I’m at a bit of a loss with my hot coat on this board I’m repairing. I’ve attached two photos showing the results of my 240-grit sandpaper I’m using on my adjustable-speed polisher/sander. You should be able to see the buildup of what I think is wax.
The problem is that the resin cures hard in the cup but comes out slightly waxy on the board. When I start sanding, the wax buildup clogs the paper and I get almost no sanding dust.
I even went so far as to buy new sanding resin and catalyst, thinking maybe the mixture was off or the catalyst had gone bad.
The board I’m working on is a PU foam Bing California with a green tint. My only theory at this point is that it might actually be a PE construction (polyurethane with epoxy resin?). There’s no indication anywhere on the board, and this job is turning into a frustrating, paper-wasting situation.
Questions; What was the initial repair? Did you put down cloth with Poly laminating resin. Did you brush on a filler or hot coat of Poly resin, styrene wax solution and MEK? Did you use UV Poly resin? Answer those questions and maybe I can help. Wild guess would be that you are not giving the styrene wax solution enough time to come to the surface and or you may be over doing the amount per volume of styrene wax to Polyester resin. In the latter case it takes even more time to come to the surface.
-Removed damaged fiberglass: Cut away loose glass around 3- to 5-inch areas damaged by the rock jetty.
-Foam repair: Used two-part 8-lb marine foam to plug holes.
-Filled small gaps around the added foam with Q-Cell mixed into sanding resin. I didn’t notice any melting or burning that would suggest the use of EPS foam.
-Lamination: Applied two layers of 4-oz fiberglass cloth with laminating resin. After curing, I sanded the resin and noticed similar wax buildup issues at this stage as well.
-Hot coat: (no added styrene wax, I’m using surboard sanding resin, Mekp catalyst added at suggested ratio, this is not UV sanding resin). Applied a full hot coat over most of the bottom. I have even waited 3 days before sanding.
The wax issue appeared again. Re-coated the board, then purchased new resin and catalyst, and applied another coat; unfortunately, the same problem occurred.
How olds your resin? I had sanding resin that was toast that still mixed, but never cured flat. Would leave similar looking brush marks that would sand out, but were a pain.
I gave up on (moved away from) polyester resin years ago, but I always thought:
laminating resin= no wax, stays slightly tacky for subsequent bonds
sanding resin=contains wax so resin can harden and then be sanded
brushed too long brushed away the wax.three quick passes including side slap enough ,and be quick aboutit should go off when you lift the brush on the last stroke. … ambrose…
You got me, but a few observations. Poly Laminating resin stays tacky and gums up your sandpaper. It doesn’t sand. The only time it is sanded is on a free lap or cut lap. At that stage the lap can be knocked down with a coarse roloc disk and a die grinder or coarse paper and a hard block. Fifty grit most commonly used. That’s the only time laminating resin is sanded. Sanding laminating resin or poorly mixed sanding resin will result in a gummed up sandpaper, just like yours. After laminating a so called hot coat or filler coat is applied over the tacky laminating resin. Sanding resin is nothing more than laminating resin with Styrene Wax Solution added as a pre-mix. If sanding resin sets for a long time the wax rises to the surface or top of the can. Be sure you shake or stir well. Whatever is going on is something you are either doing or not doing during the process. It’s too coincidental that you would buy fresh resin and have the same problem. Has to be something you are doing or some contamination on the board itself. It’s possible that someone may have waxed the board at sometime with furniture or car wax. Solutions like Murphy’s soap causes problems with recoats of any material. PS Ditch that 3M purple paper. Indasa is better quality, lasts longer and doesn’t gum up as easily.
Ohhkeedokles, you’re doing everything right, so a few things-
Yeah, wax is likely. If the residue on the disc is kinda soft, a fingernail deals with it, yep. If it’s hard it may be resin, a different thing. Resin blender X may have overdone it with the wax in the mix (check the lot numbers). So-
It’s a styrene wax, Wipe down the surface with a coarse white rag (colored rags may have styrene soluble dyes, leading to an unintentional tint job) and styrene monomer ( available at a good hardware store). That should get the majority of the surface wax off. Acetone will do in a pinch.
Go with a coarser disc and light pressure, just float it along. Finer discs can heat up more than coarse ones which in turn softens resin and, yeah, you see where this is going. If that’s the Milwaukee sander/grinder it looks like, dial down the speed as well. Again, just float it along on the surface, next to no pressure. I like to just blip the trigger, don’t give it the chance to heat up.
Those giant art gum eraser things they sell for cleaning abrasives are worth having. Especially when you’ve gummed up the last disc you had when the stores are closed. Clean the disc when you see or feel it starting to clog, a gummed up disc REALLY heats things up.
I’m sure you can figure out how I learned this, right?
I stand by my statement that you are most likely doing something during your process that is not right. It’s almost never the fault of the resin. Especially if you are using resin that is fresh and well stirred. The likely hood that you would get two bad batches of resin back to back is nearly an impossibility. You’re doing something wrong. I hear this $#!t all the time about how some noob got a bad batch of resin, but 99% of the time it’s nothing more than “user error”.
When I am doing a large fix with two patches of four-ounce glass, I usually sand down the laminating resin before the hot coat, similar to sanding down a lap. That isn’t my issue. It also isn’t a resin issue, like I stated I bought new resin and Mekp to make sure that wasn’t my problem. I bought from a very reputable source in Southern Cal, and the weather here shouldn’t be an issue either with the mixing.
I also prepped the board with residue remover and the board was sanded prior to each resin application as well, so proper prep shouldn’t be the issue.
I am leaning towards either the sandpaper-like one user stated, or improper use of my Milwaukee sander at too high speeds. On larger fixes, I use the adjustable speed 8 inch disc, this is where I seem to be having my issues. I must be doing something wrong here.
I am going to try different sandpaper and the advice of slow pumping the trigger, sanding with coarser sandpaper.
I have been fixing boards for many years and fully glassed a few, so I am not a true novice, but also wouldn’t consider myself at a level like those replying either.
Thank you all for the replys and the help. I am taking all the advice into consideration and will hopefully fix this issue
The residue on the sandpaper is removable with a blade and to me feels like hardened wax. By your response, I assume this can be caused by too high of speeds and/or pressure from the powerful Milwaukee polisher/sander. I haven’t run into this issue much with my smaller 6 inch orbital.
I have seen a lot of pros use high speed high grit sanding of the hot coat moving from 200 to 600, so I am a little surprised that my sanding was causing this. I was using 240 at the 1 dial setting on the 8 inch sander, but not pumping the trigger.
I also just put another layer down with minimal brush strokes in case the removing the wax with the brush is an issue.
I am going to try your suggestions and thanks again to everyone.
Not to be critical of 3M, they make many great products, but that Purple sticky back paper is nothing but trouble. I am pretty sure they only make that paper in the finer grits, 220, 320 etc. I tried it a couple of times and didn’t like it. And in fact it gummed up like yours. I use nothing but Indasa these days. One sheet lasts as long as three 3M. Doesn’t clog. Indasa is used in practically every glass shop on the West Coast. Industry standard. You must be a master hot coater, because most guys don’t start sanding with fine grits and go to even finer grits. Start with a coarser grit and finish with 220. As long as you don’t have scratches, you’re good to go. If you are using a variable speed Milwaukee just dial it back. Bumping the trigger isn’t necessary unless you are using an old school sander with only one speed. A lot of guys start with 120, 150 or 180. If you can start with 180 you laid down a super hotcoat. I’d like to know where all these pros are. I’ve been in a lot of glass shops, but never seen anyone run through 200(220) through 600 on a hot coat.
Just put an order in for Indasa and appreciate the advice on this. I use the 3M 9x11 sheets and then cut them into discs for my 8-inch orbital sander with spray adhesive to save costs instead of using the more expensive sticky-backed discs. I tend to feather the laminating coat with course grit, but can sand a smoother hot coat with higher grits. I’ve found you can still get a nice glossy finish without doing a full gloss resin coat. I just keep sanding up through the finer grits, then finish with wet/dry 600 or higher, and hit it with some compound and polish. I’m definitely not a pro hot coater, but I’ve learned that a decent sander and some 200+ fine paper can go a long way. When I use coarser grits, I tend to burn through too fast.
I ran a few tests and got some interesting results. I laid down a coat of Fiberglass Source Sanding (waxed) Resin with minimal brushing. After it cured, it sanded perfectly with 240 grit on the 8-inch sander at low speed. There was no gumming, no wax buildup, and plenty of fine sanding dust. Even at higher speeds it stayed smooth with no clogging or residue.
On another half of the board, I used my older hot coat with minimal brushing, and the results were very different. When I pressed my hand to it, the surface still felt slightly tacky, and I could see brush strokes in the resin. The new resin dried much flatter and smoother.
My conclusion is that the sticky results I got from the new resin were probably because I overworked the brush and caused the mix to kick too fast in the SoCal heat. I didn’t know you could essentially remove the wax from the resin with your paint brush.
The older resin was probably not mixed well enough over the year I have had it, or the wax had already separated from earlier use, which caused the uneven, tacky finish. Thanks again for the help here, the expertise is greatly appreciated.
1 I can see by your hotcoat it didn’t lay down flat… I see the brush lines, this tells me the wax didn’t rise. 2) turn the sander down, increase the grit. Heat will make resin more gummy. 3) let the resin cure longer it’s too green… soft. So use a heavier grit like 80, get that top layer of soft off. If you sand through… so what, all you’ll need to do is lay a proper hotcoat down.
So next time, use the right resin, uses enough cat, get the hot coat down in 3 mins max, ie, brush side to side once… tip out nose tail 2 times… it should be thin, and not so thick it will slab off on the rails, don’t let it pool, if you feel it could pool… you put it in too thick…then walk away… stop fussing with it. Just walk away.
