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Do I really need a hot coat?

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stevez
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Do I really need a hot coat?

Postby stevez » Tue Jul 17, 2018 6:45 am

I have a new foil board build in progress.
I'm now at the lamination stage and have done the first lamination of the top deck.
Do I really need to do the hot coat? The board is Paulownia with cork rails.
Paulownia is already pretty water resistant, and with the epoxy from the lamination, is going to be pretty well sealed if you ask me.
The whole area up to where the carbon ends will be covered with a pva deckpad. The rails will be partially overlapped, and I'll put an extra coat of epoxy on them. As for the rest, adding extra epoxy for a fill coat seems to me like just adding extra dead weight. I understand why you have to do it for a foam core, to seal and remove pinholes etc, but for wood, is it really necessary, other than for cosmetic reasons?
But I have to say I don't mind the textured look of the weave.
I think the BRM paipos were something like this - or it certainly looks like it to me - the weave is definitely visible in the end product, and they seemed to hold up ok.
Thoughts anyone?
20180717_172034.jpg

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kostantin
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Re: Do I really need a hot coat?

Postby kostantin » Tue Jul 17, 2018 10:46 am

Greetings,

yes you need it. Epoxy will be hurt by water, sun and sand. Epoxy will be whashed out and you will remaind with the fibres. The goal is not to have a glossy finish, this is nonsense anyway. Protection is the goal.
Due to the fact that you do not have peel pley on top, I would suggest in this case you look for something based on nitro. Don't work in the sun, make sure that if you work with a roll that the roll can handle nitro based paint.
Should you work with a brush, before you start make sure your brush does not loose hair during work. On the brush basis, where the metall basis is. put some cyan glue to keep the hair in place.
Later you can polish the top.
Don't sand the top beore painting or you will have nasty pin holes.

tks

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downunder
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Re: Do I really need a hot coat?

Postby downunder » Tue Jul 17, 2018 11:54 am

The weight is questionable, coz it's quite thin layer. A tt is more abraded with a sand than a HF so I would just spray it with a semi gloss PU varnish.
I spray all my boards every season to add more UV and abrasive protection. And using super gloss Goldspar Original below water Marine varnish.
Customers love shiny boards and you will too ;)

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Re: Do I really need a hot coat?

Postby BWD » Tue Jul 17, 2018 1:22 pm

Depends on the board design.
For durability, soft cores, and designs where the glass is a major strucural component (ie 8oz or more of glass) go on and do the full or hot coat.
Filling in all the waviness between the fiberglass yarns will yield a thicker skin and it’s the resin between fibers that resists buckling on the compression side of the board when the board is subject to bending and point loads. With less resin, there is less resistance to buckling.
So, is your paulownia thick or thin? If it’s <15mm I’d call it thin and put minimum 2 layers of 6oz glass on it with much more to reinforce the foil base through front foot area - extra glass patches or carbon uni strips, so the board won’t bend or break near the foil mount, and will be stiff enough to be quickly responsive to foot pressure and easy to control pitch.
If the board is thick, say 25mm+, perhaps no worries as it is already thick and strong enough. Might still want glass and carbon patching around key areas, or not depending on your goals style and weight.
If you’re light like downunder you could get away with less, obviously. On the other hand I have some buddies in the 100-120kg range who would need more like 3x6oz both sides plus carbon tapes down the middle even on a 20-25mm thick board.

stevez
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Re: Do I really need a hot coat?

Postby stevez » Tue Jul 17, 2018 2:26 pm

Thanks a lot for the tips and suggestions :thumb: :)

This is my second board. The first one seemed to work fine, and it had no carbon and just a single layer of 6oz glass top and bottom. It was about 20mm thick. It seems easily stiff enough, but I only use it with a freeride kite foil (stringy foil).

This time I've made it quite a bit thicker, about 25-26mm, though it's not completely solid. It feels stiff, quite a bit stiffer than the last one was before I glassed it. But this time I intend to use it with a surf foil, so it does need to be stiffer and stronger, especially front-to-back. So I've added the strips of 200g uni carbon in this direction from the back mount holes to where my front foot will go. I'm only relying on the fibreglass for lateral stiffness and strength. It won't have too much effect front-to-back as the carbon will take up all this load.

I'm definitely going to beef up the underside a bit, and put probably 3 layers over the base plate, extending in the area in front of the base plate, which I've found is the point of maximum stress. I am contemplating putting some carbon there, but it might not look that great.

I'll laminate the other side and see how I feel after that - maybe I'm just being lazy :P

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Re: Do I really need a hot coat?

Postby BWD » Tue Jul 17, 2018 3:05 pm

Sounds great really then, however you fill and finish the glass.
Nothing like your own personal benchmark to guide a build.
Looks good, too!

stevez
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Re: Do I really need a hot coat?

Postby stevez » Wed Jul 18, 2018 12:31 am

Thanks BWD :)

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Re: Do I really need a hot coat?

Postby airsail » Sun Jul 29, 2018 9:26 pm

When using old school polyester resins building surfboards the hot coat you refer to is called a filler coat. This was resin with wax added to make sanding the board possible. The unwaxed laminating resin is virtually unsandable, just balls up if you try but it sticks to the foam well. A thin layer of waxed filler resin fills the weave and makes the board sandable.

The hot coat is usually the layer of gloss resin applied over the filler after sanding, this is a very clear resin with a high wax content which allowed for wet sanding and polishing. This layer is often omitted now and replaced with a urethane satin spray coat to reduce weight and labour.

With epoxys all layers are sandable so no need for a waxed filler if you have the finish you desire. Also many resins are now UV resistant so no need to paint.

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Re: Do I really need a hot coat?

Postby bay surfer » Mon Jul 30, 2018 2:23 pm

Coat of poly is all thats needed to protect the epoxy from UV. Wash the surface before applying poly.


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