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post #21 of 34 (permalink) Old 07-17-2018, 04:42 AM
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Good work, there is no reason to have to pay for basic body work if you have the time and inclination to do it

I am a huge fan of West System going back 30 years. I dont tend to use it for body work as it is more difficult to work with. I actually got them to ship me a small container of Special Coatings Hardener to do my dash with on my +2 when they only sold it in large containers. Great people to deal with.

My opinion on cloth:

Save it for boats.

Lotus never used cloth to my knowledge, there are reasons.

first, it has directional strength, so while stronger, it can fold if you will

second, print through. Cloth will print through the surface. Your eye loves a straight line. once it sees one it cannot unsee it. It picks up two at right angles and it will see the whole pattern. Mat no doubt prints through, but your eye cannot see the random pattern.

25 years ago I saw a beautifully done dark blue +2. The entire nose was done in cloth and the entire surface was visible cloth pattern. The only solution was to strip to gel coat and redo

For stress cracks there is a great product called 'angel hair' or 'tissue paper' mat. I used it 23 years ago on my +2 and not one area has stress cracks or visible print through. You just paint the [stripped] surface with resin and lay it in and it disappears. A little filler and gone.

I will do a posting on my full mohawk roof repair and another recent project
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post #22 of 34 (permalink) Old 07-17-2018, 04:56 AM Thread Starter
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Originally Posted by exigegus View Post
Good work, there is no reason to have to pay for basic body work if you have the time and inclination to do it

I am a huge fan of West System going back 30 years. I dont tend to use it for body work as it is more difficult to work with. I actually got them to ship me a small container of Special Coatings Hardener to do my dash with on my +2 when they only sold it in large containers. Great people to deal with.

My opinion on cloth:

Save it for boats.

Lotus never used cloth to my knowledge, there are reasons.

first, it has directional strength, so while stronger, it can fold if you will

second, print through. Cloth will print through the surface. Your eye loves a straight line. once it sees one it cannot unsee it. It picks up two at right angles and it will see the whole pattern. Mat no doubt prints through, but your eye cannot see the random pattern.

25 years ago I saw a beautifully done dark blue +2. The entire nose was done in cloth and the entire surface was visible cloth pattern. The only solution was to strip to gel coat and redo

For stress cracks there is a great product called 'angel hair' or 'tissue paper' mat. I used it 23 years ago on my +2 and not one area has stress cracks or visible print through. You just paint the [stripped] surface with resin and lay it in and it disappears. A little filler and gone.

I will do a posting on my full mohawk roof repair and another recent project

Some more great points here. And just to clarify, I'm sure I'm not the only one who has this question. When you say print through, you mean the texture of the weave showing through in the surface of the paint later.
Similar to what you see when carbon fiber panels are painted (the faint texture of the carbon fiber showing through the paint)
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post #23 of 34 (permalink) Old 07-17-2018, 05:08 AM
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Some more great points here. And just to clarify, I'm sure I'm not the only one who has this question. When you say print through, you mean the texture of the weave showing through in the surface of the paint later.
Similar to what you see when carbon fiber panels are painted (the faint texture of the carbon fiber showing through the paint)
Yes
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post #24 of 34 (permalink) Old 07-17-2018, 05:20 AM
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You can prevent or reduce print thru on CF by using a carbon veil layer on the outside and with cloth you can combine a light layer of CSM or just use cloth that had a layer of CSM as part of the cloth. Fiber orientation to prevent the folding potential. I use two similar weight knitted/woven but one the fibers are oriented 0/90 deg and the other -45/+45 depending on the situation. I use unidirectional for strength in one direction like localized load disbursement. I use CSM as a first layer when laying up over irregular surfaces to help lock the cloth to the irregular surface. By in large I would probably use CSM on Lotus since that is closest to original material.

Most fiberglass cars started out using chopper guns and have evolved over the years in complexity and construction. I think GM uses infusion and Lotus RTM both similar offering higher fiber to resin rations producing stronger, lighter and fairer panels.

It will be interesting adapting my composite boat experience to cars. Hopefully only to make custom pieces and not repairing damage!
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post #25 of 34 (permalink) Old 07-17-2018, 05:24 AM
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My opinion on cloth:
> Lotus never used cloth to my knowledge, there are reasons.

The main one being cost. Blowing mat onto a mold or infusing a resin and chopped glass mixture is far cheaper, faster and takes less skill than laying cloth. Lotus did use cloth on Exige body parts, resulting in higher strength and higher cost.

> first, it has directional strength, so while stronger, it can fold if you will

Not sure what you're saying here, but cloth and other oriented strand products are far, far stronger than mat . . . by a huge margin. It's not even a debate in the industry. The strength in a fiberglass part is in the fiber (glass, carbon, Kevlar, etc.). The resin is only there to hold things in place. Resin, compared to glass, is very weak, so the goal is to minimize the resin and maximize the fiber in a layup. Mat or chopped fiber has a high ratio of resin compared to woven products, making the end product weaker in comparison.

> Cloth will print through the surface.

Take a look at the inside of an Elise trunk. The mat has "printed" through to the interior surface due to the amount of resin present and the lack of any surface finishing. The mat does not print through to the exterior surface because of how it was manufactured with more resin and a gel coat. If cloth, strands or mat are "printing" through to the surface (and it was unintended), that's an indication of excessive resin shrinkage, insufficient resin, insufficient surface prep for the desired finish or some combination of all three. I've done many model aircraft parts where the painted finish ends up as smooth as glass (the vitreous kind) with no discernible weave visible - and they have remained that way for decades. For example, I have a glider canopy I made with fiberglass cloth and epoxy resin: it is painted black and gets to at least 120 F in hours-long flights in the sun. It's over 30 years old and still looks great. I also make fiberglass parts where the weave is purposely left visible on the finished surface to achieve the highest strength-to-weight ratio.

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Last edited by Glen; 07-17-2018 at 05:31 AM.
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post #26 of 34 (permalink) Old 07-17-2018, 07:06 AM
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I see no evidence of cloth in the Exige

AFAIK the clams are hand laid mat, as are all older Lotus cars prior to VARI. I have never seen cloth in one. I don't know what they use in the double sided molds. AFAIK they have never used a chopper gun

The fiberglass in a newer body needs to be strong enough to hold itself up, compared to a boat where it must withstand the force of tons of force in high seas.

Remember this thread is concerning non professionals laying fiberglass. Absent some reason to believe that there is a structural deficiency in the part that one is repairing, and access to the back is not available, and there is some reason that build up is not allowed, I can see zero reason to be using cloth on the outside of a body part.

I have every confidence that you can personally create perfect parts with fiberglass cloth. I question the advisability of recommending it to the average enthusiast repairing a car. I have seen the negative results of professionals who are less particular than yourself and they are not pretty.

google fiberglass print through, I did not make this up
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post #27 of 34 (permalink) Old 07-18-2018, 06:30 AM
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I see no evidence of cloth in the Exige
You are correct. My memory confused a long-ago reading of “hand-laid” with the use of cloth.

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Remember this thread is concerning non professionals laying fiberglass.
Certainly. I’ve encountered a lot of people who think that the use of composites is a black art only revealed to the chosen few. That couldn’t be farther from the truth. It’s not very complicated or difficult and once a few basics are understood, it’s easy and forgiving of mistakes.

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I can see zero reason to be using cloth on the outside of a body part.
Those are pissing-contest words. Not very helpful.

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Remember this thread is . . .
. . . intended for contributors to share our experience with others so we can all benefit. It is not intended to answer complex questions like "what's the best, mat or cloth?" with simplistic answers that gloss over the nuances that occur in real life. We can't all experience everything. An intelligent person will be willing to consider that their world-view is largley made up of their own experience and that their beliefs might even be based on incomplete or erroneous information.

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post #28 of 34 (permalink) Old 07-18-2018, 07:13 AM
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A couple of years ago I looked into a clam hinge for my 2011 Elise. The BOE solution doesn't work because the new-style clam drops lower in the rear and would collide with the exhaust and other components. I developed my own hinge and mounted it to the rear of the clam trunk floor using a part made from a fiberglass and carbon lay up. The layers went like this:

1. carbon (90)
2 - 4. glass (45, 90, 45)
5. carbon (45)
6 - 7. glass (90, 90)
8. carbon (45)
9 - 11. glass (45, 90, 45)
12. carbon (90)

The weave direction was rotated to either 45 or 90 to provide greater stiffness and resist warping. Here is a picture of one of two molds I made to match the trunk floor at the hinge location:



I used three layers of fiberglass to test the mold before making the actual part. Here is a picture of the completed parts:



Next is a pic of a test fit of the hinge mount on the trunk floor and a pic of the clam open on the hinges:





So what's this all got to do with body repair? Glad you asked . . .

When I cut into the trunk floor to create an opening for the hinge assembly, I got to examine the structure of the fiberglass. The material has a very hard and thin skin on both sides (interior and exterior) that is resin-rich. The core is much different though. It is composed of chopped fibers that are weakly held together with a very small amount of resin. If I had laid up this part, I would have called the core resin-starved. The fibers were easily pulled apart with an X-acto blade or tweezers. The material was weak enough that I decided my hinge mount needed to be not only bonded to the trunk floor but mechanically fastened through both the interior and exterior skins of the material. This would help distribute the loads imposed by the hinge throughout the material rather than concentrating them on one hard skin that could be peeled off the core.

I think the structure of the fiberglass I examined helps explain why body damage on an Elise or Exige is often so extensive. Once the hard skin of the laminate is damaged, the part loses most of its strength and is easily collapsed by point loads. One of the challenges in repairing a part - rather than replacing it - is to create a repair that does not introduce new problems. For example, if a repair is more rigid than the original part, failure can occur on the edge of the repair when the whole part moves. This can lead to cracks in paint and resin. One way around this is to feather the thickness of repairs out over a large enough distance so that the stiffness of the repair drops back down to that of the original part. This is easily done with patches of increasingly larger and thinner layers of woven cloth. It can be done with mats of varying weights, but it is - in my experience - harder to do because mat has a lot more variance in thickness.

Most of my fiberglass experience is with model aircraft up to quarter-scale size. An original layup for a part might consist of several layers of 6 ounce (per square yard) cloth, followed by one or two layers of 2 oz. cloth. A finishing layer of 3/4 oz. cloth - with the weight and weave of a fine silk - further reduces stress risers and helps create a very smooth base for the final finishing techniques. For a patch on body work, the thick cloth would go on the back and as the weight of cloth was reduced, the patch would get larger to spread the load out and reduce stress risers. Depending on the contours and stress on the area of concern, something less than 2 ounce cloth and maybe even just 3/4 ounce cloth on the exterior surface could be used to rebuild the exterior shell of the soft-core composite originally provided by Lotus.

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post #29 of 34 (permalink) Old 07-18-2018, 07:18 AM
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<<<<Quote:
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I can see zero reason to be using cloth on the outside of a body part.
Those are pissing-contest words. Not very helpful.>>>>

When stripped of their very carefully defined context, yes
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post #30 of 34 (permalink) Old 07-18-2018, 08:30 AM
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I've been experimenting with microspheres as filler for f-glass repairs since they are supposed to expand and contract at the same rate as the parent glass rather than using bondo for fill...any thoughts? I have some deep gouges in my front splitter and a full layer of cloth seems like I'll end up with those frayed ends that need to be sealed down once I flatten it back down.

https://westsysteminternational.com/...rosphere-blend

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post #31 of 34 (permalink) Old 07-18-2018, 08:49 AM
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I have not used them, but they say they make the epoxy work more like bondo

If you do not have broken glass, you really don't need to lay any more mat. If you do have broken or cracked glass, add mat from the back to return the structure, and grind and fill the surface. If you have stress cracks, the mat I pictured is the thing to use, it basically becomes invisible. A little filler to make things flat and it will never come back
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post #32 of 34 (permalink) Old 07-18-2018, 08:51 AM
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I've been experimenting with microspheres as filler for f-glass repairs. . .
This material and others like it have been used extensively for thickening, filling and build-up. I just recently switched to the product you mentioned and it works very similar to something called microballoons (hollow spheres made from phenolic resin) that I've used for decades. You end up with a matrix of whatever resin you're using and the light weight filler, so bonding and compatibility issues are minimized. It shapes easily and usually feathers nicely so the filler won't telegraph its presence through the paint. If you slop it on, rough sand with 40 or 60 grit and get it close to the shape you want as soon as the resin is green (an initial cure that is still soft). If you need to feather it, make sure you either post-cure the resin or let it cure at room temperature long enough to be pretty hard. If you try to sand soft resin, it will roll up at the edge and leave a rough edge where you wanted it to taper to nothing. The surface will be somewhat porous where you've sanded it, so it needs sealing and filling (like with a high-build primer) prior to paint.

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post #33 of 34 (permalink) Old 07-18-2018, 09:06 AM
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Thanks Glen, that all makes sense. I have been pouring it into the leading edge of my splitter in hopes I can get some structure for light impacts. Currently it's honeycomb fill with top/bottom structure and the lower leading edge has ground away. There isn't really anything to bond to for a repair, I'm packing the cavity with cloth and back filling with the spheres in a resin paste. I have a bunch of small clam repairs to do so I thought I'd start figuring out technique on a part that won't show too much.

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post #34 of 34 (permalink) Old 07-18-2018, 09:39 AM
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. . . Currently it's honeycomb fill with top/bottom structure and the lower leading edge has ground away. There isn't really anything to bond to for a repair . .
The structure you describe is a common way to create light, stiff parts. The core is something that has just enough strength to take spread-out compression loads and support the skin. The skin is where the strength is. Comparable structures are foam-core wings, where the core is made of expanded bead polystyrene foam and the skin is made of very thin plywood covered with a layer of fiberglass cloth or other composites (used in both model and full-scale aircraft construction). Another comparable structure is the floor of most commercial airliners. Those are commonly made of end-grain balsa (about an inch thick) laminated on both sides with either fiberglass cloth or scrim. Again, a soft core with a hard shell to carry the load.

So for your spoiler, you can recreate the soft core then cover it with fiberglass and resin. Paper honeycomb is available, but it would be just as easy to use some extruded polystyrene foam board (like the blue or pink insulation board you can get at building supplies). Roughly shape the foam to fit the cavity, glue it in place with some epoxy mixed with microspheres (so the epoxy doesn't run away from the joint), then shape the foam to match the desired external contour. With the foam in place and shaped, you can lay fiberglass and epoxy over the foam and feather it onto the existing surface. This procedure puts the fiberglass where it does you the most good - at the surface. Floral foam also works, but it is relatively expensive and only comes in small pieces. Expanded bead polystyrene (the white stuff) is a poor choice since the beads tend to crumble when you try to sand it. All these foams are fine for epoxies; all but the floral foam won't work with polyester resin . . . polyester will melt the foam into a soupy mess.

If you are placing fiberglass onto relatively flat surfaces, or surfaces that only curve in one plane, there is a handy way to wet out the cloth and get it on the structure. Obtain some thin polyethylene plastic sheet that is a few inches bigger than your fiberglass all around. Garbage bags, heavy duty drop cloths or even food wrap are all good sources - plastic that is 3 - 6 mils thick and free of wrinkles is easiest to use. Now cut out your fiberglass (mat or cloth), lay it on the plastic and wet it out with resin. You can use a brush or a squeegee to spread the resin evenly and wet out the material. Then pick up the plastic and fiberglass and place it where you want it on your part. Just like if you wet out the fiberglass after placing it on the part, you’ll still need to smooth out the fiberglass and remove any air bubbles: a dry brush or squeegee works well for this. You can tape the plastic down to help hold it in place, you can stretch the plastic to help smooth things out, and you can leave it in place until the resin kicks off. This method will give you a nice surface finish, helps control the amount of resin you apply and can help feather the glass and resin onto existing structure. You can also use thicker, stiffer plastic sheets to help define flat areas if that is a problem. If you use something other than polyethylene sheet, either test it to make sure the resin will release or use some mold release. In a pinch, a couple of coats of automotive wax will work as a release agent on relatively flat parts, but mold release is cheap.

If you add more layers of cloth after using the plastic sheet, be sure to remove any mold release with a thinner then scuff the surface before your next layup.

Glen

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Last edited by Glen; 07-18-2018 at 04:18 PM. Reason: Add note about removing air bubbles when using plastic sheet
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