hello again! i have been having some huge problems when it comes to sanding, i personally like my boards lighter so i do one 4oz laminate on the bottom as well as the top and finish with a hotcoat, so on my last 2 boards i used rr epoxy and i had some major problems with the first one not curing but quickly found the error of my ways, but the second one every thing went smoothly up to the sanding. so lets start at the hotcoating, so i take a brush and gently spread about 150g of epoxy over the bottom of the board then take my squeege and squeege off the remaining epoxy to use for the other side, after that is all done and cured, i get ready to sand, and as im sanding i notice it starts to get more bumpy as i sand, so i stop putting as much pressure on my power sander and try to move it even more but dosent help much. so i continue sanding then i notice that there are little patches of foam starting to come through. i just dont understand what im doing wrong? any help would be greatly appreciated. also a good thread to bitch about hotcoating and sanding problems
btw, im using 80grit to start then moving to 150grit then to 220grit
okay thanks, that clears up alot, i was at my local shop and the guy was telling me how its important to save epoxy and less sanding to squeege it off.
For epoxy, I squeege the hot coat and then brush it out. Otherwise its like trying to paint with honey.
There’s also a lot to be said for hand sanding with a block when just learning. It will give a truer surface. Then a soft power pad for practice and getting rid of parallel sanding scratches.
If the epoxy starts getting bumpy, you are over heating it, and it isn’t fully cured yet. Semi cured epoxy is like trying to sand chewing gum.
For the amount of resin you have used #80 is too coarse.
If the lam is raising during sanding it is getting too hot.
Try not to be confused with the terminology. Different areas and people call things different things. Hotcoat? well what if I dont make it hot? filler coat? Sanding coat? All exactly the same thing as far as I'm concerned.
If I was using 150g of resin as a hot/fill/sand coat i wouldn't squeegee it off.
Pour, spread length ways while pushing resin into the pits in the weave,nose to tail, sideways brush nose to tail, all the time removing any excess and making sure of full coverage. Then lightly nose to tail smoothing out brush strokes.
You want enough resin so the brush strokes settle, but not so much that the resin slumps and separates.
Good info above. A board sands easily without bumps and burn-thrus if you have put down a good hotcoat. As Ken said it is a good idea to baste or paint a filler coat along the rail lap. Most burn-thrus with the sander occur somewhere along the lap. There is a natural tendency to put more pressure on the sander at the lap as it generally needs more attention than the flats. Blocking and sanding by hand is also a good idea if this is your first board. Takes more time by hand but creates fewer problems. A good hotcoat should not need 80 grit. You should be able to start with 100 or 120 if the hotcoat is good. Sanding a hotcoated 4oz. lam with a sander is for the experienced. Four oz. burns thru pretty damned easy.
Sanding a single layer 4 oz epoxy is fraught with problems due to the heat from the sander and the EPS expanding under it. And, it will be a very disposable board after a short time. If you want lightness, use a vacuum-bagged composite with a 1 lb EPS core.
Prepping the epoxy lam before hotcoating will minimize the sanding needed for the hotcoat. Don’t leave a mess thinking that it will be all addressed when you sand the hotcoat. Better success will be had using cut laps rather than free-lapping on epoxy in my opinion. The inherent stickyness causes lots of pulled threads which makes for more sanding if you leave them under the hotcoat. After lamination and before the epoxy is hard, babysit it for a while looking for problems. After it’s dry, hand or random orbit sand the lap edges and any rough areas, and correct any problems with the cloth. On hotcoating, use a squeegee with very light pressure to distribute the epoxy to the edges; a brush won’t pull the heavy pours around easily and lots of hairs will pull out. Once it’s distributed and thinner, use the brush. Don’t go cheap on the epoxy; I don’t understand this fixation with trying to use a minimal amount on both lams and hotcoats. You wind-up with too much pressure on the squeegee or brush trying to move a tiny bit around and get everything covered. The results are very often dry/underwetted cloth, uneven hotcoats, and lots of sanding problems.
Squeegee first and then use the brush. Brushes shift epoxy like crap but are good for smoothing epoxy that has already been spread. You can sand RR with 150 grit to start with if it’s got additive F in it. Turn your sander down too, it doesn’t need to spin all that fast. Walk up and down the board with your sander at a constant pace making sure you’re allowing the sandpaper enough time to cut through the surface. No more, no less.
