Attempting to make a hardtop (fiberglass). Advice please :)
Posted by Ok_Application5922@reddit | projectcar | View on Reddit | 30 comments
Pictures aren’t mine, but my 1989 Rx7 fc is in the same state.
I want to develop a hardtop for my convertible and was wondering how to tackle this. I’ve watched a ton of videos and have like 1 day of experience lol (helped a friend repair a bumper) with fiberglass and foam.
If any master techs here have any suggestions/advice on how to tackle this project, please let me know! Thank you in advance!
Accomplished_Door662@reddit
I just started making fiberglass molds for CF. All I have to say is good luck lol.
Gen2Performance@reddit
Most sound installers who build custom boom boxes use loads of masking tape to cover the main surfaces then over lay the fiber resin on top of that. Doing this will help you reshape the mold afterwards. Just reteach adding custom boom boxed in the trunk of your car etc.
Ubericious@reddit
For the main body start with something like this go give yourself a strong tensioned foundation to build off of.
https://www.modelshopleeds.co.uk/catalog/product_info.php?products_id=116361&srsltid=AfmBOorV_3tXT8oNhlj6CLpel8JVU_0aZlhk-cdA-6HJsyUCETXQuZpP7Os
sladebonge@reddit
Builder Creator on youtube has been building his own supercar (the Arrete) from scratch out of fiberglass and carbon fiber for years now. You can learn quite a bit from watching those vids, plus it's a fucking rad build.
killer-j86@reddit
use a sheet. stretch it tight over the area and fiberglass over it.
bluenosesutherland@reddit
Other option is build a mould.. with the advantage of being able to pop out a replacement if the first one gets damaged.
soedesh1@reddit
When I was considering doing this I obtained some aircraft covering product to use for the base because it is a heat shrink material. That would help with the stretching it tight part.
Digi59404@reddit
Other folks can correct me here. But if your car is in this state. Then the next step would be to use cloth and stretch it over the areas you want to enclose. Then fiberglass over that cloth. Typically you can use a stretchable cloth to make the shape you want. Add fiberglass to make it rigid. Then build out from there. More layers of fiberglass and glass mat to form the structure. Then inside you’d add a layer of fiberglass. Sand everything, insulate the interior?
theNewLuce@reddit
I did this exact process to make a hard bikini top for my Cobra replica.
I used the heavy canvas Horrible Fright tarp over a 1/2" EMT frame, pulled tight with tie wire and whatever I could come up with.
First make a header for the windshield by putting poly or masking tape over.
Yes, wet the tarp out with resin to make it rigid before adding glass.
Not having a proper gel coat will make sanding and smoothing a bit of a bitch, but my painter made it perfect and painted to match for $500.
Tastesicle@reddit
You can impregnate the cloth with a light coat of resin before you glass on top to make your surface more rigid so it doesn't sag as much when you add the glass sheet.
Once mostly done you trim everything away. If it was a Cabriolet style top you can roll resin on your glass and add marine grade vinyl directly on top, it has a cloth backing so should bind. Trim again and hide your sins behind trims.
Ok_Application5922@reddit (OP)
Wow that actually sounds genius. I would put the soft top on and try that, but it’s torn on both b pillars. I’ll look for some cloth to stretch over and apply some resin to harden it. The car has a removable targa top so it would just be that back portion.
Thank you!
Illustrious_Pepper46@reddit
Just make sure the first coat is very light, otherwise the weight of the expoxy will make it sag. I've only done a few smaller projects. Do a test piece. I'd even consider using a spray on "something" for the first coat to stiffen, make ridged.
Just not sure what that something is, but like a polyurethane clear coat or spray shellac. I never got that far, or something this big.
Tastesicle@reddit
Yep, spray on starch or some kind of hard glue works well (not super 77). I've even heard of using super hold hairspray because it'll dissolve out once you apply the resin.
poopmanscoop@reddit
Use fleece. It absorbs the resin really well. This is the method people use to make fancy speaker boxes, kick panels, etc.
Spike_Spiegel@reddit
Tofu motors something on YouTube has an entire series of how he did his.
pistonsoffury@reddit
For materials, look to the surf industry suppliers. Specifically greenlight surf supply. The low VOC stuff from resin research is really nice to work with.
SyntheticParanoia@reddit
Do you want to make it permanent? Or removable? The process between the two is very different.
Ok_Application5922@reddit (OP)
Removable! Here are my thoughts (please provide feedback if you wish!)
1) there’s holes all around the bottom from where the soft top “mounts” to the body. I wanna try to utilize these.
2) there’s a removable U shaped piece where the targa top attaches to the skeleton of the soft top (in the picture it’s that thing that’s covered in white painters tape). It’s metal with its own mounting points, so I wanted to use that as well!
SyntheticParanoia@reddit
Normally - on Miata and other cars with a hard top, it picks up spots where the top buttons onto/off when you're raising and lowering it. On a '72 Corvette, it uses the pins in the Tonneau where the soft top locks into. You can probably get away with using the skeleton for a shape, but you're going to need another soft-top header rail to lock into the windshield if you're going to keep the soft as an option.
I would get some thick plastic and stretch it over the soft top frame as a first layer, then some cloth, resin, fiberglass. Maybe look into boat cover twist snaps as an option for those little 'holes'.
Ok_Application5922@reddit (OP)
Thank you for pointing that out!
The Boat cover twist snaps are exactly what I was looking for!
SyntheticParanoia@reddit
Yep! Years spent doing customs and craziness. Once you get a glass 'shell' and get it separated from the soft top frame, you're going to want to add a little reinforcing steel perimeter frame. Can use conduit if necessary, easy to bend and provides a solid place to mount things like a plate to do your upper window seals and the like. Can use 1/4" square bar if you want it a little stronger. Make sure you sandwich a thin steel plate between layers of fiberglass at your rear attachment points.
V3X8TE@reddit
I think you would want to sculpt the top on the car, potentially out of block foam, lay Fiberglas’s on top to create a mold, then cast a roof in the mold.
200m-RC@reddit
So I have done this for a removable hard top for my mr2 spyder, What I did was used tape to build a basic structure and protect the car, then used aluminum tape over that to make a nice smooth release surface. I did 1 layer of fiberglass, and then used drywall mud to sculpt the final shape I wanted, sealed that, made a mold from it, then made a fiberglass top.
zshift@reddit
When you sand the fiberglass, getting in your lungs or on your skin is NOT fun. Wear a respirator. For your skin, it will itch like hell if it gets on you. Ideally wear a full-body paint suit. It sounds silly, but I really regretted not doing it when I was younger.
GTE_Engineering@reddit
As the owner of an FC RX7 convertible, I feel your pain. Unfortunately they all end up torn apart
basicKitsch@reddit
The fibreglass is the easy part. Are you planning out the attachment? The weatherproofing?
Ok_Application5922@reddit (OP)
I agree! And i’m going to use some parts of the soft top skeleton for the hardtop, they half their own weather seals, but I’m still trying to map out the rest of it!
They don’t make any hardtops for this car unfortunately :(
So it would be kinda hard to copy something
basicKitsch@reddit
cool that's where i was twenty years ago with just some drawings of a double-bubble concept car. then they released some, literal nail-on shells for the race teams... and while i was working with a local guy i met with a lot of composite experience smoothline released a full production version and i lucked out.
but that's exactly what i was working on. using one of my soft-top shells for the frame and laying fiberglass over it.
samuraizuk@reddit
Keep us updated with progress! I’d like to do the same for my xk8!
MRV-DUB@reddit
Fiberglass does not stick to the back of Duct tape. First cover the car and interior completely with a thick plastic. Cut 1/4 foam board into desired shape and tape it together , you can usea $15 fleece blanket instead of expensive glass mat. Clamp it at the edges and soak in the resin.