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Hi! I have damage to the surfaces of
some traditional gesso panels I made: traditional gesso on muslin on Baltic
birch ply. The surfaces have been damaged. In some cases the muslin fabric
below the gesso has been exposed. In other cases, I hesitate to sand away
scratches in case of exposing more fabric. My understanding is that gesso
layers should be applied while just dry to the touch, and not after the
layers have cured, as is the case with my panels. Any advice on the possibility
of repair would be much appreciated. They will be used for egg tempera, so
surface aberrations are unfortunate given the thin nature of tempera. Thank
Move this whole section up, swapping places with the section above it.
It is true that it is preferred to apply all layers on the
same day. Applying addition layers after the lower layers have completely dried
can result in pinholes. I would try this, dampen the whole surface with water using
a brush. Leave this for a minute or so and then apply your additional layers.
If, after it has completely dried and if you do have pinholes, you can try to polish
them away. Take a lint free cloth, fold it on itself until you have a dauber
about 2 or 3 inches with a smooth surface. Dip this into water and polish the
surface dissolving and redistributing only the uppermost layer or two.
Hopefully this will fill in the pinholes at the surface. Let the ground
completely dry and then use fine sandpaper to complete the smoothing. This may or
may not work to your satisfaction, but it is the only method that I know of.
Brian's covered the topic well. My input would be that I've seen adhesion problems when applying fresh gesso to older layers of gesso - newer layers may be more apt to chip or pop off when the panel is sanded or if it's mishandled. So I would first scratch up the surface of the old gesso using rough sandpaper, to provide some grab for the new gesso (make sure to brush off any dust that generates); then moisten the surface, as Brian suggests, either by spritzing or using a brush (just don't make the surface too smooth if you opt for the brush).
I've had success getting rid of pinholes exactly as Brian suggest - it works well. I've also had success attending to pinholes while applying gesso. Work attentively, in raking light; if you see pinholes start to emerge as you apply a layer, brush at the surface somewhat aggressively, dragging the brush back and forth over the problematic area as if to insist that the pinholes fill in and go away. They often will.
Thank you Brian and Koo,
This is helpful and clear.
One other odd aspect of these surfaces is that there are areas that appear to be pinholes that have emerged after sanding. They were not visible in the upermost gesso layers and I have never encountered the emergence of "hidden pinholes" before. I've noticed the texture of the fabric encourages many pinholes in my first few layers that must be (as you describe) brushed out insistently. Perhaps they were somehow preserved...
I am able to massage hem away with a wet cloth, as you describe. Thanks.
Pinholes can occur at any point in the accumulation of gesso layers; I've seen a perfectly smooth surface, no pinholes, suddenly manifest pinholes in the final layer of gesso (sigh...). It's less usual that pinholes which occur in early layers do not persist into later layers, because once a pinhole appears it tends to continue into the upper layers (unless vigorously brushed out as soon as the pinholes appear, as described in the previous post). Still, it's perfectly possible you had pinholes in an underlying layer, not in the upper layer, and sanded down to them as you describe.
I know you already have the list below, but for the benefit of those who don't I'll paste some of the reasons pinholes appear in gesso panels. Be attentive to these concerns and you should be able to keep the pinhole population under control.
Best wishes from Koo
1. Gesso is too hot. Never heat gesso above 135 degrees, about the temperature of tap water. Use a food thermometer if necessary. Keep gesso just warm enough to stay liquid (i.e. you can comfortably stick your finger into it).
2. Gesso is excessively mixed and agitated, causing air bubbles. Be careful in your preparations. Let gesso sit overnight (refrigerated) to let bubbles dissipate.
3. Gesso is squeezed through cheesecloth. Use a mesh strainer (less likely to generate air bubbles). Or, instead of straining, let gesso sit overnight (refrigerated) to come together.
4. Gesso is applied with sponge brush or air brush. Try alternative application method (brush; or, if gesso has solidified, trowel)
5. Gesso is applied too thickly. Apply thinly. Several thin coats will dry faster and be smoother than a single thick layer.
6. There is too great a temperature differential between the surface of the panel and the gesso; i.e. the panel is cool and the gesso is warm, or vice versa. Don't work in a cold space. Have panels sit overnight in the room in which you'll be working, to get them up to room temperature. Don't overheat gesso.
7. Waiting too long between layers, creating surface tension between the layers that encourages air bubbles. Apply next layer as soon as previous one is dry.
Other suggested remedies for pin holes:
- Add a flow-aid to gesso such as: Liquitex; 1 teaspoon sugar; or 2-4 ounces denatured alcohol.
- Vibrate panel as gesso is applied, to dissipate air bubbles.
- Let gesso cool and set up a bit, then apply with a trowel.
Thanks again Koo. From experience I can attest to most of these points, haha! Cheers. : )
I'm happy that I found this old post as it answers my pressing question about how I might add additional gesso layers to already dry gesso in order to repair damage. To enlarge the problem/discussion, in some areas of this large 4' x 8' panel the damage is so bad that the hardboard is showing through. In this case I can apply new gesso without worrying about adhesion, but in other areas the damage is so great that applying additional layers may make it worse and I'd like to remove the gesso and apply it anew. Would it be safe to soak off the gesso in areas about 2-3" and then reapply? What about the edges next to the dry gesso? Would this be a problem? Most of the panel is just fine and I've already begun the painting so hate to scrape it all off so I'm left with making these repairs. How these damaged areas came to be is another story having to do with making gallons of gesso and losing track of the glue strength in some bottles, so I think some of it did not have strong enough glue. I'm an experienced gesso maker and never had a problem like this before. Thanks so much! Lora Arbrador