glue application and prep

[peter havriluk]

Last week I bumped into a video of someone in the UK building a model for a prize in a fundraiser.  What surprised me (never had considered it before) was that he didn't scrape the paint off joining surfaces, just glued it up.  I have always scraped paint away from glue joints.  Am I missing something and wasting my time?

 

Thanks!

[Jamie Cheslo]

I am certainly no glue expert, but I suspect it is highly dependent upon the type of glue you are using. I don't believe if CA glue, for instance, cares much if it is gluing two painted or non-painted surfaces. Tenax, airplane tube glue and others of their ilk actually weld the plastic pieces together. It seems to me that these types would require direct access to the surface of the plastic in order to bond correctly. So, if you are not certain how the particular glue you are using will react, then a safe rule of thumb would be to always scrape away the paint. This way, you cannot go wrong by erring on the side of caution. Hope this helps. 

[marvin20]

My experience with painted surfaces and CA glue has not bee a good one. It seems that the CA will adhere to the paint and not the plastic and create a weak bond. So if using CA glue, I'd suggest that you clean off the paint between the mating surfaces prior to applying the CA glue. Just my opinion.

[ElectroSoldier]

18 hours ago, Jamie Cheslo said:

I am certainly no glue expert, but I suspect it is highly dependent upon the type of glue you are using. I don't believe if CA glue, for instance, cares much if it is gluing two painted or non-painted surfaces. Tenax, airplane tube glue and others of their ilk actually weld the plastic pieces together. It seems to me that these types would require direct access to the surface of the plastic in order to bond correctly. So, if you are not certain how the particular glue you are using will react, then a safe rule of thumb would be to always scrape away the paint. This way, you cannot go wrong by erring on the side of caution. Hope this helps. 

Its the other way around.

CA glue is a contact adhesive, it will bond the two surfaces regardless of what they are made of, or it will at least try.
That is not to say that bond will be a strong one, it will stick the two painted surfaces together, but that paint might not stick as well as the CA glue will to the plastic surface.
The "hot bond" glues we use these days are different to those of old, they will melt the plastic together, it is best to remove the paint but as the plastic melts so, usually, does the paint but not always.

Its best practice to remove the paint regardless of what glue you use but with the hot weld action glues those glues will usually break down the paint, to it to a mush and the two plastic halves will bond together and the two mush together.

[Jamie Cheslo]

4 minutes ago, ElectroSoldier said:

Its the other way around.

CA glue is a contact adhesive, it will bond the two surfaces regardless of what they are made of, or it will at least try.
That is not to say that bond will be a strong one, it will stick the two painted surfaces together, but that paint might not stick as well as the CA glue will to the plastic surface.
The "hot bond" glues we use these days are different to those of old, they will melt the plastic together, it is best to remove the paint but as the plastic melts so, usually, does the paint but not always.

Its best practice to remove the paint regardless of what glue you use but with the hot weld action glues those glues will usually break down the paint, to it to a mush and the two plastic halves will bond together and the two mush together.

 

I think we are saying the same thing. That is I completely agree with you. Perhaps you were more clear.  But yes, as I mentioned above, it is always safest to scrape the paint away before gluing. I have always done this and never had a problem with de-bonding. cheers!