Kevlar to Fiberglass adhesive

[Christopher Crowe]

I need to bond Kevlar fabric to a flat fiberglass composite panel. What is the best adhesive for joining the two materials?

Thank you,

Chris

[Dennis McCarthy]

West System Epoxy

http://www.westsystem.com/ss/

[Brian]

I second the West System epoxy. It comes in cans and you can get a handy pump set that automatically disperses the correct ratio of epoxy to hardener.

When you are adding layers of kevlar to an existing layup, you are relying on pure mechanical bonding to create the strength. Epoxy is best at this. You need to prepare the surface of the part by first cleaning any wax or other contaminant off the surface, then grinding/sanding any coating (gel coat, paint, random overspray) off until you are clearly down to the fiberglass layer. You prepare that layer by grinding/sanding with 80 grit, everywhere, to a smooth finish. If you have blobs or spots with excess resin from previous repairs or otherwise shoddy work, this is a great time to grind off the excess resin (resin adds weight with no strength, and if you leave it there, you will be bonding your new material to something with no strength).

Clean with acetone, mix up your expoxy/hardener, and you have around 30 minutes to work, longer if you select a slow hardener (they have three speeds). Have all your kevlar pre-cut, since cutting the stuff is a PITA. Wet out your surface completely, use more than you think you need, you take off the excess later. Lay on the first layer of kevlar, roll it into the wet epoxy, push it down with your brush, add more epoxy and get it completely wet. Repeat with the next layers, remembering your working time. The last step is critical - get lots of paper towel, and soak up all excess resin! push down, get it all as dry as you can, soak up every last bit, use the roller to press it all out of the layers. You want to end up with a fully wetted out layup that has the minimum amount of epoxy to kevlar ratio. If you have a layer of peel-ply, add that and that will help with this stage and give you a better finish.

As in all things, preparation is key. The last time I did this, on RF-85 side panels, getting the panels fully prepped took two weeks of repair, grinding, sanding, cleaning, cutting the kevlar took a couple of hours (that stuff sucks to cut), and the actual application took a half hour. Be aware that the West system stuff takes around 12 hours to cure, and make really sure that you set your panels up so that they are in the exact shape you want them to be in after everything cures - if you just lay them on a bench and they are warped a bit, they will keep that shape after they are a lot stronger with the new layers of material bonded in to lock in the warp.

West System has books on how to do this, btw. Very good ones, actually.

HTH, Brian

[924RACR]

Regarding cutting the kevlar... after a couple of years fighting with ordinary scissors to cut my carbon, I finally, with my first purchase of kevlar blend, bought a proper set of Kevlar scissors - Fiskar brand, with the micro-serrations and some really nice coating - $35.

Finally used 'em - boy, was I a nut for refusing to get them for so long!!! They really are fabulous, they cut through the Kevlar like a hot knife through styrofoam. The old scissors fought simply to get through carbon, I can't imagine what they'd be like on kevlar...

Really is worth considering, if you're doing much more than a brief patch job...

Here's the ones I bought:
http://www.solarcomposites.com/compo....html#scissors

(PS - I've also found Soller Composites, the link above, to have killer close-outs on carbon etc... highly recommend them, always been very pleased with their product and service, not to mention prices)

[P. Howarth]

Great link!
thanks

[R. Pare]

Chris:

If this is your first time whetting out kevlar, you will find that it is many times harder and slower than whetting out fiberglass. I'd suggest that for this first go-round you use the slow-cure resin.

To decrease weight, vacuum bagging will give you the best results - much, much better than trying to mop up the excess by hand. Drum liner bags work great in many cases.

I may be wrong on this, but since most likely your original panels were made with regular polyester resin, vinyl ester resin may give a better bond than an epoxy. Someone in the know can correct me if I've got it wrong.

[brownslane]

Chris:

If this is your first time whetting out kevlar, you will find that it is many times harder and slower than whetting out fiberglass. I'd suggest that for this first go-round you use the slow-cure resin.

To decrease weight, vacuum bagging will give you the best results - much, much better than trying to mop up the excess by hand. Drum liner bags work great in many cases.

I may be wrong on this, but since most likely your original panels were made with regular polyester resin, vinyl ester resin may give a better bond than an epoxy. Someone in the know can correct me if I've got it wrong.

Richard is correct about the vinyl ester. Better choice. And here is a tip: I use slow hardener and warm the resin before application. A warmer resin will wet out the material more quickly and, with the slow hardener will still have a reasonable pot life. A warmer mix of vinyl ester will also squeegee more readily, allowing more resin to be removed per Brian's instructions.

There is an interthane product that can be used that is specifically formulated to mix epoxies to vinyl ester or polyester.

You may not know this, but polyester resin is available in waxed and unwaxed versions. The waxed is the most often used in OEM (from the manufacturer) bodywork as it releases easier....it also leaves a film of wax on its surface when it cures....Roughing up the surface really well is critical to any sort of bond. Same deal with preparing the bonding surface with acetone.

Best,

[RobLav]

I've been using Aeropoxy. I seem to have better luck bonding things with it than I did with West system years ago. The normal speed hardener takes quite awhile to harden up, so it gives a lot of time. You can get away without vacuum bagging by using a little trick Steve L told me. I used to use pieces of shower curtain laid out on a flat table with the cloth on top - then roll in the epoxy - then install where I want it. Steve suggested to add a layer of plastic on top after wetting out then squeegee out the excess epoxy. This has worked very well.

On edit - yes - Tom's suggestion to warm the resin is a good idea. I do that too.

[Stan Clayton]

(PS - I've also found Soller Composites, the link above, to have killer close-outs on carbon etc... highly recommend them, always been very pleased with their product and service, not to mention prices)

For anybody looking for carbon fiber cloth, I sell 6 oz, 50" wide, 2x2 3k twill (the 'normal' motorsport cloth) for $25/yd with no minimum order size. Contact me offline to order. EIP.

[brownslane]

Is what I use. I have purchased bulk from Stan twice and found the material excellent. Recommended

[Christopher Crowe]

We aquired a small industrial oven, around 3' x 2.5', originally used to dry flux on welding rods. In that we're free to drill holes in the thing, etc. -- is there a possibility of making a poor-man's (kinda-sorta) autoclave?

Oven to heat. Bags inside the oven. Clearly, the first problem would be finding some kind of higher-temp bagging material -- also higher temp hoses. Also, would the pump overheat, or might you just maybe get by with it?

To make this work, maybe you keep the temps relatively low -- 200, perhaps a bit more.

I'm sure someone in history has tried something like this, so any insights or a simple "forget it!" from someone who knows would be great.

[brownslane]

Christopher, you could use a higher temp cure in the resins you use.. The oven could allow you to get to that thermo limit....but, honestly, it is probably not worth the effort givenn the size of the oven required.

A "poorer man's" way to achieve a higher temp is to do layups on a glass table....I got a couple of sliding doors from a home reno....and then place heat lamps underneath to radiate the heat through flat layups (side panels, etc). Otherwise, on a layup on, say, an existing body panel where it does not lay flat, you can use a fan, a couple of heat lamps and a big plastic bag or tarp.....create a high-temp environment as it were.

Otherwise you are just going through a lot of effort.

FWIW

Tom

[provamo]

as mentioned previously the kevlar cutting shears are absolutely essential

[Mike Devins]

We aquired a small industrial oven, around 3' x 2.5', originally used to dry flux on welding rods. In that we're free to drill holes in the thing, etc. -- is there a possibility of making a poor-man's (kinda-sorta) autoclave? .

An autoclave is pressure vessel that your parts go into - it isn't just heat and vacuum.

Bag it with a room temp epoxy and then add some heat to post cure. Heated blankets for your bed will work great. If you wrap the part in them and then add some additional insulation such as packing blankets you will be surprised how warm you can get the parts.

Depending on the size of the parts and where you live sunlight and black garbage bags are a poor mans post cure oven.

[provamo]

i don't think i would ever let those heated blankets enter my bedroom again after the cure LOL

[Christopher Crowe]

Will proceed with your good recommendations.

Chris