Finishing a 14' race board

[peterwSUPr]

Hi, just joined after lurking for quite a while.  I’ve been building windsurfers since I was a teenager in the 80’s and kiteboards since 2000.  My most recent board was a 6’1” kite surfboard with EPS and bamboo veneer top and bottom.  I am thinking about making a 14’ race board – my first SUP build.  I might do a couple rec races a year, but mostly just paddle from my house, but would like to make the board nice and light and fast.

The thing I’m looking forward to the least on this build is the final finishing.  On all the lightweight vacuum bagged windsurfers I made I ended up doing lots of filling and sanding after glassing, using lightweight filler, and then paint it pretty bland looking (white) after filling, usually with a OK but not great looking spraying skill. 

I suspect that this method might be the lightest finish, but have to say that the painted rails (on the foam) and bamboo finish on my recent kiteboard look pretty decent with a lot less work.  The question is, does anyone have any idea how much difference it makes just flowing resin into the surface, versus filling sanding and painting after?  Will I notice the board being heavy if I go the traditional surfboard gloss resin finish versus filling and painting after?  I have enough bamboo to do the deck of the SUP, and I think it can replace one glass layer.  Or is bamboo too flexy to replace one 6oz E layer on the deck when board stiffness is an issue?

Thanks for all the great info on this forum, looking forward to more!

Peter

[Dwight (DW)]

Stringer or not?

I built a few vac bagged race boards before getting out of it and concentrating on surfing SUPs.

The lightest board is the most fun. You can hit 22-23 lbs on a stringerless all carbon that will be very durable.

I don't believe in adding wood. Too much weight. I did a second carbon patch on the deck.

I used filler and painted.

If I were doing them again, I might stick with my current method used on my surfing SUPs. Cheater coat weave fill using cab-o-sil and squeegee. Then thin hot coat. No paint. On carbon, I'd add white pigment to all my resin batches. It would be a white smear look common today.

I think either method would weigh about the same, but my current method is easier.

[peterwSUPr]

The plan right now is for no stringer.  I might go carbon, but am not sure if I want to go all the way with that for #1, since getting this stuff in or shipped to Canada always bumps up the price.  Actually, I'm giving more serious thought to replacing one of the layers of 6oz E with a 7.3 oz unidrectional E cloth where about 90% of the fibers are along the long axis.  I've used it a lot on twintip kiteboards, and on some test strips that I laid up over 1/8" corecell, it came out similar to the 6oz carbon test strips I laid up similarly, (but much cheaper).
http://www.aircraftspruce.com/catalog/cmpages/rutan.php
Of course the thing with this stuff is you give up some strength in the lateral direction, which might be an issue for foot denting or dings, but not overall board structure.  You can maybe use it for one layer, but need another of something else I think for toughness

My bamboo I just weighed and measured a scrap I have and I think it comes to about 280 g/m2 or about 8.4 oz, but it soaks up almost no resin so its not too bad if its strong.  I'll have to lay up some test strips with just that to see if its stiff or really flexy.  (I just make them all the same dimensions and flex them by hand).

But, getting back to the original question if anyone has ever weighed their board before final filling and smoothing and painting and then again after, I'd be interested to hear how much difference it makes depending what method it used.

Thx,
Peter

[TallDude]

I weighed my unlimited at every step of the build. The Bondo, paint, and sealer (top only) didn't even register any change on my digital bath scale. So it was at least less than half a pound. I sanded the Bondo on the patches almost completely off.

[peterwSUPr]

I assume that the paint must have been a very thin coat too.  I think that a two-part yacht paint, which I remember using many years ago seems to be thick enough that it would probably register some weight on a scale.

As for what I said about carbon, I was just noticing that www.sollercomposites.com has some pretty decent sale prices and I think I'd get more stiffness and lightness for the money with carful use of one length of 50" wide cloth than 2 lengths of the 38"uni-E with only a marginal price difference.  Too bad carbon gets so hot in the sun, a black carbon board might look nice!

Can anyone guesstimate how much resin they would mix up (volume or weight) if they were going to do a gloss coat of resin on a 14' board?

Thanks,
Peter

[Dwight (DW)]

860 grams per side. That includes harder weight.

[Dwight (DW)]

I did a light dusting of white primer on the bottoms. Primer and paint on the top. I never leave carbon exposed. Just too hot.

1 LB stringer less needs carbon. I tried none. I tried carbon rails. Until I went full carbon bottom it vibrated too much.

[55NSup]

Stringer or not?

I built a few vac bagged race boards before getting out of it and concentrating on surfing SUPs.

The lightest board is the most fun. You can hit 22-23 lbs on a stringerless all carbon that will be very durable.

I don't believe in adding wood. Too much weight. I did a second carbon patch on the deck.

I used filler and painted.

If I were doing them again, I might stick with my current method used on my surfing SUPs. Cheater coat weave fill using cab-o-sil and squeegee. Then thin hot coat. No paint. On carbon, I'd add white pigment to all my resin batches. It would be a white smear look common today.

I think either method would weigh about the same, but my current method is easier.

Trying to decipher your shorthand.
Layup is carbon then glass. Coat glass with cab-o-sil with squeege. Sand. Then Thin Hot coat.
 No sanding  after hot coat??

Whats cab -o- sil?  is that epoxy with silica additive? 

[peterwSUPr]

Cabosil is a filler, and it has some fibres in it.  It's greatest asset is that it does not run or sag like resin with microballoons does on a vertical surface.  However, for the lightest filler, it's better to use microballoons ("glass spheres").  They can either be bought as a rusty red colour (ugly) which mixes into the resin easily an maybe are cheaper or as white powder (nice) which is harder to mix in, but not a big deal to mix in and well worth using over the rust coloured stuff.

Thanks for the resin gloss coat weight info!

Peter

[Dwight (DW)]

Yeah, I'd use micro balloons on the cheater if I didn't care about the color. I'm doing color pigments. Cab-o-sil maintains the pigment tone.

[TallDude]

I used automotive paint (on the top ) with concrete 'wet look' sealer on the whole board. Not as glossy as a hot coat.

Check out these specials. This is my supplier.  http://coastalcomposites.com/default.asp?f=products_view&d=estore&clientid=5296&id=437&cat=Specials

[SUPflorida]

Cabosil has no fiber in it..if you have ever seen a microscopic picture of it....it looks somewhat like an elongated sand spur.

Epoxy with cabosil filler only (no glass bubbles) is hard, and much harder to sand than epoxy/glass bubbles mix...and heavier...

[Dwight (DW)]

Epoxy with cabosil filler only (no glass bubbles) is hard, and much harder to sand than epoxy/glass bubbles

I take advantage of that. Bridges the open weave left by bagging and as a cheater coat, helps prevent sand throughs later. 😄

It makes the hot coat soooo much easier.

[55NSup]

How about this: micro ballons and epoxy squeegee on- sand. Perhaps repeat locally to make sure weave is filled.  Roll on and brush off a Matt finish 2 component polyurethane. Alternatively roll/ brush on gloss poly urethane and give it a sand  off with fine grit to make it Matt.

Not worried about looks ( yet)

[SUPflorida]

DW you have good company with that technique...We use to use a cabosil fill coat pulled tight to the cloth on multimillion dollar one off custom yachts and Sports Fishermen. We would make it up thick and apply with a 9" to 12" drywall knife, not a flexible squeegee.