Choosing the right filler for an infill is one of the most frequent decisions in restoration. A mistake here can compromise the mechanical stability of the treatment, alter the visual reading of the artwork, or, in the worst-case scenario, damage the original layers. In this guide, we review the most common types of fillers used in conservation-restoration, their properties, and when each one is suitable.
What is a restoration filler and what is it used for?
Filler is the material used to volumetrically reconstruct gaps, missing parts, or losses in pictorial layers, supports, or polychromy. Its function is twofold: to mechanically stabilize the affected area and to create a base surface on which to apply chromatic reintegration.
A good restoration filler must meet the following criteria:
- Mechanical compatibility with the original support
- Reversibility: it must be removable without damaging the original
- Long-term chemical stability (no volume changes, no acidity)
- Suitable surface for retouching paint
Most commonly used fillers
Traditional protein-based fillers
The classic formula of animal glue (rabbit skin glue or hide glue) with a mineral filler (calcium sulfate, calcium carbonate, or whiting) remains the standard for old works on panel or canvas with traditional preparation. They are compatible with original materials, respond well to humidity changes, and allow for work in multiple layers.
When to use them: artworks from the 13th to 19th centuries with gypsum or carbonate preparation. Ideal when maximum historical compatibility is desired.
Limitation: they are hygroscopic. Not recommended in environments without climate control.
Modostuc
Commercial putty based on calcium carbonate and polyvinyl acetate (PVA). Widely used for its ease of application and good surface finish after sanding.
When to use it: small to medium gaps in works on canvas or panel where maximum reversibility is not required.
Limitation: PVA ages and becomes less soluble. Avoid in high-value heritage works.
Polyfilla Fine Surface
Fine-grained acrylic plaster-based powder putty (also commercially known as Polyfilla Interior). Good dimensional stability, low shrinkage upon drying. It can be applied in thin layers and sanded to achieve very controlled textures.
When to use it: flat gaps in contemporary painting or where a very precise finish is needed. A good general option for C&R.
Lascaux Gesso
High-quality semi-absorbent acrylic preparation formulated for fine arts and conservation. Porous and matte surface, with good adhesion to any support. Once cured, it forms a firm base that accepts oil, acrylic, or tempera retouching without migration.
When to use it: contemporary works where a base with controlled absorption is needed for retouching. Especially suitable when working with aqueous techniques or watercolor retouching.
Lascaux Primer
A denser and less absorbent acrylic preparation than the Gesso from the same brand. Firm surface with less porosity, designed for supports with higher technical demands or when minimal absorption is required in the final retouching layer.
When to use it: gaps where the original work has a very dense priming, contemporary acrylic works, or when the retouching is in an oil medium and no absorption is desired.
Key difference from Gesso: Primer is more impermeable; Gesso is more absorbent. The choice depends on the intended retouching technique.
Quick comparison
| Filler | Base | Reversibility | Ideal for |
|---|---|---|---|
| Animal glue + filler | Protein | High (hot water) | Old works, panel, historical canvas |
| Modostuc | PVA + carbonate | Partial | General use, small gaps |
| Polyfilla Fine Surface | Acrylic plaster | Good | Flat gaps, fine finish |
| Lascaux Gesso | Semi-absorbent acrylic | Partial† | Contemporary works, aqueous retouching |
| Lascaux Primer | Dense acrylic | Partial† | High technical demands, synthetic supports |
† Cured acrylics are not water-soluble; they can be removed with specific solvents (acetone, acetone/alcohol mixtures). Do not confuse "partial" with "non-reversible."
Application tips
- Substrate humidity: lightly dampen the gap before applying protein-based fillers to prevent them from absorbing too quickly and shrinking.
- Thin layers: multiple thin layers are better than one thick one. This reduces shrinkage and provides greater control over the final level.
- Finish level: the filler should be slightly below the original level so that the retouching does not sit on top of the paint.
- Isolate before retouching: a layer of varnish or consolidant between the filler and the retouching prevents color migration and facilitates future removal.
In summary
There is no universal filler. The choice depends on the support, the age of the artwork, the conservation environment, and the type of retouching to be applied. The key question is always: what level of reversibility do I need and what original materials am I working with?
At Innovart, you will find the main filling materials used in professional conservation-restoration. If you have any questions, write to us at info@innovart.art — we respond with technical criteria in less than 24 hours.
Explore restoration materials at Innovart →
Where to buy restoration fillers and putties in Spain
At Innovart, we work with curated conservation and restoration materials and provide real technical advice: if you have a specific intervention and don't know which product fits, you can ask us before buying.
→ View rabbit skin glue at Innovart
→ View Lascaux Gesso at Innovart
→ View all fillers and preparations
Still have doubts about your case? Write to us at info@innovart.art and we will help you choose. This is not a sales form.