Most plaster problems come down to one of four root causes: substrate preparation, application technique, environmental conditions, or curing and timing. This guide is organized by symptom so you can identify what's happening and what to do about it.
If your issue isn't covered here or you're unsure, you can schedule a Technical Consultation with a plaster expert.
Cracking
Cracking is the most common concern. The type of crack tells you what's causing it.
Hairline cracks in straight lines. Fine, linear cracks near doors, windows, corners, or along framing lines. They typically appear after the plaster has fully cured.
Why it happens: Building movement — all structures expand, contract, and settle over time. Lime plaster is rigid and mineral-based, so it reflects substrate movement as fine surface cracks.
What to do: These are cosmetic and do not affect durability or breathability. They may reappear after repair if the underlying movement continues. For Tadelakt, see the Tadelakt crack repair article for a step-by-step filling and resealing method.
Y-shaped or spiderweb cracks that appear while drying. Short, irregular, branching cracks that form as the plaster dries — often within hours of application.
Why it happens: Shrinkage cracks caused by plaster applied too thickly or drying too fast. Internal stress develops as moisture leaves the material unevenly.
What to do: Apply thinner coats and control your drying environment (see "Drying Too Fast" below). Severely cracked areas may need to be sanded back and recoated.
Cracks along seams or joints. Cracks that follow a straight line corresponding to where substrate panels meet (drywall seams, cement board joints, plywood edges).
Why it happens: Substrate joints were not properly taped, mudded, and finished to a Level 4 standard before priming. Panels expand and contract at different rates, and unfinished joints telegraph through the plaster.
What to do: The substrate must be properly finished before plastering.
Reinforce joints with fiberglass mesh tape embedded in a quick-set joint compound.
Sand smooth.
Re-prime with Primer Grit before reapplying plaster.
Blistering and Bubbling
What it looks like: Small raised bumps or bubbles forming in the plaster surface during application.
Why it happens: Air or moisture trapped beneath the plaster layer. Common causes include:
Applying over a sealed or non-porous surface that doesn't allow moisture to escape
Aggressive trowel pressure at the wrong stage, pushing air under the plaster
Primer not fully dry before plaster application
What to do:
If blisters are small and fresh, press them flat with the trowel while the plaster is still workable. Avoid overworking blisters — often they go away as the plaster dries more.
If blisters have set, allow the area to dry completely, sand back the affected area, and reapply the finish coat following the full application sequence from that layer onward.
Prevention: ensure primer and each base coat are fully dry before the next step, and use consistent, even trowel strokes without overworking the material.
Delamination and Peeling
What it looks like: Plaster lifting off the wall in sheets or flakes, separating from the substrate or from a previous coat.
Why it happens:
Primer Grit not used — without the mechanical bonding texture, lime plaster has nothing to grip on smooth substrates like drywall or painted surfaces
Incompatible primer — glossy, solvent-based, or high-VOC primers can prevent adhesion
Dirty or dusty substrate — dust, grease, or loose paint between the primer and plaster breaks the bond
Finish coat applied over a base coat that wasn't properly cured — or applied over a surface that was too dry and didn't provide adequate suction
What to do: The affected area needs to be removed, the substrate re-prepared with proper primer and Primer Grit, and the plaster system reapplied from scratch. There is no shortcut — adhesion failure means the foundation wasn't right.
Uneven Color or Blotchiness
What it looks like: Patchy, inconsistent color across the wall — some areas darker or lighter than others.
Why it happens:
Mottling from burnishing — if the basecoat is not flat or has texture, the high spots on the wall receive more pressure when burnishing. This can result in those areas becoming darker in color, and it's more pronounced with deeper shades of plaster.
Plaster hasn't fully dried yet — wet plaster is significantly darker than dry plaster. Areas that are still drying will look different from areas that have dried. This is normal and resolves as the wall dries completely.
What to do:
Wait at least 24–48 hours before judging color. Plaster lightens considerably as it dries and carbonates.
For burnished finishes (Tadelakt, Marble, Stone), some tonal variation is inherent to the material — more burnished areas will appear darker and more polished.
Won't Polish or Burnish
What it looks like: Burnished finishes (Tadelakt, Marble, Stone) remain matte and chalky instead of developing a sheen, no matter how much you trowel.
Why it happens: Burnishing is entirely timing-dependent. The plaster must be at the right stage — firm enough to resist indentation but still soft enough to compress under trowel pressure.
Too early: The trowel sinks into the surface, leaving marks and dragging the material
Too late: The surface is hard and dry; the trowel skips across it and can't compress the plaster
Dirty or nicked trowel: Residue or imperfections on the trowel leave marks instead of polish
Environmental conditions: High temperatures or drafts accelerate drying, shrinking your burnishing window
What to do:
Work in smaller sections so you don't miss the burnishing window.
Check the surface — the plaster should feel firm but slightly cool and damp to the touch.
Use long, even strokes with progressively increasing pressure.
Keep the trowel clean and smooth at all times.
Control the environment — avoid direct airflow on the wall and work in temperatures between 50–80°F.
Surface Too Rough or Won't Smooth Out
What it looks like: The plaster feels gritty, has visible trowel lines, or won't achieve a smooth finish even after multiple passes.
Why it happens:
Material setting up too fast — you're working too slowly for the conditions, or the environment is too hot, dry, or windy
Trowel not clean — dried plaster residue on the trowel drags through wet material
Applying over a coat that's started to set — once the previous coat begins firming up, new material won't blend smoothly into it
What to do:
Mix adequate batch sizes to give yourself working time.
Keep your trowel clean — wipe it frequently with a damp sponge.
Maintain a wet edge and work systematically across the wall.
For Marble Plaster specifically, strain the material through a paint strainer before use to remove coarse aggregate — this step is required for a smooth, polishable surface.
Drying Too Fast
What it looks like: The plaster firms up and becomes unworkable before you can finish smoothing, burnishing, or completing a section. The surface may show shrinkage cracks or a chalky, rough texture.
Why it happens: Direct sunlight, HVAC blowing on the walls, low humidity, high temperatures, or working in a drafty space.
What to do:
Turn off HVAC in the room during application and for the first 24 hours of curing.
Close windows to eliminate drafts.
Block direct sunlight with coverings if needed.
Aim for ideal working conditions: 50–80°F, moderate humidity, no direct airflow.
Drying Too Slowly
What it looks like: The plaster stays soft and damp for an extended period, delaying subsequent coats or the burnishing step.
Why it happens: High humidity, cold temperatures, or poor air circulation in the room.
What to do:
Improve airflow with gentle fans (not pointed directly at the wall).
Maintain room temperature above 50°F — lime plaster curing slows dramatically in cold conditions.
Use a dehumidifier in high-humidity environments.
Do not apply subsequent coats until the previous coat is properly set.
Never apply plaster in freezing conditions — frost can permanently damage the material.
Limewash Looks Flat or Washed Out
What it looks like: The Limewash finish appears uniform and paint-like, without the characteristic mottled, layered depth.
Why it happens: Very light Limewash colors over light primers reflect light evenly, reducing visible tonal variation. Uniform application technique also contributes to a flat appearance.
What to do:
Use diagonal or crisscross brush strokes (X-pattern) instead of straight lines.
Apply a slightly darker base coat and a lighter, more diluted top coat for depth.
Allow each coat to dry fully (12+ hours) between layers for best tonal clarity.
Consider a mid-tone primer instead of bright white under light Limewash colors.
When to Contact Earthaus
For complex situations, schedule a Technical Consultation with a plaster expert (phone, Monday–Thursday).
Questions?
Email support@earthausplaster.com or text 1-800-917-2414 — our team is happy to help.