I plan on painting on rigid, absorbent supports (HDF/MDF/hardboard etc.). Is it okay to speed up the drying time of PVA sizes and acrylic dispersion grounds using a hair dryer? Specifically, is it okay to:
1) Speed up the drying time of the size before applying the next layer?
2) Speed up the drying time of the ground before applying the next layer?
3) Speed up the drying time of the ground before painting?
In any case, how long should I wait before starting the next step/how do I know that the layer is dry enough? I have read the 24 hours drying time recommendation for acrylic ground before beginning a painting, but are there any estimates for the rest?
You mention oil and alkyd, but with acrylic ground, is it fine to apply the next layer after the previous one is dry to the touch?
The acrylic ground I use is usually touch dry within two hours, sometimes even less. Provided the surface gloss is gone and there are no signs of lifting when dragging my hand over the surface, would it be fine to apply the next layer?
It may by OK to speed up the drying of size layers using a fan, although they dry pretty quickly on their own so I am not sure why this is necessary. These are generally very thin in consistency and less likely to have the surface set while underlayers remain fluid and moveable. Even with this I could see the potential for trapping water beneath a coalesced surface film. It is probably OK to apply a second coat of size or even a water born ground after the size feels dry to the touch. I would wait a day before applying an oil or alkyd ground. One should never try to speed up the drying of a ground. This is especially true of natural glue grounds and true gesso which can crack badly if this is attempted. Even with acrylic dispersion grounds, you may get a situation where the surface has dried but the primer beneath is still somewhat fluid.
Yes it is likely fine to apply a second coat within 24-48 hours, depending on the relative humidity of your working environment of course.
That should be fine.
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