Can CSM (Chopped Strand Matting) Be Used With Epoxy?? 

hi Andy. appreciate the tutorial but I thought you'd be filling holes on the console today.

Best restoration boat channel on youtube.

Here in Asia much of the resin Polly and Epoxy come with no mono styrene so neither will wet out any glass. You have to really understand resin formulation to use it at all. We just add mono styrene to both and all is well... If you want to use epoxy with matt just add mono styrene four parts resin to one part mono styrene. All glass needs to have the binder dissolved to work well be it weave or matt.If you want the epoxy to get in all those nooks and crannies you need mono because all glass has a binder.

Andy, that was a good demo for the basic diy guy but as someone who has been in the boat and industrial fiberglass industry for 40 years a couple of points. Glass is not all the same. There are glass products made for different resins. Glass has a variety of 'sizings' added to them to make them easier to process , like the woven cloths have different sizing (think lubricants for the weaving machinery) than the stitch mats, like 1708 or the CSM. Many of these sizing are washed off or heat removed. The cloths in particular commonly used for epoxy military laminates can have coatings added to enhance the wet out of the fibers to get the required epoxy resin to glass ratio required ( ignoring pre-preg laminates). Similarly for polyester resin different coatings can be used. But as you know stitch mats and cloth products have little to no binders so work ok with epoxy or poly resins for general purpose laminating. FYI continuous creels of 'roving' used to create the chopped fibers, with a 'chopper gun' used for some production fiberglass work have different sizings on them to help the product run thru the equipment before it is fed into the chopper head. The fiber binder(glue) used on CSM you correctly point out is made for polyester/styrene monomer resins. Over the years the binders have improved , powder bound and water based are just 2 varieties and provide different properties. But they all require the styrene to dissolve them to allow full wet out of the fibers as the binder can get deep into the tiny glass fiber bundles. If you use epoxy resin with a binder bound glass (CSM) it will not dissolve the binder so will not fully wet out the glass , the bundles of glass will not wet out with epoxy. This is one of the main reasons your epoxy laminate was not wet out properly. Also there are other coatings on the CSM made to help the poly resin properly wet out the fibers after the binder has been broken down. In the same way some cloths have coatings to assist the wet out of just epoxy resins. The other thing that effects the wet out is ,of course, the viscosity and thixotropic properties of the actual resins. Epoxy resin are by their chemistry not possible to make with the same easy workability as polyester resins, (read easy wet out) hence why the hi strength epoxy laminates are all done using combinations of heat and pressure for the ultimate properties. For general boatbuilding open laminating the increase in properties from epoxy are mainly limited to the improved secondary bonds to substrate IF proper preparations are done. But I am with you, that for many applications quality polyester resins will produce better results in a diy situation because of the superior workability of the materials. Cheers Warren

Andy, you sir are a master of your craft. Thank you so much for teaching those of us that aren't as well exercised in boat repair I live watching your videos.

Baltek told me years ago that I couldn't use epoxy with CSM because of the styrene binder... But I had no idea that stitched fabrics with CSM, such as 1708, didn't have that binder. Thank you for clearing that up!

Awesome video as always, Andy! :)

Man your channel is a goldmine for those taking their first steps in boatmaking

Very interesting. I had never heard not to use CSM with epoxy. Great explanation and demonstration as to why you shouldn't. I'd love to see the strength test!

A clear, concise explanation and graphic demonstration of a simple, but important, fact of life in laying up plain, chopped strand mat only. For those who didn't know the whys and wherefores, you and I do now! A New class next week I presume, same time, same channel. I'll be there! Thanks Professor G King, SV Intuition

Answered the number one question I’ve had for a long time! The only place I’ve seen/heard the answer about 1708 and epoxy 👍 Thank you, great video....as always 👏👏

Epoxy vs poly is always like a ford vs chevy debate lol, Im running my boat 2 more seasons b4 a substantial rebuild and almost complete restoration and these videos have helped me immensely on what products and how and when to utilize them,,now when someone tells me only use epoxy or vise versa i can give them the "scientific "reason why and actually know what im talking about!LOL,once again thankyou so much,this is my favorite thing to watch on RU-vid! Thankyou andy!...best boat vids on RU-vid hands down!

It might be helpful for viewers to see the entire process before they made a decision. Having to use PVA for curing and re-sanding before reapplication could be deciding factors. Epoxy is stronger and if pin rolled between each layer would produce a stronger layup in my opinion. Vinyl is much cheaper. Also, the strength difference may not be enough to sway one to use the epoxy. Great video. Thank you for your efforts.

Andy, I did indeed find this video very helpful. Getting to the core of these kinds of topics is critical to underling the best practice approach to working with fiberglass. More of this type of video will be welcome at my home shop. Thanks!!!

I am sure you have mentioned this in other videos but this one kind of put a lot of the pieces together and after just reading your Resin guide this all makes sense now. thank you and keep up the great work you do for the boating world.

"It just looks happy" makes perfect sense to all of us who've had success and failure with glass laminating. Love your videos, so helpful.

Andy worked in a commercial boat manufacturing plant built the hulls out epoxy resin skin the hull out with stranded mat never had a problem. Strength wise hull was stronger due to using epoxy resin and the scheduled lay up of glass. The engineers always said because of the epoxy resin it created a lighter and stronger hull.

Hello Andy, I've found that a heavier initial wetout of the primary surface (wood panel) and bubble rolling of each successive layer overcomes these "problems" quickly and easily. It's too bad that European mat is so expensive here in the states.. Nice demo, thank you.

West Systems suggests using a release fabric or 4 mil plastic to thin out the layup and remove bubbles. It's an extra step, but it's workable if you're wanting to avoid having some parts poly and other parts epoxy on the same boat.

Andy, thank you for making this video. There definitely is a fair amount of confusion out there on this topic. You cleared it up very well.

Andy- Great explanation of why epoxy is not ideal for CSM; clears it up for me (and now I know how often I've done it wrong). I used to teach a strengths of material class at Temple Univ and we would create simple set-ups for testing the strength of student projects. Let me know if you want some ideas on how to tests these to get comparable results.

HOORAY, new video !!!! :) great topic, I am the exact guy you described in the lead ! Went from clear as mudd to clear as a bell, Double Thanks for producing these videos.

Thanks for that demo. I've heard you tell us not to use epoxy with chopped strand, but now I really know why.

That was a really cool video, thank you. It's the counter point of "Why can't I?" "Because I said so." Well done!

Excellent information given, you educated me and stopped me from spending a boat load of money on the wrong glass. Thanks

NOW you tell me!!! LOL. I have never worked with fiberglass or epoxy and of course I start with a life size statue I made out of paper mache. I had an extremely hard time getting the fiberglass mat to stick and it mostly stuck to the brush only. What a pain! I tried fabric and it worked much much better. I have watched many of your videos and they have been SO helpful, especially for a beginner. Thank you so much!

Andy, can you also comment on the advantages/disadvantages of using epoxy vs poly resin for laying up fiberglass. you have awesome videos. Thank You

Neat trick stumbled upon the other day: Wheat flour as thickening agent with epoxy. Not as lightweight, but stronger than micro balloons. It looks like custard!

Thankyou very much for helping me with decision on epoxy resin over polyester resin. Used polyester repairing boats in past and local panel repairer talked me down over suggestions on polyester repairing.

I used epoxy and the first thing I thought was “wow it needs a lot of epoxy” now I know why. I will try polyester and compare. Great info for sure!

This is tremendously helpful. I have always used West Systems Epoxy just because I guess. I've also used TotalBoat epoxy, but since I am a firm DIY'er, I kind of use what's on the shelf and West is much easier to source, albeit more expensive. All that being said, poly has always intimidated me a bit. I feel very comfortable with epoxy probably just because of familiarity. This video has done a lot toward demystifying polyvinyl resin for me. I know you've done a video in the past and will look for it, but how, when and can you use both poly and epoxy? Will they sit on top of each other? What would you say the top applications are for each? I've always thought of epoxy for structural uses -- hull repairs, etc. -- and the others for use in less "critical" areas or applications -- although none seem to come to mind. I love your videos -- your way of explaining complex things simply and understandably and your craftsmanship are incredible.

I have used the stitched chopped strand mat (for epoxy) from US Composites, it has no binder at all and works very well !

Andy - Thanks for this. Can you explain the compatibility of epoxy and poly? If doing a major (or minor) deck core replacement and you don't know what resin was used on the existing boat, what do you suggest to do?

It helped me a lot ,because i was used to working with Cars ,like Shelby's & Corvette 's ,I was more able to picture it & since I was doing floors patches at one or two of chopped mat 5" by 8" on wood and fiberglass floor sections I believe it worked out well for me since I mixed it to slow dry in a day or longer depending on cool weather I',m having in east Texas outside ,I move boat in warm 68 70 degrees temp and back under shed at night seems to be OK ,keep up the great videos . Jim.

great demo.....I just made a couple of fiberglass panels for my boat and couldn't figure out why I was having such a hard time wetting out the chop strand matting compared to your previous videos....and yes...I went through a ton of epoxy resin in the process....woven matting wetted out much easier..to the point i vowed to never use chopped strand stuff again....this video explained why....if only this was out 3 weeks ago! I did have that metal roller to push out the excess resist and air bubbles though...what a awesome tool! That was from seeing you use them in your videos btw......

You da Man !!! Someday I hope to be half as good of a fiberglass Man as You are.

Seems to me, being a layman, that you would have to hardroll every layer when using epoxy in order to get rid of any and all air bubbles. Secondly, I would be curious to see if you could get ahold of EU-glas to compare.

Thanks Andy! Way more relaxing than going to the movies! Have not done any composite work since i fixed an old whaler a few years ago where your videos were of phenomenal help. Patreon done.

Thank you for answering my 1708 csm question! Makes perfect sense

Good explanation on using CSM with poly or epoxy. I am about to glass the interior of a water ballast tank which means all of my glassing will be upside down on the underside of the boat's floor. I was going to use epoxy with CSM but since I will be fighting gravity, it seems poly would be the best choice for absorption. (US made CSM)

I would be interested to see a strength test.... I'd think you could put half of it over a workbench and then suspend a weight (like a bucket that you could fill with water or sand) on a rope tied through a hole cut say 1" from the end of the CSM... just keep adding until it breaks along the workbench edge (or pulls through the hole). You might want to do it outside though as it may make a mess when it fails!

"but don't take my word for it" Why though you explained the concept perfectly

I like this comparison. I've asked this question before, but never got a good answer. The visual is great with the Poly, which means it's probably lighter and stronger and costs less to do. Thanks!

Great video. Love the music and good audio production. Your in the class A team.

Thanks Andy! I was watching this, thinking about a 17:08 epoxy layup I did a few years ago on some structural knees of my sailboat. Although the repair has worked just fine, I was getting worried, watching the video, about the strength of the repair. Felt better after you mentioned 17:08 at the end!

amazing. thanks for this video. i´ve asked about this once. I can see you read your coments sections. regards from brasil. I´ve learned a LOT with this channel.

comments from a longtime surfboard builder, also some boat work... It cannot be over-emphasized that the builder should wet the surface to receive the CSM before applying the CSM. This way, 1) the CSM is held in place and doesn't fall off the surface (if you've worked on vertical or overhead surfaces it will become immediately apparent; 2) the CSM will wet out from both sides rather than just the top; 3) the surface wetting will help fill the substrate which may otherwise absorb resin and leave the glass too dry. 3 isn't usually an issue when working with CSM but can be with woven product. Less resin = stronger (generally) finished product. other item niggling point... the dry glass product doesn't "absorb" resin. The resin displaces air between the fibers or yarns. I call it "wetting out" rather than "absorbing". But overall a good point about the sizing used on glass fibers.

Thumbs up for a strength test! 😁

Thank-you Andy this was the exact question I have been thinking about for months, I needed this answer for my next job!

Great explanation! Thank you. Just learning how to do this and everyone said you are the #1 source for info. They were right!!

Very informative as always Andy. The demo made it very easy to finally understand.

Glad I found this... I had forgot about the Styrene Binder and almost used Epoxy.

It was previously my understanding that the old type of CSM used a binder that was not dissolved by epoxy, but composites like 1708 & modern CSM had a binder that did dissolve in epoxy. I guess that I need to keep my eyes open when buying CSM

Have used epoy with chop many times. The trick is , you must fin between layers. In your demonstration, if you had finned between layers, you would not have had to use extra epoxy. Yes , it is more work but thats what you have to do if you want to use epoxy

I totally agree with you on epoxy & chopped strand just don’t mix. I wish it did. Mixing epoxy creates some many bubbles, especially if you don’t degas it.

Thanks, great informative video! So basically you can use CSM with epoxy if you get the right one with the correct binder. I wish you had made a third test! :)

Thank you Andy you’re videos have taught me lot

There are Chopped Strand Matting that has cornstarch as a binder. Those can be used with either epoxy or polyester resins. But good demo of using standard CSM with epoxy.

Super useful and practical information about glass and resins, thanks.

Good job as always. Thanks Andy for sharing your knowledge and experience. I have one remark and one question. R) If you are willing to make a strength tests, please ensure you compare samples of the same weight. There is no point to test whether epoxy sample having the same amount of glass (as the poly sample) and an extra portion of the resin is stronger or weaker. Even homemade test might be valuable if carried out with physical basics taken into account. Q) I have heard many times about a sort of “osmosis” after a couple of years in case of laminating over wood with polyester resin. Only epoxy is usually found suitable for covering over wood. What do you think about it? What is your experience? Have you ever seen delamination of glass laid over wood with the poly resin?

I only use epoxy on cloth. Poly will shrink 10 % and epoxy will shrink 1 %. You can put an epoxy piece back in the mold but poly project has distorted to where it will not fit well back into the mold. I work mostly with fiberglass cloth and carbon composite, that is why I use mostly epoxy. Plus exoxy will stick to metals where poly doen't so well.

1/10th ratio of acetone in your epoxy with dissolve the styrene binder. Once I figured that out I use epoxy with CSM all the time.

YES. You just answered all of my questions!

Hi Andy thanks for sharing your knowledge,in Seychelles we more polyester resin cause it easy application & easy access too

I use epoxy and CSM with great results, complete transparency. I use the powder bound CSM rather than the emulsion bound CSM which is not for use with epoxy. Emulsion bound is non compatible and never intended to be used with epoxy. It maybe some of your issues with epoxy and CSM may be because your seem to use the emulsion bound CSM for both. The epoxy will not dissolve the emulsion binder and allow the strands to move and settle. Emulsion and epoxy is a little like water and wax. I finished watching the video and you did explain this. However you need to source some powder bound CSM as it does seem to be widely available. I'm in NZ.

Thanks for the lessons Andy! Keep up the good work you do

That’s a really good video. I was wondering about the 1708 and the chopped strand backing. Thanks Andy

I really enjoy these videos. I do have a question: Do you have a video on how you gauge how much resin you will use on a project? It seems you nail the quantity pretty close in the videos I've watched. Unless.... You are ALSO a great video editor!! :) Keep up the great work. Not sure if we're sharing with you our latest snow storm down here in Eau Claire.

That answers a few questions all in one episode.

Thanks for the demo, appreciated. A couple of points: You did not consolidate the epoxy with the CSM as you went along, instead you added more resin; so I think this was a bit misleading. Emulsion-bound CSM is the default in Europe, however, powder bound is readily available.

Ok couple things here but first I’m new to fiberglassing 1 why did you not mention using pva or the finishing resin when you used the polyester resin 2 I was told by total boat technical guy specifically to use 1 teaspoon of hardener with 6oz of resin. I think you were doing 8oz batch in this vid and only used 25cc which is for lack of argument 1/2 of a teaspoon. Now here’s the question and you can ask for a email to further this conversation because I really am just trying to learn and have questions. But how did you arrive at 25cc of hardener for 8oz of hardener and I was told a teaspoon with 6oz of hardener

Always prefer show don't tell. Thanks!

Love you're videos. This is my first time restoring a boat and had to replace the transom. Got a LOT of information from your channel and i really appreciate you! Dont know how you do that resin work indoors without a respirator. Im working outdoors and I can't hardly stand the stuff without a respirator.

Thanks for the explanation. There was a guy with an actual fiberglass company who did a comparison saying poly is more porous and able to absorb water easier, and that it wasn’t as strong as epoxy. Is this more like a mechanic Vs. car engineer comparison where the guy actually using these products daily knows better from experience? 😂🤣😂

Thank you. This video answered some questions I was having 👍

Do you think you should mention stitched chopped strand mat?

Hi Andy, Nice video! To me this it is a bit abracadabra. Since glass does not absorb anything, there are just spaces between the strands that are being resin filled. That amount about is physically about the same for both samples. Things why a difference may, so is my guess, occur are the viscosity, the surface tension and there is the styreen coating on the CSM which may attract polyester more easy than epoxy. It might be interesting to see samples made on a non stick surface and test the strength without the variable of the wood used. While polyester bonding with the styreen of the CSM would be better, and thus might be stronger, the epoxy in itself is stronger. Who wins? Styreen is a cause of osmoses. Does unsolved styreen in epoxy when in contact with moist or water form a risc?

Thank you for the demonstration!

Thanks, I have to fix a big hole in my S2 8.0 sailboat hull. The hole was there for the OMC saildrive to stick out. Replacing it with a new 4 strole 9.8 outboard.

Hi, I really enjoy your videos. In UK you can buy CSM with different binder, for both types of resin.

I am uncertain what to use ? my comment 4 years after this is posted , I don't know if your still around . I have watched so many of your videos and they are helping me get to the point that I can make somewhat more informed decisions . My project is not boat related , but an old fibreglass travel trailer I am restoring . I have stripped out the plywood floor from the fibreglass not really a great bond originally . sanded down the glass . I have prepped for hole repairs [ large and small ]. the remaining deck < pardon the boating terminology, the floor is what I am referring to . I want to create the strongest and most water resistant floor possible .

I am in the UK and emulsion bound chop strand is the most common but you can easily get powder bound chop strand for use with epoxy. If you need the extra adhesion strength epoxy brings you would be stupid not to use woven for the strength as well.

I would like to see the samples sliced then put on under a micro scope. I agree the appearance to the eye was more consistent with the poly. That said when using fast and slow set hardener it's also different to the eye. If I fill a hole and 2 weeks after I have no flexibility on the patch only time will tell. Thank you

Chop strand vs matt strengths would be interesting. By rolling out a lot of resin, that is making the glass stronger....i did not realise that.

Good points, but a couple of things also need to be mentioned. Epoxy has a much better bonding strength to existing GRP than polyester or vinylester resin, and it is also more flexible and less likely to crack. So if it's a structural repair rather than a merely cosmetic one, epoxy can make a stronger repair. It is a lot more expensive though. But if strength is the primary issue, epoxy with fiberglass cloth or roving is probably better than using either epoxy or polyester with chopped strand mat.

Another good video Andy. I am laying up my first time glass today (although a bit cold out) for my house boat engine compartment. Its your videos that convinced me it can be done pretty easily. Can you actually sand that Poly you laid up right now? I have a primer coat on and intend on filling the plywood cracks with thickened poly then use 3 layers of chop strand, total fair, then gel. I intend on a non skid so I will watch your other video again and again:)

I’ve never done it that way round but I have used CF with a poly resin, not as anything requiring strength but just off cuts when mould making. Seems to work OK.

Best on the Web…thank you !

I wish I saw this a week ago...I knew the limitation of epoxy, I just didn't realise it was that marked of a difference. So as I had plenty of Epoxy on hand I was chop stranding the lining on my new shower/toilet area with epoxy. Man oh man was it hard going on vertical surfaces and its a below average job.

Good video....solved it.....1708 only with my Total Boat or West epoxy products! Thanks, Andrew

Terrific information, can 1708 be used with epoxy? Thanks!

Of course, the main reason to use chopped strand mat is to confirm to current surfaces. Even if the epoxy eventually soaks through the mat, it is doing so AROUND the styrene coating on the fibers. Thus, the fibers are still glued together, and won't confirm to a curved surface as well. I'd like to see how well epoxy works with styrene-bonded mat on a compound-curved surface.

thank you so much for this.. your experience and knowledge are very much appreciated and will be used in my life thank you thank you thank you

Depends on which CSM you use or which epoxy resin you use. You can use powder bonded CSM a which is compatible with expoxy west systems epoxy. The key is not use a CSM that is bonded together with a binder that requires a solvent poly resins have a solvent that breaks down the binder in CSM and allows a bond of the individual fibers when you wet up. BUT MOST epoxy resins do not. Powder bonded CSM (will be label as compatible with epoxy resin). Is a Mechanical bond that breaks down as you roll it in to the epoxy resin and will bond just fine. Works well in a layup alternating CSM and woven mat in the layup.

Very interesting Andy, thank you for sharing that, wonderful info...

I understand it looking happy! 😊

Andy, Acetone "melts" styrene. Can't you thin epoxy with a percentage of acetone to help melt the binder and increase saturation and bindability? (not a word, but you know what I mean.) Thanks!

You can use a light touch with a blowtorch to get rid of some air bubbles...

Another informative video, thanks.

I counted almost 40 separate movements with the steel roller on the poly going in both x and y directions. Maybe 12 fin roller motions with the epoxy, making it almost seem like....?