Step 5 (continued):
When spraying on the PVA make sure that there is not too much air in the mix of the spray gun settings. If the PVA goes on dry, without forming a flowcoat, it will leave a rough, pitted finish on the final product.Getting it right takes some practice, but if you are
conservative, you will likely have good results from the beginning.Rather thanspray it on too heavy and get runs, spray repeated
light coats untilit is just slightly wetand begins to flow together.
After the PVA has thoroughly dried for
at least 45 mins., it is time to start the actual lay-up.
Step 6:
I like to start byapplying a thinned-down layer of epoxy over the entire surface of themold(except the flat flanges); and, letting that partially cure out (usually overnight, as it has usuallytaken me all of my first day to get to this point anyway). While many might view this as extra weight (as epoxy, by itself, does not add strength), as explained below, I think the penalty is worth it:
1. The layer of PVA is extremely fragile.Even aslight touch can frequently scratch, remove,or pull the PVA away from the mold surface. This THIN layer of epoxy protects the PVA.This extra protection is especially important when filling the radius of sharp corners with microballoons in the next step, wiping up drips, etc.
2.Without this initial layer, I find that there are too many pinholes. Priming, filling, and sanding to fix these pinholes end up adding most of any weight savings back on, anyway; plus, then you have extra steps to complete which adds extra time, mess and expense to the project, as well.
3. This layer also gives me
just a little something to sand to help even/smooth things out when needed, without immediately sanding into the cloth.
As stated previously, I always have to try something different. This time, I tried spraying on my thinned epoxy layer using my compressor and an old detail gun. I thought this might make it go on smoother, eliminate air bubbles that I am always trying to brush out otherwise, and speed up the process beings I am foolishly doing 3 at a time. In my opinion, it wasn't worth it:
1. It was too hard to clean the epoxy out of the detail gun, so time saved resulted in extra time cleaning up.
2. I forgot to take off my new glasses
(Man!, getting older really sucks!) The overspray coated everything, including my new glasses.
3. It didn't flow together quite as well as I had hoped.
4.Now I have epoxy on the flanges, too! Oops, I didn't think about that outcome before I did it.
That may come back to bite me big-time when I need to clean up the molds prior to their next use. I have found that epoxy alone, without fiberglass backing It up, tends to not come off of the mold surface very easily.
So, bottom line: my normal method of merely brushing the initial layer of epoxy is the better method of the two.
The pictures below are the molds completed up to this point:
1. First is the P-47 (the round, stubbyfuse with no incorporation of a vertical fin make it easy to identlfy)
2. Second is the P-51 (the open bottom and 2-piece cowl make it easy to identify)
3. Third is the P-39 (this is a round fuse, like the P-47, but incorporates a vertical fin and hatches into the structure)
Pictures 4 & 5 are all the molds lined up.