This experiment is mainly for a foam paddle board fishing skiff that I want to build but can be utilized for many other purposes.

I worked for a major exhibit fabrication company for many years. We used to protect the foam with latex paint and then applied what we called a Hot Coat of polyester resin. A hot coat is made by adding a lot more catalyst than normal causing it to kick so fast that it doesn't have time to attack the foam. Then other coats can be applied without worry after a light sanding to roughen the surface.

Both foam boards are polystyrene foam - one is just extruded from a mold and is a bit denser (pink), and the other is expanded (white). It's not necessarily the heat that's the problem with using polyester resin on polystyrene, it's the chemical reaction between the two. Extruded polystyrene has a melting point of 210°C, for example. But epoxy resin works fine on polystyrene foam (which proves it's not the thermal reaction that damages the polystyrene). Epoxy and polyester resin are different, despite most folks conflating the two.

Well sir, you have conducted a experiment that I've been curious about for years. Very interesting. Thanks for sharing.

Thanks for taking the time to do and post this. I've been wondering about this myself. You do things like I do them, in my back yard. Really appreciate you.

It's not heat that's melting the foam. It's just a chemical reaction. That type of foam is "soluble" in polyester resin.

Exactly what I was looking for. Thank you for taking the time, that I didn’t, to do this for the world.

Thank you that's what I was looking for, very clear and went directly to the subject as the title says, a rare honest person

Very helpful! In fact the best test for this on KZfaq! THANKS!

Excellent demonstration - thanks for sharing!

Thank you so much for doing the experiment and providing the results. I am about to embark into a project to make a hard top for my caving cruiser, and this will help out greatly!

Great news!! Thank you so much for doing this experiment. I'm going through a carbon fiber project that begins with a sculpted XPS foam block. Been scratching my head on what to use to coat it before i make the fiberglass mold from it. This'll save me some time!

Thanks for the tests. They really change things for me.

Awesome info, thanks. I’m going to build a slide in camper for my pick up and I want to use foam and frp fiberglass and now I have the info I need. Thank you.

This is huge for me. I’m making a big speed square / cutting jig for house framers to quickly chop sheets of plywood. Thanks man

Thank you for making this video this will help me out alot with future projects.

Awesome test, and exactly what I was looking for.

Years ago I had a book on fiberglass and the author suggested using multiple coats of common wood glue over eps foam, before applying the fiberglass. It worked fine.

Coating the substrate like an insulator stops you from getting the benefit of bonding to the substrate (core) Proper design of composites includes the substrate as part of the structure and your painted layer prevents the connection to it. You are shooting yourself in the foot pal. At best you have created an eggshell arrangement negating the cores help in making a strong composite part. P.S. pink, blue, or straight polystyrene foams offer no help structurally . Each time you walk or put weight on it , it will deflect and Disbond at the insulating layer inside causing the eggshell to move loosely around on your supposed substrate. The space between foam and resin is now free to collect water or even inflate itself in sunlight . This continues and allows polyester especially to flex and crack allowing more ingress of liquids etc.= total failure. Pony up to the bar and use proper materials or suffer for your mistakes. This has been well known for many years. Cheers!!

Thanks for doing this experiment. I too want to make a fishing skiff out of foam but had imagined covering with brown paper strips and diluted glue as a base.. this seems easier

You just saved me a ton of time THANK YOU you are awesome

Excellent - For about 100 years I've thought about making my own ice chest, 'some 6" thick on all surfaces - thank you for posting this

Wow! Im using standard styrofoam now. Im thinking to apply thin layer of cement before applying the fiberglass resin. Until I watched this video. I will now apply this method of yours. Thank you!

Great job! Thanks for the experiment.

Thank you for doing this experiment and informing us so we don't have to waste precious materials

Plain water down wood glue works great. Made a 14 ft launch out of Styrofoam and Vynilister resin with no issues. Over 18 yrs later still floating with the kids I gave it to.

Amazing test! Thank you for sharing!!!

Great experiment ! Thanks !!!!

Thanks for sharing your experiment. Now I know what I going to do in my next boat projects. From Ontario Canada

Finally you answer all my questions, God bless you 😉

this is perfect for making molds for live wells !.

Great job, man. Many thanks! Saved me some time and headache.

Thank you this actually helped me make dinos out of pink foam for the base structure and how to protect it from fiberglass covering

Nice video! Great way to go with cheap open cell foam. Thanks

Thanks @seasic very helpful video. You’re a hero

Wicked video man. Thank you.

Great video with controlled expirement

Thanks for sharing this very informative video. This is what I'm looking for

I just watched your video and its been a couple of years since you did this but, I'd love to know what you ended up doing plus a couple of suggestions for you. We know that there are a couple of things that the polyester won't stick to and I use them all the time. The three that I know of are waxed anything but I'm talking about wax paper or parchment paper both are used in cooking or baking. It makes it nice to be able to tape it down then fiberglass right over it or use a gel coat then fiberglass either way will work plus if you do that it helps take the sticky film off it because wax is also a hardening agent . Next right out of the kitchen is aluminum foil . For some reason it will not stick to aluminum. And the third is glass so if you want some flat and awesome panels do it on glass. I helped a friend a couple of years ago now to fiberglass a teardrop trailer that was made on top od an aluminum frame boxed with aluminum angle to box out and adhere to then 4 inches of the green foam board but we have done it on the pink and white but, I like a more dense foam board that we wrapped in wax paper we did the inside and outside then top coated with a white gel coat. Yes it was a little work but, the savings over the epoxy was quite large and time wise it cures faster; The whole thing empty was 350 pounds with the tires but, it was empty. To do the inside we just tipped it on its top or sides because it was so light and yes you leave the wax paper on it because it protects the foam and is way cheaper than paint and time wise as well. I hope it all went well I will check your page to see if there is any updates but, give it a try and see.

I was gonna cover my whole roof with Styrofoam and epoxy fiberglass on top! Gee, i’m sure glad i watched your video first! Idea; What about trying epoxy paint underneath instead of latex paint? I covered my garage with it and its holding up well years later!

Awesome and useful video thanks, strong and light. I will use latex paint now on my car bumper mold. Polyester has less flex than epoxy but is stronger. Also it is not heat that melts the styrofoam but styrene (gas), the thinning agent in polyester resin

Great job! Just a little off on what actually causes the foam to melt. Styrene foam is a curious thing in terms of petrochemical resistance. A white foam cup is a good experimental container. Take a cup and drop a little gasoline in it. Be sure there is something under the up to catch the mess, because the gas almost immediately melts through the foam. Oddly, aviation gasoline, which is the same basic feedstock as automobile gasoline, will not melt the foam. It is all about the solvents, not the heat of the exothermic reaction. Other petrochemicals, particularly “hotter” solvents will also melt styrene foam. Lacquer thinner, MEK, and similarly hot solvents pass right through that cup. Mineral spirits will not attach the foam as quickly. Interesting side note: polyester resin and epoxy resin are both thermoset resins. The chemical reaction leading to molecular cross-linking is accelerated by the exothermic reaction. Too much catalyst creates a rapid reaction and more heat, especially with polyester resin/MEKP catalyst. It is possible to create enough heat to actually make resin in a container smoke. While I have never seen it I am told it can create enough heat to create ignition of the resin. (Polyester or vinylester will do this, not necessarily epoxy). In thin cross-sections, like a lay-up with fiberglass this is rarely a problem. Another important thing to keep in mind is resin shelf life. Epoxy components have a VERY LONG shelf life. Polyester or vinylester require the addition of a “promoting agent” typically CONAP and DMA. If these agents are not in the resin it will not cross- link from the MEKP catalyst. Downside is that the promoting agents significantly reduce shelf life. You will find that old polyester resin will not harden as the promoting agents have degraded over time. SOOO… if you’re in a long term project don’t buy more polyester resin than you can use in a month or so. If epoxy resin (either A or B, unmixed) develops a crystalline participate you can gently warm it to get the crystallized particles back in solution and you’re ready to get back to work! Old polyester that will not harden cannot be helped. It must be disposed of.

Great job man

Great test. Thank you

I've been working with resin, fiberglass and foam for over Forty years. It's dirty, toxic and messy. If you're going through the process of building something that you want to last i would use epoxy resin. I've hit lava rocks with my epoxy surfboards and didn't even ding them. If it was polyester resin I would've destroy the area that hit the rock. Polyester vs. Epoxy.....They're two totally different beasts. I'd never waste my time using polyester resin again regardless of the price!

Great video !

Thank you for sharing this video, very helpful ❤❤❤❤

Very informative video! Thank You!

Bro exelent video..just what I need it to learn.. thanks

wow that amazing sir... im reseaching one that problem for a long time :( im planning to built a kayak from foam with fiber resin... but worrying about the chemical reaction... now you solved my problem :) thanks a lot sir... you saved me new sub here sir more power to your channel

Thanks for that. Very helpful.

What you need is an A B pour foam that you can pick up from your local fiberglass store. It's designed for polyester and vinyl Ester resin. It's a cousin to the A B spray insulation foam at your hardware store.

Thank you for this very helpful video!!!! Regards from the Philippines!

Dude you are the best human on earth right now 🙏💪☀️⚓⚓⚓

Thanks man for this,

Thank you sir. Very helpful.

Great video. Thank you for making it.

I'm glad to have ran across this video. I had assumed I would need to cover the foam with wide masking tape. In fact I've used this tape trick for making shapes of missing piece in truck hoods as a backer form. I've wanted to build a nice angler kayak with this method , now I know it'll work with only latex as a resin barrier. Many thanks and 👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍👍

WOW, Thanks for the video

Interesting video. Having built a few boats, I have always been told that you can use epoxy over polyester resin but you cannot use polyester resin over epoxy as it will not adhere. Depending upon your ultimate goal it might be simpler to use a West System type epoxy for your project instead of going through the hassle of coating the foam with latex paint.

Great video, was very helpfull, was going to build a boat and its very difficult to buy poliuretan boards where i live, so this is the ansewer, thx 🙂

That’s pretty awesome. I have a plastic canoe that I’m bass fishing from with a 55lb thrust trolling motor. Have been try to figure out how to make the floor a bit more stiff. I’m thinking the pink foam painted. Then fiber glass. Maybe use some sort of caulk to get it to stick. Then I may make an outrigger as well using foam and fiberglass

Great info, thank you

I've tried to find a good cheap way to strengthen foam board. I wanted to try (synthetic quick crete?) Anyway... as a family effort every July 4th our family has a pontoon boat parade float using a lot of foam board. Fiberglass/resin seemed risky.. but you made it look possible. I've also use paper mache for more detailed pieces but even with a few coats of water poly...it still doesn't do well.. if it gets wet. I'm hoping to try your resin idea this year. It time to start planning but haven't decided what to make this year still. Google searching this year lead me to a giant loon with a swivel head or the semi truck pontoon. We would win every year...so last year they made our family the boat parade judges...but I still have to keep upping my game. Thanks for the tip.

Interesting. Thought about this for making camper cabinets. One thing that I have found using pink board is that people lay down a barrier material to add tensile strength. Ive seen people use canvas, bedsheets, nylon window screen, etc on top of a layer of latex paint with another top coat of paint. Try that with a fiberglass top coat or even epoxy...

Thank you for the video.

Very helpful, thank you.

Some latex paint may work others may not. The top grade paints, infinity, and signature have titanium dioxide which will act as a heat shield. . . . while the cheaper stuff uses clay. . . . interesting and awesome video. Thanks for making this.

Fixed many paddle boards with foam inside. I just don’t use fiberglass. It cracks easier, and doesn’t last as long as epoxy and a sandpaper destroyer. Epoxy with fiberglass cloth and u have a proper repair. Easy to sand, paint, then add the top coat, sand and polish. Job done. If u wanna be cheap (since epoxy slightly more) use wood glue as a shield coat and then add the fiberglass. But epoxy still the best option.

Wow thanks for sharing

Awesome!!

Uda man! Im looking to make a skimboard and would have thought 1-2 layets of latex would be ok.... Now i know 5+ is the way to go. Thanks brother!

This is awesome I want to make some stabilizers for my boat and I think this may come in handy 🤔

Thank you brother appreciate it!

Thanks for sharing , I tried polyester resin also had a melting . I tried a cheap boat paint 2 coats , worked but yeh 4 coats probly better.

I am looking to make a low weight pickup/camper rv out of PVC pipe (frame) and xps foam board for walls/roof-floor all wrapped in a s grade fiberglass. There is a primer that can be sprayed over the foam to prevent deterioration of the foam allowing you to use polyvinyl , polyrester, or epoxy with your fiberglass. I believe I saw it on the fiberglast website.

That’s Awesome! That’s going to save me a ton of money!!! Thank you!

Thank you sir! I was looking on how to make a kayak, you gave me some ideas :)

Awesome. Foam slide on sleeper that's light enough so I can still tow the boat.... here we come! Thanks heap. Might go 6 coats just in case.

Thank you for this information🌹

Thanks for doing this!

FANTASTIC HELPFUL VIDEO ! Thank you. You have raised and answered my questions on this topic and i am very pleased that this works. One thing i want to say is that a lot of youtube videos have irritating sound tracks but yours are brilliant. can you share any links please ? regards J of UK

If you’re looking for an affordable board to fiberglass over look up plascore scrim backing honeycomb panels. About $45.00 a sheet and you can purchase directly from plascore. No worries when using polyester resin either. Good video.

I know this video is a bit old but, you should try homemade chalk paint. It has Plaster of Paris in it which deflects heat extremely well. Basically, you just add Plaster of Paris to latex paint and a bit of water to thin it, then it will adhere to most surfaces. I have made and used homemade chalk paint for years but I think it would completely solve your problem with the heat and you would only need one coat. In fact, I'll bet you can just mix Plaster of Paris with PVA glue and water (to thin) and just paint one coat of that on. It also dries in a very short time and will add structure to any flat surface. Great video and thanks for taking a hit for us all out here. Good luck 👍👍

I was in the same questions to build some projects, thanks for the information!

Great tip dude my project thanks you:)

Can u do video of long term durability in the future and see if it worth doing

Good informative video.👍👍👍👍👍👍

Thanks for the video, I do experiments like this also to try to save some money on materials. If I remember correctly, there is a foam you can get at the big block stores similar in cost to rigid pink foam that can handle the polyester resin, it’s called Polyiso rigid foam insulation (polyisocyanurate foam). If memory serves, I got the idea from a forum discussing how they make surfboards using polyester resin. Look for a foam board with gray paper and either side and in large blue letters it says: R MAX R-MATTE PLUS-3

Thank you for sharing your interesting poly..merci beaucoup 👍🏼

RC model plane hobbyist's feedback: iron on wraps like Monokote worked for my plug application. Super thin no added bulk, Cheap, quick apply, no mess, heat shrink conformity w/o wrinkles. No pva release necessary.

Nice one ang galing naman

thats a lot of work. My go to at the moment is to cover the foam using aluminium foil with 3m 70 spray adhesive. Works very well.

Wish I had seen this last weekend waisted custom door panel I was making with pink foam board.

If you are trying to save money, check with a roofing supply company. They sell a roofing foam board (isocyanurate) that is similar to polyurethane foam in it's ability to withstand chemical attack from polyester resin. The last time I bought some ( about two years ago), it was $28 for a 2" thick 4'x8' sheet. Urethane foam at the marine place is about $100/sheet. The insulation value is about R6 per inch if I remember correctly, the same as urethane, and better than polystyrene. The roofing board has a fiberglass reinforced paper face on it but it isn't an issue. Polyester resin will adhere to it as well as anything.

Helpful

good intro ..... brilliant thanks

Legend!

Just got a 57 15 foot fiberglass boat with corrugated solid floor. Would this method be a safe efficient lightweight way to make floor solid? Amazing video you have a teacher approach much appreciated

Great test and its clear that the fiberglass does not PENETRATE the polystyrene or styrafoam board BUT how does the fiberglass then BOND to these boards with 4 to 5 coats of latex paint ?