Hot coat problems

Hi everyone,

Just got to hot coating my second long board and have had some problems with uneven drying with the resin… that is all the large flat horizontal surfaces are drying as per normal, but as the resin rolls over onto the rails and down to the tape, it is remaining tacky to the touch and is taking 2-3 days to fully cure…and looks like the wax hasn’t come to the surface. My first board was hot coated with premixed filler coat resin and every hotcoat went without a hitch.

The board has a glass on fin and it has been a nightmare as well with both vertical faces of the fin remaining very tacky and not sandable at all.

Temps have dropped down here coming into winter and the temp this morning when I did the hotcoat was 17deg. celcius or 62 deg.F. Wax in Styrene ratio was 2.5% and catalised at 1.5% due to the lower temp. 30 mins worktime before it kicked which surprised me. The wax solution was mixed for a full 2mins with a drill and stirrer attachment, and once catalised mixed for a further minute. As far as I can figure… I have done everything by the book, but every batch of filler resin I make up, I have an irregular drying problem.

I called my supplier and he has had no other complaints and was unable to offer any help other than to up the ratio from 2% to 2.5% for the lower temp, which I did but had the same outcome. Both the Laminating resin and the Wax in Styrene are from top shelf companies and good quality product, not cheap stuff.

Also, I am noticing quite a lot of pinholes after sanding. I am presuming this could be from the amount of aggetation I am doing? And using the mix pretty well straight away. 

Will letting the mix stand for a time before using it rid the mix of the bubbles, and is there a better way I can mix my resin without creating the bubbles in the first place?

Any help would be much appreciated.


You did one or a few things here, you either had the resin slab off by putting too thick of a hot coat, or you kept messing with the hot coat right before it was goin to kick, and or you didn’t make it a hot enough hot coat.

The quick fix is try putting wax paper on the rails where it’s stil wet, Sometimes this will allow the resin to do it’s thing. The other step is to put a fresh light thin hot hoat over the area.

So let us review…The hot coat didn’t do this on the bottom, or on the flats of the deck because it’s flat and the resin pools, but on the radius of the rail, it decided to slab off dragging the surfacing agent with it to the abyss of the shop floor. So to was either too thick on the rails and the weight and tension pulled it off. his usually shows iself a a brain like looking pattern on the rails


So next time just put eough resin to fill the weave, not pool on top of it. Brush it out, and walk away. Don’t fuss with it…walkaway…brush, brush…walk.  And make sure you put enough catalyst in itso it kicks fast enough so it doesn’t get a chance to slab off.


Pin holes.

Pinholes are caused by pulling too much resin out of the cloth during lamination.

Think of the cloth as a spongee. If you you squeeze all the water out it will pull in air, If you leave it saturated it will drip out, if you wet the spongee and slightly squeeze it, it will be perfectly wet where no water drops out or pulls in water.





Have you fixed your tacky problems yet?  On the tacky parts you can mix a batch of sanding resin and brush it on to the tacky parts.  Once that dries sand as normal.  

If you have Dirty tacky spots on your board you can take Styrene and use that to clean your board before do more SR. 

Know that if you put more sanding resin on sandable sanding resin you will not get a good adheasion between the 1st coat of SR and 2nd.  That would need to be scratched up to get at good bond.  Don’t do this before all of your board has good SR because you will create dust that will stick to the sticky parts and be ugly.

Clear as mud?  


That weather temp is fine for hot caoting.

If it catalysed in 30 minutes then you did not use enough MEKP. I prefer under 10 minutes to kick. Definitely needed to add more catalyst given the lower temp. Maybe needed to add another tablespoon or two of surfacing agent, but the real problem was long curing time and as Resinhead said, the wax is on the floor as opposed to on the board.


I always go generous with the MEKP for hotcaots and glosscoats.




i would like to mention that drew is an experienced glasser, and a faster kick is what he likes best. However its probably a good idea to not shoot it too hot.

 Be the Goldilocks of MEKP. Right in the middle. 

Enough time to work, but hot enough to help make things kick n cure a little faster. 



If you can make a quick vacuum bag,  Resin doesn’t go non tacky exposed to air.  Slip it in a vac bag, suck the air out, and come back later.

everysurfer is correct. Standard poly surfboard resin is known as “air inhibited”. That’s why sanding resin has the wax additive. It forms a barrier to the air and allows a full, non-tacky cure. So, a coat of resin that’s not exposed to air will dry hard, not tacky. There are many ways to achieve this. Wax paper is one, and a vac bag will also work.

Hot coats are called that because the resin is typically mixed “hot”, as compared to a lamination. My guess is similar to what others have stated. Too slow a cure and maybe too thick. It slabbed and the sanding agent didn’t do its thing.


62  don’t get it.  Gives it more time to run off snd slab(as they say)  At least 70 degrees and a hot mix.

Thanks everyone for the feedback. So it seems I can eliminate the concern I maybe had a bad batch of materials first of all, and pretty sure the problem was personal error, in too slow a kick time.

2 - 2.5% wax styrene is what is recommended and I’ve been told by my supplier not to exceed that so I think it simply boils down to not enough MEKP for the cool temp of the day. On average I use around 700-800 mls of resin to hotcoat a 9’8’’ board, so just how “hot” is hot enough to kick in 10 mins @ around 62-65 deg.F. [current daytime temps here] How many mls of MEKP?

Oh…one last question. Whats the best technique to use to hotcoat the glass on fin to still flow out, but not sag being a vertical surface?

Once again guys, thank you for all your replies and help.

…that s where the problem is: too much resin; 220cc per side is all what you need.

yikes… 800 mls… like Reverb said… WAYYYY too much. You should use no more than 300 per side. at 300 ml I would kick it with about 25 cc


When you hot coat the deck, also reach underneath and hot coatt the fin. And then when you flip it over, sand the fin and hot coat again when you do the bottom

And to answer your question about your mixing…

What your doing is pretty overkill.

Just use a stirstick or old egg beater/whisk -  30 seconds is all you need.

OK… so it’s overkill all the way. Too much mixing…too long a kick time… too much resin. 

In reality, I do not use the entire 700 - 800 mls on the board. There is usually 150-200 left over, which again is stupid and wastful, and in the end costly… These couple of boards are my first longboards and estimating quantities of resin is still a bit hit n miss for me. I’ve figured it’s better to have leftovers than not enough, but I think I get the point now… Thanks guys

 Butt, Butt What



much resin. Very glass. Wow.