Fiberglass/Epoxy Question

Hey guys,

I just applied a fiberglass layer to the bottom of my new build. I used 19oz triaxial and Raka epoxy. I wet out the glass and everything looks good, but I will not be able able to recoat the surface right away. The surface does not appear to have any blush, but I was wondering the best way to prep the surface for subsequent coats. The surface shows the weave and it rock hard already.

I could sand the area to create a good bond, but the weave of the fiberglass isn't filled all the way and it seems like I would be removing a lot of material to really scuff the surface. The low areas of the weave will still be shiny and unscuffed.

Hopefully this makes sense. Let me know what you guys would recommend to make sure the subsequent coats of epoxy to finish the bottom adhere well.

Thanks!

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Permalink Reply by Rick Newman on July 1, 2013 at 7:18am

Jason, System 3 and West System suggest that 72 hours is the magic number. That is you can apply more epoxy without roughing the surface. Larry at Raka might be a good source of info for his epoxy. I don't know if Raka has any issues with amine blush.

Rick N

Permalink Reply by tungsten on July 1, 2013 at 9:24am

As Rick says,get another coat of  thickened goo on there.You do not want to be sanding this until the weave is full.

Pending on temp and what hardener used but 8-12 hours is normally good between coats.

Permalink Reply by Eric Loudenslager on July 1, 2013 at 8:34pm

Amine blush can be removed with water....warm with a little soap will take of that issue. Bonding between layers is a different issue. If you are outside the window of recoating, but have a rough surface because the weave isn't filled, you may want to consider using System 3 quick fair, or make your own fairing compound from Raka epoxy and fillers, then fill the weave with the fairing mix. It may not chemically bond to the low areas in the weave, but it might lock into the depressions. Then you could sand the fairing mix and top areas of the weave and proceed to finishing your lamination.

Permalink Reply by Jason Knight on July 2, 2013 at 3:45am

Thanks for the info guys. 

I talked to Raka yesterday and they suggested scuffing the surface and wiping everything down with denatured alcohol to make sure there is not dust on the surface. I coated it Saturday morning and most likely will not be able to work on it until the end of the week. I will let you know how it works! (or doesn't) :-)

Jason

Permalink Reply by tungsten on July 2, 2013 at 6:24am

Well that's quite the pickle your in.At least the surface will be rough with little depressions.Maybe just a pass or two with a scraper to knock down some of the bumps and then fill.

 

Easy to sand mixes like quick fair,i use  for final finishing easy to sand quick to cure.But I question if it would be good for filling a bottom?Being easy to sand in my mind doesn't really fit into a bottom layup.I would go the route of something that's hard to sand like wood filler and such.Hard to sand = tuff, which is what we want for a boat bottom.

Permalink Reply by lhedrick on July 3, 2013 at 8:55am

I have used many gallons of Raka epoxy.

I have always worked with the slowest speed hardener for larger glass layups and plan my windows so I can re-coat in 24 hours.  It's always worked fine.

I work in very low humidity and have never seen any blush after using close to 100 gallons of the stuff in 10 years.

If you go past 36 hours, you should rough sand first.  This is a pain when working with thick fabric, especially with biaxial and triaxial stuff.  Sanding is a pain and it will cut into fibers.  If possible, just roll on a fast coat with slow gardner.  It doesn't take long and will extend your cure window so you don't need to sand.

I think it will be in your best interest next time to hold off on the glass work until you have the time to work 3 coats with 10-12 hours between. The thick fabrics like the stitched axial types are so rough after wet out that you won't really be able to sand.  You will just be cutting into the fibers which are at the top of the layup.  You will be much better off waiting till you have the time to work within the cure window so you can fill and not sand.

Best of luck.

Permalink Reply by Jason Knight on July 3, 2013 at 10:09am

In hindsight that would have made the most sense. Lesson learned. I will need to do a bit of sanding and be sure to complete the rest of the coats within the window to avoid any more sanding. Luckily the humidity here has been really low and there is no sign of blush on the epoxy that I noticed.

Permalink Reply by Jason Knight on July 6, 2013 at 8:18am
So I used a paint and rust stripping wheel from 3M to scuff the surface of my wetted out glass surface. It worked awesome because it has a semi spongy feel and was able to rough up all of the surface, even the low spots. Best part is it didn't really cut into the glass weave at all. Cleaned up with denatured alcohol and am doing my subsequent coats today. Took about an hour to do the bottom with the wheel attached to a drill motor.
Permalink Reply by tungsten on July 6, 2013 at 9:25am

That's a good idea using the wire wheel,scuffs it all without really sanding the glass.I'll have to remember that.

Permalink Reply by Jason Knight on July 6, 2013 at 9:35am

Yeah it wasn't bad at all. I had the wheel from some other project and saw it sitting there on the bench... tested it and before I knew it the entire bottom was nicely scuffed.

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