First time making a “real” mold…
First time using chopped mat…
115 degrees, single handed….
what could possibly go wrong.
Today I laid up the aft top cowl mold. It was a hot, long day. The temperature was over 100 by 0845 and 115 by the time I finished the layup. I started by doing my 3 coats of PVA. To my surprise, I actually got the PVA on there pretty well without running it. Maybe I am learning.
Then it was cut some cloth and get to the layup. I did 1 layer of deck cloth then 2 ply of chopped strand mat. Now, this is my first time working with chopped strand mat. There was a bit of a learning curve. Before I started, I didn’t think anything of it. But turns out, I had a lot to learn. Fortunately, I got lucky.
Chopped mat is thirsty and requires a lot of epoxy to wet it out. I mean copious amounts of epoxy. In fact so much epoxy that I nearly ran out. I used my last ounces of the epoxy I was using in the final ply. I was thinking I had gobs of epoxy and it wasn’t even nearly a concern. But I was naively anticipating that the mat would use about the same amount of epoxy as a woven cloth would use. Not smart.
In hind sight, it would have been smarter to do a test layup with a new to me material that is vastly different than anything I have used before. I would have immediately seen how much epoxy it required and used my West System epoxy since I had a couple gallons of that. But I lucked out and was able to finish my second ply of mat.
It also doesn’t like to wet out along the hard manufactured edges or in its manufactured compressed state. In fact, I found it wets out best when it is torn and the edges are feathered. I am glad that I have watched a lot of YouTube videos about mold making, vacuum bagging, infusion, etc. That is where I have seen this idea before. I didn’t consciously know what I was seeing when I was watching those videos, but somehow I remembered and tried it today. Much easier to wet out that way.
While I was making the mold the epoxy was curing quickly. That was exacerbated by the fact that due to my lack of prior proper planning, I had to use not only slow but fast hardener as well. I didn’t have enough slow for the needs of the mat. Not ideal to use fast hardener on a layup that big. Much less a layup that big, doing something I’ve never done before, with a material I’ve never used before, in 115 degree hangar. Oh and single handedly. Did I say I got lucky doing this layup?
As it was, since it was curing so quickly there were areas that were gelling and getting well past the green stage as I was working. It made it necessary to work in small areas and quickly in order to get the best wet out I could. Even so, there are more air bubbles in the mat than I would like. Apparently it is not terribly abnormal to have air bubbles in the mat from what my mentors are saying. There are simple fixes if the mold won’t seal for a vacuum bag as well. Maybe I am being a little hard on myself in light of the challenges I had today. The proof is in the pudding I guess. . I am optimistic that we will have a good mold when it is released tomorrow.