Lap Sanding Problem

Hello :slight_smile:

Im new to swaylocks and pretty new to building surfboards.

The shaping goes ok for me, as does the glassing. But when it comes to sanding the laps (free laps in this case), I expose the weave to get them flush and when I hot coat, I can still see the weave at the edge under the hotcoat. It happened on the laps on the board and the fins (glass on fins).

I don’t know if im sanding too much or not cleaning up the laps after sanding them or what…???

Its pretty frustrating and Im guessing its purely cosmetic but id like to know what is going wrong

Its a PU blank with polyester resin


Any help would be much appreciated!



Im a beginner also, just wondering what do you mean by exposing the weave to get them flush? During lamination you should be able to see the weave everywhere. If your laminating and cant see the weave after, your probably leaving too much resin (laps too thick).


It could be your leaving too much sanding dust or particles that can build up along those lines?


It could be your using too much pressure with the squeegee resulting in air coming in along those lines. I realized on my last board I did I was pressing down too hard and air bubbles were forming as I went, to fix that i was trying to press down harder which made them worse. Ha, lesson learned. Too bad you cant just press pause during laminations to look up questions on swaylocks.

or it could also be none of those things, thats my beginner to beginner advice.


I also have a question about the laps, what kind of tools do others use besides sand paper to get the laps down? I have a hard time just sanding the laps. I end up sanding a little foam in areas too which bugs me…




Let the resin harden up a bit more, don't sand it when it's green.  Also use fresh sand paper. Make sure you are cutting the cloth and not mashing it.  if necessary, baste the laps with sanding resin if you have some really crapy areas to pre ...pre prep the sanding.  it all depends on how clear you want to get it.

Also a better lamination job should mean that you really don't need to prep the laps. The only places you should eventually need to prep would be the nose overlap and the tail corners.  But that comes with practice.

Also make sure your laps and fin area when laminating are fairly wet.  Having glass thats full will let you cut the cloth when you prep for hotcoat better than just straight cloth that's wrung out dry with the squeegee. Fairly wet means no voids in between the cloth (air pins), but not so wet that you can't see the top of the weave.

Also the kind of cloth has a lot to do with the clarity and sandability...4oz? 6 oz?  Warp,E or S cloth.

it sounds like your not sanding the laps as much as needed but like what resinhead said it has alot to do with the type of cloth you are using, some pics would help see what your talking about

I used 2 layers of 6oz for each side of the fins. I have some pictures. It could be that I am not pulling enough resin out on to the surrounding areas? It could be the sanding dust too, I shape and glass in the same place (a shed). Thanks for the initial thoughts!

For whitelightning, I think I mean expose dry fibres not weave. I have used a curved surform blade before but I wasnt entirely sure what I was aiming for in the first place!

Sorry about the quality of the pictures

Thanks again

As resinhead says


and try basting the sand area's with thinned out resin.

that will help to saturate the frays

Try and stagger the two layers of 6 on the fins.  First one shorter than the last will help prevent an edge. 

My steps for glass ons are once the fins are glassed on I'll take the the angle grinder with the 2" 36 grit pad and flatten the edges out.  Then do a baste/cheater coat on the fins, fins base and bottom laps all at once with sanding resin with a small amount of surfacing agent mixed in for easy fluffy sanding.  Then give it all a quick sand with 100 to flatten it out. 

Fins, laps into the glassed bases of the fins, cloth folds, and nose all get sanded pretty flush.  Then a full sanding coat over that, then the final sand. 

The little inbetween step allows you to expose high spots that will show weave and the final sanding coat covers it all up.


    Howzit Matt,I think resinhead hit the nail on the head and you are sanding before the resin is hard enough but kensurf and DMP both have good insights to the problem also. If you decide to do a baste coat on the weave use some styrene on them and then baste ASAP since once the styrene dries it won't do any good. You will see the weave disappear when the styrene hits it but get that resin on there now. Aloha,Koua

I coat my boards with a satin clear spray paint after I’ve sanded them. This takes care of any visible glass.

Thanks guys they are really helpful points!

I’ll give them all a try, I’m sure my glassing will get better with practice too.

I’d never thought about basting the laps but that sounds like a good idea :slight_smile:

This is such a helpful site, I’m glad I came across it





That my friend is mashed fiberglass cloth.

Let it kick next time until it's rock hard, and use quality 3M sand paper. 

Thanks for identifying the problem! Really helpful.

Just wondering, when I’m sanding, how far can I sand through?? Should I be aiming to feather the resin in till its flush with the board? Or should I be sanding to expose the fibres and feathering that in??

Sorry if it sounds like a really basic question! I’m gonna do some rail mock ups and practice I think





I think you hit the answer on the head when you typed "feathering".  For poly after the baste I allow myself to be more aggressive and will sometimes use 60 grit on a hard pad for larger boards.  I try not to use heavy pressure, just let the more aggressive grit cut the high spots off with light pressure.  Idea is to take care of any trouble spots before you do the last sanding coat.  If you had a tight lamination on a clean shape your final sand shouldn't have any weave showing.  Emphasis is "shouldn't", there are little tricks and trouble areas that you'll learn to deal with as you sand more boards.  Also swaylocks has a treasure trove of "how to fix its", just type in "weave" and you'll see.  

You can go to town with any grit and get everything perfectly flat but you will cut into the glass, especially on glass ons.  While this will look better cosmetically you're weakening the board.  So cloth folds, nose and tail high spots no problems but fins and laps shouldn't be sanded completely off.  It's a balance of technique, time, and materials.  You can also sand the baste coat and baste it again, sand, sanding coat, final sand, etc.

Also a tip I can warn you about is the pad can gum up with laminating resin from the non basted areas.  Be careful it's easy to heat up the lammed glass with a gummy pad and do a crappy prep sand.  Better to clean the pad or use a fresh one.  A little soak in acetone will take the gum right off.

Lastly the persistence of weave showing can drive you nuts.  You can go back over several times trying to fix it just for it to pop up again during sanding.  Either gloss the whole thing or just let it go and ignore it.