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Brotus7
Brotus7 Dork
10/14/21 9:57 a.m.

I searched the forum and didn't find a thread with quite the info I'm looking for.  I'm at the point where I need to start doing fiberglass work on my Europa and am looking for links to your favorite how-to's, products, techniques, lessons learned.  First order of business is to replace the "firewall" on my car.

What (think) I've learned so far:

  • Lotus originally used polyester resin
    • Thanks for correcting my misunderstanding
  • Epoxy resin will stick to epoxy and polyester
  • Polyester will not stick to epoxy
  • Polyester will melt foam, epoxy won't

Questions:

  • Does epoxy resin require a specific fiberglass vs polyester?
  • When do you use chopped mat vs sheets?
  • How do different systems compare?  Is it just curing time, or are some easier to work with than other? Cost?
  • Favorite reading/watching material for someone itching to get into fiberglass?
Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
10/14/21 10:03 a.m.

I have been reading "composite materials" 1, 2, and 3 but I haven't started much actual composite work yet. I do recommend the books. 

Mr_Asa
Mr_Asa PowerDork
10/14/21 10:04 a.m.

Answers:

Nope.

Not quite sure, but I think if you are making a mold, chopped.  Otherwise fabric.

EDIT Realized I read the above wrong.  Chopped mat is usually a base layer, woven is usually a top layer for a better surface.  Chopped mat has the same strength in all directions where woven has to be oriented parallel to loads.

Systems as in various branded bundles, or what?  I didn't play with many different ones, but above a certain quality level I think its just about having everything in the same ecosystem

See if you can find my boat threads, or anything where I specifically talked about fiberglass.  I got a bunch of good videos recommended in them that I can't quite remember right now.

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
10/14/21 10:15 a.m.

Interesting.  I'm using fiberglass to repair various plastic or composite issues on my F body.  Those posts seems to get more interest than other posts too.  I wondered if maybe I should write a fiberglass article for the site / magazine.  
 

You will sadly need to use epoxy resin which is harder to sand than polyester (main benefit of polyester resin in my experience).  I tend to use epoxy for structural parts and polyester for pretty parts that will be painted. 
 

One thing to consider is fiberglass cloth "weight."  For structural I use 2oz to 5oz (per square foot) glass cloth.  I buy large mats and sometimes rolls and cut it to size with scissors.  You actually cut it a bit oversized and trim after. X acto knives are perfect for trimming loose cloth when you are done.  
 

Most of my fiberglass experience is on small flying things (RC airplanes) so I have some 0.1 oz glass cloth too.  
 

For a firewall patch I would use multiple layers of 0.5 glass cloth.  I would make a plywood backing and coat it with wax paper or parchment or coat it with wax.  I would tack it over the hole (to be cut off later).  I would then lay the 1st layer of cloth over the hole with at least 1" overlap all around.  If feasible more overlap would be better.  Then I would squeegee on a layer of epoxy completely soaking the cloth but keeping the layer thin and smooth.  Then you want to sand it.

OH!  IMPORTANT! Sand the area the patch will overlap on the firewall too.  The scratches from the sanding give the epoxy a better surface area to attach too.  Rough 150 or 200 grit makes nice scratches for grip.  
 

Now install layer two of fiberglass over the first.  I'd rotate the next layer 30 or 45 degrees so the weave is cross angled to make both layers stronger.  On something like a firewall, I'd think 3-5 layers of 5 oz cloth would be needed.  A lotus person may know the original structure.

Since you are doing big fiberglass repairs, I would try and get industrial amounts of fiberglass and resin.  I know stitch and glue kayak suppliers have it in large quantities.  I'd check out Chesapeake light craft.  

I've bought rolls of glass cloth from Thayercraft in the past.  
 

For body repairs you will want to use multiple layers of lighter cloth maybe 2oz-3oz or so.  
 

 

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
10/14/21 10:18 a.m.

Also you can make the epoxy easier to sand by adding filler.  I use micro balloons.  This will help with the sanding and filling on painted body parts.  You can also use body filler / putty once you have a decent surface and structural strength but keep it super thin and flexible.  Fiberglass can move a lot under vibration and load which will make thick filler just pop off.  That's why epoxy and filler like microballons alone is a lot better.  It's still epoxy just a lot less dense.

David S. Wallens
David S. Wallens Editorial Director
10/14/21 10:31 a.m.
maschinenbau
maschinenbau UltraDork
10/14/21 12:10 p.m.

In reply to Brotus7 :

From what I've gathered I'm pretty sure the Lotus Europa body is a polyester resin. 

Mr_Asa
Mr_Asa PowerDork
10/14/21 12:13 p.m.

In reply to David S. Wallens :

Honestly, that video was the kicker for me to just get to work.  Nice and concise, no extra frills. "Hell," I thought, "if a GRMer can do it so can I."

This place really is the best group of enablers. 

 

Sidenote- autocorrect tried to change GRMer to GOMER. 

David S. Wallens
David S. Wallens Editorial Director
10/14/21 12:17 p.m.
Mr_Asa said:

In reply to David S. Wallens :

Honestly, that video was the kicker for me to just get to work.  Nice and concise, no extra frills. "Hell," I thought, "if a GRMer can do it so can I."

This place really is the best group of enablers. 

 

Sidenote- autocorrect tried to change GRMer to GOMER. 

Awesome to hear and, yeah, Tim and Chris did a killer job on that video. (Tell your friends.)

Thanks. 

Mr_Asa
Mr_Asa PowerDork
10/14/21 12:23 p.m.
maschinenbau said:

In reply to Brotus7 :

From what I've gathered I'm pretty sure the Lotus Europa body is a polyester resin. 

I was also wondering about that.  Epoxy resins have been around for a while, but I know in the 50s polyester resin was the norm.  I'm not sure of the cut off.

RoddyMac17
RoddyMac17 Reader
10/14/21 12:27 p.m.

The Europa is polyester, and is entirely chopped strand.  From doing the bodywork on my car, and from helping/observing repairs on other Lotus, here are a few tips:

-Do not use woven as a top layer, it prints through

-Do use surface veil / tissue as a top layer as it's a very fine CSM

-Do structural repairs first, you can use CSM or fabric/woven

-Bevel out any spider cracks and fill will tissue (multiple layers if needed) but leave it just below the final surface, top coat with a thick resin layer as this is what you'll be sanding (there will a metric sh&% ton of cracks, I spent the better part of a years worth of weekends fixing them all)

-if you're going to do multiple layups use unwaxed poly for the bulk of the work and waxed for the final layup/surface

I don't see any reason to use epoxy on anything unless you're gluing structural panels together (sill to floor flange if you want to get rid of the rivets).  All of the repairs on my car were done with polyester.    After all the filling and sanding I top coated my car with multiple layers of polyurethane high build to level everything, and even after that it still needed some remedial work once I handed it off to the paint shop.

 

Mr_Asa
Mr_Asa PowerDork
10/14/21 1:01 p.m.

In reply to RoddyMac17 :

Regarding waxed/unwanted.  "Interior" and "exterior" gelcoat is in relation to a molded part and where the part will be when released.  I would wager resin is the same way.

Exterior is unwaxed because it is the first and most layer(s) of the mold, when its released it is on the exterior of the part. Exterior has to be unwaxed for the next layers to stick to it.  Interior is the final layer and is waxed in order to help it cure.

Its backwards and you feel silly asking why your part didn't cure when you used exterior gelcoat. 

Brotus7
Brotus7 Dork
10/14/21 1:12 p.m.

Just watched the Elva video - I agree, that was great.  I read the Elan build last night, but it didn't get in the itchy details that the video did.

I'm glad I asked before I spent money!  So, polyester and not resin - CHECK.  Fixed my understanding in the OP.

The firewall will be plywood sandwiched between fiberglass, so that seems like a decent first project to mess with since it'll be buried and not visible.  Lotus originally used a material similar to ceiling tiles that was notorious for rotting. I'm hoping to fix the firewall and likely make some flares in the spring.  Maybe someday I'll try to make it look nice, I'm sure the front end has a ton of spider cracks.  Rod, your build came out great.

AnthonyGS - thanks for the detailed response!

RoddyMac17
RoddyMac17 Reader
10/14/21 1:14 p.m.

Unwaxed resin is more or less the same as exterior gel coat, the underside (mold side for gel) of the unwaxed cures, but the exposed surface stays tacky.  You can then topcoat with waxed to finish the surface.  My old coworker who was a FRP guy once told me you can cure unwaxed by covering the surface in cling film/tin foil/etc but I've never attempted it.   With waxed, the wax forms a surface on the layup to eliminate contact with air allowing the resin to fully cure.  The wax can be removed mechanically (sanding) or chemically with a wipe down using acetone.  

maschinenbau
maschinenbau UltraDork
10/14/21 2:24 p.m.

What about gelcoat? Do you really need it and what does it do? Or could you just epoxy primer + high build + paint like on a metal body?

buzzboy
buzzboy Dork
10/14/21 2:47 p.m.
Brotus7 said:
  • Lotus originally used polyester resin
    • Thanks for correcting my misunderstanding
  • Epoxy resin will stick to epoxy and polyester
  • Polyester will not stick to epoxy
  • Polyester will melt foam, epoxy won't

Questions:

  • Does epoxy resin require a specific fiberglass vs polyester?
  • When do you use chopped mat vs sheets?
  • How do different systems compare?  Is it just curing time, or are some easier to work with than other? Cost?
  • Favorite reading/watching material for someone itching to get into fiberglass?

Epoxy will stick to epoxy or poly but be sure to rough it up really well first. I use 80grit. Even then, I prefer to use the same resin as the original part.

Polyester resin will melt EPS(extruded or expanded polystyrene). Polyester resin works great over urethane foam(traditional surfboard consturction. Epoxy also works fine on urethane foam.

Use whatever cloth. Depending on how structural you need the part to be and the original thickness would determine what cloth I would use. At work I have everything from 4oz up to woven roving and matt.

Epoxy wets out cloth better than poly. For that reason I end up using less of it. However, it costs more. Epoxy cures at whatever speed it is formulated to cure. I keep two speeds of hardener(from the same system) depending on what I'm doing.

Conversely polyester doesn't wet the cloth out as well, but it's a little cheaper and a little more forgiving. I can decide roughly how long it takes to cure depending on how much MEKP9 that I add to a batch.

For surface finish most of what I do we use a thin sanding coat with wax. That is poly or epoxy, just a different thinner but the same wax. I also do some of my surface finish with lightweight body filler.

Lastly, chemical safety is important. You can become sensitized to epoxy. Do not get it on your skin. Do not sand it until it is completely cured. Polyester has bad fumes. Work with good ventilation and use a respirator. Both can be cleaned up with acetone but if you clean your epoxy tools with acetone, then that 'tone is tainted and you have to be sure not to get it on your skin.

TurnerX19
TurnerX19 UltraDork
10/14/21 3:03 p.m.

A point no one above has mentioned is that chopped strand mat is held together with uncured polyester resin, and as such should not be used with epoxy resin. Since the OP's car is Lotus, chop strand and polyester is the proper material. I would use a heavily waxed plywood or aluminum form on the engine side of the firewall and just two or three layers of chopstrand with unwaxed polyester resin. Remove the form when finished.  

Mr_Asa
Mr_Asa PowerDork
10/14/21 3:08 p.m.
RoddyMac17 said:

Unwaxed resin is more or less the same as exterior gel coat, the underside (mold side for gel) of the unwaxed cures, but the exposed surface stays tacky.  You can then topcoat with waxed to finish the surface.  My old coworker who was a FRP guy once told me you can cure unwaxed by covering the surface in cling film/tin foil/etc but I've never attempted it.   With waxed, the wax forms a surface on the layup to eliminate contact with air allowing the resin to fully cure.  The wax can be removed mechanically (sanding) or chemically with a wipe down using acetone.  

Can confirm, a coating tight enough to be anaerobic will cure it, how I solved my issue. 

Mr_Asa
Mr_Asa PowerDork
10/14/21 3:09 p.m.

In reply to TurnerX19 :

Huh, I've never heard that.

RoddyMac17
RoddyMac17 Reader
10/14/21 4:13 p.m.

chopped strand mat is held together with uncured polyester resin

I learned something new today, I knew there was a styrene soluble binder in the CSM, but didn't realize it was polyester.  But, according to West, you can use epoxy with CSM, the binder doesn't dissolve, instead goes into suspension.

pinchvalve (Forum Supporter)
pinchvalve (Forum Supporter) MegaDork
10/14/21 4:17 p.m.

Fiber Glast

This site helped me a lot when I was refinishing the boat. 

Mr_Asa
Mr_Asa PowerDork
10/14/21 5:24 p.m.
AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
10/14/21 8:36 p.m.

You can add filler or resin filled with microballoons to fill any weave pattern you see.  I can achieve glass smooth finish on RC airplanes doing this easily.  I use as little resin as possible to attach cloth because light is even more important for flying things.  If you get an airplane tail heavy by going crazy on resin they get real heavy when you have to add lead to the noise to balance them aerodynamically. 

Now when I was patching busted console holes and spider-webbed holes on the console of the F body I wasn't worried about weave.  None of those repairs can be seen.  Even my lower fender mount repair is going to be well hidden from view (unless someone crawls under the car).  Structural things like the firewall worry about strength first (curing, no air in the cloth, and fill the weave).  You need to soak the cloth all the way through on structural things.  On the fender repair I squeegeed the cloth with resin, flipped it over and placed it wet side down and then squeegeed more resin into the relatively dry side of the cloth.  This repair wasn't about weight, but strength.  It's far stronger than the original composite fender material now.  I need to redo the holes and then put a thin 2nd layer of light cloth over it (mostly for my piece of mind; don't want to have to mess with it again).  Then I will prime and paint it.  It only needs to look good from 20 feet, so no worry about filling the cloth pattern.  If you do heavy cloth and then a final coat of light cloth, the weave is less of a concern. 

 

buzzboy
buzzboy Dork
10/14/21 9:22 p.m.
AnthonyGS (Forum Supporter) said:

You can add filler or resin filled with microballoons to fill any weave pattern you see. 

Are you laminating with a little bit of microballoons in your resin? We recently started adding a little of it to our hotcoats to make them sand out better. Does it make the resin not wet out clear? On surfboards we're trying to keep the cloth clear to show the color underneath.

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) SuperDork
10/14/21 10:10 p.m.

In reply to buzzboy :

Honestly I've never checked if it is clear because I'm always priming and painting over it for airplanes.  Surfboards....  yes clear would be needed and same for boats.  I guess you lay clear down sand and polish like clear coat.  

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