MITRA Forum Question Details

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.

Koo Schadler  

​Hi Eli,

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

Causes of Pin Holes

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.