Help troubleshooting vacuum layup w/ Polyester

[mbam]

Thanks in advance for any help here!!

I am making new deck panels to replace the rotten plywood on my cruiser and am having problems with the laminate that is next to the peel ply. Let me add this is my first attempt at vacuum bagging.

¾ Polyumac 6 lb foam with 1 layer 1708 0-90 biax on each face. I am only concerned with the finish on 1 face, so are trying to do this in one shot. On the first attempt I was concerned about running out of time so only went 1% on the hardener with the shop at about 75 deg. The layer against the table looked pretty good and hardened properly, but the top side was still soft after 12 hours. We were able to pull the glass off the foam & it also looked dry. We are using peel-ply and some Trivera as a bleed layer, 15” vacuum on this attempt. Our local supplier said too much vacuum.

Second attempt was better, went 1.5% on the hardener and 7-8”, still not great however. Looks dry in spots and is still soft in some areas. We also had added a 2”wide x 3/4 rib down the center – so it was bottom layer of biax- wet out – foam(we wet it with resin) - layer of biax - wet out – place rib – add 7” wide strip over the rib (which is chamfered to a knife edge all the way around).

I’m pretty sure we are using enough resin, first try we weighed the glass and did the math for 50/50, added 20% or so. Second try we manually wet out & rolled adding resin until it looked OK, same way as if we were doing a conventional layup then added the peel-ply & Trivera. The 7” vacuum was not enough to pull the biax against the sides of the rib, but we are just using 4 mil poly for the bag and it does not stretch very well so that did not help.
We are doing this on ¾ melamine board laminated to a piece of ¾ mdf. Have an oil-less compressor that we are using as a vacuum pump, it will pull 28” if needed.

Me thinks the problem is with my peel/bleed set up. Removing too much resin? How much vacuum is normally used?

I'll add some pictures tommorrow when I get back to the shop.

Thanks again !

[waikikin]

Maybe your sucking some vital components out of the resin or theres something up with your resin or batching technique/calcs on catalyst, a foam core can hold/insulate the exotherm against the table for good cure & the bagside can cure at a different rate, also you dont need much vac to bed a core on a flat panel- do the math on your psi & square inches, gets impressive but unnessesary, plenty of good panels have been made with out vac bagging, by all means aim for a nice tight job with the bag but a 2" squeeze on a flat panel for a cruiser(you probably got some spare hp & you don't have to chase weight like a raceyacht build) will "probably" do the job, also do some time test to gel on your products before committing expensive? core. All the best from Jeff.

[JRL]

If you are using the piece of melamine as the tool surface. There is a good chance you are pulling air through the wood and directly into your layup. Especially the bag side surface.

I witnessed this first hand on an infusion. The layup was 2 layers of 1708 on each side of a 1/4" divynicell core. It ws still usable as all it was was a casting deck that was to be painted. Still, was far from spotless as it normally would have been.

[mbam]

We are getting closer, put a piece of split loom around the piece and there is no question the vacuum was more even. I think we were pulling air across the piece, inhibited cure and pulled resin with it. The last couple of test pieces looked pretty good.

I did think about porosity in the table, it's 3/4 melamine board glued to another piece of 3/4 MDF. I think we are going to coat the underside & edges with resin just in case.

Instead of trying to do this both sides at once I think we are going to do 1 side at a time. We need to add some stiffening ribs and it will look better if we add those last against a finished panel, 3 of the pieces are hatches so they have to look semi-presentable. We did one tonight before we went home & put peel ply on the side against the table. Am I correct that we won't have to grind this surface to add the ribs later? How long can this set to be considered a primary bond?

[JRL]

Originally Posted by mbam

We did one tonight before we went home & put peel ply on the side against the table. Am I correct that we won't have to grind this surface to add the ribs later? How long can this set to be considered a primary bond?

You shouldnt have to grind, but, poly doesnt like to stick to poly. So depending on what your going to bond the ribs with, you may have to grind.

Most everything I do is with epoxy, so, if that were the case, is wouldnt grind. Im under the impression that you need really deep scratches to get poly to bond to itself. Like 40 or 60 grit. Im sure somebody with more experience with poly will chim in.