hi dan.
i had a similar prob on my first
on the second board i sealed the balsa before lam
i put some micro balloons in the sealer but the resin was still pretty runny
the other thing was to do the filler coat before the lam cures
i found only a few tiny pinholes and they may have ben caused by dust.
im thinking of using Everdure to seal balsa next time cause that really soaks in and creates another water barrier…
yeah and temperature control
cheers mate
Hi dan! are you sure they are airbubbles? I got the same surface after hotcoating my board
with RR epoxy, and I did wipe with a RAG and alcohol.
After closer examination it wasn’t airbubbles in my case, I think it was particles(dust) that has ripped off from the rag while wiping the board…
Jimmy yoshio shibata.
I could definantly see air in about half of them. One half of the board was covered with them while the other half only had a few. So I think it was air, but in a multipurpose garage who knows…
Dan –
i had that same problem with my first few tries with epoxy. i thought my problem was too dry of a lam. anyhow, i got pinholes with the finish coat, too (so maybe not too dry a lam). i started adding a cap of denatured alcohol to the mix and that really helped it lay flat and smooth. sometimes, i don’t even need to sand the final coat (if i get lucky).
All the guesses here have the possibility of being correct. My guesses are:
Dry lamination. Even with sealing I still occasionally get my laminate too dry, which causes bubbles in the hot coats. Then I have to baby sit the hot coats until the bubbles stop. Not my favorite way to spend an evening. Also sealing balsa with resin should help next time. Balsa can be a bit absorbant. If you know your laminate is dry when you finish that step, then do a cheater coat when the laminate is tacky. This will save you from the babysitting chores. A 3 oz cheater is all you need.
Contamination in the hot coat. Dust and such. Again, babysit the hot coat or sqeegee it off and hot coat it again right away.
Also the denatured alcohol in the hot coat is an old trick I forgot about. This can work in some cases. Using more Additive F when it’s hot also helps. Double it in over 90º.
Warming the resin a bit also can help. To about 100ºF. Get the stuff out of the bucket quick though. I’m one of the fastest hot coaters ever and I’d get caught on about the third one out of the bucket. I used to just do two at a time.
Greg,
When applying the cheater coat how tacky should it be? What consistency should the lam layer be before applying the cheater coat? …maple syrup consistency or wet bubble gum?
I’ve noticed that flat areas will dry out first but the rails are still wet, is it at this time when you do it or before it gets to this state? I realize curing is highly dependent on ambient temp.
~Ghost
I just wanted to post an update to let everybody know that I discovered what the cause of all the bubbles was…Temperature! Today I hotcoated the deck this morning around 7:30 and the bottom tonight around 8:00. All my prep was done exactly the same and the only difference that I could see was temperature. In the morning the garage started off at around 79 degrees and had reached a little over 80 by the the time the resin had set. The bubbles were popping everywhere. I was able to take care of most of them with my squeegee/roller technique, but I concluded that I was the worlds worst hotcoater. Tonight I had my halogen lamp turned on the board to speed cure a patch on the finbox. The rest of the garage was around 82 degrees. I poured out the resin and the bubbles started popping. I thought - oh well better break out the squeegee. I decided to open the garage door to see if I could lower the temperature a bit more. In a minute or so the temperature had dropped to 81 degrees and almost magically half of the bubbles disappeared. When the temperature hit 80 degrees most of the remaining bubbles disappeared. I would never have believe that such a small change in temperature could make such a hugh difference. I’ve learned my lesson - NEVER HOTCOAT IN RISING TEMPERATURES! Thanks again for all the help.
I’ve noticed the same thing. In fact, before hotcoating, I’ve started a sunny-day practice: I’ll pour the resin only (no hardener) into a clear bucket. Tape a piece of clear plastic over the top so no bugs get in. The plastic over the bucket acts like a little greenhouse too. Put the drip tape around the board perimeter. Put the bucket & the board out in bright sun for 15-20 minutes. I rest the board on a couple of buckets so the tape stays hanging down.
Then grab the board & bring it back in the garage. Grab the resin, pull off the plasic, mix in the hardener, and hotcoat. This way, even if the garage is super hot (mine was 86*F on Saturday), the board will be cooling down just by coming out of the sun & into the shade. It only takes about 45 minutes before the hotcoat is set up pretty well if you work it like this. So after an hour, I bring it back out in the sun for another hour or so.
Then its ready to pull the tape, surform the ridge, flip, retape, and put it out in the sun to do the ther side. I had both sides done - hotcoats - on Saturday in about 5 hours total, ready for sanding. I was also painting a shed so I had other stuff to do in between coats, so it all worked out nice.
Just for the academics, I think this is an EPS foam issue, not a resin issue. I’d be interested to know if anyone using epxoy on PU has the same issue. I’ll bet not.
But I do this over a composite sandwich. No EPS contact for hotcoats…there’s a layer of glass, a sandwich core, another layer of glass, and a seal coat between the hotcoat & the EPS…
This weekend’s board has a sandwich core of bamboo (thanks, Oneula) and d-cell rails that were sealed with epoxy & microspheres & then double-wrapped with the outer layers of glass from the top & the bottom. No EPS breathing going on at all.
But…it could certainly be that my hand lay-ups are too dry. I’m so used to epoxy now that my use is absolutely minimal. I can move the epoxy around at just the right speed that I get no foaming or soaking into the substrate, but complete saturation of the cloth. I laminated a 7’ round nose with 4oz E - single bottom took 8 oz of resin, 2 oz of hardener, and I had about 25% left over. Deck got 2 layers 4 oz E - 12 oz total of mixed resin & hardener - and I had a bit left over there too. The resin use is so low its crazy when you really get used to epoxy…but it might leave too many micropinholes?
I don’t think that it is an eps issue, but rather a balsa issue. To test this idea I’m going to pretreat the balsa by squeegeeing a very fine layer of epoxy directly to the balsa, let it dry, then sand it smooth before I bag on the glass.