Air Bubbles during hot coat

I had problems with air bubbles during hot coat on the deck so before I did the bottom I read the forum and tried suggested methods as below
-Used a new clean container
-Mixed and pour in a flat container with bigger surface area and let it sit until air bubbles disappeared
-Use a masking tape to clean the brush loose strands
-Pour the resin and spread as shown on video Epoxy 101
-Bubbles appeared again so I tried the heat gun method.
-I put the electrical heat gun to 200 degree C and put it on low blowing rate. Kept the nose of the heat gun about 1 feet away and blow on the epoxy. I could see the bubbles were popping out fast. But there were some stubborn bubbles that would not pop. Specially the bigger ones
-Another thing I noticed was that upon applying heat the bubbles popped (not All) but also parted the epoxy and left a small circular dry spot on the surfboard (much like Moses parting the sea)
-I re-brushed the epoxy and the bubbles appeared again.

I don’t know what else to do. Is there some trick to this? Please help.


well…I disagree with almost everything you have done…It’s no surprise your hot coat is not so hot…clean container is a good start…
I can’t help you today… because I’ve walked too many people thru this…only to have the next guy come up clue less…
search “first epoxy glass job”
Then search “not my first epoxy glass Job”. …and don’t send me a PM…I will not respond.


Most likely have an aired out lamination.

I keep hearing about “Aired Out” laminations hefe on Sways of late. Both in reference to Epoxy and Poly lams. Since I’ve never experienced such a thing; I was wondering if the Sways Boyz could tell me exactly what an aired out lamination is. This dilemma was spoken of as being the source of trouble in another thread recently but no explanation regarding the cause. Enlighten me.

It’s not the epoxy, it’s the EPS blank blowing the air. Epoxy by itself has no capacity to create air bubbles (unless you stir air in), so where do you think they come from? Blanks vary with the amount of air they will blow. Air that is locked into the spaces between the EPS beads will try and exit the blank via the point(s) of least resistance as a function of temperature/pressure differences between the blank and outside surroundings. As you apply epoxy as either a lam or hot coat the blank will heat up and the trapped air will naturally move to a cooler place. No problem when you lam one side, but once both are lammed the exit air paths are cut off. Even if you have an opening for a fin box or whatever, it will may not be the path of least resistance for air to flow all the way from the nose and bubbles will appear. Usually it will be at lap lines or at the rails. The trick of heating an area with bubbles is hit or miss; you will pop the bubbles at the epoxy surface but you are really heating the blank underneath which squeezes out more air. There’s several things you can do:

  1. Don’t glass above 70-75 max F.
  2. Seal the blank with an epoxy slurry and not air-permeable spackle. This in itself will greatly reduce any bubbles.
  3. Try and get the lam sealed as much as possible. Babysit any areas on the second side where bubbles appear until the epoxy gets too stiff. Apply a thinned cheater hotcoat (xylene) on both sides to seal any bubble-holes. You can repeat this if necessary.
  4. Cut openings for any embeds after the lam so you have some venting for the hotcoat thus minimizing bubbles.

The best way is to cure a vented lam in a hotbox, this will “air-out” the lam. Same for hotcoats. The trick with hotboxes is to regulate the temp such that it’s always a bit hotter than the blank temp. And there’s other methods that people use, most just let bubbles happen and fill them and a later stage. Bubbles are one of the main reasons that production-style import EPS boards are painted, they let bubbles happen and then fill the holes with high-build primer before finish coats. I’ve seen some that where bondo’d before primer with huge bubble holes. Just remember that bubble-holes are paths back to the foam and will suck water.

petec for the win.

I can help you a tad further…Heres the only tip you need. a) if at all possibly only hot coat when the blank is cooling down. This will ensure the blank is sucking in air…and not blowing air. This means even if a little ray of sunshine is hitting the board…this will make the board gas a bit and blow out your little holes, fin boxes…or leash plugs.
Ya see… ya fucked up with the heat gun…now you are heating up the blank and creating more volcanoes. Leave the heat gun for small areas and when you need to get the epoxy to flow before it thickens up. fish eyes…let me guess? right where your big jalopy greasy hamburger stained fingers touched the board…bingo!

Hi Petec,
I had the air conditioning turned on, I am pretty sure the room was below 75.
I may sound stupid but what is an epoxy slurry that you prefer over spackle?
Also you suggested to baby sit and apply cheater hotcoat, xylene, to seal any bubble holes. How do i apply the xylene? This will fill the holes? Thanks

Hi resinhead,

I read a lot about the air bubbles before i hot coat the bottom in this forum. I tried to follow as much suggestions as i could. As suggested by you here an suggestions read previously, hot coat when the temp is going down, i made it a point to start in the evening when the sun was going down. Since there was already bubbles in the coat, I did not know what else to do so i turned to heat gun as experimented by someone in this forum (previous thread i read).
As for the greasy hands touching the board causing fish eye, I am guilty.

My experience is somewhat limited when it comes to EPS. I had heard of this before, but it didn’t even cross my mind. Makes perfect sense. Lowel

Did you use additive F? I don’t care what anyone says. Always use it. Trust Greg L.

Hummmm, ok then. A few potentials for problem. 1) crappy foam for the blank. lose open EPS will gas no matter what you do. Sometimes the light cells like 1-1.5 lbs foam will gas like Stingrays grandma after shes has too many SlimJims. What kind of blanks, and what kind of epoxy did you purchase?

Since the Clark SNAFU, the EPS blanks have become much better, and companies like WNC in San Diego are making better blanks than companies like US Blanks or Marko. You can really tell when you work the blank with 80-100 grit, the better blanks wont get ’ Fuzzy". Some of the superfused blanks are good…I’ve never had them gas even when putting in a leash plug.

I was one of the heat gun guys, but it was pretty much used to laydown an epoxy gloss coat, or a hot coat that was going down on a good solid wet lam…If the lam had quite a bit of dry lam air pins, then no heat gun.

I can’t figure out why burger grease causes problems but french fry grease doesn’t.

Xylene is used as a epoxy thinner, very toxic. Add only enough to a premixed epoxy batch to cut the viscosity so that it’s the consistency of poly gloss resin and brush on. I use it for shitty glosscoats on epoxy: Sand the hotcoat to 120, wipe it down, apply, pull tape when it won’t run anymore, use a blade on the tape lines, and leave it as-is (learnt that from Stingray).
Epoxy slurry is a batch thickened with cabosil and some micro balloons (to add color for visibility). If you make a fairly thick mix, you can also install all your embeds with it at the same time.
Resinhead is absolutely right about good EPS blanks, the extra $$ are worth it both for shaping (less tearing with the planer) and them bubbles when glassing.

some of that there foreign grease…made from that bio fuel.

That’s wrong. It’s because you didn’t order it “animal style”.

Yes I did Jamie. I was following instructions from Epoxy 101 DVD.

Hi Resinhead
I got the EPS blank and Resin research epoxy from Greenlightsurfsupply.