Acrylic dispersion ground adhesion problems with acm panel ApproveRejectUn-ApproveSubscribeUn-Unsubscribe
Question asked 2021-03-07 06:08:25 ...
Most recent comment 2021-03-09 02:34:43
Acrylic
Grounds / Priming
Oil Paint
Hello,
I'm an oil painter that has had good experiences with using ACM panels with an acrylic dispersion ground as a substrate to paint on. However I noticed some adhesion issues with the last batch of panels I primed and was wondering if anyone has any advice on how to move forward, things to consider etc..
My process for preparing the ground has been as follows;
1) Lighlty scuff/sand the polyester surface of the ACM panel making sure not to sand down to the aluminium surface.
2) Clean the surface with 97% Ethanol
3) Apply a first layer of Golden Acrylic 'gesso' mixed with GAC 200 in a ratio of roughly 60/40 - 70/30
4) Leave to dry for 24 hours
5) Apply a second coat of the Acrylic 'gesso' with a little bit of water added to improve consistency for easier brushing on the primer. (Max 10% of water) I don't measure those amounts precisely, doing just by feel.
6) leave to dry for 24 hours
7) Repeat steps 5) and 6) 2 times.
8) Finish the ground with a layer of pure Golden acrylic gesso, no water added.
I live in Belgium and prepared these panels last month when it was pretty cold (wintertime) although the temperatures in my studio were normal room temperature during the day. During the nights it will have beeen colder however, so some temp fluctuation will have occurred. I left the panels to dry for 2 weeks and performed an adhesion test on one of the panels by crosshatching with a blade making little 1/10 inch squares and applying a piece of ducktape and swiftly ripping it off. Result: over 50% of the primer stuck to the tape and came loose...
If I take a palette knife and scratch the side over the delaminated area trying to remove more paint I have to apply some pressure to scratch it off, so there is some amount of bonding but I'm not happy with that result.
How to move forward? Will all of these recently prepared panels be totally unsuitable to paint on? Do I have to worry about more severe delamination of the painted surface in the future? What risks do I take when painting on this surface? Are there ways to improve the current state of the grounds without completely sanding off all of the layers and starting over?
Any advise highly welcomed and appreciated.
Kind regards,
Tom
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Moderator Answer
(mkinsey)
I'm not sure if this is precisely the reason for the poor adhesion described, but since studio temperatures were mentioned: With most acrylic dispersion primers, for a film to achieve the best strength, temperatures should be maintained at 50 degrees F/10 degrees C consistently, including overnight, for several days while the film coalesces to full integrity. (The manufacturer will be the best source for information regarding specific brands, but 50 degrees F is normally the minimum even for architectural/house paints.) If your studio temperatures are dropping below that at night, a tungsten light bulb in a utility lamp might be enough to make a difference, if you can keep one on safely near the primed panels. If you are not able to keep a heat source safely near the panels, it's best not to schedule priming until warmer times. The first few days after application, while residual water and glycols leave the touch-dry film, is the critical interval.
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Moderator Answer
(mkinsey)
To the best of my knowledge, if the acrylic film has been affected by cold temperatures, there is no way to improve it after the coating has coalesced. Keep in mind, however, that we don't know for certain that this is the source of the issue you are describing. Also, I am a studio artist and not a conservation professional so my remarks are just guesses. It does seem to me, however, that the best course of action would be to remove the failed primer and apply a new coat, if it's obvious that the existing primer is not performing correctly.
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Moderator Answer
(brian baade)
Unfortunately, it is very difficult to improve a lack of interlayer
adhesion or cohesion on a solid panel covered with a cured acrylic dispersion
ground. Additional binder added to the surface would not be able to penetrate
through the ground enough to do what you are looking for. Most of it would stay
at the top of the ground creating a slicker surface but with little change to
the adhesion of the ground.
However, there would be no harm in trying. I just doubt that
the results would be what you are hoping for. Repriming may be the only real
option. So sorry.
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Moderator Answer
(ssands)
A couple of things to add to the discussion - duct tape is a WAY stronger adhesive than the tape recommended for adhesion tests of architectural coatings. Regular masking tape is much much closer to what is used. Also, did all the layers of the ground delaminate from the panel, or is there a specific layer in-between? It could be that moisture was pulled down with each coat and there was never enough sustained warmth to get full adhesion in the underfyling layers, or to pull out other volatiles within the paint film, so even though the top of the ground might feel dry, there could still be curing happening within an interlayer level lower down. To test for this, it might be good to first take a panel and keep it in a consistently warm and dry environment for several days and retesting. I have definitely seen films that had so-so adhesion at 2-weeks and be quite strong at a month - so 2-weeks is not necessaily the end of the development of adhesion.
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