DIY fairing boards

brendan gardam · Aug 5, 2020

waikikin said: ↑

Haja,
I try to leave the reinforcing fibre there to do it's job & do the fairing in the fairing compound. Ifn I'm gunna chop some glass down it's Zec discs and the soft pad to finish, just part of the arsenal. Sometimes I wish someone would steal all my sanders so I don't need to be doing that
Jeff.
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whats your preferred fairing compound for glass jeff.

waikikin · Aug 5, 2020

brendan gardam said: ↑

whats your preferred fairing compound for glass jeff.
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Depends on the substrate & job. If I was finishing some mdf plug with a seal of glass to build tooling it would generally be Q cells with a dash of colloidal silica and similar for any polyester job with the paste pre mixed in buckets(power stirred with the mixer through a hole in a board to keep the dust in) and catalyzed later . Sub waterline generally better to go epoxy and same required over any epoxy substrate would use Qcells, or the purple brown phenolic micro balloons again with a little colloidal silica added- this helps the filler come off the broad knife a bit smoother and neater. On epoxy we'd sometimes use a final screed of West microlight mix as it goes on sweet and smooth but use the cheaper extenders for bulking out. Often now I'll just get the pre blended International 833 or the equivalent Jotun or other brand- often called "frog bog" as it's green
Edge tools such as planes work very well on extended resin, they do need a touch up on the oilstone now & then but a lot more satisfying than grinding away on the torture board all day- where they really come into great use is where you might need to "top up" some small areas to height- the action of the plane actually just cuts the high spots off whereas sanding can give a halo effect around the top up. Some jobs with heaps of energetic(young & cheap) labour can be achieved with a bulk overfill then apply the boards and labour wholesale... I'm a bit older and slower so like to sneak up on the surface fairness, usually three careful screeds will get there. The use of a fairing/torture board will always be required for the best result but I use a combination of board, plane, 8" planetary action rupes sander, 6" rupes random orbital, 7" festo rotary sander. Guide coat always handy as without easy to get snowblind as to what & where the surface is at. Another trick on flattish surfaces which are actually harder than curvy ones is to use bog battens to define edges and mid panel fair lines, I think in auto trades now they call them "splines" but basically smooth battens that get loaded with filler, applied to surface then taken off after setting- (they need release agent). I use 25mm 12mm x 3mm aluminium channel as cheap and sits pretty fair.
So choice dependent on substrate and on budget also, I'm getting to old to enjoy the dust in both mixing and sanding so dont plan on doing to much in future but who knows as work and business very variable currently..
Jeff.

fallguy · Aug 5, 2020

The guide coat to spray on...how do you not interfere with epoxy bonds of follow on layers of epoxy compounds?

brendan gardam · Aug 5, 2020

waikikin said: ↑

Depends on the substrate & job. If I was finishing some mdf plug with a seal of glass to build tooling it would generally be Q cells with a dash of colloidal silica and similar for any polyester job with the paste pre mixed in buckets(power stirred with the mixer through a hole in a board to keep the dust in) and catalyzed later . Sub waterline generally better to go epoxy and same required over any epoxy substrate would use Qcells, or the purple brown phenolic micro balloons again with a little colloidal silica added- this helps the filler come off the broad knife a bit smoother and neater. On epoxy we'd sometimes use a final screed of West microlight mix as it goes on sweet and smooth but use the cheaper extenders for bulking out. Often now I'll just get the pre blended International 833 or the equivalent Jotun or other brand- often called "frog bog" as it's green
Edge tools such as planes work very well on extended resin, they do need a touch up on the oilstone now & then but a lot more satisfying than grinding away on the torture board all day- where they really come into great use is where you might need to "top up" some small areas to height- the action of the plane actually just cuts the high spots off whereas sanding can give a halo effect around the top up. Some jobs with heaps of energetic(young & cheap) labour can be achieved with a bulk overfill then apply the boards and labour wholesale... I'm a bit older and slower so like to sneak up on the surface fairness, usually three careful screeds will get there. The use of a fairing/torture board will always be required for the best result but I use a combination of board, plane, 8" planetary action rupes sander, 6" rupes random orbital, 7" festo rotary sander. Guide coat always handy as without easy to get snowblind as to what & where the surface is at. Another trick on flattish surfaces which are actually harder than curvy ones is to use bog battens to define edges and mid panel fair lines, I think in auto trades now they call them "splines" but basically smooth battens that get loaded with filler, applied to surface then taken off after setting- (they need release agent). I use 25mm 12mm x 3mm aluminium channel as cheap and sits pretty fair.
So choice dependent on substrate and on budget also, I'm getting to old to enjoy the dust in both mixing and sanding so dont plan on doing to much in future but who knows as work and business very variable currently..
Jeff.
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excellent. thanks.

brendan gardam · Aug 5, 2020

sailhand said: ↑

I use a guide coat for everything, if your not using a guide coat its going to take a lot longer and be more expensive than it otherwise would be. You must also really like sanding if you dont use a guide coat and by some gumboots so you can paddle around in all that bog dust/money thats laying on the floor under your job.

The next step after your first bog is a jack plane for the ridges and lumps. A block plane then for finer work. Planes are great because they cut fast and no dust at all just fine shavings. You can get rounded and curved hull shapes pretty fair running the plane on different axis to suit the shape usually +- 45. By now at least half my guide coat is gone so I'm about halfway there and not a hint of dust. Next comes my helicopter blade on a big sander polisher, you must keep it moving in figure eight type movements as I do with pretty much all my sanding tools to avoid digging any hollows in your work.

Now I am 90% there and its time to fill the hollows which are easily visible as they are grey from the guide coat and contrast really well with white bog, the white bits are almost perfectly fair by now. I fill slightly proud with a good quality plasterers broad knife, usually 6 inch, unless I have a really large area and then I use a trowel. I use one edge of the broad knife hard on the fair/white part of the hull and slightly raise the other side a millimetre or two over the middle of the hollow to get a slightly proud patch. Now possibly a touch with the block plane and then a quick helicopter or longboard on the patches.

Then its high build and guide coat number two and torture board time. I like plain 12mm mdf as its a particle board and less likely to warp from grain in real timber. Our local hardware in aussie, bunnings, will slice it into 110mm wide strips for free and you are good to go. I use cheap lightweight gyprock/dry wall plastic sanders and simply glue one each end of the board for handles, lightweight and simple. I use various length boards and smaller ones have only one handle. I check my boards with a metal rule to make sure the are straight and then velcro. I always store them flat on a flat bench or on the job to keep them straight.

The art of a nice fairing board for me is a rock hard straight surface with the thinnest velcro I can get, like the thin velcro on most sanding pads. I want to cut the highs and leave the valleys. I find any sort of soft rubber padding allows the paper to be pushed into the valleys and you really dont acheive much except make the bog thinner everywhere. You cut the lows as well as the highs so your just moving the ripples closer to the hull. You create a lot more expensive hard earned dust to paddle around in but achieve little else. I just want to cut the high parts down so straight and hard boards for me work the quickest by far. Its really minimal torture boarding and you know as soon as the guide coat is gone move on, its fair. I like the figure 8 type movements and progress in one direction, say bow to stern, and cover the panel vertically by moving the figure eights up and down. I will also do a light 45+- to make sure. Time for primer and another guide coat. I use a black quick drying paint misted over the job or commercially available black powder type guide coats which are basically ready to go immediately after application. A quick long board and the guide coats gone, just scratches and small marks which really stand out as they are dark from the guide coat. I use a product that panel beaters use called glazing putty, nothing to do with windows, that I get from panel and paint supply shops. Get the right colour putty to suit your top coat. I used highbuild thickened with qcell until I became allergic to it. The guide coat tells you when your finished, otherwise your guessing. The experienced guys might get away without it but Ive yet to see anybody acheive fair hulls faster without using a guide coat.

A final note, if you are fairing and you hit glass then stop immediately, and move on. That is a hill that you shouldnt cut down its the structure of your boat. You need to build the rest up not cut the glass down. A good indication that you have the minimum amount of bog on your job is that you just touch the glass in one or two places. If you keep sanding after that you are just making hollows, wasting sandpaper and bog, not to mention shoulder muscles and lungs. Put enough bog on to cover the job and then start fairing, if you hit glass stop sanding and move on. It just means you will have more dark hollows full of guide coat to fill. If you dont hit glass anywhere then youve probably got a bit too much bog.

I generally build fair, that means not too much bog and torture board. Fairing battens are your best friend and will save you heaps of work later in the job. I forgot to mention my fairing batten that I use for fairing. When I am at the jack plane stage I have a nice aluminum extrusion 25x25mm box section with sharp edges , not rounded, and it bends in a nice fair consistent curve. I have various lengths that I use up to around 3.6 metres for hulls. These are great to just press up on the job and spot your big highs and lows. You can then jack plane these down in minutes dust free, and your half way there. Old sail battens do a reasonable job as well, aluminium flat bar works for tighter radius hulls.

Good luck, stick to the rules and dont chase out hollows when your sanding and you will get there a lot quicker with a lot less work.
Cheers
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great post

waikikin · Aug 6, 2020

brendan gardam said: ↑

great post
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Agree Brendan, seems Sailhand uses a very similar process, I've evolved mine to minimise the effort and material use. One of the best tools for small areas is a planetary action sander, I've had the Rupes model for I think about 27 years, if its a panel say 600 x 900 it will be sorted in no time if you float the machine right. I've personally never used the machine style that Sailhand also posted though I can see that they'd be pretty handy if on an open panel with no chance of an inside corner, I saw a hydraulic model used years ago but the guy just hired it and had little idea despite good advice. Be very careful of vibrating machinery as they will do damage to your hands and fingers. One issue I have is after 40 years my "trigger/rude" finger to right hand has a tendon pain... lots of spraying, jockying screw guns and MIG welder triggers has taken toll with vibrating machines not helpful either.
Jeff.

sailhand · Aug 10, 2020

I typically mark around any depressions/holes/scratches that appear after sanding with guide coat with a pencil. Once marked everywhere I scuff out the guidecoat with sandpaper by hand for small areas and a random orbital for larger areas being careful not to remove my pencil marks. Just basically remove the guidecoat if using a spray paint misted on. If using the powdered type guide coat a quick wipe with acetone and then a light key sand only if the bog is older than a few hours. It also depends on size of the hole. If its a tiny scratch glazing putty is quick and easy if its a large area then a good keysand for secondary bonding is essential. The guide coat should only be the lightest of mists and therefore easily removed. You will be surprised how much it stands out against snow white bog, really easy to see.

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DIY fairing boards

brendan gardam Senior Member

waikikin Senior Member

fallguy Senior Member

brendan gardam Senior Member

brendan gardam Senior Member

waikikin Senior Member

sailhand Senior Member

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