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A poster to the Acoustic Guitar Forum posed a question that I wished I knew the answer to:

Can protein glues be used on top of one a other?

Hot hide glue can be used on top of more hide glue, can the same be said for fish glue?

I responded:

Darn good question. I've used fish glue over hide glue without any short-term bad effects, but I don't know about how they work together in the long run.

Afterwards, I realized that he might actually have been asking whether fish glue can be used over fish glue, without needing to remove the original glue, as you can do with hide glue.

In either case, I figured that John Hall would be the logical person to answer this question. Hence this post.

I don't know I never did it. I try not to mix glues if possible.

tippie53 wrote:I don't know I never did it. I try not to mix glues if possible.

Have you used fish glue over fish glue, as one would use hide glue over hide glue, without removing the first application?

yes
what I do is apply a little hot water then work in fresh Glue
I also allow about a 24 hr clamp time. I don't know if you really need to but I figure it won't hurt.
jh

I've done the same thing that John said.

In fact, last summer I decided to conduct a bit of a test to see if fish glue worked over other cured, dried glues. I found found that it will stick to dried CA glue, but I can't remember if I did both or one of Titebond and Duco.

I'll start another test right now of CA, Duco, and Titebond, with fish glue and update the post, so we can be 100% sure.

I've done an experiment with the fish glue.

I had a piece of scrap cherry and pieces of mahogany binding. I spread fish glue, CA glue, Titebond, and Duco, onto 4 pieces of left over mahogany binding. I allowed them to dry completely.

I spread fish glue on top of each of the glues, and put them onto the cherry yesterday afternoon. I allowed them more than 24 hours to cure. Today, I attempted to remove the mahogany binding from the cherry. This is the result:

1. Fish glue to fish glue: The fish glue created a very strong bond. I would have broken the wood if I'd tried to separate it. So, fresh fish glue will bind to dried fish glue.

2. Fish glue to CA glue: The fish glue adhered to the CA glue, but I was able to break the bond easily. Don't use this combination.

3. Fish glue to Titebond: The fish glue created a bond with the Titebond, however I was able to break it with moderate pressure.

4. Fish glue to Duco: The fish glue created a strong bond to the Duco. I was able to break the mahogany away from the cherry, but it took quite a bit of pulling to do it.

From left to right (on mahogany binding)

1. Fish Glue, 2. CA Glue, 3. Titebond (original) 4. Duco Cement (green tube)
All glues dried completely before gluing to cherry.

Mahogany binding with dried glues, re-glued using fish glue to cherry:

1. Fish glue/fish glue 2. CA glue/fish glue 3. Titebond/fish glue 4. Duco/fish glue
Results:

Fish glue to fish glue bond strong. Fish glue to CA glue created weak bond. Fish glue to Titebond created a moderate bond. Fish glue to Duco created a moderate bond.

Many thanks for this. This is useful info and I must see if Sean Large can set us up a reference section for these kind of tips

I'm chuckling because the one combination you haven't tried is the one that I asked about in the first place: fish glue over hot hide glue, and hot hide glue over fish glue.

So, if you get inspired to do another round of experiments, I'd be most grateful if you'd include that in the line-up.

JLT wrote:I'm chuckling because the one combination you haven't tried is the one that I asked about in the first place: fish glue over hot hide glue, and hot hide glue over fish glue.

So, if you get inspired to do another round of experiments, I'd be most grateful if you'd include that in the line-up.

I didn't forget you. I would have tested it, but I have no hide glue to test. I use Titebond. LOL

When going to through old forum posts, I saw a couple of other questions about glue combos. I decided to test those that I have on hand. Should I ever get any hide glue, I'll test it and let you know.