acrylic glue leaves tinny bubbles

[bbbobbb]

I am making an acrylic display case and the glue I use always leaves tinny bubbles. I want it to look professional with a nice clear joint. I use Weld-On #3 and sometimes #4. (But mostly #3)
I was told that this is not the best for glueing. when I join the pcs I don't let them move till dryed , can anybody help ? Thanks Bob

[reeftoker75]

First off dont use 3 anymore. Stay with 4 or maybe 16. I use 4 all the time with great results. Have you ever tried using the pin method. The bubble you are getting is from air traped between the joint. With the pin method it help to get a better seem. let me know if you have any more questions.
Brad

[bbbobbb]

Thanks Brad, I do use the pin applicator, So your saying you get no bubbles when using these thicker glues ? I buy a lot from McMaster online, were do you buy your stuff from ?

[nehjo]

I've been experimenting with different glues and have had a range of experiences from no adhesion to burning the plastic. I've also seaarched the Internet, but not too many people are doing what I'm doing (or my search is flawed).

I need to glue mirrored plexiglas together in layers. No angles or corners - just one laer on top of another. The glue cannot deform the plastic, otherwise the mirror finish is warped. For this reason I have not trie anything that says "weld". Also, the back side of teh mirrored plexi is not acrylic - it's some kind of mirror backing.

This thread indicates the products shown here: http://www.ridoutplastics.com/adandcem.html is what I need.

This is the right stuff?

[wildwestpat]

Hi Nehjo

Try using the specialist glues made for use with mirror backed plastic sheet and these are either acid free silicon or acrylic gun type adhesives. I have used the silicon type but it is not perfectly clear and it has shown no signs of lifting or etching the mirror as seen from the front.

For bbbobbb's display cases I have used Tensol a nasty solvent based glue made by ICI which is fluid enough not to trap air but requires some support whilst it sets. Using UV helps with the cure but needs a jig to keep parts together.

Good luck both - regards Pat

[nehjo]

Hi Pat,

Thanks for the pointer - you kicked loose the mental roadblock and I think I found what I need. I was looking for acrylic adhesives, when I should have been looking for mirror adhesives. Well, I'll see how well they work.

I spoke to the plastics manager at a plexiglas manufacturer today. He never heard of what I'm doing and could not recommend an adhesive as most acrylic adhesives attack the mirror backing (causing the distortion I've been experiencing). He recommended 3M 9500PC double sided tape, which is also in their fabricator's guide.

So what I'm going to try is mirror mastic or Liquid Nails mirror adhesive (LN 930). The adventure continues . . .

N.

[wildwestpat]

Hi Nehjo

Difficult to say as adhesives have different names either side of the pond. You should find the mirror grade in one of those DIY outlets just take care as some of those gunable type adhesives give off an acid that acts on the mirror coating and mars the surface.

Regards - Pat

[nehjo]

Hi Pat,

So far . . .
contact cement attacks the mirror
epoxy won't stick to the slick surface
carpet tape works great but is a pain to cut
mirror mastic (the gunable one you mentioned) works well but takes days to cure
DAP adhesive does not stick to the slick side.

I have 2 more adhesives to try out.

The plastic manufacturer I spoke to says they have mirrored plexiglas that comes with adhesive pre-applied. This does not solve my problem now, but they are going to send me a sample for future purchases.

Thanks for the help.

N.