I’ve been making quite a few boards recently, all glassed with epoxy (Kinetix) on PU blanks and I wanted to check on the process pre-hot coat that I’ve been using.
As a general rule, I fully sand the lam coats before hot-coats - as I was under the impression that the lam coat needed to be sanded in order for the hot coat to bond well (is this true?) - and when I say “fully sand”, I mean, soft pad #120 overall, #100 or #80 hard pad on hard spots, hand sanding on #120 depending on the quality of my lam job.
I’ve read the archives and there seems to be different opinions based on time between lam and hot coat for example - I never hot coat within 24hrs of the lam coat by the way…
So the question is: if the lam coat is good, then I sand the laps/bumps/rough spots, can I get away with not sanding further and going straight to the hot coat?
Reading your comments I’ve been completely wrong for over 10 years. You need to do what works for you…
What I do is not even close to your method…
So you make several boards lately… good for you. We all need to surf more.
It’s simple: if you work in good weather condition with a Blush free resin you can hotcoat in a 24h Window without sanding. If you are Blush free and wait more lightly key surface for cleaning surface. Hot coat don’t need “structural” adhésion, just to be clean and Blush free. Sanding improve mechanical adhésion, for structural gluing you must sand if precoat resin is no more Green. Main problem could be Blush.
Hey stingray - what is your method? I’m still a newbie so would be great to hear…i’m trying to decrease production time so if I could get away with not sanding the lam it’d be great to know…thanks mate.
I don’t know about that brand of epoxy, but I labor, on rare occasion, under the delusion that the epoxy I use, (Resin Research) works just fine without any undue sanding. Works well enough for me.
Thing is - again, I don’t know your epoxy, but from what I understand, epoxy does not use a “hot coat”/lam-layer like polyester resin, so you don’t really have to wait any longer than you wait to be able to sand down anything you want to sand.
funny stuff Cayman… I guess you need to do some searching… try “first epoxy glass job”… or something like that…
Never need to sand a Lam… maybe knock down some corners… no sanding…
I use kinetix and the resin by itself (when xylene/wax not added) tends to separate when the lam isn’t keyed up. Usually caused by oily fingers, dust etc best to key the board up and fill straight away to avoid contamination. I key the board up with a soft pad on an orbital sander and a light hand sand on the rail. Also helps for a smoother fill coat as some lumps and bumps can be flattened at this stage.
also if you want a simpler option filler coat in polyester resin as kinetix was designed for that. The board below is a kinetix lam with polyester fill coats.
Careful handling, hot box about 8-10 hours and hotcoat adhesion will be good. 2 or more days at room temp and I would sand it as it’ll pick up contaminants during the cure. No different than if you left a poly lam in a dirty area for a week then tried to hotcoat it. Chemical bond vs. mechanical bond isn’t the issue since we’re talking about epoxy over epoxy. It’s really just a surface prep issue and sanding works better than a xylene (or other solvent) wipe down. Not crazy sanding which will effect color work on the lam or even weaken it, just surface prep.
We are always seeing posts about fish eyes, color defects, pin holes, etc. on epoxy. My opinion is that most people just don’t have a clean enough area to allow for a 48 hour+ cure at 70-75 F, or have dirty cloth, epoxy, mixing stuff, etc. Probably both. You can get good poly results in poor conditions just because it cures so quickly. It’s my experience that all kinds of crap happens during long epoxy cures in open areas. This is why I’m big on the hot boxes, faster cure and you can better control contamination within the box. And the board will reach full strength at the higher temp by the time the hotcoat is sanded. I’m not 100% convinced that any epoxy will ever reach full strength at 70-75F based on what the advanced composite guys have told me.
Cured température affect all epoxy. Near all epoxy can blush in bad weather. That’s way RR develop Add f + it help chemical bond between layers and allow a higher hardness at low cure temp. Key surface is the way to go when surface is no more tacky or at least green for structural adhesion. Peel ply can be an alternative.
Resin Research is awesome. Temp over 70F… DRY, CLEAN shop with no air movement… no crap… no greasy engines or Girlfriend doing the laundry… Wash Your Hands@!!! Lam the bottom, flip in 2 hours. Lam top. wait 2 hours. Hot coat top, wait 2 hours…flip and hot coat bottom…Done deal…
Altcomposites.com.au have a pdf for each Kinetix epoxy.
They recommend washing and sanding between coats. Personally I’d be very careful washing a lam coat due to introducing contamination from the water or sponge. Either skip this or use distilled or de-mineralised water. I’ve had success both using de-mineralised water or missing this step. Try to handle the lam coat as little as possible with your hands (oils).
Health and Safety. Use heavy duty nitrile gloves and protective clothing at all times as the resin is rated moderate sensitising. Wash up with citrus cleaner never solvents. Wear a decent mask.
so wrong.
You Aussies are very good surfers… Totally wrong when it comes to epoxy resin…
Thank goodness the USA has Resin Research Epoxy Resin! The only thing that happens between coats is wait time…
No stingray, not so wrong. Dépend technologie use for hardener. Washing lam is common and an obligation with high Blush resin. I saw this many Times in small composites air plane production, even for parts vaccum bag with peelply they used to water scrubb before structural gluing. That’s way Greg Loeher said addF was a real improvement for epoxy at that Time Blush was a real problem with most epoxies.
Hotboxes can be also used for curing painted blanks and straight poly gloss coats, besides UV and epoxy like McDing pointed out. They also will cook out any amine blush since it will be released until full cure which may be weeks or months at normal temps. In my previous post I addressed contamination during cure as the most common problem when re-coating, but blush can also be as Lemat stated.
Amine blush is a surface deposit released as epoxy cures. Sometimes it’s visible and sometimes not. Some epoxy blends blush more than others and some take so long to cure it’s not readily apparent. Blush is water soluble and needs to come off before sanding AND after if re-coating. If not, it will be driven in by sanding and will never come out. Re-coating over blush will cause separations, fish eyes, etc. and probably yellowing. With so many different types of epoxy available now, what does blush badly I don’t know. If you are using a particular brand and not experiencing any blush or related problems, then don’t change your material or process (i.e. temp, cleanliness of your area, timing between coats, etc). If you are having blush problems then start washing. You may not think you have problems until clear hotcoats yellow, or bonding to the lam problems are apparent when dinged. I’m always amazed by the lack of effort to get predictable results. Whether it’s taking an extra process step or spending $20 more to insure the best possible results, many just won’t do it and the same problems keep coming back (or a new one everytime).
Some time ago, Kokua said he washed sanded boards (soap and water) before re-coating or polishing on poly’s. Tried it and it did make a difference at the next step. The surface wax in poly hotcoats is very much like epoxy blush. Once mixed with sanding dust it also comes off with soap and water. I add a final wipe with xylene or acetone in case any crap blew out of the compressor.
Pete, to be clear, you are accelerating the cure with the hot box, not a post cure to increase epoxy strength?
what temperature are you suggesting for the acceleration cure? Do you also do post cure? At what temperature and duration? For my post cure of epoxy I’m raising the temp to 120 for 4 hours and allowing it to gradually come to room temp.
I haven’t found much authoritative info on post curing epoxy surfboards, but I notice the epoxy is more crisp and sands a bit easier. I infer that that the strength has increased.
