best sandable adhesive for gluing in new foam for repair

General Discussion
1

Hey Swaylockians,

This is my first post here. I finally have a question that I have not seen answered yet, and looking forward to getting your feedback.

I have shaped a few boards, and repaired too many. I’m very confident in my skills, except I continue to have one problem when using donor foam to repair, instead of filler.

This weekend, I ripped the glass off of an 8 foot egg (PU foam), and started to re-shape it into a shortboard. I wanted to glue in a new hunk of foam into the rail because the glass ended up ripping out a lot of foam, and it was too much to use filler for. I used sanding resin and cabosil to glue in the foam. The issue is that the resin sands down slower than the foam, so I am having a really hard time keeping everything smooth and level, and I end up having a raised ridge where the resin is. I have seen many people use this technique, but they seemingly do not have problems with their adhesive sanding down at a different rate than the foam.

From reading through here for a few hours last night, it seems like Gorilla Glue is the adhesive of choice when gluing foam to foam (although it seems like most people are doing this with EPS. I’m surprised that there isn’t much about PU and this particular topic), but I could not find anyone talking about GG sanding properties.

I met the guy who owns and operates Frankenstein surfboards (cannot find a link for his website). For those of you who do not know them, they take foam chunks from old dead boards and glue it all together to make “new” blanks. Some of his shapes had over 100 different pieces of foam glued together, and his shapes are flawless. I asked him how he glued it all together to make it so easy to shape, and he just said “Stringer Glue”. After a bit of research on here, it seems as though he was just talking about poly glue, like GG, but I cannot be certain. Before I try this again, and end up with ugly ridges on my shape/repair, I wanted to put this to the experience of the members here.

I apologize for not having pictures, as I am at work for the day. I will be able to take and post pictures later tonight.

Please let me know what you have tried, what has worked, and what hasnt. I really appreciate all the help.

2

Although not 100% sure (Gorilla Glue is not distributed here in France, or not under this brand), I think that GG is a polyurethane glue. This means that it will behave just like foam does (expanding) and will cure just the same, i.e. with a surface “skin”. You need to clamp your piece of foam to the existing blank if you want to keep a thin glueing line; Otherwise, the glue will expand too much between both foam pieces. Once cured, it will sand just like foam and you won’t get the ridge you’re talking about. Only hangup is that the glue usually isn’t white but that doesn’t matter much for you, does it?

3

Balsa is correct.

If you are wanting to do something like the frankenboards then I would avoid an expanding poly glue like GG.

Most wood working shops will sell a non expanding poly glue - 

Like resin the glue can be tinted as well - it can also be found in a white color. 

4

Thanks Balsa,

 

Thats the assumptions I’ve made doing my reading on Swaylocks, but they were just that, assumptions. So thank you for clarifying!

So, any polyurethane glue should have the same properties?

5

GG also comes in white.

6

Gorilla Glue isn’t as hard as resin, but it’s still harder than foam when it cures. I used it to glue a nose back onto a board when I did a reshape of an old Harbour. It still leaves a ridge because it doesn’t sand at the same rate as the foam. Never again.

7

Your best bet (whatever you use) is to not use too much adhesive.  Cut your replacement chunk so it’s a tight fit.  A bit of adhesive on the hidden part of the seam (I.E. not oozing out all over the place) will hold it in place while you shape it down flush.  If there are any gaps between the patch foam and the original blank, fill them after sanding with resin/cabosil putty. You can fair the putty out at this stage so no further sanding is needed before the fiberglass patch is applied to the outside.  If done carefully, and the entire ding is covered smoothly, this (before fiberglassing) is also a good time to spray some acrylic color with an airbrush if color matching is something worth doing.

8

I have used it for glue lines in a blank - I didn’t have this issue. 

9

Johnmellor,

Perfect. I think that is the advice I was looking for. Much appreciated!

10

What Tate says: no glue, tight fit

And if you do want to use a glue, try the ones in a rattle can, like 3M glues. They dont leave those ridges.

If you go the GG route, use VERY little

In France they sell Axton Pate Legere de finition: a super light weight, ultra white, ultra bright, perfectly sandable filler in Leroy Merlin. This store has world wide branches. Try look for that

Or try to make something yourselves with acrylic paint and microballoons as a basis.

cheers

11

B Pryce, how much resin to cabosil are you using? I use that mix a lot for adding pu foam to dings and use extra cabosil so that it is thicker which seems to allow the cured mix to sand out great. Having the ratio higher on the cabosil side (more cabosil than resin) might help. If you are only using a little bit of cabosil then there will be more resin and will be harder after cured.

12

Like Bluefin, I use more cabosil than epoxy resin and I also use microballons to lighten up the mix.  MBs will turn the resin mix white so it blends better. Also use a lot of MBs in my fin box sets.  Even loaded with MBs the mix is much stronger than the foam that surrounds it and being less resin rich, it reduces heat.

But if you are just gluing foam on foam, no need to slather the resin mix (is that a word?) on thick.  Just a thin line down the centerline of the part so that it covers but doesn’t ooze out.  If you are doing colored glue lines, then you will want a heavy slathering, and oozing.

BTW, I have tried to use white glue (Elmers) with no luck.  It won’t harden between two pieces of foam.

all the best

13

Agree with Wideawake!

Have used GG for many glue ups.

shapes fine

better than resin 

and when it really counts GG is flexable vs resin.

I use pigment to color GG.

just a hassle with the expansion.

Wideawake…

I like and have checked out your suggestion

“Most wood working shops will sell a non expanding poly glue”

Gonna give it a go…

Thanks +1

14

I had the same issue with GG. It left ridges that took longer to sand than the surrounding foam. I would try spakle. I read somewhere on here (can’t find link) that somebody used a glue gun to set their fin box. Maybe that would work for foam as well. Somebody else ever try this?