I was given a couple gallons of no name no info poly resin. I’ve used it to make a few fins and it works fine. Then yesterday I figured I’d seal coat my balsa/palownia composite. Turned out nice. Then today I tried sanding it down…it gums up the sand paper REAL FAST.
So, the question… How can I sand/smooth everything down? Buy lots of cheap sand paper? Also, I plan on glassing it with RR epoxy. Is there some type of prep I need to so the glass/epoxy will adhere properly?
Thanks in advance!
Les
Les a very course grit will sometimes do the trick, but you’d have to watch out for sand throughs. Do you think it is laminating resin? Could just do a thin coat with wax additive, then sand it down.
Sand throughs will be no problem there is no glass under it just the wood. Haven’t used poly resin so not sure what wax additive is… and would the wax additive hender the addhesion of the glass/epoxy that will go on next?
The poly resin you have must be laminating resin. It remains sticky so that the next layers of glass adheres properly. When you want to sand the laminating resin and layers of glass you’ve layed, there needs to be a coat of lamininating resin with wax additive. Otherewise you will be in a frustrated mess getting that thing sanded and it will always be sticky. Sanding additive can be found at a boat supply store or online at foam ez and you want to add about 10 percent to the laminating resin to get a good sandable surface. As for putting epoxy over poly, I’ve tried it but it doesn’t seem to bond very well and chips away, once you start with poly ya end with poly. Hope this helps.
Howzit woodfoot. 10% S.A. is kind of overkill. 6-7% is plenty and the reason I bring it up is the cost of S.A… If you buy a gallon or more the price is not bad but a lot of stores sell 4oz jars for 25% the price of a gallon. If it’s a one board shot then get the small can, if you are doing 10 boards a month then get a gallon and sell or give to friends in need since there is a shelf life to SA. Aloha,Kokua
Thanks WoodFoot and Kokua!
I’ll check at West Marine, closest boat store here, to find the SA.
So, I guess I’ll have to finish this board with Poly? I have enough so that’s OK, I just really like the way epoxy works.
Les
Les, if you do another coat of resin with wax additive, you will need to sand it good to get the next layer to stick. Maybe do a slightly thicker layer and give yourself enough to get a flat finish without messing up the wood. If you can sand the current coat down without adding another coat then wipe it with some acetone before you glass it I think you’d be better off. You’ll have a nice sticky surface for the next layer to grab on to.
I haven’t tried epoxy over poly, but I don’t see why you couldn’t do that. I think some of the others here may know better. Poly over Epoxy tends to have issues with chipping, or not sticking as well, but I think you are planning to glass it, so that would be different. Just leave it really course whichever way you go.
Hey Shark!
I went to the garage this morning and tried sanding again using 80 grit glued onto a piece of foam. Seemed to work OK. Very little stickyness. I have plenty of Poly Resin so will continue glassing with it. I used UV crystals with it last time and it worked pretty good so will put the glass on using UV also. I just ordered more UV, MEPK and sanding agent from Foam EZ so I’ll have all I need to used Poly now. I like using it for my fins!
This board is my next greatest SUP but next I will be using HD XPS Foam for the blank, Gorilla Glue to adhere the balsa/palownie deck/bottom then glassing…using RR epoxy on this one. I know you have used XPS befor… I’ve read the help links/posts.
I’m experimenting using GG to hold the wood down rather than epoxy. I did that on a board a few years ago and it’s lighter and still holding up just fine.
Thanks for your help!
Two possibilities to explain the gummy resin. It is lam resin with no SA. Or, you brushed it too much and the SA didn’t do what it should. Lam resin can be sanded, but you have to use a coarse grit and go slow. Unless you have good experience sanding boards, don’t use a power tool, just hand sand it.
You can determine if you have lam resin, or not. Mix a small batch and pour it out on a piece of scrap wood. Don’t brush it or otherwise disturb the puddle of resin once it’s poured out. When it cures solid, it will have a filmy surface and be really easy to sand with any grit if it’s sanding resin and already has SA in it. If it stays gummy after a day or two and you can leave obvious fingerprints in it, it’s lam resin.
Super Sammy! More info! I’m experienced with epoxy but new to Poly so all this info is GREAT! Thanks, I’ll test it.
Les
Les, I have not tried using GG to adhere the skins to the XPS foam. I use it to glue sections of foam together. I think my brother has used GG to glue skins, but normally we use epoxy with a layer of glass under the wood.
I think the XPS makes lighter boards. I’ve been making them without a wood skin most recently, and before that as the rail on EPS boards. HD EPS will make a light board, but it’s not nearly as hard, so you need the wood skin. XPS doesn’t need the skin because it’s hard like PU, but glassing it is more of a pain. It tends to bubble up if you work in hot ambient temps like I do.
I think you, your brother and I have been paralleling our experiments! I am thinking that using the wood over the XPS MIGHT stop the delaming. Most of my boards I’ve used epoxy and glass (4oz) under the wood. I won’t be starting the XPS board till I finish this one but will let you know how it goes.
It is a known fact that Epoxy adheres very well to Polyester. So you do not have to finish your board with Poly. In boatyards the first layer of fiberglass is almost always done with Poly. Thereafter subsequent lay-ups are done with Epoxy. The opposite is true of Polyester and its adhesion to Epoxy. Most likely the resin you used is laminating resin and will remain tacky. You can solve the problem by appying a hot coat or sanding coat to the resin. This will result in a coat of resin that will not remain tacky and will not gum up your sandpaper. A hot coat is a coat of resin with a wax additive that makes it easy to sand. It is applied with extra catalyst so that it sets up fast.
