DIY FIberglass Repair - LotusTalk - The Lotus Cars Community
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post #1 of 34 (permalink) Old 07-12-2018, 06:19 PM Thread Starter
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DIY FIberglass Repair

So I've turned into a pretty firm believer that if you own one of these cars it should be a prerequisite to learn some simple fiberglass repair. After Spending about $3,500 at a corvette shop, and still finding multiple additional cracks, I had to learn how to patch them.

I repaired 3 or 4 areas on the car where I had to repair and then restore or create the body lines. Cracks at this point where we're essentially just sticking peices back together I consider mindless and there were plenty of those as well but I wanted to highlight a couple of the fixes done over an edge or curve which are a bit more difficult to restore that curve.


This was the final repair, This video represents about 6 hours. The corvette shop repaired the edge of the front clam without having the car to reference the body line and it was WAY way off. So I decided to buck up and get after it.

Using a similar method I repaired my door:









I also ordered a new engine cover because the old one was cracked, and I ended up recieving 2 in a row which were both cracked during shipping. this was just cracked, but I carved too much fiberglass out while grinding out the cracks and made a lot more work for myself:
In order of work:









So if you have some cracks and some questions, post up a picture. I'm no expert but I've become pretty handy in short order due to necessity.
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post #2 of 34 (permalink) Old 07-13-2018, 04:14 AM
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I just ordered a couple handbooks and am planning on doing the same. Bodywork is the only part of the car I can't do myself, and the people I have dealt with set the bar way too low. I think I'll still leave paint to the pros, but my plan is to get the whole car down to the glass by this winter and start all over. I've got lots of the same damage, so I may be sending you some questions as I go

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post #3 of 34 (permalink) Old 07-13-2018, 04:48 AM
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Composites are awesome! I love them so much. Probably my favorite part of working and building my car. Sculpting molds and making parts is so rewarding.
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post #4 of 34 (permalink) Old 07-13-2018, 05:04 AM Thread Starter
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Originally Posted by cyow5 View Post
I just ordered a couple handbooks and am planning on doing the same. Bodywork is the only part of the car I can't do myself, and the people I have dealt with set the bar way too low. I think I'll still leave paint to the pros, but my plan is to get the whole car down to the glass by this winter and start all over. I've got lots of the same damage, so I may be sending you some questions as I go
I'd highly suggest that approach. That was the approach I took out of necessity because I had so many auto body shops flake on me. Only now I'm finding painters are complete idiots too, so I might be updating this with my experience painting the car as well.

I can at least give you feedback on how hard the repair looks. Post some pics in this thread of what you're dealing with, that way others can benefit.

BTW I would suggest youtube, you can assimilate data a lot faster watching someone else do it, and after you watch a dozen or so videos you can start to see patterns and similarities

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post #5 of 34 (permalink) Old 07-13-2018, 06:30 AM
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I'd highly suggest that approach. That was the approach I took out of necessity because I had so many auto body shops flake on me. Only now I'm finding painters are complete idiots too, so I might be updating this with my experience painting the car as well.

I can at least give you feedback on how hard the repair looks. Post some pics in this thread of what you're dealing with, that way others can benefit
I will once insurance BS is sorted out.

Yup, I share that distrust of painters, too, but there are some good ones to be found. The ratio of hay to needles isn't pleasant though.

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post #6 of 34 (permalink) Old 07-13-2018, 06:43 AM Thread Starter
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BTW some points from the video on products I used.
I used Fiberglass sheet with Epoxy resin, Epoxy seems to be stronger overall, and from everything I've read, there's less chance of it shrinking (or at least shrinking a lot less) making the chances of it coming back to haunt you later, less.

I'm using FIberglass cloth. Clotch is stronger than mat, in fact it's probably stronger with the epoxy resin than the original panel.
I also used an epoxy resin with a bit of flexibilty, called GFlex by west systems. I can't recommend this yet, as other than myself and another local lotus I don't know how it will work long term, but from reading on it, it has all of the advantages of any other epoxy resin with the added flexibility, which makes more sense to me than something rigid which could crack.

It seems like videos on the internet disagree on repairing the crack from the back or the front or both, but the way I look at it, if I can repair from the rear I will, because the longest portion of repair is making it pretty. So if I can repair from the rear I will take a cutting wheel and cut along the line of the crack and absolutely no more. That leaves me a cut in the panel about 1mm wide (or the widdth of the thinnest cutting blade I have) that follows the line of the crack (getting to the end of the crack is very important (and shining a bright light through the panel once you've ground the paint off will surprisingly illuminate everything for you and the crack will appear more visible) Then I reinforce from the back and I go overkill on it, then just fill in that little slit I cut, with some fiberglass reinforced filler.
I believe evercoat makes a very good product here. I used a bondo product that can be found in any hardware or automotive store.
It was a "short strand" fiberglass reinforced filler which is not as strong as "long strand" but we don't want to get strength from filler, we want strength from fiberglass, we just want filler to have similar properties to what we're putting it over.

And then when you sand that flat you're going to have imperfections in the surface thats where spot or glazing putty comes in. That's the pink stuff you see in the video. Again you can buy this at an automotive store, but I would recommend only using a 2 part spot putty. THey make a cheap "squeeze it out of the tube and go" version, but supposedly it's more likely to shrink and who knows what else.
2 Part just means it comes in 2 tubes and you have to mix them.

Always hear a pea to a golfball, I typically use too much hardener, because I'm paranoid it won't harden, and within reason the only downside is that it'll get hard on you quick. like within a couple mins, especially if it's hot outside.


If you don't have access to the rear of the panel, you'll need to do your reinforcing from the front, thats where you'll need to cut out the crack, then use a grinder to create a V or channel around it, so you have enough surface area for the fiberglass you're able to fill it with to bond to. Then just grind the fiberglass flat and fill with filler or spot putty depending on how ugly the finish is after you're done bringing the patch flush with the body.

Which one you use depends on how big the void is you're trying to fill.
Large gaps = Fiberglass
Small / Medium gaps and dips = FIberglass reinforced filler (puke green/brown stuff)
Uneven surface or small holes = Spot putty (pink stuff)
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post #7 of 34 (permalink) Old 07-13-2018, 06:55 AM Thread Starter
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Primary things to be concerned with:
Shrinkage, other than being a personal problem in cold water, it can be a problem especially in fiberglass repair. Like I mentioned already using epoxy. This will advoid most of hte issues, as the bulk of the material in your repair should always be FIBERGLASS, not a FILLER or putty. The latter should only be to basically make the fiberglass look pretty, and if you're using many coats of this stuff it's not going to end well.
Here's some smarter people than I talking about Fiberglass and epoxy resins and shrinkage rate:
https://www.researchgate.net/post/Ep...curing_process


Despite using epoxy resin, I'm still going to wait a while before painting the car. This could be a process more indicative of the old days, but typically high end shops would do their fiberglass repair, then wait several months to let the car sit and the material to shrink before they'd paint it. Then they'd come back to it, and if the material had shrunk they'd fill it block sand it out and then spray paint it.

So if you're in an area like I am where we have a long off season, doing your fiberglass in the fall at the end of the driving season, and then planning to paint in the spring is typically a good idea.
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post #8 of 34 (permalink) Old 07-13-2018, 07:05 AM Thread Starter
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Guide coat is your bestest of friend, and all it does is make the surface black. Dry guide coats are essentially a fine black powder, and spray guide coats are essentially cheap black rattle can paint. After the surface has been darkened by guide coat when you start sanding it, you'll notice that some areas are getting lighter and some are staying dark. What you realize is, that a surface that looked pretty smooth, is actually a bunch of peaks and valleys, and the tops of the peaks get sanded off and all of the valleys stay dark, so you instantly see where those low spots are so you can sand right up to them, and no further. Otherwise you are 100% flying blind.
You might start with 80 grit (very course) just to get the general shape of things
And you might start using 180 grit to take the coarsness off the finish and start defining the edges a bit. This is still pretty coarse, you can certainly change the shape of body lines and especially edges with this grit, quickly too if you're using tools.
Once you get above 180 the scratches are too small for you to see, and even if you see them, you won't see all of them.

I found that guide coat will nicely highlight scratches and uneveness in the finish almost all the way to 1000 grit. It starts getting a bit flaky around 600-800 grit, where the surface is so smooth the guide coat comes right off, but this is smoother than you'd ever need for a paint job.
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post #9 of 34 (permalink) Old 07-13-2018, 07:56 AM
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Quote:
Originally Posted by Ls1Rx7 View Post
Primary things to be concerned with:
Shrinkage, other than being a personal problem in cold water, it can be a problem especially in fiberglass repair. Like I mentioned already using epoxy. This will advoid most of hte issues, as the bulk of the material in your repair should always be FIBERGLASS, not a FILLER or putty. The latter should only be to basically make the fiberglass look pretty, and if you're using many coats of this stuff it's not going to end well.
Here's some smarter people than I talking about Fiberglass and epoxy resins and shrinkage rate:
https://www.researchgate.net/post/Ep...curing_process


Despite using epoxy resin, I'm still going to wait a while before painting the car. This could be a process more indicative of the old days, but typically high end shops would do their fiberglass repair, then wait several months to let the car sit and the material to shrink before they'd paint it. Then they'd come back to it, and if the material had shrunk they'd fill it block sand it out and then spray paint it.

So if you're in an area like I am where we have a long off season, doing your fiberglass in the fall at the end of the driving season, and then planning to paint in the spring is typically a good idea.

I got some bad ghosting from where I had a turn signal delete done. In my experience, I don't think time was as big a factor as UV/heat. When I do it again, I am going to let the parts "age" outside on dry days to encourage any natural shrinkage.

And yup, the plan is to start in the fall so I can take all winter to do it right. Lot's of good information condensed here and very good timing!

As an aside, you can save a little bit of money by removing collision coverage if the car will be sitting for a while. I usually save something like $30/mo by doing that, so, on principle alone, it is worth it. Just make sure to keep comprehensive on it in case the garage burns down or whatnot.

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post #10 of 34 (permalink) Old 07-13-2018, 08:05 AM
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I have been recently reading as I consider getting into autobody and paint.

Read someone mentioned fiberglass 'Mat" which has randon strands instead of 'Cloth'.........I think the rationale was something about woven projecting it's uneveness up thru the layers of primers?!? I dunno

I do know I was using resin to overlay some CF fabric over some plastic parts. The stuff I used was impossible to sand....I'll try to find out what type of resin it was, but man it sucked.

So many options.....kills me just trying to figure out what compressor I should buy much less which air guns.....
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post #11 of 34 (permalink) Old 07-13-2018, 08:53 AM
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There are three basic types of resin, polyester, vinyl ester and epoxy. Fiber reinforcements come in many weights, weaves and styles. CSM is chopped strand mat commonly used in repairs and cloth is various weights and fiber orientation for optimal strength.

Epoxy gains strength as it cures typically in a week. I use several types of epoxy from WEST system 105 with different hardeners dependent on the temp and size of the project. There's G Flex which is more flexible great for canoes etc.I used it on solar H2O heater repairs. When using epoxy be sure to remove the amine blush between coats with 3m pad and water. Epoxy is the most impervious to water and is structural in strength. I use Pro Set for infusion.

Vinyl ester is more expensive than polyester but much more impervious to water and much stronger. Both cure in the absence of air and for all resins I use a peel ply over the repair. That has it cure without tackiness and gives "tooth" for the next layer. use a wax added to the resin.

When possible vacuum bagging of the repair area is the prefered method for strength.

I note that here on LT everyone refers to CF as either dry or wet and in the boatbuilding and composite world more commonly referred to as pre preg or wet layup (either vacuum bagged or infusion). Vacuum bagging and or infusion can yield similar weight as prepreg without the costs involved. Ideally I shoot for 50/50 on weight but prepreg can yield lower ratios and weight. Too little resin ratios lead to pinholes and dry spots.

Being adapt in glassing is going to come in handy once I get my Elise! I have a $400 roll of CF uni and am getting ready for a project for one of my boats. Typically I stock rolls of 1802, 1708 and CSM and get my WEST 105 in 5gal all others in gals since ester based resins have a shelf life. Looks like I will be getting more familiar with CF in making Elise parts.
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post #12 of 34 (permalink) Old 07-13-2018, 09:28 AM Thread Starter
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There are three basic types of resin, polyester, vinyl ester and epoxy. Fiber reinforcements come in many weights, weaves and styles. CSM is chopped strand mat commonly used in repairs and cloth is various weights and fiber orientation for optimal strength.

Epoxy gains strength as it cures typically in a week. I use several types of epoxy from WEST system 105 with different hardeners dependent on the temp and size of the project. There's G Flex which is more flexible great for canoes etc.I used it on solar H2O heater repairs. When using epoxy be sure to remove the amine blush between coats with 3m pad and water. Epoxy is the most impervious to water and is structural in strength. I use Pro Set for infusion.

Vinyl ester is more expensive than polyester but much more impervious to water and much stronger. Both cure in the absence of air and for all resins I use a peel ply over the repair. That has it cure without tackiness and gives "tooth" for the next layer. use a wax added to the resin.

When possible vacuum bagging of the repair area is the prefered method for strength.

I note that here on LT everyone refers to CF as either dry or wet and in the boatbuilding and composite world more commonly referred to as pre preg or wet layup (either vacuum bagged or infusion). Vacuum bagging and or infusion can yield similar weight as prepreg without the costs involved. Ideally I shoot for 50/50 on weight but prepreg can yield lower ratios and weight. Too little resin ratios lead to pinholes and dry spots.

Being adapt in glassing is going to come in handy once I get my Elise! I have a $400 roll of CF uni and am getting ready for a project for one of my boats. Typically I stock rolls of 1802, 1708 and CSM and get my WEST 105 in 5gal all others in gals since ester based resins have a shelf life. Looks like I will be getting more familiar with CF in making Elise parts.
Talk to this guy if you want more info on which resin to use and specifics. I just wanted to lay groundwork and get the conversation started.

I'm glad I wasn't crazy for going to my local marine supply shop to buy resin for my car. West systems seems like good stuff and I've been considering using their clear additive on a panel I'm planning to wrap in carbon fiber.
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post #13 of 34 (permalink) Old 07-13-2018, 10:01 AM
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If you can find a local fiberglass supply place you will save 30-40% over marine store prices for WEST system products. Hey I'm just a DIY'er as well I just do more than the average guy and learned back in the 60's. Funny I took a Buell seat fender shell after repairing for a friend and painted it in my front yard with a $10 HF HVLP gun in satin black to a local custom shop and showed them the before pics and the owner called all his guys over to look and then offered me a job as their head painter in front of them. If looks could kill lol I told him I wouldn't want to do it full time!

Like you Ls1Rx7 I encourage everyone to go practice a little and then go for it!
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post #14 of 34 (permalink) Old 07-13-2018, 11:57 AM Thread Starter
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Originally Posted by eZg View Post
I have been recently reading as I consider getting into autobody and paint.

Read someone mentioned fiberglass 'Mat" which has randon strands instead of 'Cloth'.........I think the rationale was something about woven projecting it's uneveness up thru the layers of primers?!? I dunno

I do know I was using resin to overlay some CF fabric over some plastic parts. The stuff I used was impossible to sand....I'll try to find out what type of resin it was, but man it sucked.

So many options.....kills me just trying to figure out what compressor I should buy much less which air guns.....
Mat is just unorganized idividual strands of fiberglass lightly woven together. Cloth is literally like someone took time to neatly stictch together stands of fiberglass into a thin blanket.
From what I've read you can use mat or cloth with epoxy resin, but cloth is stronger, and using mat with epoxy can get messy and annoying and possibly not be strong because, the mat when it gets wet just releases individual strands of fiberglass everywhere.
Usually people use polyester resin with mat because the mat has a chemical in it which allows it to "wet out" with polyester, which basically means that the polyester resin turns the mat into a clump of gelotonous material that sticks together. When you do the same with epoxy, all the strands go everywhere and when it comes to repairing something with strength you can't have a bunch of loose strands, with air pockets throughout it.. It'll be more honeycomb in texture when it dries and that's not strong.

That might also be what they're talking about showing through the primer later.
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post #15 of 34 (permalink) Old 07-16-2018, 02:27 PM Thread Starter
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Bringing in a post from my build thread:

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Originally Posted by gstomp06 View Post
I also recommend checking out the youtube channel "B is for Build" and watch the series on rebuilding a Lotus Evora. He shows a pretty good example of his learning curve with fiberglass repair and some of the mistakes and adjustments he made in the process.
Posting videos for reference:

Just watched it, and I would suggest some caution when using that as an example. He made some pretty big concessions, I'm guessing because he was in a rush
There were a few major things I noticed and he mentioned some of them.
1. Using rattle can primer. This is the foundation of your paint job literally everything you do rests on the adhesion of that primer and the surface you create with it. I would rather apply good primer with a foam roller, or paint brush than cheap primer from a spray can. A 2k primer is all you'd ever want to use outside of a race car paint job, or some cheap job on a beat up honda. Google your local automotive paint supply shop. They accept walk ins, so you don't need to be a professional to go there, and ask the guys behind the counter what the good stuff is. What are the professionals buying and using. They'll tell you, most of em have worked in the industry a long time, and will basically give you free advice on how to do the bodywork.
2. He didn't mention the stripper he used but I'm assuming he would have mentioned it, if it was specifically designed for fiberglass. Certain strippers, as he alluded to will literally eat away at your fiberglass. This is a massive potential problem, and you should always be aware of the solvents and strippers you're using on fiberglass. It can cost you your car.
3. Adressing the cracks up front. He handled the primary crack just fine, same as I mentioned above, and he tried to dig out the spider cracks, which is smart, because trying to grind them all out and create massive craters everywhere can get REALLY ugly, REALLY quick. But he just adressed the major spider cracks. There's no way he got all of them. When he zoomed in they were everywhere on that bumper. Basically the whole surface 6" to a foot from either side of that big crack was all spidered paint. He should have at least taken some 80 grit across that whole area, sanded it all the way down to bare fiberglass done the same on the back, and then shined a flashlight through the panel to illuminate the cracks. You could also probably use guide coat to illustrate the cracks too, but just the act of stripping the panel probably would have taken care of most of them, and there's probably dozens more small ones he never touched. Those I would either continue to sand the fiberglass with 80 grit until I sand through them, or if they're showing up all the way through I would continue to dig them out / cut them out. Then if you've taken a lot of the thickness off the panel grinding them out, you need to lay new fiberglass over it in as smooth of sheets as you can manage. And this would be a lot of work, because now you're rebuilding the surface of the panel, and you've got to re-contour it to make it smooth and straight again (read block sanding which is a pain in the ass, cant do it with your powertools). Also right before he was about to lay paint he pointed out a section that might have been painted with the original white, or it was bare fiberglass. Thats kinda a big difference, you should have primer everywhere. Bare fiberglass can suck in the paint and that section will look odd down the line when it dries, plus potential adhesion issues. Same with the rear wing, you can't just start spraying primer until you're surface is uniform, or else "wierd **** happens" as he said.
4. Which brings me to 4, where;s your guide coat. If you're not using guide coat and you're trying to spot highs and lows (as a noob anyway, I'm sure experts can get away with lots of stuff) you're completely flying blind. So for every high or low spot he mentions there's probably scratches and other spots that you'd never see.



It seems like overall he was mostly in a rush, so that probably explains it, but this process I think would get you equivelent to a cheap paint job, maybe a bit better than a Maaco style. For cars this nice, I wouldn't do that. It takes a lot more time to do it right, and I mean A LOT more, and its nearly impossible to do without a DA sander, and a Mini DA sander. I picked up the mini 2-3" DA sander from amazon for like $60 and it's a beast. Thats what you'd use to attack those areas he said were too tough to reach.

Also despite us living in the 21st century, there still happens to be a MASSIVE difference between cheap and good sandpaper. Like 5-10X difference. When my painter told me to buy 3M Cubitron II sanding discs and I spent nearly $300 on sanding paper alone I cursed him out. When I tried sanding the panels later with cheap paper from amazon and my paper was getting totally loaded up every 20 seconds I understood where he was coming from.

BTW loading up the paper is what happens when you try to sand surfaces and rather than falling off as sanding dust, that residue starts to collect on the sanding paper and fill in the abrasiveness of the paper so it stops working. Some paper sheds dust shockingly better than other paper instead of collecting it. Also has to do with what you're sanding, if it's soft and gummy it won't turn into dust that falls out of the way, it turns into gummy black garbage that coats the surface of your paper.
Sanding is the #1 time suck in prepping for a paint job so spending the money is worth it always.
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post #16 of 34 (permalink) Old 07-16-2018, 03:16 PM
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I highly recommend Harbour Freight air tools if you have one in your area. On sale their HVLP guns are $10, 6" DA/RO self vacuuming sander is $25 and their 2" mini is fantastic and cheap around $25 as well. I use one gun for primers and one for colors and one for white. Sometimes it's just cheaper to replace than to clean.

Sandpaper is important to match to the material like you were saying. Some I get for the specialized sanders on amazon and I use some big box and some amazon for the 6" and 8" disks.

There are some great "how to's" online some even showing how to make your own molds and then carbon fiber parts if so inclined. Here's PT 1 of a three part series.
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post #17 of 34 (permalink) Old 07-16-2018, 05:02 PM
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A couple of notes regarding posts above.

- Fiberglass mat is not woven. It is typically random fibers blown into a mat with a relatively constant thickness. The fibers are usually held together with a chemical binder (that resin will soften), although some mats might be bonded to tissue paper or have very large stitches of thread helping to hold everything in place. My experience is that mat works just fine with epoxy. Mat has lots of voids, so it takes a lot more resin than woven fabrics. I prefer using woven fabrics for better strength and less weight, but mat does have its applications for really weird shapes, high build-up and where weight doesn’t matter.

- Polyester resin leaves a wax on the surface when it cures. This needs to be removed with a chemical like denatured alcohol. Trying to remove it with an abrasive just works the wax into the scratches left by the abrasive and will result in a poor bond with the next application of resin, paint or filler. Polyester resin on top of epoxy resin is usually a bad idea - the polyester can react with epoxy components and fail to cure or bond properly. Most “Bondo” products at the local auto parts store are polyester resin and filler. Be extremely careful with polyester resin catalyst: get some in your eyes and physical damage is immediate and permanent, often leading to blindness. Use eye protection!

- Epoxy usually shrinks less than polyester. Post-curing will help eliminate further shrinkage. I usually post-cure West Systems epoxy at about 140° F for 6 to 8 hours. This is easy to do using a cardboard box and a small electric heater. Use extreme caution to avoid a fire when doing this. Don’t heat liquid epoxy above 120° F . . . you can get lots of bubbles and quite a mess. I always let things harden at room temperature before attempting any post-cure.

- Epoxy resin allergies are very common and usually develop from lots of exposure. Do yourself a huge favor and always avoid skin exposure by wearing gloves and use lots of ventilation to avoid breathing the off-gasses while handling the resin. Once you become sensitized, you won’t be able to stand ANY exposure. Epoxy is handy stuff, so preserve your ability to be around it.

- Don’t use “extra” epoxy hardener just to be sure. It changes the mechanical properties, usually making the result more brittle with less strength. If your layup is sticky after a room temperature cure using the right amount of hardener, post-curing with heat will fix it up. If your shop is below 70° F, you’ll probably need to post-cure anyway.

Glen

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post #18 of 34 (permalink) Old 07-16-2018, 05:47 PM Thread Starter
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Originally Posted by Catsailr27 View Post
I highly recommend Harbour Freight air tools if you have one in your area. On sale their HVLP guns are $10, 6" DA/RO self vacuuming sander is $25 and their 2" mini is fantastic and cheap around $25 as well. I use one gun for primers and one for colors and one for white. Sometimes it's just cheaper to replace than to clean.

Sandpaper is important to match to the material like you were saying. Some I get for the specialized sanders on amazon and I use some big box and some amazon for the 6" and 8" disks.

There are some great "how to's" online some even showing how to make your own molds and then carbon fiber parts if so inclined. Here's PT 1 of a three part series. https://www.youtube.com/watch?v=UgKvDw1E60E
I do have a Harbor Freight and it's a glorious place!!
I ended up skipping the $10 purple harbor freight gun, and I got their "professional" 2 pack set of guns, because the big one comes with a 1.8 tip which is a better fit for most primers:
https://www.harborfreight.com/profes...kit-94572.html
Anything to save some sanding time and headaches is worth $40 plus the little spot gun I used on the wheels and they came out flawless. Like zero sanding needed.

(10 seconds in) When the first panels you shoot come out so well you blow your own mind:

Anyway I'd highly suggest psending a bit more although the purple gun certainly works great.
BTW good info on carbon fiber, I tried to wrap my 2010+ Exige wing center section in carbon fiber and I failed miserably. Think I'll need to make a mould and just re-create it.

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Originally Posted by Glen View Post
A couple of notes regarding posts above.

- Fiberglass mat is not woven. It is typically random fibers blown into a mat with a relatively constant thickness. The fibers are usually held together with a chemical binder (that resin will soften), although some mats might be bonded to tissue paper or have very large stitches of thread helping to hold everything in place. My experience is that mat works just fine with epoxy. Mat has lots of voids, so it takes a lot more resin than woven fabrics. I prefer using woven fabrics for better strength and less weight, but mat does have its applications for really weird shapes, high build-up and where weight doesn’t matter.

- Polyester resin leaves a wax on the surface when it cures. This needs to be removed with a chemical like denatured alcohol. Trying to remove it with an abrasive just works the wax into the scratches left by the abrasive and will result in a poor bond with the next application of resin, paint or filler. Polyester resin on top of epoxy resin is usually a bad idea - the polyester can react with epoxy components and fail to cure or bond properly. Most “Bondo” products at the local auto parts store are polyester resin and filler. Be extremely careful with polyester resin catalyst: get some in your eyes and physical damage is immediate and permanent, often leading to blindness. Use eye protection!

- Epoxy usually shrinks less than polyester. Post-curing will help eliminate further shrinkage. I usually post-cure West Systems epoxy at about 140° F for 6 to 8 hours. This is easy to do using a cardboard box and a small electric heater. Use extreme caution to avoid a fire when doing this. Don’t heat liquid epoxy above 120° F . . . you can get lots of bubbles and quite a mess. I always let things harden at room temperature before attempting any post-cure.

- Epoxy resin allergies are very common and usually develop from lots of exposure. Do yourself a huge favor and always avoid skin exposure by wearing gloves and use lots of ventilation to avoid breathing the off-gasses while handling the resin. Once you become sensitized, you won’t be able to stand ANY exposure. Epoxy is handy stuff, so preserve your ability to be around it.

- Don’t use “extra” epoxy hardener just to be sure. It changes the mechanical properties, usually making the result more brittle with less strength. If your layup is sticky after a room temperature cure using the right amount of hardener, post-curing with heat will fix it up. If your shop is below 70° F, you’ll probably need to post-cure anyway.

Glen
Some good points here that I wish I knew before starting.
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post #19 of 34 (permalink) Old 07-16-2018, 06:40 PM
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Originally Posted by Catsailr27 View Post
There are some great "how to's" online some even showing how to make your own molds and then carbon fiber parts if so inclined. Here's PT 1 of a three part series. https://www.youtube.com/watch?v=UgKvDw1E60E
I just watched all three videos in that series. OMG. So damn cool.

That guy with that ducktail spoiler needs to make a mold and produce them this way!

.
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388hp (342whp) BOE RevX 1676lbs.
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post #20 of 34 (permalink) Old 07-17-2018, 03:16 AM
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Originally Posted by darkSol View Post
. . .That guy with that ducktail spoiler needs to make a mold and produce them this way!
That guy has made one or two posts in several different threads offering to make parts. Then everyone trips over themselves to say they’d buy it. Then that guy never responds. Giant, red, flashing WARNING signs to stop holding your breath and look elsewhere I’d say.

Glen

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