Glass the hull.  Immediately apply the second layer with no drying time.

You will have a strong chemical bond between the two layers this way.  Letting anything dry means you’re relying on a mechanical bond to keep the two layers bonded together.  

I agree with Jason about the chemical bond issue, but please keep in mind that it might be considerably more difficult to arrange the dry fiberglass over the first wetted out layer.  I would make sure you have both layers laid out and cut to the approximate shape/size before you mix any epoxy.  If you squeegee out the first layer so there's no extra epoxy, it might not be too bad to lay the second layer on.  I've never done it, but just trying to think it through.

For the reasons noted above (chemical bond, etc.) it's common practice to wet out both at the same time. With such light weight stuff (4oz?) that's really not tricky. The two layers will wet out easily in my experience. Trying to position/smooth out a layer of glass on a tacky surface however sounds really dicey.

You might see some difference in opinion on whether to put the reinforcement "patch" on top or under the solid/complete layer of glass.

My preference is to put the smaller cut piece underneath as this *seems* to help prevent fraying of the cut edges when "squee-geeing" away excess epoxy, and results in a smoother surface. Others might be concerned with lifting the outer layer away from the wood, but with 4oz glass especially, I don't think this is a big deal.

Good luck!

Patrick

+1 on immediate application of second layer before cure of first. Second smaller layer on top, if underneath you can’t feather out edge without cutting through outer layer of glass. That’ll eliminate structural integrity of glass.

Adding a second layer as a smaller patch can create a gob of glass fibers that pull out from the edges when you squeegee the epoxy out. I’ll cut the patch roughly to size and fray the edges by pulling several warp threads out of the sides and weft threads out of the ends. You can see in this photo… (if i can post the dang thing.)

Pulling the warp or weft of glass weave prevents a lot of grief but the real trick is to cut a pice of substantial (4-6mil ish ?) plastic sheet somewhat oversized for the patch. Place it over the second layer of glass and squeegee through that. Goes a long way to prevent threads from pulling out around the edge and the fringy edges are way easier to feather into the first layer.

I feel like I haven’t been able to get many converts to the curved carbide paint scraper but it works extremely well for me in situations like this. The carbide lasts almost forever and the curve let’s you focus material removal with precision. It’s also easy to adjust angle of attack and skew to fit in all kinds of areas. They’re readily available and pretty cheap.  

Apparently Flickr broke their photo posting ability. Here’s a direct link…

https://www.flickr.com/photos/31735445@N06/38747219910/in/dateposted-public/

First off, you're building a Petrel, not a high speed powerboat. The "mechanical" bond is plenty strong for that boat.

Second, depending on the conditions, epoxy can take up to a month to fully cure. Until it is fully cured, there will be a "chemical" bond of some level. As long as you can dent the epoxy with your thumbnail, it's not fully cured.

So put down the first layer, wait until it's just past the tacky stage and put down the next layer. You'll still get your "chemical" bond and have an easier time with the second layer.

Smaller pieces on top, too.

Laszlo

ditto laszlo....

my view when working with large pieces is not to try to do too much at one time.  it is much easier to wet out and keep organized a single large piece at a time.  when that has kicked and is not tacky, come back with the second piece.

h

So do I put any addtionals coats of expoxy on the first layer to start fillng the weave or put second layer right on top of first layer when it is no longer tacky?

The instructions were ambigiuous.

Thanks

Anthony

 Never fill the weave for interior glass. Only fill the weave on the outermost layer. Filling interior weave results in a heavier, weaker and more expensive layup.

Laszlo

   This was good timing, I'm preparing to glass my sheawater sport. The instructions imply that you do all 3 layers on the hull at the same time, but one at a time seems a lot more sensible, especially for a first timer like myself. :-)

As a side note, last night I placed the fiberglass on the hull. At first I didn't think there was a chance in hell that it would conform to the stern without cutting. However with patience, using my hands and a paint brush I was indeed able to shape it to the hull.