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 Post subject: Pre-cured topsheet question
PostPosted: Mon Jan 30, 2012 1:40 am 
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I'm trying to find a good alternative to PBT/Durasurf etc for the topsheet of my boards because there doesn't seem to be any suppliers in Australia and postage makes the price to rich for my budget.

I've seen in a couple of posts people refering to 'pre-cured' and have seen the great results on the 'Porker' board a couple of years back. But, there doesn't seem to be any more info on how to do it and when you can and can't use it.

I'm guessing it means pre-cure a layer of light glass on a flat smooth surface and that put it into the layup as a finished product. But I've got a few questions that would be great to have answered before I commit resin to glass.

1) Does it just mean cure a light layer of glass on a shinny surface?
2) What weight glass is best?
3) Is it necessary to vacuum bag it to get a good finish and resin ratio?
4) Is it necessary or useful to put peel ply one one side to for better bonding in the lay-up?
5) what's the best way to avoid getting air bubble locked in the weave? I've tried a few different ways (elbow grease, roller) but still end up with a few too many?
6) how well will it conform to the curves on a board? Obviously it ain't going to bend around corners but will the curves you normally get from sanding a core so that its thins out smoothly towards the tips and the rails be too much for it to conform to?

Any other tips or suggetions greatfully appreciated.

Cheers


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 Post subject: Re: Pre-cured topsheet question
PostPosted: Mon Jan 30, 2012 3:33 am 
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Joined: Sat Aug 29, 2009 11:25 pm
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Location: The Naki
i've heard that vac bagging a top coat with mylar gives a glass like finish you simply peal the mylar off afterward. so its essentially a resin layer.

haven't tried it myself yet tho!.

let me know if it works.


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 Post subject: Re: Pre-cured topsheet question
PostPosted: Mon Jan 30, 2012 6:51 pm 
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plummet wrote:
i've heard that vac bagging a top coat with mylar gives a glass like finish you simply peal the mylar off afterward. so its essentially a resin layer.

haven't tried it myself yet tho!.

let me know if it works.

It works a treat trust me :-)

The purpose is to obtain a thin skin which is resin as that is the only way to obtain a full and deep gloss/sheen :-)

yes I vac bag mine.

The objective is to make a cured and finished thin laminate.

Thickness is up to you but I normally do a 2oz or thinner scrim layer with decals next followed by a layer of 4oz. Leave to sure then bond

If done right you end up with a completely finished fully glossy outter surface to your board.

Once the topsheet is cured leave thay Maylar if you like sheet attached, dont remove it.
skuff the top sheets bonding side with 40 grit and clean the dust off. Now simply go to your rocker table lay up the normal structural layers and put the pre-cured top sheet on and after the normal vag bagging process has been done, you can remove that film layer to reveal the goodness.

Here is a link to a video which shows a mate of mine revealing his new board many years ago now, not the best finish possible but this was a prototype process for me back then, they come of perfect noe :-) watch his face :-)

http://www.youtube.com/watch?v=bdVr7wWR ... _iN9xWZ1sN

Image

Image


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 Post subject: Re: Pre-cured topsheet question
PostPosted: Mon Jan 30, 2012 11:50 pm 
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Brilliant! Thanks for all the great info and the video. Your mate looks very happy with his efforts and rightly so.

Can I just check one thing. When you wet out the scrim/decals/4 oz you don't put that under a vac bag? Just working it by hand an leaving it to cure is fine?

Using fibreglass scrim is a very good idea. I hadn't ever thought about it before. I guess the larger spaces between the fibres means there's very little chance of getting air bubbles locked in there. And, like you say its effectively a thin layer of resin with a glass backing for adhesion.

Cheers
Matt

http://myvirtualshed.blogspot.com


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 Post subject: Re: Pre-cured topsheet question
PostPosted: Tue Jan 31, 2012 12:18 am 
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Joined: Thu Nov 02, 2006 5:12 pm
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mattma wrote:
Brilliant! Thanks for all the great info and the video. Your mate looks very happy with his efforts and rightly so.

Can I just check one thing. When you wet out the scrim/decals/4 oz you don't put that under a vac bag? Just working it by hand an leaving it to cure is fine?

Using fibreglass scrim is a very good idea. I hadn't ever thought about it before. I guess the larger spaces between the fibres means there's very little chance of getting air bubbles locked in there. And, like you say its effectively a thin layer of resin with a glass backing for adhesion.

Cheers
Matt

http://myvirtualshed.blogspot.com

The topsheet is wetted out on just a sheet of normal glazing glass and then vac bagged flat, there is a or two trick here but I will leave you to discover them to make it perfect.

Think the other way around :-)

Took me a few tries from scratch to work this process out and make it a 100% repeatable process.
Another tip is "a simple addition to the pile before bagging"

Good luck

That said there are many ways to do it :-)


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 Post subject: Re: Pre-cured topsheet question
PostPosted: Tue Jan 31, 2012 1:28 am 
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Cheers. I love it! More than enough great info to have a good go at it with enough mystery to make it my own when I finally crack it :thumb:

I'll make sure I post my attempts and thanks again for the greatly appreciated help.

Cheers
Matt


http://myvirtualshed.blogspot.com


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 Post subject: Re: Pre-cured topsheet question
PostPosted: Tue Jan 31, 2012 1:46 am 
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Joined: Sat Aug 29, 2009 11:25 pm
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Location: The Naki
indeed interesting ideas. i'm about to embark on a build. i'm adding all this to the fold...


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 Post subject: Re: Pre-cured topsheet question
PostPosted: Tue Jan 31, 2012 5:09 pm 
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mattma wrote:
Cheers. I love it! More than enough great info to have a good go at it with enough mystery to make it my own when I finally crack it :thumb:

I'll make sure I post my attempts and thanks again for the greatly appreciated help.
Cheers - Matt
http://myvirtualshed.blogspot.com


Cool as fella :-) and good luck.

I forgot to say you will be supprised just how much a thick sheet like this will deform to cover a smooth 3D shape. The Porker of mine was built this way using a pre-cured top sheet.

Also leaving the film on the sheet till after the board is vaced allows you to mark it up for alignment purposes and stops any excess resin spoiling the finish.


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 Post subject: Re: Pre-cured topsheet question
PostPosted: Tue Jun 05, 2012 11:28 pm 
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Joined: Mon Sep 19, 2005 12:49 am
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Location: scott klandl burlington, VT
Ive been in love with mylar for years, works great on my bottom sheet, and tried for a while with my top sheet in a one shot build but always got air bubbles migrating to the top sheet and causing problems,

have you any problems with air bubbles with the precast top sheet? or is the precast sheet enough to prevent bubble formation or do you make some holes over foot and fin insert packs?

also, has does the pre cured topsheet handle more complex top shapes? my mylar always buckled causing wrinkles but 4 oz glass would have more strength to it... attached a pic, can you take a look XS and think if this is too much shape for 4 oz glass + rice paper to conform well too? Planning on pre curing topsheet to old glass door than attaching to board


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 Post subject: Re: Pre-cured topsheet question
PostPosted: Wed Jun 06, 2012 9:33 am 
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Joined: Thu Nov 02, 2006 5:12 pm
Posts: 76
scklandl wrote:
Ive been in love with mylar for years, works great on my bottom sheet, and tried for a while with my top sheet in a one shot build but always got air bubbles migrating to the top sheet and causing problems,

have you any problems with air bubbles with the precast top sheet? or is the precast sheet enough to prevent bubble formation or do you make some holes over foot and fin insert packs?

also, has does the pre cured topsheet handle more complex top shapes? my mylar always buckled causing wrinkles but 4 oz glass would have more strength to it... attached a pic, can you take a look XS and think if this is too much shape for 4 oz glass + rice paper to conform well too? Planning on pre curing topsheet to old glass door than attaching to board


Good day.

Not had any issues with air bubbles at all but as I use a carbon pre-cured top sheet i would not be able to see them anyhow :-)

Take a look at my Porker build, that used a pre-cured top sheet, not sure yours looks any more complex in shape than mine.
TBH it amazes me just how much it does conform and can handle conformity in may directions and without fault but then again my cores were always smooth as possible in the transitions.

You also ask about holes near heal areas, I always perforate my cores heavily around the heal impact zones creating little support pillars of resin between the skins and so far no issues.


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