Wood stain flaking off – finding the causes and restoring it properly
Contents
What you need
Project template “Paint and oil outdoor wood”The short answer: A wood stain does not flake off because it was "bad" but because a film-forming coating sits on wood that is too damp or moves. Moisture gets behind the film – through end grain, cracks or a wood moisture content that was too high when painting – and pushes it off. The only remedy: remove the loose coating completely, let the wood dry to the permissible moisture content (dimensionally stable ≤ 15 %, limited dimensional stability ≤ 18 %), prime if necessary and then rebuild with an open-pore or eroding stain system. Painting over without removing it leads guaranteed to the same damage.
Step 1: diagnosis – why is it flaking off right here?
Before you buy material, clarify the damage mechanism. Three checks are enough, and together they take less than ten minutes.
Adhesive tape test
Press masking tape firmly onto a spot that still looks intact and pull it off with a jerk. If flakes of stain stay on the tape, the coating has no adhesion over the whole surface – then the entire surface has to come off, not just the visibly flaked spot.
Water test
Put a few drops of water on the wood. If they bead off, protection is still present. If they soak in dark within 30 seconds, the wood is already open and absorbs moisture – that is the real cause of the flaking.
Measure wood moisture
Check at several spots with a pin-type moisture meter, especially at end grain and near the ground. Above 18 % no coating may be applied – whatever the product.
Step 2: the six most common causes
| Cause | How you recognise it | What to do |
|---|---|---|
| Film-forming coating on wood that moves | Fence, board cladding or garden furniture was painted with varnish or an opaque thick-film coating. The film cracks at the edges and flakes off over a large area. | Complete removal, then switch to an open-pore or eroding stain. |
| Wood moisture too high when painting | Blisters under the coating, often already in the first year. Typical after rainy spells or with freshly installed wood. | Let the wood dry: dimensionally stable ≤ 15 %, limited dimensional stability ≤ 18 %. |
| Unprotected end grain | The damage starts at the board ends and migrates into the surface. | Seal end grain with additional coats; with a medium-build stain, pre-coat beforehand diluted with max. 10 % white spirit. |
| Missing primer / tannins | Brownish haze on oak, larch, framire; the coating comes away in spots with discolouration. | Use an isolating primer that blocks water-soluble wood constituents. |
| Wrong weather window | Matt, chalky spots or clouding directly after painting. | Apply water-based stain not below +10 °C and not above 80 % rel. humidity; apply solvent-based medium-build stain between +5 °C and +35 °C. |
| Second coat too early | The build-up feels soft, stays tacky or comes away in strips. | Observe overcoating times strictly: medium-build stain approx. 16–24 hrs., primer approx. 24 hrs. (at 23 °C). |
Step 3: the restoration route
Remove the loose coating completely
Remove with spatula and wire brush everything that will come off, then sand the transitions out with sandpaper (grit 80–120). Why: Every loose flake that remains becomes a predetermined breaking point – the new coating flakes off there again within a season.
Check: Scratch across the surface with your thumbnail. If anything still comes away, the preparation is not finished.
Let the wood dry out and check the moisture
After removal allow at least two dry days, considerably more for components near the ground. Why: Moisture has built up under the old film; if it is trapped, blisters immediately form again.
Check: Reading at three spots – dimensionally stable components such as windows and doors ≤ 15 %, limited dimensional stability such as cladding and fences ≤ 18 %.
Prime – if tannins or mixed substrates are involved
On oak, larch and framire, and on components with a metal or plastic connection, first apply an isolating primer. The GORI 23 Multi-Primer blocks water-soluble wood constituents and in addition adheres to zinc, aluminium and rigid PVC. Why: Without a barrier primer, tannins bleed through and undermine the new build-up.
Check: Dust-dry after approx. 1–2 hrs., overcoatable only after approx. 24 hrs. (23 °C / 60 % r.h.) – this time is needed for the full blocking effect.
Rebuild with a suitable stain system
For fences, cladding and play equipment, an eroding thin-film stain is the safe choice: it forms no closed film and therefore cannot flake off. For windows, doors and profiled facades an open-pore medium-build stain is suitable, which lets wood moisture escape. In both cases plan for two coats.
Check: The second coat must cover evenly, without absorbent spots showing up matt – otherwise apply a third coat on these areas.
Which stain system suits your component?
GORI 33 Sensitiv – thin-film stain
Water-based, eroding weathering: no flaking, no cracking. For components with limited and no dimensional stability, also suitable for playgrounds and kindergartens to DIN EN 71 part 3. Usage approx. 80 ml/m². Not for terrace and balcony floors.
View GORI 33 Sensitiv
GORI 88 Compact – medium-build stain
Open-pore alkyd resin gel stain to EN 927-1 and EN 927-2. Thixotropic, so drip-free on vertical and profiled surfaces. Usage approx. 65–80 ml/m² per coat, overcoatable after approx. 16–24 hrs. Not for pressure-treated wood, teak or bangkirai.
View GORI 88 Compact
GORI 23 Multi-Primer – adhesion primer
Water-based acrylate adhesion primer with an isolating effect against water-soluble wood constituents, additionally rust protection on ferrous metals and adhesion promoter on zinc, aluminium and rigid PVC. Usage approx. 5–8 m²/l.
View GORI 23 Multi-PrimerYou will find a complete overview of all systems in our category Wood stain & wood preservation.
Limit values and waiting times at a glance
| Characteristic | Value | Check |
|---|---|---|
| Wood moisture, dimensionally stable (windows, doors) | ≤ 15 % | Meter at 3 spots incl. end grain |
| Wood moisture, limited dimensional stability (cladding, fence) | ≤ 18 % | Meter, also check components near the ground |
| Application of medium-build stain (GORI 88) | +5 °C to +35 °C, dry | Thermometer and weather forecast for 24 hrs. |
| Application of thin-film stain (GORI 33) | not below +10 °C, rel. humidity ≤ 80 % | Hygrometer; also note the night temperature |
| Dust-dry GORI 88 | approx. 2–3 hrs. (23 °C / 50 % r.h.) | Finger test at an inconspicuous spot |
| Overcoatable GORI 88 | approx. 16–24 hrs. (23 °C / 50 % r.h.) | Surface must no longer give way when scratched |
| Overcoatable GORI 23 Multi-Primer | approx. 24 hrs. (23 °C / 60 % r.h.) | Observe the time, otherwise incomplete blocking effect |
Common mistakes – and how to avoid them
- Only touching up the flaked spots. The rest of the film usually has no adhesion any more either. The adhesive tape test decides, not the eye.
- Staining over the old varnish. A stain soaks into the wood – on a closed layer of varnish it cannot do that and stays as a loose film.
- Painting straight after sanding. Under the old coating the wood is almost always damper than the surface suggests.
- Forgetting end grain. A multiple of the moisture gets in through the board ends compared with the surface. Always treat additionally.
- Mixing batches. Both GORI stains require that on one surface only material of the same batch is used – otherwise visible colour deviations arise.
- Painting the component in the sun. The stain dries on before it can level; starting points and flaws arise. Shady side first.
Frequently asked questions
Can I simply paint over flaking stain?
No. The new coating adheres only as well as the layer beneath. As long as old stain can be pulled off with adhesive tape, the damage keeps migrating under the new coating and becomes visible after one season.
Why does a thin-film stain not flake off?
Because it forms no closed film. It weathers by eroding, that is, it wears away evenly. There is no layer that could come away from the wood – that is why renovating later is considerably easier.
How damp may the wood be when painting?
Dimensionally stable components such as windows and doors at most 15 %, components with limited dimensional stability such as cladding and fences at most 18 %. These values are not a recommendation but the application limit of the stain.
Do I always need a primer?
Not necessarily. It becomes necessary on woods containing tannins such as oak, larch or framire, with discolouration from the wood, and at connections to metal or rigid PVC. There an isolating primer prevents constituents from bleeding through.
Can I still paint in autumn?
Only in stable weather. Water-based stains need at least +10 °C and at most 80 % relative humidity – at night too. You apply solvent-based medium-build stains between +5 °C and +35 °C. Autumn fog and dew formation are enough to ruin a fresh coating.
How much material do I need for the restoration?
Allow approx. 65–80 ml/m² per coat for the medium-build stain, approx. 80 ml/m² for the thin-film stain. With two coats and strongly absorbent old wood you had better allow a 20 % reserve.
Further reading
- GORI 33 or GORI 88 – which wood stain suits your project?
- Staining garden timber with GORI 88 – step by step
- Refreshing, cleaning and maintaining WPC decking boards
Questions about your specific component? Give us a call: Baustoffheld, Lindenstrasse 56, 47623 Kevelaer, tel. +49 (0) 2831 - 916 77 03.
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