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How to Fiberglass: Fixing a Cracked Kiteboard

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This Instructable explains how to work with fiberglass cloth and resin. In this project, fiberglass cloth and resin are being used to fix a crack in a kite board, but the information included here applies to virtually anyone working with fiberglass.

I had help from my friend Danny, an experienced boat builder, but for the most part, I was working with fiberglass for the first time. Writing guides from the beginners point of view has yielded good results in past Instructables, so I am doing this one in the same style. As a result, there might be information in here that will seem obvious to the experienced fiberglasser, but that same information might be valuable to someone who is just starting out.
 
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Step 1: Background

In its most simple form, the process of fiberglassing starts with very small strands of glass that are either woven together like a cloth, or chopped and then pressed together to form a mat. This material, which comes off of a roll, is then saturated with a two part epoxy or polyester resin that gets painted on in a thick viscus liquid. When the resin dries, the entire structure hardens and becomes rigid. Fiberglass can be used to make volumes and structures ranging from speakers to snowboards and is a valuable medium to work in when you want to create something that can't easily be cut out of wood or metal - curved 3D objects for example.

If the fiberglass is applied on a flat surface, it hardens into a flat sheet when dry and will act like any other rigid material.

However, if the fiberglass is applied over a form, say the ribs of a boat hull, then it can be used to create strong, lightweight volumes that can take on virtually any curve, contour or shape.

Because it can be used to create rigid curved surfaces, it's a process that is generally reserved for specialized building projects. See the following steps of some specific Instructables to see what I mean: step 11: Create subwoofer retrorockets and midrange 'eyes', step 16Fiberglassing your beaver, Creating a fiberglass snowmobile trailer and trebuchet03's amazing video/Instructable on making a fairing for a human powered vehicle. When you need to make something that is rigid and curved, fiberglass is definitely the way to go.

Terms:

Working with fiberglass comes with a whole new set of terms and lingo that it might be useful to know. I can't say that I will be using all of these words in my Instructable, but they are good to know anyway.

Fiberglass - very thin glass fibers that are treated like threads in a textile
Woven vs. Chopped Mat - woven mats contain fibers that are aligned and woven together like fabric, while chopped mats are made up of randomly aligned short fibers held together using a binder.
Resin - resin is the syrup like liquid that wets out the mat and then dries hard. It's activated by a hardener or second part.
Polyester vs. Epoxy Resins - polyester resins are cheaper, heavier and older then epoxy based resins. Polyester resins are activated by adding around 1.5% - 2% of total volume of resin that you are mixing of a hardener (MEKP). Epoxy resins come in a two parts that are mixed in more equal ratios )generally between 1:1 and 1:4). Epoxy based resins are stronger, have better adhesive properties then polyester resins and are more resistant to cracks and water. The major drawback is their price.
MEKP - Methyl Ethyl Keytone Peroxide - polyester resin catalyst (hardener)
PVA - Polyvinyl Alcohol (film mold release)
Cabosil - the white silica filler being mixed in (trade name - aka Aerosil or fairing filler)
Tool - negative mold used to make parts
Micro Balloons - air filler encapsulated in silica glass (creates a lattice matrix structure in resin)
Gelcoat - provides a high quality finish to composite tool surface
Composite - material made from two or more substances (in this case fiber glass and resin)
Exotherm - reference to the heat generated/required by the resin to cure
Pot - Catalyzed batch of resin
Pot Life - Working/usable life of pot. After this time, the chemical reactions between catalyst and resin "take off"

**Much of this list is copied from Trebuchet03's fiberglassing glossary which originally appears here.**

Safety Gear:

Working with fiberglass is actually one of the more hazardous processes out there. The small fibers from the mat can cause skin irritations and tend to get all over the place. Fumes from the resin and cleaners that are used can cause long term damage and are full of all kinds of nasty VOC's (things that mess up the brain and the baby maker). And then there is the large amount of very fine dust that is created when sanding. It's not that working with this stuff is deadly, it's just that it must be dealt with in the proper way and using the proper precautions. When working with fiberglass you should be wearing:

  • Goggles
  • Gloves
  • Respirator
  • Painters suit (to keep the itchy dust off)
  • Working in a well ventilated workspace (preferably outdoors)

Take everything that you were wearing and throw it away. You really don't want to wash clothing that has been exposed to fiberglass, or dust from sanding fiberglass with other clothes in the washing machine because you might just end up spreading the itchy strands all over your once safe clothing.

Tools:

Aside from the resin and fiberglass itself, some other tools are required.

  • Power sanders
  • Sanding pads and sandpaper
  • Mixing bowl (a disposable plastic container is fine)
  • Mixing stick (piece of scrap wood)
  • Measuring tools - pumps that dispense the resin and the hardener in the correct ratio or a measuring cup
  • Scraper
  • Disposable paint brush
  • Rags
  • Solvents for cleaning

Useful places for more information and supplies:

There are tons of good tips already published right here on Instructables. Here are just a few.

Mixing Polyester Resin by Trebuchet03
Handy Tricks (for removing fiberglass from skin) by TimAnderson
Epoxy Laminating Systems by freemanmfg
Fiberglass Tools and Tricks by unclesam
Using Paper, Resin and Fiberglass to be the Master Chief! by Dr.Professor_Jake_Biggs

Here are some companies that sell fiberglassing supplies.

US Composites has a wide range of resins.
West System is a good source for marine resins and fillers.
System Three has tons of marine application resin
products.
TAP Plastics has many locations in the bay area and stocks a wide range of resin's fiberglass mat, and the tools needed to work with it all. They also have some informative .pdf's located in their FAQ section.

Check out your local store to get an idea of what you'll need and then see what's online. If you don't happen to be next to a major retailer of fiberglass supplies, it could be a good idea to order online since the price of resin varies wildly depending on where you get it.
Crucio2 years ago
This is exactly the kind of tutorial I was looking for. Thanks so much for all the detail!

Are you still using the kiteboard?
b-train5 years ago
nice instructable, ive been looking to just play around with fibreglassing but the glass is like 20bucks per square meter, for the sake of playing around, would sum of that fibreglass roof insulation work as the glass?? i know it wouldnt be anywhere near as strong but wld it be possible, i think they have additives that make it flame retardant and stuff,
noahw (author)  b-train5 years ago
The fiberglass insulation for roofs is totally different than the fiberglass cloth that you want to use. The cloth is strong because it's woven together. Fiberglass roofing insulation is just big clumps of fiberglass fibers and won't preform at all like the cloth. You could experiment, but I wouldn't hold much hope.

http://www.shopmaninc.com/cloth.html among many other online retailers of fiberglass cloth has lots of different weaves for between $6 and $7 a yard. $20/sq meter sounds a bit pricey.

Good luck,
Noah

imac495 years ago
Thanks for the good info provided. I was "taught" by a very experienced 73 year old guy who offered to repair my damaged boat. Many of your details mirror his words and I have enjoyed reading the clearly explained steps. Working with fibre glass and resins is a "life skill" that is under-rated in my opinion.
bduffman6 years ago
1, painters mixing cups work well just thro them out in the end 2, that fiber glass u were using looked really thing like material like 3, woven is used for flat and choped for curves 4, ripping choped works better then cutting uneven means it bonds together better 5, another thing is waiting times between resins can cure for days 6, i hope u sanded ur start proget back far enough to take off the clear coat other wise the bond wouldnt be to strong 7, i dont no y u didnt just lay the glass first normaly its material resin let dry fiberglass body filler primer paint ( but thats from scratch ) in this u wouldnt need material as u have some thing to work off if any one is really interested in fiberglassing check out www.fiberglassforums.com its a great forum and so many pros that could help u out
wow this is great! aha i've always wondered how people fiberglass stuff. i thogtu it was some melted plastic that you mold haha
Leon Close6 years ago
Brilliant tutorial. I know quite a few people who this would help greatly.
Really cool Instructable, kiteboarding looks fun. I wish I could try it someday...
trebuchet036 years ago
Another thing to note with polyester/epoxy resin (in addition to what dan mentioned).... Chopped glass mat may not be compatible with epoxy resin because of the binder used to hold the strands together (contact mfr to see if their mat is compatible). Not a problem for woven composites as they are held together by stitching. I agree with dan wrt epoxy versus polyester. If you're working on smaller projects like this, epoxy is the way to go and a gallon will last a long long time. For larger projects (the HPV tooling, boat hulls, etc.) - polyester is choice. Boat making primarily uses polyester resin (and they go through a boatload of it :p). Tooling for the HPV project used 10 gallons of polyester resin. <-- polyester is $135 per 5 gallons versus Epoxy at $245 per 5 gallons.
darkmuskrat6 years ago
Can you make a metal wire frame and use fiberglass to make it into a 3D form?
dan6 years ago
polyester resin is quite toxic - both to touch, and it releases considerable amounts of toxic styrene fumes (OSHA's permissible exposure limit is 100 parts per million).

I recommend always using epoxy, never polyester. the cost difference is negligible for most projects. A gallon of polyester resin is about $30, a gallon of epoxy is about $45. Here is a good source for low cost epoxy: http://www.uscomposites.com/epoxy.html
a gallon will last forever! you could build a car with that much. for a kiteboard you might spend an extra $2 to use epoxy, but you won't have to worry about all the toxic fumes, plus the epoxy is a lot stronger.

There is only one property of polyester resin which is useful - it does not yellow like epoxy does under long-term sunlight exposure. if you want your epoxy not to yellow, you need to either paint it or coat it with a clear UV protective coating (which is commonly available since its a common problem).