or Vinamold) works well as a detachable mould when casting with polyester (or fibreglassing also) and doesn’t need an additional mould release substance, in fact better not to .. keeping it simple. So .. no problems!

  6. Hi David,

    Your article was very informative and you seem quite knowledgeable on the topic of polyester resins, so I’m hoping you can perhaps help me with a problem I’m having. I use polyester resin for sign making. Designs are routed into solid surface materials using a CNC and then resin is poured into the design and once cured I sand and finish the overpour. I use strictly colored polyester resins that vary wildly in color but I’ve always had a particular issue with orange and red resins cracking during/after curing. Normally the solution is to cut back on catalyst and the resin will cure out with minimal cracking which I later repair.

    For a current job I have to use a particular shade of orange that seems to (for whatever reason) crack an uncontrollable amount compared to the orange I typically use. I’ve experimented with catalyst and styrine levels with little luck thus far. I typically use a 12 oz. squeeze bottle of resin, then mix in approx. 1.5 mil. of catalyst (approx. half the amount I use with other colors) and then a small splash of styrine, with an ambient temperature of 70 degrees F, or just below. I also tend to pour thick ammounts to fill a design, and have yet to experiment with pouring in thin layers. This resin I’m using is brand new from my supplier and shouldn’t be anywhere near the end of its shelf life which adds to my confusion. I’ve contacted the supplier and the only advice they were able to give me was to add more catalyst (which is confusing because typically less catalyst is the solution) and to pour in thin layers rather than thick ones. Would you happen to have any advice that may help me reduce spiderweb cracking in my resin using the information I’ve provided?


  7. Hi David. I bought my husband some clear casting polyester resin quite some time ago. He has never even opened the bottle but I have just opened it and it’s the thickness of treacle. Can I rescue it or is it destined for the bin.

    • If it’s like that .. must be a year or two old? It does sound like it’s no good anymore, or at least won’t behave as it’s supposed to. You, or he, could try mixing a little with the recommended amount of catalyst and see what happens?

  8. Hi David – I wonder if you can help me. I have acquired a monster block of waste’polyester resin that has dripped into a ‘resin berg’ during the manufacture of surfboards. I am trying to make jewellery with it and have had some success but what would you recommend as the best way to cut the big chunk into workable pieces? I’ve tried a reciprocating saw (destroys blades in minutes), a hand saw (takes forever), a band saw (but its only big enough to cut bits of the edges of the slab).
    Any thoughts would be greatly appreciated, many thanks

      • Thanks for the reply David, I did wonder if the water jet cutting would be a possibility. looks like it is back to elbow grease then! Thanks for your help


  9. Hi can we use any another storage container, for keeping the whole resin such as glass jar, or steel or any other container.

  10. Thank you for the info on polyester resins! I have been trying to create jewellery using casting polyester resins and the surface always cures slightly tacky. I was wondering if there was anything I could do to either cure or seal the tackiness? Would adding resin wax solve this problem? I’m worried it will cloud my castings however. Thank you in advance!

    • Yes! Either a wax needs to be added to the resin so that it floats to the top surface and seals it while casting, or the top surface can be ‘sealed’ by putting a piece of clear acetate sheet there (or stretching clingfilm) .. anything to stop the air i.e. moisture getting to the curing resin. I don’t know who sells the type of wax to be added to polyester resin though.

    • Yes you’re right to be cautious! I would avoid any plastic except HDPE (marked on the base usually) meaning ‘high density polyethelene’, this is chemical-resistant. This includes milk containers, but these are very thin, better if thicker. Glass is safe, but not so practical. Polyester resin is almost always sold in metal containers but I don’t know whether these are coated inside with something special.

  11. Hello, I have this resin problem that does not heal on the outside. It’s sticky. I do not know what to do anymore, and I have already done a lot of tests with the ratio of the catalyst, I already removed it from the mold before it healed, so as not to “drown” the mold. Then I read on your page that the polyester crystal resin is ‘air inhibited’. I am very confused. How will I close the mold completely so it does not get in the air? Would I have to put the mold inside a plastic box with a lid? I await your response, because I still have gallons of resin and I can not stand sanding to remove the sticky part and polish. hug

    • There’s a special additive containing an amount of wax which can be added to polyester resin mix to prevent this. The wax settles on the surface and prevents the inhibition. I think Tiranti in London sells some, if not East Coast Fibreglass. You could alternatively cover the curing mixture with a sheet of acetate or maybe clingfilm i.e. anything which will prevent air from affecting it.

      • Hello!
        Thank you for responding.
        I found resin wax very interesting!
        I think I found, would this “https://tiranti.co.uk/products/wax-additive-30ml/” be?

        I already covered but unfortunately it did not help. I’m almost giving up.

        I contacted the company to see if you can send it to me.

        A big hug!

      • Hello Claudia,
        Yes, that’s the one! It may be difficult, or expensive, for them to send it to you because it’s classed as a ‘hazardous’ material though. Best if you can find a similar additive where you are, if there is one.
        best, David

      • Hello! I found it on several sites but unfortunately, as you said, because it is a dangerous material, it is very expensive for transportation. Here in Brazil there is nothing about it, and the company that bought resin never heard of it. I’ll change supplier. Thank you again.

      • Hello David
        I think you should not add wax with polyester resin, but apply wax on moul. Wax is a mould release.Right

      • Yes, it can be used as part of a mould release method, but I’m talking about another special wax/styrene additive, re link I’ve given.

  12. Hi, David. Great write-up. I recently got my hands on some Polyester and I enjoy the mix but I kinda left it for some while and when I got to use it again the resin is a whole lot thicker. Application on the fibre mat takes time. Pls how would I be able to reduce its thickness and get it to its former state. Thanks

    • Hello Mezi. It means it’s going ‘off’, changing .. but perhaps not too late, it may still work. I would do a test of a small amount, mixing in catalyst first as normal but then mixing in a little acetone to see if that thins it. See if that sets as strong.

  13. Hi David, how are you? I am new here. I have a question about polyester resin. Do you know of any product/s that can be mixed with polyester resin to reduce the strong odor of polyester resin?

    • Hello Joe,

      No, as far as I know one can’t oneself. But there are some polyester resins which are formulated to have ‘low styrene emissions’ (i.e. Tiranti do one .. I think it’s their ‘multi-purpose’ one) which is supposed to be less hazardous. The thing is .. the same health precautions need to be taken anyway, regardless, and even a ‘low styrene emissions’ polyester will smell just as much! See comment previous to yours about putting polyester work in a sealed container while curing, this might help.

  14. Hi David. I was wondering if you can use an airtight container to hold in the fumes whilst it is curing. I can only do the casting outside and the weather doesn’t hold for long this time of year, so if i can pour it and leave it in a container inside overnight it would help.

      • Hi again. Just to let you know that I have successfully made 3 castings using a container now. I mix my resin outdoors and place the mould into an airtight food container. I pour into the mould and then put the lid on. I then bring it indoors for a couple of days. After that I take it back outside to open it in case there are fumes. Works well. Thanks again.

  15. Wanting to “seal” a fiberglass kit car body. Tried polyester casting resin/mekp but after cure is too hard to sand…it did cure and seal well. However…still need to seal body. I feel that there has to b a poly-resin that is easier to sand while still “sealing”. I am sealing purple metal flake molded dune buggy body. Removed previous owners’ flat red paint…have sanded to original color but not into any fibers. What would u recommend. Thanks in advance.

    • Hello Ramona,

      If I’ve understood you right, you just want a reliable primer? I ‘swear by’ RustOleum ‘Plastic Primer’, suitable for most plastics including fibreglass and easy to sand. Actually ‘RustOleum’ does make a good swearword if said strongly enough!

      • Primer AFTER ‘sealing’ w.resin. But a resin that is sandable….like w.an orbital sander…not handsand. Casting resin just balls up from the heat created by rotation of orbital sander. I guess it could b said i.m wanting to ‘encase’ the fiberglass body w.resin. Then prime…block sand where needed….paint and clear. Thank u for any advise!

      • I think the only ‘resin’ that is sandable in the way you want would be car body filler i.e. UPol (a filled polyester, so it would adhere I imagine). But very difficult to apply smoothly, unless it could be thinned i.e. with acetone perhaps. No other ideas I’m afraid.

  16. This website is an excellent resource, I’m impressed and I’ve only just dipped a toe.
    I just thought it would be useful to share a source for resins and casting supplies which has been very useful with my previous experiments with resins, casting and laminates.
    Currently I am researching methods I can use to make moulds of live flowers to cast using water clear polyester with translucent dyes.
    Thank you.

  17. I have a strange question. I want to infill routered shapes in table tops and I was wondering if coloured polyester resin would be the best way to go. Also will it bond to the wood, and can I sand it level with the top, with a polishing finish at the end?

  18. Hi David

    I want to know what type of resin can be mixed with different materials from nature (without affecting its hardening) such as earth, sand, leaves, grass, wood, small stones etc. to get interesting effects. Thank You.

    • The resin most commonly used for embedding natural items i.e. insects, seashells, colourful stones, even flowers .. so that they can still be seen clearly .. is Clear Casting Polyester, if embedding is what you mean. This can also work well with some clear epoxy resins. But if you also mean adding some of the things you list more like a filler i.e. earth, sand etc, I’ve found polyurethane resin behaves better for this because it’s usually much thinner. The crucial thing with this is that the material must be totally dry because moisture will affect the setting of all three resin types.

  19. Hi David, I understand that clear cast resin is unsaturated polyester resin. Can you throw any light on casting/using this on acetate for a water effect? Do I need to splash it on? Thanks so much for your time and experience….

    • This does not make a very good ‘water’ simulation, because the surface exposed to the air tends to go cloudy and can even stay a little tacky (more so the clear casting than the ‘general purpose’). Epoxy resin on the other hand would behave very well either in droplets, stippled or spread thin (see the photos under ‘Epoxy resin’).

  20. Hi David, Firstly I would like to say how useful your site has been during my studies as a stop motion animator so thank you and keep up the good work!

    I had a question that is similar to another article of yours involving resin. I was wondering if you know if you can mix plaster with polyester resin to use as a filler? If so how would this effect the cure time etc? Would this work in a RTV silicone mould

    Many Thanks

    • I haven’t tried, but I don’t see why this shouldn’t work as long as the plaster is completely dry. It shouldn’t effect the cure time and, yes, it would be compatible with a regular silicone mould. Best to do a small test yourself.

      • Thank you for the reply. Was curious if there would be a terrible reaction but it shouldn’t be a problem at all to test 🙂

  21. Hi David. excellent page, do you know of any thoxotropic agents for water clear casting resin, the idea is to coat a large half open mould with it then a second coat of lightly pigmented/glittered water clear resin. In our experiments we’ve found the the water clear resin is too runny to give a thick coat.
    That or find some gelcoat which is water clear. our supplier didn’t seem to think that such a gelcoat exists, the stufff we have is rather brown on curing… thanks for any help

  22. Hi David, what a wonderful resource you have created here. I am looking to pour fill a mould to act as a base for a sculpture. It is pretty big and I wondered what I could throw in there to use less resin. I’m not talking about fillers, but debris (old bits of resin for example) to help fill up the mould. I Wondered what insert materials I could use (plastic, metal, glass?). many thanks.

    • Hello Claire, Sorry about the delay. With polyester resin you need to be especially careful to avoid moisture. If it’s a case of wanting to bulk up really cheaply while adding weight I would normally suggest coarse sand or even gravel .. as long as whatever it is is fully dry! I’m assuming that anything else (i.e. what you’ve listed) would also be ok as long as nothing is chemically active still (greasy, not properly cured etc).

  23. Pingback: Polyester Casting Resin | Purathrive

  24. First I want to say what a wonderful resource you’ve created in this website. Thank you.

    Now my question: If even small proportions of fillers can make resin hard to work with how do kitchen worktop manufacturers produce mixtures with typical proportions of 95% ground-stone and 5% resin?

    • I think this is fairly easy to answer .. firstly the resin used is unlikely to be polyester or PU, rather an industrial epoxy or acrylic. and they probably use both heat-curing, injection and pressure techniques, beyond the means of home users. Secondly the ‘aggregate’ filler is probably very coarse so doesn’t in itself effect the resin.

      • Hello David
        I have a problem with unsaturated polyester resin color, it’s a yellowish. And I want it water white transparent for lamination purpose. So what to add In yellow resin to make it clear.

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