No sanding between hot coat layers needed for epoxy build?

General Discussion
1

This might be a stupid question that´s already been answered, but I can´t find it in the archives so here goes:

So far I´ve always needed to do two hot coats on each side of the board since my coats always have had pinholes etc. I´ve always sanded the first coat with about 100-120 grit and removed most of the shiny spots before applying the next coat. Could I save some time by just applying the second layer without any sanding when the first one is still tacky or slightly harder than tacky? Two layers of epoxy would mean less sanding than one, right? Or could I even do it after a day or so without sanding? I´m using resin research epoxy.

2

You are correct in that you could add a second coat while the first is still tacky or just past tacky. Less sanding, or twice as much sanding later, depending on how flawless the fill coat goes on. I usually end up doing several fill coats, very thin, with a little sanding in between, (with RR epoxy), but that’s just me.

3

you could try to go really really thin with your first coat, you might ever use a squeegee instead of a brush, and then apply the second “proper” fill coat. made a huge difference for me and also saves weight and amount of sanding you have to do.

Do a search for “cheater coat”, a lot of threads should come up. Also, stingray did a nice write up, it’s called “my first epoxy job” or something along those lines.

But as with most stuff, you’ll likely get a lot of different answers. Some prefer to coat while still tacky (you’ll hear something about chemical bonding), others prefer sanding when the first is dry (physical bonding).

Try different stuff and do what works best for you.

4

For recoat with epoxy the facts are : if dry you need to sand or at least keying with sandpaper on blush free surface, if tacky no prep needed. RR+additif F is a blush free system. RR without additif F is blush free in good weather (hot and dry air).

5

All good advise from the above post. Just keep in mind that a second Hotcoat is primarily used to compensate for errors in the initial Hotcoat or yourlack of experience in the application. So your goal should always be to get down a dust free Hotcoat the first time. But all of the above methods will work. Squeegee on a "cheater coat and then brush a hot coat is a good bet… Lowel

6

Also instead of washing after sanding the lam or using any solvent, instead take a long piece of tape and pull it cross ways for the full length of the board to trap any dust or particles.

7

Ok, I just tried laying out a second layer when tacky, looked decent when I finished it, hopefully it´ll stay that way. I wish I had the skills to do only one hot coat but I have a long way to walk until that happens…Will try the cheater coat next time around.

Thanks for your help!

8

Zinken, how much resin are you using for what length board? GL says use 1 oz per foot of length for short boards. I use a little more to make sure the resin flows over the tape line. Saves some sanding later. But if you are not putting a thorough coat on, it could give poor results. I also do the squeegee cheater coat method mentioned above after sanding by hand lightly with 100 grit.
all the best

9

The way I look at it is the first hot coat gets sanded period and that is the final step in the shaping process. Then the final coat is to seal it up which also gets sanded and glossed if necessary. Two coats over a lam without sanding inbetween will only add weight and more sanding before realizing you need a third coat to to seal all the weave showing from trying to sand two uneven coats instead of one.

10

I´m quite a beginner (a dozen boards) , but get very consistent results by following the advice of the gentlemen above.
I know everybody has slightly different methods, but there are some ways that seem to be widely accepted by the experienced guys here and I tried to follow those advice.

I scuff the glassing lightly with 100grit. No water, no solvents, no dirty fingerprints.
I do one hotcoat/fillercoat which consists of first scraping the board with a hard bondo squeege and a very thin layer of epoxy. Immediatly after that I apply appr. 1oz / ft with a brush.
I leave it alone and let it cure.
Then I do the sanding (100-120 grit) and I totally understand why it is consodered as the last step of shaping.
(This was a big help for me / quite opened up my eyes when I read that description the first time over here and it improved my understanding a lot, thank you for that swaylocks community btw)
Again no solvents, sanding sometimes wet, but last step is always dry for me (avoid contamination and it´s easier to see when a burnthrough is about to happen)
I remove every shiny spots and stop when I have a very even and completely sanded surface.
I never have any fisheyes, pinholes or anything with this routine.

Last step is a thin “fake” glosscoat. Basically the same procedure as the fillcoat, but only 80% of the amount of resin. I leave it as it is (no polishing) as the final state most of the time. Or simetimes scuff it to a semigloss finish.

For one time I tried laying two coats on top of each other while tacky. Much more sanding, not a better result for me. I did not like it at all.
I try to focus on a tight glassjob and a good clean onelayer fillcoat. Least work and best results for me.

11

I use almost twice that amount. My boards are pretty wide, I use 6 oz cloth and I´m pretty new to surfboard making

12

It usually takes 3 thin layers to get above the weave…let it set between coats (ie past the tacky stage)…wipe it over with metho (denatured alcohol) between coats to de-oxidize , and let that evaporate…squeege on the next thin layer , then use a foam roller to work it all over , including around the rails to the other side. If you get any sandthroughs , just complete the sanding job , and do another thin layer . The 3 layers will all harden together perfectly as one over a day or 2 , depending on the weather…it works for me.

13

Greg Loher (sp?) uses crazy small amounts of resin. I use 2 oz/foot for the hot coat and 1.5 oz/foot for the gloss coat, in PE resin terminology. I do like the cheater coat idea and will probably try it this spring.

14

interesting so each layer is squeegeed and the foam rolled? about how much resin per light fill coat?

15

Personally, I don’t like the no sanding method you described.

Firstly, you are going to get lost in the thickness. Some areas may be thicker than others.

Secondly, epoxy sticks fine to dry clean epoxy, just as long as its clean and dry.

Thirdly, it shows. When you sand, you are going to be sanding through the outer coat, and hitting the inner coat. In the right light, you will see the flash between coats.

Here’s the way I like.
Do your first hot coat. Lay out a thick coat onto the lamination. I use Fiberglass Hawaii Thick and Fast for this coat. Let it cure to hard. The longer you wait, the harder the coat gets, and the sandpaper cuts better, and gums up less. Give it 48 hours in a warm room. Just bring it inside if its winter.

Then sand it flat, until you just kiss the weave in spots. Your goal is to make it flat, and get rid of any high and low spots. After the power sander, finish with a light sand with a hard rubber sanding block. Once you kiss the weave, just stop. Don’t sand into the cloth.

Now that its clean sanded, wipe it down with a clean rag. Go to the paint store, buy a bag of painters rags. Straight out of the bag. You don’t want to contaminate anything with a dirty rag. Otherwise, you get fish eyes.
Mix up a small batch of epoxy. maybe 1/4 of what you are going to use for the whole board. Brush it on, squeegee it around, and squeegee it off. You have just gotten rid of any crap that is still on the board. Now immediately mix and apply the finish coat.
This last coat is the finish coat. It can be thinned with a bit of Xylene. It is just a cosmetic coat. You flattened everything on the last coat, so this one you want to be thin.

Wait a full day with the board inside a warm room. Two days is even better. Let the epoxy cure hard. Start you light sanding with 220 or even lighter if the coat is smooth enough.

If you want gloss, then use two part spray afterwards.

EDIT: I should have read MiWie’s post closer. I just about repeated what he already said! Nevermind, and carry on.

16

An average 6ft board only takes me 30 to 40 milligrams per coat…any more and you get runs on the rails…also , the texture left by the sponge roller prevents the resin from forming runs over into the rails…in favorable weather , I can do the next coat in half/three quarters of an hour…it’s amazing how far you can spread a small amount of epoxy resin with a sponge roller…one drawback is that it takes a new roller for each coat…buy cheap bulk rollers…when the weave is covered , the job’s done . If the shaper has finished his shape neatly , and the lam coat is prepared properly , all 3 (or 4) coats will flatten nicely with a 320 grit…then you can go with a finer grit to prepare for a finish coat…a common mistake is using a hot-coat to cover shaping and laminating flaws…labor times are not much more than yer average poly job…just forget quick flip-times , and let the epoxy do it’s thing…the main thing is to get all layers curing together for maximum bond and strength…whenever possible , I let the three coats cure for a week before flat sanding.

17

Interesting descriptions of epoxy finish Here. We can see the two way to go that exist in other industrial application of epoxy too. One is multi thin layer wet on wet, other is thick layer sand and finish. Both are valid and mostly depend of resin thickness and finish clarity. Often first tech is use with clear thin on wood for ultimate clarity.
The only big problems you can have is blush that need to be clean before sand If not wet on wet. 25 years ago when i worked with epoxy each batch blushed. With modern resins no more a real problem.

18

lemat , wet on wet is no good . If the epoxy has not reached an initial set level , applying another coat will disturb the first one , and the overall thickness becomes uneven . … epoxy will keep moving until it sets…and the thicker the coat , the more it will move due to weight and gravity , until the viscosity slowly changes…it may work on a flat level surface with good effect …mind you , I don’t use any type of quick-kik additives , which may change the characteristics of the process…in any case , an overthick hot coat just turns money into dust , and makes an unnecessary mess in my workshop…Epoxy is not poly , yet people keep trying to make it perform like poly…not good IMO

19

You are right when i say wet on wet i better say on taky or green or B stage resin = gel resin still taky, just before blush can form. You can make thick epoxy coat work à la poly with fast tixo resin like RR KK.

20

Yeah , timing is everything…I tend to let go a bit past the tacky stage , so the metho wipes clean , and evaporates quickly… I mix the next coat as the metho is drying…always at the mercy of the weather…the epoxy I use is very sensetive to weather .