Bubbles in resin lap problem!

[Garyh]

Hi guys,
Just a little problem when I poured my resin lap this arvo on my plaster tool I got a heap of big bubbles forming down near the contact with the plaster.
I let the resin cool so it was rather thick and flowed out of the pot nicely without bubbles. After a few minutes the whole lap was riddled with bubbles.

I left the top of the tool just plain plaster with no sealer etc but the rest has been epoxied and the tool has been curing for a few months now.
Any ideas as to why this has happened? Should I seal the face before I try again?
Didn`t have any problem with my first lap as that was poured onto a glass tool.
Any suggestions or help would be very appreciated!
Ta Gary

[CoombellKid]

Gary,

If you dont get to many answers try joining this group
http://www.atmlist.net/

Where you will find a wealth of info on your type of problem

regards,CS

[Garyh]

Thanks for that Rob!
Have checked out info here before....
I think I know why it happened! After removing the resin from the lap I discovered that there were some bubbles very close to the surface in the plaster that have broken out when the hot resin hit the tool causing the air to expand and bubbles to rise into the resin.
Redone it today, this time heating the tool for a good 10min with a hairdryer on hot to get it much hotter. Also poured the resin on rather hot as well so it was fairly fluid. Still plenty of bubbles came up but most of them came to the surface.
Done a heap of pressing and trimmed the tool for a lap thickness of 5mm.
I hope that is enough? Still some depressions from bubbles remain on the surface but I don`t think that matters?...

cheers Gary

[Roger Davis]

Depends on their surface area. Small ones don't matter too much, but larger ones can reduce the amount of polish in one area. Keep doing hot and cold presses you want good contact. Always seal the plaster with shellac. (The real deal, flakes and metho.) Having done a few mirrors I believe that this is the only way to go. I haven't used a glass tool in over 20 years.

[Garyh]

Thanks Roger for that.
Have cut the channels now and gave it another quick press.
Shall do another one tonight to get better contact...
I painted the polishing tool with a epoxy paint which worked well with the tile tool but doesn`t seem as good with the resin. Must be the volatiles in the resin stopping the paint bonding as well especially where the hot resin ran down the tool sides.
Shall post some pics as soon as I have it ready to start polishing!

[Ian Robinson]

http://stellafane.org/atm/atm_grind/atm_pour_lap.htm

If the pitch is hot enough and fluid enough you might be able to get bubbles all to drift to the top and then maybe if you let it solidify you can skim off the bubble rich top layers.

You might have to keep the pitch very hot and molten for several hours to do this , unless you can centrifuge it somehow while hot and molten. BUT so long that the volatiles evaporate , that will make it hard.

Depends on the viscosity and density of the pitch when hot and molten.

[DavidH]

Gary,

What method are you using to cut the grooves in your lap? I have always had a problem with doing this. The resin tends to clog a hacksaw blade etc, and is too hard to cut with a stanley knife.

Regards,
David.

[Garyh]

I did get most of the bubbles skimmed off and with heaps of pressing 90% of the bubbles are gone.
I shall do what Roger mentions and use shellac next time for the tool.

David, I used my 80w soldering iron to make the grooves initially with a piece of thin brass attached to to the soldering tip shaped in a u shape.
Its slow work and took a hour to do but you get nice grooves and no breakage..After that I have been trimming with a sharp craft knife with a plastic ruler as a guide...If you hold the ruler against the resin square nice and firm and score a few times it breaks very cleanly!
cheers Gary

[DavidH]

Thanks Gary, should have thought of that. Have had a soldering iron within arms length for about ten years!

Regards,
David.