When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Gonna chime in here about epoxy for repairs. I do lots of FG boat repairs and would recommend for any fiberglass (SMC included) structural repair - and the floor pan should be considered this - with epoxy instead of polyester resin. Hat tip - anything that says bondo uses poly as the resin base. As a general rule, polyester resins are great for initial layups, i.e., creating the boat/car/airplane etc., but fair poorly for repairs because polyester resins have much weaker mechanical bonding properties and strength. Polyester strength comes from a chemical bond - molecular crosslinking to underlying layers - which can't happen once the primary surface cures. At that point any layer added only has a mechanical bond to the underlying layer.
Epoxy on the other hand is - basically - glue. It's designed to maximize mechanical bonding. There are lots of different epoxies out there, I prefer West Systems. Costs a little more but well worth it. Just follow the mixing ratios - the old resin trick of adding hardener to speed things up does not work with epoxies. Your drying times will be longer than polyester but worth it, and your working time with epoxy will be much longer too. As an added bonus epoxy smells much better than polyester!
Disclaimer: not trying to start a polyester vs. epoxy war here - but for the average DYI repair it's the only way to go IMHO.
without an explanation as to why other smc panel bond /epoxy wont work your comment is not terribly useful.
If you mean have I dont laboratory testing to confirm the structural superiority in a controlled environment against all other brands then no I have not. I have however done extensive research on wests products and used it extensively to rebuild a very old kevlar race car body as well as other various projects. Its very easy to work with and is very strong. I just wouldnt risk using anything that doesnt have West's reputation on a repair like this. The work that goes into a repair like this can be extensive and time consuming and using a crappy product is not respectful to your own work.
They also have a product for plastic which remains flexible which I have used.on an RV. My comment was simply an opinion and I would expect anyone taking this on would check the reference. Go look at their product pages, they do not screw around.
Sorry, I was being a little short and flippant ... I guess I just really appreciate good companies like 3m and just a few others.
FWIW, they also make a great powder filler that can be added to smooth things out if it gets ugly.
I got no skin in the game here, just spent hours and hours researching and real-life use.
I have used Poly and west Systems for race boats, aircraft and automotive. If the repair is done well the poly resin and cloth will hold well.
I have done repairs on my 85 which have lasted 10+ years using poly resin and cloth. Remember cloth comes in different styles. (I was an R&D engineer in high strength composites in a previous life so my knowledge is most likely more than most)
There are numerous flex additives for both poly and epoxy resins. There are also numerous thickening additives for both. The trick to using the Poly resin is to allow for a slow cure, not a fast cure which can make it brittle and hinder bonding.
I would not consider this area a high structural area. I think with proper prep and cure the poly will work fine. I have actually seen the repair done with a thin AL angle and pop rivets, that lasted for years,, until they sold the car.
The Bondo Hair is OK, but lacks the strength to properly repair the tear. I would use cloth with the hair, thinned with resin to wet out the cloth for a longer lasting repair. You should be able to get some cloth from a Marine Supply shop for little money.
I am afraid my post, and my understanding, may not be massively helpful and may simply muddy the water.
Ive done a bit of research and it appears that smc is actually a process more than anything.
and that polyester and epoxy based “fiber board” exist.
It looks like to epoxy can be used as an adhesive quite well. Thats what i did.
and now, im no longer even clear if the tub is a polyester smc panel or an epoxy smc panel.
im super confused now about whats what. i tried to find a definative source for info on exactly what type of resin and what type of fiber mat or strand was used in the c4...and cant.
In reference to my repair in posts 19 & 21 is the product I bought (link provided in post) sufficient for a quarter size hole in my floor board?
The products mentioned (west marine) seems like the way to go with a large repair like the OP, but it is costly and most of what was left would sit on a shelf for years and go bad.
In reference to my repair in posts 19 & 21 is the product I bought (link provided in post) sufficient for a quarter size hole in my floor board?
The products mentioned (west marine) seems like the way to go with a large repair like the OP, but it is costly and most of what was left would sit on a shelf for years and go bad.
Its actually west system I believe, I saw someone reference west marine and also made the mistake of repeating it. Sorry about that. https://www.westsystem.com/
Just buy a small repair kit on amazon.. Keep the extra on the shelf.. you will be surprised how handy it will be one day. Shelf life is very long because its a catalyst process.
I wouldnt even waste my time with the bondo poly product you reference. Ive used it before and it is garbage.
Just a follow-up on SMC repairs - I found this on an auto body website:
"A new composite material is gaining widespread use in the automotive, industrial, and personal watercraft markets that presents unique repair problems. It is called SMC, or Sheet Molded Compound. Recognizing SMC from other types of FRP composites is critical so the proper repair can be performed. Parts made with SMC are produced in compression molds, so they are smooth on both the inside and outside. That is the first clue to look for when identifying them. Next, SMC parts do not have an outer gel coat, but they are usually painted or color molded. When the paint is sanded off, the underlying surface has a marble appearance. Finally, when damaged SMC is sanded, short coarse fibers are exposed and a dryer powdery dust is produced compared to conventional materials. These hints will make SMC identification quite straightforward.
SMC is a polyester-based material, but it cannot be repaired with polyester resin. This is due to the mold release agent that is present throughout the entire SMC part. Unlike conventionally molded parts where release agents are applied to the mold surface, SMC is compounded with them in the resin mix for quicker processing. This means that as the damage is sanded to prepare a good bonding surface, fresh mold release agent is exposed. Polyester resin products are not strong enough to adhere to this surface. SMC SHOULD ONLY BE REPAIRED USING EPOXY-BASED RESINS, FILLERS AND ADHESIVES. When painting, use only catalyzed type paint systems."
Another clarification, West System is a company specializing in epoxy products, West Marine is a boating supply store, though West Systems can be found at West Marine. Confused yet?
Just a follow-up on SMC repairs - I found this on an auto body website: . SMC SHOULD ONLY BE REPAIRED USING EPOXY-BASED RESINS, FILLERS AND ADHESIVES.
^^ this is what i also found when i did my repair on my massive hole. That is what the evercoat stuff was i used. i honestly dont think there could be that much difference BUT obviously i concede to the guys with tonnes of experience. DUB is a user here who has plenty of that and he followed on my repair thread and his advice i took.
What i didnt know at the time were the real details of WHY the epoxy based repairs were necessary. Nor did i know that the smc was in fact a polyester based resin. I thought smc by definition was epoxy but i see that as wrong now. smc appears to be a process. and if polyester resin was used, this mold release mixed throughout the resin seems to be the reason why later repairs can only be done with epoxies.
Very interesting thread!!
I have seen MANY repaired C4’s back ends where polyester bondo type material was used and it did NOT bond at all. obviously i have no idea how well the prep work was done.
another observation is that the factory appears to have used some sort of epoxy adhesive to bond panels to each other and to the frame throughout the car.
. The quart size is only half the cost of the gallon kit but it takes a really big repair to go through a gallon. Follow the application and curing temperature guide - temps below the lower limit doesn't mean a longer time for the mix to cure, it means the mix will never properly cure! Chemistry at work here.
. This is the cloth I like to use. 1708 is 2 layers of ~8 ounce cloth with the weave at 45 degree angles with a layer of mat stitched to it, full weight about 20 ozs. Its a good all-around cloth for typical repairs. Hat tip: for thickness build-up it takes 6 or 7 layers per 1/4" of thickness.
A note on which cloth to use: fiberglass cloth is the stuff that looks like its weaved - it is. Chopped strand mat is the stuff that looks like random fibers pressed together. Either can be used with epoxy resin but cloth (especially the lighter weights) will conform better to irregular surfaces and corners. CSM has a binder in the mat that is dissolved by polyester resin making it more pliable when wetted out. This binder is not affected by epoxies so the CSM will not be as pliable as cloth. Cloth will also have more structural strength by weight than CSM.
Final note: Proper prep is the key! Get a good grinder with at least a 36 grit disc (and a good dust mask or respirator!). Taper the repair area a few inches away from the break and build the cloth into the "valley". No hard corners! This will create a weak point that will fail eventually. I haven't repaired SMC but with regular resins they have an "amine blush" after curing that must be removed - a scrub with a scotchbrite pad and water works here - before sanding or grinding to add additional layers and an acetone wipe before adding the next layer.
Look through the tip and advice section on the West System website, lots of good info there, plus tons of videos on Youtube about FG repair.
If anyone's interested, here's a thread I've got going on the repairs I've been doing on my 40' sailboat I'm repairing after being sunk during hurricane Matthew: https://forums.sailboatowners.com/th...atthew.182553/
I certainly have enough of this fiberglass mat stuff that I don't need to be stingy. I'm thinking maybe 4 or 5, as much as it takes to bring the repair flush with the rest of the floor pan, then grind the bottom side a bit and do a few layers there.
My hole is right in the corner, I think my biggest difficulty will be building something up to keep the the stuff in place while it cures. I think I may try and cut something out of foam to match the contours of the pan in all three dimensions, then glue wax paper or something to it.
