Keel Fairing 101

Tools, Equipment and Supplies:

Safety

• Mask:
• Mask Cartridges (that are OK for organic vapor)
• Goggles (because dust gets into your system through your eyes)
• Ear Protection (air tools are LOUD)
• Gloves (you'll make a mess, disposable latex ones are the best, thick rubber ones will work but you'll have to wait for all the epoxy you got on them to set up between use

• Belt Sander: For rough/quick removal of old material, never for new material sanding
• Angle Grinder or Die Grinder: Use with a grinding disk for rough/quick removal of old material in tight areas and the keel hull joint. Be careful, it can get away from you and remove too much material! Use it with a cutting disk for really tight areas.
• Inline air sander: Saves a lot of time and gives really good results.
• Compressor(s): To use the inline sander you'll need a lot of air. To use the ones that buzz loudly, like most found at Sears, you'll have to hook two together or sand for a little then wait for the compressor to catch back up, then sand for a little, etc…
• Air Line Tee: This can be made from a few dollars worth of parts so that two cheap compressors can be hooked together to supply enough air to actually run an air tool.

• Sanding Block: This and the air inline sander are your primary tools. Even on curved surfaces these will give you a smooth finish, as long as you sand using the method described below. Anything flat will work, I usually use a flat 2x4 and tack the sandpaper to the ends on the piece with screws or nails. The longer the better, the longer the sanding block you use the less likely the keel will be wavy when you are done. Even if you don't have an air inline sander, you can still use the paper made for them, its narrow and long, perfect for this job.
• Sand Paper: 36 grit: Rough removal of old material and rough initial sanding of new material. 80 grit: Intermediate sanding of new material. 120 grit: If using a barrier coat, this is the final sanding grit. 220+ grit: You can keep sanding with finer and finer grit to get a more smooth surface, if you wanted to you could work you way to 2500 grit and use your keel as a mirror. It all depends on how much time you want to put into it.
• Flexible Sander: Use only when necessary, a little sanding with the flexible sander can lead to a wavy surface and a lot of trouble fixing it, so be extremely careful. If it looks or feels like the surface is starting to get uneven or wavy stop using this and go back to the sanding block. If the regular sanding block is too large to fit, make a smaller one.
• Sureform: For extremely rough removal of runs and sags in unsanded new material.
• Foam Block: For light fine final sanding only. Once the surface is even and smooth use this lightly with high grit number paper to give it a fine finish.
• Your Hand: NEVER sand anything just using your hand!!! ALWAYS use a block!!! It will not be smooth if you don't use a block!!!
• D/A Sander: These are good for some things, but not for sanding keels! If you use one of these you're keel will be bumpy when your are done. They'll be large bumps, roughly the diameter of the disk on the sander, and it'll be hard to tell but they will be there. If you use one of these and then go over it with a sanding block, you'll see what I mean
• Your favorite beverage: This is thirsty work, keep a cap on it to keep the dust out.

sureform

2x4

• Pumps: Use these to make sure you mix everything in the right ratio. You'll waste more epoxy than it costs to buy them if you try to guess or use measuring cups.
• Mixing cups: Buy cheap disposable ones, you'll need a lot of them. If you can pop all the leftover hardened epoxy out, then you can reuse them, but most of the time you can't.
• Spreaders: Buy a few packs of BONDO spreaders, or West System ones. The Bondo spreaders are softer which make it a little harder to get a smooth coat when you are applying the epoxy, because the epoxy is thick..
• Mixers: Anything clean and strong will work for this. I usually use an old screwdriver and clean it off immediately after done mixing.

• This is what I used:
  • West System 105 epoxy resin
  • West System 205 slow hardener
  • West System 207 fairing compound filler
    • Click here for more info on fillers

• Directions to sand in:
  • Start sanding in one direction, then sand 90 degree to the original direction and keep alternating. This will smooth out any surface. If you sand too long in one direction you'll get grooves, so alternate often. DO NOT sand in a circle, this will make the surface wavy and bumpy.
• What tools to use when:
  • You'll use the sanding tools in this order:
    • Sure form (to knock down sags and runs)
    • Air inline or hand block sanding 36 grit
    • Air inline or hand block sanding 80 grit
    • Flexible sander 80 grit: Only on the areas you can't smooth out with a block
    • Air inline or hand block sanding 120 grit
    • Flexible sander 120 grit: Only on the areas you can't smooth out with a block
    • Foam block 220+ grit: for final finish smoothing
• What tools not to use (D/A, hand), Once again, DO NOT use:
  • Your hand, NEVER sand anything just using your hand!!! ALWAYS use a block!!! It will not be smooth if you don't use a block!!!
  • D/A sander, These are good for some things, but not for sanding keels! If you use one of these you're keel will be bumpy when your are done. They'll be large bumps, roughly the diameter of the disk on the sander, and it'll be hard to tell but they will be there. If you use one of these and then go over it with a sanding block, you'll see what I mean

• How thick
  • For the vertical surfaces of a keel, add filler until its like thick peanut butter
  • From what I remember, it took about 3/4 of a can of 207 filler to thicken up a half quart of resin, but don't necessarily quote me on that. Basically, you add filler until you can't mix it anymore.
  • Remember that when you add the hardener it will thin it out somewhat
• How much working time
  • This will vary a lot, depending on how large a batch you mix up and the ambient temperature. I usually mix up as much as I can use in 10 minutes.
• When to know to stop using a batch
  • Once the epoxy "kicks", you can't use it anymore. When you are spreading it on,or picking some up with a spreader, you'll notice that it starts to look and feel kind of gritty and thick. Stop using that batch at that point, it won't spread very well or adhere to the keel good anymore.
• Make sure its all mixed!
  • If you don't mix it completely you'll have areas on your keel where it will never harden. When this happens you have to scrape it all off the best you can before applying another layer. This is hard to do and makes the surface bump and rough, so mix until it all looks even, then mix for another minute or two. Be sure to get the mixer into all the corners of the cup so that there aren't pockets of uncatalyzed resin.

 

• Also, one thing to note: If you mix in more hardener you'll get a "hot" batch, it will set up faster. In addition to losing working time, you'll also end up with hardened material that isn't as strong as a properly mixed batch, so try to avoid this.
• If you are doing this job in the spring when its cool out, bring your epoxy inside your house at night so that it doesn't get really cold overnight. Cold epoxy hardens really really slow, if its cold enough it may never harden.

• Epoxy = A two part thermoset polymer. Thermoset means that it is a chemical process that links together the molecules contained in the epoxy. When in liquid form, the molecules are not linked, as a chemical process takes place the molecules bond together and it turns into a solid. Unlike a thermoplastic, like nylon, a thermoset forms molecular bonds between the molecules. The parts are Resin and Hardener, mixed together in varying proportions depending on the type used.
• Resin = The main ingredient in epoxy, contains the molecules that get linked together.
• Hardener = This ingredient in epoxy is what gets the chemical reaction going to link the molecules
• Catalyst = See hardener.
• Filler = 1) An additive to epoxy to change its physical properties, such as making it thicker. Its usally in power form, examples are microballoons, talc, and fumed silica. 2) The combination of resin, hardener and powder filler mix, as applied to the keel, this is what I mean when I say filler in the discussion below.
• Kick = The point in the chemical reaction when the epoxy begins to noticably change from a liquid to a solid.
• Gel = See Kick
• Pot life = The amount of time before a batch of epoxy kicks
• Polyester = A thermoset polymer resin which is similar to epoxy, but generally has lower strength, absorbs water more easily, and is about 5 times cheaper.
• Bondo = A name brand polyester resin and talc filler mix. This should never be used below the water line! The combination of polyester resin and talc filler makes it very suseptable to water absorbtion.
• Gel coat = A thin polyester resin used to add color and make a smooth surface on top of layers of fiberglass.
• Phenolic beads = Very small bead of pheolic resin, used as a fller with epoxy to thicken it and make it easier to sand
• Microballoons = Very small hollow glass beads, used as a fller with epoxy to thicken it and make it easier to sand
• Talc = A mineral used as a fller with epoxy to thicken it and make it easier to sand
• Fumed Silica = A filler used as a fller with epoxy to thicken it. This is very dangerous stuff to work with, its very bad for your lungs! DO NOT breath this stuff in.
• Fiberglass = 1) Long glass strands woven into fabric 2) The formed combination of epoxy or polyester resin and glass fabric.

• The first thing that you want to do is to remove all of the old filler that is on the keel. Its probably really uneven, and since its old it'll be hard as a rock. So it all needs to go.
• For this step: BE SURE TO WEAR GOGGLES, A BREATHING MASK AND GLOVES! you'll probably sand into the keellead a little, and if you breath it in, get it into your skin etc... it will make you dumb. So be careful, bring a change of clothes, wash up really well after, and contact the lead as little as possible.
• To remove the old filler, I used a belt sander with a 36 grit belt. It eats through everything quick and did a great job. If your belt clogs quickly, either sand a little slower or try a different brand of belt. Basically, just grind it all off. Be careful though, belt sanders with 36 grit take off material FAST, so make sure what you are sanding is what you want to remove!

• Now that the old stuff is gone, its time to put new filler on. Mix up a good thick batch and start spreading it on. Its hard to get it even, but do the best that you can. You probably won't be able to mix up a large enough batch to cover an entire side of the keel, so put on as much as you can then put a batch on the other side. After the filler has set up, lightly sand the edge where it will meet up with the next batch so that the two stick well to each other and continue covering the keel. Don't worry if it all looks really ugly when you are done, the goal here is just to get as much filler stuck to the keel as possible.

• If your keel is as uneven as ours, one coat won't be thick enough to do the job. You want to have enough on there so that when sanding with the block you can sand everything down to the lowest spot and not see any keel lead. Holding a straight edge to the keel will give you an idea of how much you'll have to remove. Its a lot easier to add another coat now than to try to blend in additional coats on low spots later. Your template is the lead of the keel at this point, it may be very far from where you want the final shape, so it might take a lot of filler.
• Before you apply the second coat:
  • Lightly run the sureform over the surface to remove the runs and sags.
  • Scuff up the entire surface with 36 grit sandpaper, so that the next coat sticks well.
  • Clean the surface with some solvent, talk to someone at a boat store and find a kind that won't harm fiberglass. I used a special kind made just for cleaning fiberglass before painting. DO NOT USE ACETONE! it turns fiberglass into mush

   

• NOTE: The photos shown are mostly of the point after the first coat was applied, sanded into a rough shape, then the second coat applied.

• Once you have enough filler on the keel its time to start sanding for real!
• Start with the sure form and knock down all the runs, sags and really obvious high spot.
• Then fire up the inline sander with a 36 grit sheet and sand until your arms feel like they are going to fall off.
  • Start sanding in the direction of water flow
  • Then sand 90 degrees to this
  • Then finish back to the water flow direction
• Sand it down until it looks relatively smooth and all the odd low spots are easily seen.

• This is a tricky part. If you have enough filler on the keel and your coats went on nice and smooth, you can just keep sanding until the low spot are gone. If, like me, your coats went on bumpy and you're not sure there is enough filler to sand down all the low spots without getting into the lead, then you'll have to add some more filler, selectively.
• Circle all the low spots with a pencil before you mix up your batch, so that you can find them easily when you are racing against time applying the filler
• Rough them up with 36 grit, and clean them out.
• Add filler so that they are slightly higher than the surrounding area, you'll sand them down smooth in the next step. If you fill them in so that they appear even, they'll be low again once you start sanding.

• Before you start sanding the whole keel again, smooth out the filler over the low spots first. This is best done by hand, using 36 grit and a sanding block.
  • Carefully sand the new filler. Try as hard as possible not to touch the previous filler until it is almost smooth, otherwise it will end up wavy. This is hard to do, and takes a little practice. You can close your eyes and feel across the new filler, sand until you can't tell where the previous filler ends and the new filler starts

• The back edge of the lead on our keel was about a half inch wide after all the old filler was removed. So it needs more filler to get it nice and sharp like it used to be.
• To do this I used wide masking tape to support the filler one one side and I spread the filler from the keel onto the tape. It took a couple of coats to build up enough so that I could sand it down smooth and to a nice sharp edge.
• This step probably could have been done right after applying the second coat of filler over the whole keel, but I've never been that good at planning ahead.
• Tape can be used to support filler put onto the bottom of a horizontal surface.

• Now that all the low spots are filled in and the edges look decent, its time to start working towards a perfectly smooth keel.
  • Start with 36 grit again, just to clean up anything funny, not too much with this grit though
  • Again, sand in the direction of the water, then 90 degrees to that. If due to the angles of the keel you can't sand in the direction of water flow, sand as close to this direction as possible, then switch to 90 degrees to that, then finish in the original direction. The key is switching back and forth to smooth everything out, without getting waves.
  • Work your way from 36 to 80 to 120grit.
• Now and then, step back and look up and down the keel. The shadows can help to show you where you are taking too much off, or not enough. Also you can run your hand over the keel, if you feel anything wavy or a dip somewhere then pay some special attention to that spot and carefully remove material to fix it, hopefully without cause another wave or low spot while you're doing it.

• The first few inches of the keel are the most important, so pay special attention to them.
• Start by sanding up and down the front edge, to kind of square off the very front.
• Then sand to either side of this to add a facet, then do it again and again until you reach the side of the keel.
  • Do a lot of looking back and forth between the sides to make sure its ending up even.
  • Keep the number of facets even from side to side.
• Once the facets are even, then take a sheet of 36grit paper that's about 2-3" wide and holding the ends in your hands:
  • Lightly pull the paper back and forth across the facets to smooth out the sharp edges.
  • Keep the amount of time or number of strokes even from side to side, to keep the shape of the front of the keel even
  • Stepping back and looking at the shadows can help to tell you how you are doing.

Apply a guide coat and sand some more

• Buy a spray can of sandable automotive primer and spray on a light coat over the whole keel.
• Now take your sanding block and sand off all the primer, this will show you wherever you have a low spot. If you find any, sand to fix them.
• At this point is safe to use a flexible sanding block, just don't push too hard.

• Now do some sanding with the flexible block and 220 grit sandpaper. Once you reach this point, you don't have to worry about what direction or making it wavy by not using a stiff sanding block. Sand it lightly until its smooth, keep an eye out for ridges here and there from using the stiff block, if you find any then sand them down with the flexible sanding block then the foam block, carefully.

Foam block sanding

• To make sure that there are no sharp edges or facets left on the keep. Spray on another guide coat and sand using a dense foam block and 220grit sandpaper. Don't push hard, just glide the sandpaper over the surface. This will finish the keel off nicely.

Barrier coat

• Adding a barrier coating at this point is a good idea. Epoxy is much more resistant to osmosis and blisters than polyester, but why take a chance, unless you aren't sick of sanding at this point and want to do it again next year...

DONE!

• That's it! how do your arms feels? Tired of sanding yet? Its a lot of work, but worth it when you clean up on the race course.
• After doing all of this, the only thing that I would have done different was how I put the filler on in the first place. It would have saved me some sanding, and lowered the chances of everything going wrong if I had:
  • Put on a third coat of filler, since I got into the lead during the final sanding in a few really high spots on the keel
  • Covered the entire keel with filler before I started sanding. I wouldn't have had to spend so much time blending coats together or run the risk of a bad transition. The reason that I didn't was that it was still cool out in the spring while I was doing this, so the filler was hardening very slowly. If I had waited to cover the entire keel before starting to sand, it would have added two weekends to the project, and we would have missed the first two races of the year.
• Overall I'm pretty happy with how it came out. Templates are available for some boats keels, even ours, but I didn't use them. Who knows how close to the true designed shape of the keel I got it, but at least its smooth now to keep that flow attached.