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Graphics and pre cured top sheet

Posted: Fri Jan 25, 2013 10:39 am
by sijandy
Iv'e been making boards for a while now and want to start including graphics in my lay up as i have
only ever previously painted boards. I have read a number of threads on the subject and a pre cured topsheet using mylar seems to be one of the more popular methods but there are a few things i'm not sure about and would like some help with. What is the best method for bagging the topsheet, is it best to go mylar(back side down), then graphic(face down) then thin glass layer? Also is the graphic printed directly on the mylar sheet or are they separate? Finally, when you do the main lay up and put your pre cured top sheet on as last layer before bagging how do you deal with the excess resin? Normally after my final layer i put perforated release and breather but the pre cured top sheet isnt permeable and therefore no resin will draw up through it? Any tips or advice on the above or graphics in general will be greatly appreciated as i can no longer afford to experiment and waste anymore materials. Cheers.

Re: Graphics and pre cured top sheet

Posted: Mon Jan 28, 2013 6:22 am
by mattma
The mylar is only there to provide a smooth surface to cure the FG against and provide some scratch proofing while handling it. The best example I've seen on the forum is the guy who made the Porker (well worth looking over again if you haven't already seen it).

Although some people put FG tissue ( 1 oz scrim) down first I always had trouble handling it so haven't used it after the first messy attempt. I'm sure there are many variations but I put 6ox FG first, wet it out, then graphics ( I use a standard ink jet printer and print on to acid free tissue paper), then peel ply and release film+ breather etc. Peel ply leaves the weave print which helps bonding.

Excess resin under the impermeable skins is common and in my couple of attempts its added a couple of hundred grams to the weight. If you are still doing a wet layup of the inner layers of ply and then sandwiching it between the pre-cured skins then the best approach is to make sure you have removed as much resin as possible first. A friend of mine who is a yacht builder recommended wet the FG out on a separate table and removing as much excess as possible there and then transferring it across. In some cases they wet it out on a piece of cardboard so that some of the excess drains down through the weave while working it. I've never tried using cardboard so don't know the practical issues of it. Finally, when its transferred across all that remains is to roll out air bubbles.

Also, heat will cause the resin to thin and be more mobile and easier to squeeze out. It will of course also speed up the curing process.

http://boardbuilders-forum.1077691.n5.n ... td406.html


Re: Graphics and pre cured top sheet

Posted: Tue Jan 29, 2013 10:15 am
by sijandy
Thanks, that's really helpful. Another thing i want to try is using liquid urethane for the rails, there are many different types and i'm not sure which one to use as I have no experience of this?