laminating - air pockets?

[ElBichoMalo]

Started my first laminating today (just a small "stern seat" recore job), but I think I am going to have a problem with the finished product. Here is what I did:
Using all fgci products (they are local for me) polyester resin 1.5% MEKP mix, mixed in milled fibers, used to "glue" down the core material. I used a composite "foam-like" board from fgci. Can't remember the name of the product...starts with diab... same stuff Gause uses (because the sheet I bought was earmarked for them - guy says they buy it weekly - Gause is local too). I mitered the edges of the core, glued it down and let it cure overnight. This morning I did this:
coated the core/hatch with resin, then layed a layer of 1708, wet out, using a combo of a ribbed aluminum roller and a chip brush. Looked nice, but then I kept thinking there was trapped air. Everytime I would try to roll it out to the edge, it just made it worse. Everything I read says the whole point of rolling is to get rid of the air. What am I doing wrong?

P.S. I also added one more layer of 1708, slightly larger than the first, while the first was still wet. It this the right process? The whole point of me starting with such a small meaningless piece was to get this learning curve out of the way before something important, and I am glad I planned it this way. Now help me!

[JohnB]

Did you wet the part the 1708 was going onto first? then wet out the 1708 that is facing down, then lay it down, then wet over and roll on top? If you layed it down dry, and tryed to "force" the resin through it, you might have some problems.

[sponge]

You may want to invest in a small vaccum bagging kit.
You can buy them cheap that hook to a small air compressor.
Mine works great. You get stronger and lighter parts.

[ElBichoMalo]

Well, it has cured out. The part seems to be structurally sound and looks like I thought it should. I did wet the surface first, but did not wet the "down" side of the glass. Next time I will do that. Need to get some visqueen I guess. Is that what you guys do, just put the cloth on some plastic to wet it out, then put that side down on the piece?

Overall, I am happy with my first glass work, and think I'll only improve as I work through the hatches (all of 'em) and then of course...the TRANSOM. (did you imagine suspense music when you read that)? What I am not looking forward to is cutting/grinding/sanding the rest of the cores out. Itch Itch.

[JohnB]

You got it, wet out the piece that your laminating too, then wet out the facing side on a piece of visquin, then take it and lay it on it, start from the middle, and work the air out, they come back with a little more resin, to make sure it's even and wet all the way around. I don't do much with glass anymore, I use epoxy for most things, and it is the same with that, only you get quite a bit more working time.

BTW, if you are working in direct sun, and it's hot, sometimes fiberglass resin will kick off hard/fast, and I think sometimes it outgases, causing bubbles. Usually when it does this, it gets pretty hot. Your really only supposed to lay one layer at a time with fiberglass, and not hot coat multiple layers.

[ElBichoMalo]

Can someone confirm or deny what John said about hot cooating with polyester resin? I thought that if you allow it to cure in between layers, that you had to sand in between. Hope someone knows, because I guess I really don't.

[76Red18]

Never heard of haveing to sand it only haveing to wash the blush off. Not sure about poly resin hardners but epoxy blush can be controlled with medium or slow hardener. It has to be mixed with precision , but for a novice like myself, epoxy is more foregiving but more expensive. John has alot of posts with glassing advice with very few if any negative replys from others. He probably knows what he's talking about

[JohnB]

Can someone confirm or deny what John said about hot cooating with polyester resin? I thought that if you allow it to cure in between layers, that you had to sand in between. Hope someone knows, because I guess I really don't.

We are talking regular polyester layup glass, not epoxy or vinylester, right?

If so, this is what I have experienced. I like the "tighter" lamination that hotcoating gives, and it uses less resin, etc.

The down side, is this, sometimes....
If you hotcoat, and put a lot of glass up at once, lets say 1/4" or more in total thickness, and if the weather is warm, the stuff will get hot. Part of the curing process involves outgasing, and from time to time, I have had glass bubble "air pockets", actually outgasing underneath. It doesn't do it every time, but if the ambient is above 70 degrees, and you mix the stuff at ratio, or too hot, and it is in the sun, it will bubble, especially where it is thick, in corners/etc. Not all the time, but it will from time to time. I have seen this in SeaCraft hulls, on the chimes, it looks like they throw a lot of resin in those tight corners, and I have seen a fair number of voids right there. I am not sure if this is a tight corner issue, or a outgasing from heavy layup, but I have seen this in other boats too.

That is one of the reasons I use epoxy. The MOS stuff from BoatUS and the Marine Epoxy from BoatBuilder Central DOES NOT blush. West and some of the others DO. Most Vinylesters that I have used do too.

Hope this helps, and I hope others will offer their experiences for you.

[ElBichoMalo]

John,

I wasn't trying to knock you, and I don't think you took it that way. Yes, I am talking about Polyester Laminating Resin, so no blushing. John, since we are talking poly, not epoxy, does that mean I can let each layer cure out and still not sand before the next one?

[JohnB]

I didn't take it as a knock, I just wanted to make sure what materials your using.

IMHO, if your doing layers within 24 hours you don't need to sand. What I do is take a grinder or small roto grinder, and knock any of the high spots or strands back, since they stick up, and cause an air pocket in the next layer. That is something you don't have to deal with when hot coating. Generally, I will rough the surface up with the grinder, just the high tops, not grind into the fabric between coats.

I wasn't trying to make a federal case about it, and putting down 2 layers at a time saves time and resin. I tend to make the first layer a little less hot with the catalyst, and then make the second layer standard ratio. I try to do it when it is under 70 degree, and in the shade, and have less problems.