Your fiberglass repair kit

[Frank818]

I notice a very thin layer at a specific section my engine cover and it started to crack already, through the gel coat. I need to add fiberglass, cloth and resin to strengthen and prevent bending.

Is 3M Bondo a good repair kit that doesn't bend when applied? (EDIT: NO IT'S NOT! It's crap)

http://www.ebay.com/itm/3M-420-Fiberglass-Resin-Repair-Kit-45-Pint-New-/381276474651?hash=item58c5d94d1b:g:QN8AAOSwl8NVZ7a T

Or what other good solution you know about?

I heard some used carbon fiber to harden the hood and other parts, but I don't know what to buy and I don't know how to apply from underneath the panel once installed, cuz it needs to be at the correct position when it hardens.

[Hindsight]

Hey Frank, best bet is to buy resin and cloth separately. That's all you need. I suggest West System Epoxy. For glass cloth, the thick stuff you get in kits like Bondo's is too stiff to conform to curves, often times, so you are better to buy glass cloth online. Another forum member suggested this stuff which works GREAT! http://www.uscomposites.com/cloth.html#eglass

Get the 7781 or 7725. Both conform nicely.

West Epoxy is nice because it is very strong and they have several different hardeners. Get a kit on eBay that comes with resin + hardener + pumps. The pumps make it great to work with. Get some small plastic cups for mixing at the grocery store.

To add strength under the panel, wet the area with epoxy, put a piece of glass cloth on it, then use a roller or brush to press it in and get it fully soaked with epoxy, then add another layer of glass and repeat until desired thickness. For most things, about 5-7 layers should be enough. Don't go too wet... you want all fibers of the cloth soaked, but add no more epoxy than is needed to do just that.

If you are looking to add rigidity instead of just thicken, use foam. This stuff http://www.fibreglast.com/product/vinyl-foam-5-lb-density/Foam

A trick I have yet to try with the foam, is to take some VHB tape, cut into 1" squares, then place a square on your foam reinforcement strips every 6-10" or so. Then take some epoxy thickened with cabosil, and butter the foam with it... all areas except on the vhb tape. Then you should be able to stick it on the foam and put the foam in place on the panel. The VHB should hold the foam in place until the epoxy cures, but again, I haven't tried it yet. A more sure-way would be to drill small holes and screw the foam in from the top side but you'd have to go back and fill the holes with gel coat and then re-finish the surface after you did that. I will be trying the VHB method when I add foam to my engine cover and hood. That check-list item got moved lower down the priority list after my last track day uncovered more important things I need to work on, so it could be a while before I get to it, but I will post an update with pics when I do.

[Frank818]

Well that's a great post, man. Everyone should know about it. I'll follow that plan. You can see on the pic where it cracks. The more I manipulate the cover the bigger the cracks get, I need to fix that pretty soon. Also cutting the humps to fit Craig's louvers removes a lot of strength and I won't get it back until I fix the louvers in place.

58329


Now I have a good question for you, would you use the same resin to coat carbon fiber as a gloss finish? Or that requires an epoxy resin for carbon fiber? I read that on google. I need to fix some resin cracks and apply a better and glossy coat of resin on my splitter and diffuser (only the parts visible, though, not the huge portions hidden under the car).

I'll keep an eye on your thread if you ever try the foam before I do.

[mikeinatlanta]

Have to disagree on the West System. Epoxy does not play well with the original material vinylester and when mixed you take unnecessary risk.

The original bodies from FFR are made of vinylester and should be repaired with it for reasons that get a bit long winded and over the top technical for the forum. If looking for a repair filler you will want to use 3M HSRF as it is the only vinylester based repair filler on the market. It is a marine product and not available through automotive channels. Besides, vinylester is cheaper than epoxy.

For glass stick with a fairly lightweight mat. Cloth is stronger but much more difficult to work with and not necessary.


One good source is US Composites. http://www.uscomposites.com/polyesters.html

[UnhipPopano]

I suggest that you get some samples or small quantities of the different materials and set up some tests using the flanges that will be removed or locations where it will not be seen. You may find that they all work, but you can choose what works best for you.

[mindinclouds]

Have to disagree on the West System. Epoxy does not play well with the original material vinylester and when mixed you take unnecessary risk.

The original bodies from FFR are made of vinylester and should be repaired with it for reasons that get a bit long winded and over the top technical for the forum. If looking for a repair filler you will want to use 3M HSRF as it is the only vinylester based repair filler on the market. It is a marine product and not available through automotive channels. Besides, vinylester is cheaper than epoxy.

For glass stick with a fairly lightweight mat. Cloth is stronger but much more difficult to work with and not necessary.


One good source is US Composites. http://www.uscomposites.com/polyesters.html

I have done a huge amount of work with composites in my line of work (light general aviation aircraft).

West Systems epoxy is totally safe for laminating onto previously cured polyester or vinylester resin as long as the surface is properly prepared (true when re-laminating on any cured composite).

The danger is going the other direction.... never apply polyester or vinylester resin to a cured epoxy lay-up.

[Frank818]

...properly prepared...

What's your definition of the expression?

[UnhipPopano]

If you do some RTFM, wax is added and floats to the surface. you need to remove this wax by sanding, as well as the sanding increases the surface area.

[TouchStone]

Whats the danger/risk? After reading this it sounds like I've done all the wrong things. When I attached glue on studs to the body panels I used 2 part epoxy to initially place the studs and then went over it with bondo fiberglass resin and mat. I didn't have any problems during and since the install. Will I have problems later on?

[UnhipPopano]

Chances are that the bondo stuff was epoxy based. If it does delaminate at some time in the future, it should be easy enough to fix.

[mikeinatlanta]

I have done a huge amount of work with composites in my line of work (light general aviation aircraft).

West Systems epoxy is totally safe for laminating onto previously cured polyester or vinylester resin as long as the surface is properly prepared (true when re-laminating on any cured composite).

The danger is going the other direction.... never apply polyester or vinylester resin to a cured epoxy lay-up.
You are correct, however, making one small repair with epoxy will forever mandate that all subsequent repairs in the area be with epoxy. Not only that, but epoxy on vinylester has no stronger bond than vinylester on a vinylester laminate. West System epoxies do have properties a bit better than vinylesters, however, when making a repair the bond strength is the limiting factor, so absolutely no advantage using epoxy, but many disadvantages.

Advantages of West System epoxy repair on vinylester:
You can bond cheap non structural foams (Styrofoam) and make the job look like a proper structural foam reinforcement.

Disadvantages:
Cost at least double
Free amines in the epoxy will degrade or defeat any future vinylester (and possibly polyester) repair cure
Requires very precise ratio of resin to hardener (must use a precision scale)
No structural advantage due to equal or lower repair bond strength as compared to original resin
Different properties increase the risk of repair picture framing

[mikeinatlanta]

What's your definition of the expression?

Sanded to remove surfacing wax (paraffin) and cleaned with a non residue solvent such as acetone.


If you do some RTFM, wax is added and floats to the surface. you need to remove this wax by sanding, as well as the sanding increases the surface area.

Exactly correct. Many believe the sanding is to give the resin something to grab, but when using liquid adhesives sanding actually gains bond strength due to increased surface area and the side effect of a thorough cleaning. Think about it this way. The firm adhesive on tape sticks best to smooth surfaces like glass, and the coarser the surface the lower the adhesion of the tape. However, when the adhesive is liquid it can conform to the surface irregularities and the added surface area increases bond strength.


Whats the danger/risk? After reading this it sounds like I've done all the wrong things. When I attached glue on studs to the body panels I used 2 part epoxy to initially place the studs and then went over it with bondo fiberglass resin and mat. I didn't have any problems during and since the install. Will I have problems later on?

Depends on the epoxy you used. Your problem MAY come from excessively stiff resin. Generally speaking you will get the most durable bond in that situation using a urethane adhesive. The bono resin and glass is an inferior product and will produce results commensurate with the product quality. I wouldn't worry about it unless it falls off. If that happens, sand and rebond the whole thing (glass and all) with urethane.


Chances are that the bondo stuff was epoxy based. If it does delaminate at some time in the future, it should be easy enough to fix.

Pretty much all Bondo branded composites products are polyester based, and the lowest quality products available.

[Frank818]

With vinylester you don't need to mix anything?

[mikeinatlanta]

Vinylester is cured with a catalyst such as MEKP, just like polyester. It's a best of both worlds resin, near epoxy properties but tolerant of less than perfect mix ratios. It will also dissolve the sizing agent in mat where epoxy will not and requires using cloth.

[mikeinatlanta]

I just reread this thread and noticed there are few answers to the OP's original question. My apologies.

In a perfect world you would stiffen up the panel using a core material such as urethane foam, honeycomb, balsa, etc. and then laminating carbon or kevlar cloth properly orientated over it, however, the simplest thing to do is to stiffen it up a bit by adding more thickness of glass.

I recommend using glass mat instead of cloth because it will produce a quasi-isotropic laminate with no need to consider how plies are arranged. Cloth is superior, but mat is much easier to work with. It is better to use more than one thin layer of mat or cloth rather than one thick layer.

For resin: As already stated, your body is made from vinylester and that is the best product to use for repair. When sourcing, you will find some that includes surfacing agent (paraffin wax) and some that don't. Generally speaking, sources that sell without wax carry fresher and better quality than those that sell product with wax already added. The wax is cheap at about $2 per bottle and it's best to add yourself. The wax is needed because polyester and vinylester products will not fully cure on the surface due to interaction with air, or more specifically the moisture in the air. The surfacing agent forms a very thin barrier and allows air cured parts to fully harden on the surface. ALL polyester products such as resin, body filler, etc. have this added while gelcoats do not.


Panel alignment: What you can do is first make sure the component can perfectly aligned in the first place. build any necessary tooling to hold the panel in a perfect position. You will then remove the panel, lay the repair materials on the back of the panel, and then place the panel back in correct alignment wile the resin is curing. Hold the panel in this position for at least a few days and preferably give it a heat cycle with heat lamps of about two hours at 150f AFTER it is cured. Even if the resin is starting to harden, it will be soft and take the permanent position you give it for cure.

You most definitely do not want to use the product that you posted a link to. It is the cheapest of the cheap resin and will not take underhood temps without deforming. The property you would look for in specs is Tg, or glass transition temperature, but any vinylester or epoxy such as West system will take the heat. It also uses thick glass cloth which is not ideal for this job.

For these materials I use US composites. They have great pricing, fresh product, and great service.http://www.uscomposites.com/index.html

The Divinycell foam posted in another link is some awesome stuff and what to use if you want to go all out and make it real nice. Here is a pic of a roadster trunk lid reinforced using it. This is before the glass was added over the foam. If you want to use this method I can post more details of how it is done.

58383

[mindinclouds]

There are other advantages....


You are correct, however, making one small repair with epoxy will forever mandate that all subsequent repairs in the area be with epoxy. Not only that, but epoxy on vinylester has no stronger bond than vinylester on a vinylester laminate. West System epoxies do have properties a bit better than vinylesters, however, when making a repair the bond strength is the limiting factor, so absolutely no advantage using epoxy, but many disadvantages.

Advantages of West System epoxy repair on vinylester:
You can bond cheap non structural foams (Styrofoam) and make the job look like a proper structural foam reinforcement.

Need to add "Epoxy actually has reasonably good temperature stability". Unlike poly or vinyl, which is the reason for all of the warpage and fitment problems of the body parts

Disadvantages:
Cost at least double
Free amines in the epoxy will degrade or defeat any future vinylester (and possibly polyester) repair cure
Requires very precise ratio of resin to hardener (must use a precision scale)
No structural advantage due to equal or lower repair bond strength as compared to original resin
Different properties increase the risk of repair picture framing

[mikeinatlanta]

There are other advantages....

Have to disagree with that one. The warping comes from not being completely cured when removed from a mold, or too low a glass transition temperature. The early mold removal problem would exist regardless of the resin used.

Lets compare West 105 to Vinylester:

Tg (glass transition temperature): This is a specification for the temperature when the resin loses it's rigidity. West 105 is 129F onset with 142F total. Vinylester is 210F t0 240F Bondo 180F

Tensile strength: West is 7,900 psi, vinylester 11,000-12,000 psi Bondo 5,800 psi

Compressive strength: West 11,400psi, vinylester 16,000-17,000 psi

Flexural modulus at 105psi: This is the ability of the resin to bend. Stiffer is not necessarily better here. West 4.61, vinylester 4.5

Tensile modulus: This is what will make the component stiff. In this case, stiffer is better. West 4.08, vinylester 4.9

Keep in mind that there are epoxy resins that will blow away the vinylester, but West is pretty much bottom rung epoxy with massive marketing. I have epoxy on had with at Tg of 350f plus, but it also costs about $250 a pint and over $400 a quart.

EDIT to add Bondo resin data where 3M provides

[Frank818]

Tnx for the info. Well to try it out and get the hang of it I went with Derakane M470-300P vinylester. It's true those are much cheaper. I think it's wise for testing. Also it was easier to get hands on it in Canada, as coming from the US, Customs can confiscate the shipment and then I'm screwed.

I think I don't care much about the vinylester not fully cured (still tacky), cuz I will put some sound/heat insulation on all my panels and over most of the places I will use resin. Good if it's tacky, the insulation will stick better.

I will probably use Divinicell at some point, but that may be after I pass inspection and I have completed the car. I'll keep you name in mind.

[mikeinatlanta]

I think I don't care much about the vinylester not fully cured (still tacky), cuz I will put some sound/heat insulation on all my panels and over most of the places I will use resin. Good if it's tacky, the insulation will stick better.

You will care if you don't use a surfacing agent. The tacky is not they type of tacky that will help anything stick, it will prevent it. Check with the manufacturer or supplier of your resin and find out if it has the additive. If it doesn't then they will be selling it in small bottles. If they say that they don't know then it most likely already has it. If you don't get a good answer, do a small test piece.

The main reason resin is sold without surfacing agent is to allow multiple layups and cures without having to sand. Same for gelcoat. It allows more resin to be directly applied over cured but still tacky gelcoat without sanding. Anywhere you have air contact with the final surface needs the wax.

If by chance you do not have wax and end up with a tacky surface on your repair, you can clean off the tacky stuff with acetone and some elbow grease.

[carbon fiber]

I totally agree with mikeinatlanta on using vinylester on vinylester. This has been discussed in several 818 threads already. I've had bad results from using epoxy on vinylester in the past myself. As far as retaining the position of the panel in order to add glass to the bottom of the part, build a lightweight wood framework that will contact the part (on the outside) in multiple key points and bondo the two together at those points. (while it's mounted in it's proper position) Remove it, flip it over onto the frame and reinforce the part. Then after it cures remove the frame and sand down the bondo.

[Frank818]

Tnx!
I will mail my Canadian resin place and ask the guy about surfacing agent and resin for glossy carbon fibre. I'll get a bit of MEKP at the same time it's super cheap and the FFR bottles I have will be old by the winter.

Is FFR geal coat mixed with wax already?

[mikeinatlanta]

Tnx!
I will mail my Canadian resin place and ask the guy about surfacing agent and resin for glossy carbon fibre. I'll get a bit of MEKP at the same time it's super cheap and the FFR bottles I have will be old by the winter.

Is FFR geal coat mixed with wax already?

I assume you mean the FFR gelcoat repair kit. Any repair kit SHOULD have wax added, but I would check with them.

[Frank818]

Well after discussing a lot with the guy at Composites Canada, he confirmed that vinylester on vinylester you can't go wrong. Other epoxy could work but can't go wrong with vinylester. And also that the 1st gen CF parts FFR built are very cheap, cuz chopped strand matt for CF is a very cheap way of building CF parts. But we knew that already. Also chopped strand matt is incompatible with epoxy, so if, like me, you plan on fixing scratches, cracks and adding gloss to the CF parts, don't use epoxy.

In the end I will use some vinylester for the FG parts, mix wax to it for the last coat. For the CF parts, I will use something compatible with what FFR used, that has high gloss, add some top coat for UV protection and stone chips protection and that's it. The guy at Composites Canada has a CF hood with that top coat on, 60k km (sorry guys, that's 37.3k miles) and NO chip at all, no discoloration as well. On painted hoods, no chips for 40k miles, I've never seen that.

[mikeinatlanta]

Sounds to me like you found someone with some knowledge on the subject. Ditto on the carbon parts being cheap. Reality is most aftermarket carbon parts are made this way, not just FFR. Doing it "correctly" costs some pretty serious money, and most just want the look anyway. I could be wrong, but I believe FFR uses vinylester on their carbon parts as well. Regardless of parent material, clear coating with something more like paint is a good idea for bare carbon parts. Composite resins are made for strength, not appearance.

BTW: Also an aviation guy but 37 years. Have developed composite training programs and authored text books for a major airline. Developed cutting edge training with feature article in AMT magazine. Currently a technical consultant for an airline.