Epoxy resin floor sticky or blotchy – causes and solution
Contents
What you need
Project template “Coat garage and cellar floors”In short: If a 2K epoxy coating stays permanently sticky or soft, there is almost always a mixing error – the wrong ratio of base resin to hardener or material that was not mixed through completely. It does not cure afterwards and has to be removed mechanically. Milky haze, blisters and blotches, on the other hand, come from the substrate: too high a residual moisture, lack of load-bearing capacity or oil and grease residue. These cases can usually be restored zone by zone.
Step 1: diagnose first, then restore
The biggest mistake with a failed epoxy floor is to immediately run a second layer over it. Depending on the cause that makes the damage bigger: a sticky layer does not carry another coat, and a blister under the coating keeps growing. So first assign your damage to one of the following pictures.
| What you see | Probable cause | Repairable? |
|---|---|---|
| Surface stays sticky or soft after days, can be pressed in with a fingernail | Mixing ratio wrong or hardener not mixed in completely | No – remove completely |
| Only edges, corners and border strips sticky, middle of the surface hard | Material at the bucket rim not picked up, stirred unevenly | Yes – remove the affected zone |
| Milky-matt haze or clouds, in places a sticky film on top | Moisture or condensation on the surface during curing | Yes – sand and reseal |
| Blisters, craters or pinholes, burst open when driven over | Residual moisture in the substrate over 4 % or air from the concrete | In part – open up, prime, recoat |
| Coating flakes off together with concrete crumbs | Substrate not load-bearing – pull-off strength below 1.5 N/mm² | No – remove the substrate as well |
| Coating can be pulled off over a wide area, concrete underneath smooth and intact | Grease, oil or release agent residue, missing primer | Yes – degrease and prime |
| Dark spots and tyre marks at parking spots | Plasticiser migration from car tyres into a system not designed for it | Yes – chemical-resistant system |
| Cracks in the coating over existing cracks in the concrete | Sealer does not bridge cracks | Yes – crack-bridging system |
The four most common causes in detail
2K epoxy cures chemically, not by drying. If hardener is missing, the reaction is missing – permanently. With the Düfa EP floor sealer it is 4 parts by weight of base resin to 1 part by weight of hardener, 2 to 3 minutes with a slow-running mixer at 300 to 400 rpm. With Sikafloor-264 there are exactly 7.9 kg of component A and 2.1 kg of component B in 10 kg – pouring off by eye goes wrong here. Always mix the complete pack, never estimate part quantities.
After mixing, the reaction runs in the bucket – even if the material still looks liquid. The pot life of the Düfa EP floor sealer at +20 °C is around 2 hours. Anyone who still processes leftovers at the end gets poor flow, streaks and a layer that no longer bonds properly. Better to mix in portions that you can safely work off in the time available.
The limit is clearly stated: maximum 4 % residual moisture. Above that, water vapour presses against the coating from below – the result is blisters and surfaces coming away. Fresh screed and cellar floors without waterproofing are the classics. Sikafloor-150 is expressly approved as waterproofing beneath floor coverings at elevated residual moisture up to 4 % and solves exactly this case.
Coating and substrate form one system: the weakest layer decides. Sikafloor-2510 and Sikafloor-264 both require a compressive strength of at least 25 N/mm² and a pull-off strength of at least 1.5 N/mm². If the coating flakes off with concrete crumbs, the paint was not to blame but the surface underneath. It must be level, fine-textured, firm, dry and free of grease and oil.
Limit values and waiting times to check
| Characteristic | Requirement | How you check it |
|---|---|---|
| Residual moisture of substrate | max. 4 % | CM measurement before coating; alternatively foil test – tape 1 m² of PE foil down tightly, no condensation droplets after 24 h |
| Compressive strength of substrate | min. 25 N/mm² | Cannot be scratched with a screwdriver, no sanding under the thumb |
| Pull-off strength of substrate | min. 1.5 N/mm² | Pull-off test; simple preliminary test: adhesive tape pull-off test releases no concrete particles |
| Mixing ratio Düfa EP floor sealer | 4 : 1 parts by weight | Weigh, do not estimate; stir 2–3 min. at 300–400 rpm until no streaks are visible |
| Pot life Düfa EP floor sealer | approx. 2 h at +20 °C | Note the time when mixing; dispose of the rest after expiry, do not apply |
| Usage Düfa EP floor sealer | 180–220 g/m² per coat | Calculate pack against area – considerably higher usage means applied too thick |
| Usage Sikafloor-2510 | 0.1–0.2 kg/m² per pass | Same calculation; several thin passes instead of one thick layer |
| Usage Sikafloor-150 as primer | 0.3–0.5 kg/m² per pass | Go by saturation; outdoors two passes, brush in the first pass intensively |
| Full loadability Düfa EP floor sealer | 7 days at +20 °C and 65 % rel. humidity | Do not drive on before; cooler means wait longer |
How to restore the surface
Sticky areas have to go – they do not cure afterwards. Mill or grind the affected zone down to load-bearing concrete and vacuum free of dust. Then check the residual moisture before you rebuild: if it is up to 4 %, prime with Sika Sikafloor-150, which penetrates deep into the substrate and in this case acts as waterproofing at the same time. With two passes you broadcast quartz sand 0.4 to 0.7 mm – that gives the top coat mechanical grip.
For the new top coat the load decides. In garage, carport, cellar and hobby room with light to medium load, Sika Sikafloor-2510 is suitable: water-dilutable, low-odour, waterproof and vapour-permeable. Where oils, chemicals and tyre plasticisers attack, the Düfa EP floor sealer is the more robust choice – it is expressly resistant to plasticiser migration from car tyres and does not soften under thermal load. You will find all systems in the category Floor coating & epoxy resin.
Important distinction: A sealer is not waterproofing. Sikafloor-2510 seals surfaces that are driven on, but does not bridge cracks. If the slab has cracks or there is living space underneath that has to stay dry, you need a crack-bridging waterproofing such as Sikafloor-400 N Elastic – which, however, is approved for pedestrian areas only. Both products solve different tasks and are not interchangeable.
Common mistakes – and how to avoid them
- Second layer onto the sticky first one. Epoxy that has not cured carries nothing. The new layer briefly looks like a solution and then comes away together with the soft layer.
- Hardener dosed by eye. With 4 : 1 parts by weight a small error sounds harmless, but permanently tips the reaction. Use scales.
- Stirred too briefly or too fast. 2 to 3 minutes at 300 to 400 rpm are the requirement. A high speed draws in air and produces pinholes, stirring too briefly leaves streaks with unmixed base resin behind.
- Forgetting the bucket rim and corners. That is where the typically sticky border strips come from. Deliberately pick up the walls and bottom of the mixing vessel as well; with Sikafloor-2510 first stir component A mechanically before mixing.
- Applied too thick. The usage figures are not a lower limit. 180 to 220 g/m² or 0.1 to 0.2 kg/m² per pass – several thin layers flow better and cure more evenly.
- Old coating not checked. Before reworking an existing surface, compatibility has to be tested – a sample area saves the complete renewal.
- Driven on too early. Full loadability after 7 days at +20 °C and 65 % rel. humidity. In a cold cellar it takes longer, and tyre marks in the fresh layer remain.
Further reading
If you are rebuilding the surface from scratch: Coating a garage floor with epoxy resin takes you through the complete procedure. For outdoor surfaces that need waterproofing, Waterproofing and coating a balcony is the suitable guide. If the problem lies deeper in the build-up, Bonded screed – build-up and bonding bridge and Applying levelling compound help further.
Frequently asked questions
Can a sticky epoxy floor still cure afterwards?
No. 2K epoxy cures through the chemical reaction between base resin and hardener, not by drying. If the ratio is not right or the hardener was not mixed in completely, the layer stays soft permanently – even after weeks. It has to be removed mechanically.
How do I tell whether the substrate was too damp?
Typical are blisters that burst open when driven over, and surfaces that come away over a wide area although the coating itself is hard. The limit is 4 % residual moisture. As a simple preliminary test you tape 1 m² of PE foil down tightly: if condensation droplets show after 24 hours, the substrate is too damp.
What do milky hazes on the surface mean?
They arise when moisture or condensation gets onto the surface during curing. Unlike a mixing error this affects only the top layer: sanding, vacuuming free of dust and resealing solves the case as a rule.
Do I need a primer before coating?
On absorbent concrete and cement screed yes. Sikafloor-150 penetrates deep, binds the surface and, at residual moisture up to 4 %, acts at the same time as waterproofing beneath the covering. Usage is 0.3 to 0.5 kg/m² per pass, depending on absorbency. Without a primer, adhesion is lacking above all on dense or slightly oily surfaces.
Why do tyre marks show in my garage floor?
There are two reasons for that. Either the surface was driven on before reaching full loadability – with the Düfa EP floor sealer after 7 days at +20 °C and 65 % rel. humidity. Or the system is not designed against plasticiser migration from car tyres; the Düfa EP floor sealer is expressly resistant to that and does not soften under thermal load either.
Can I simply rework an old epoxy coating?
Only after checking. Compatibility with old coatings has to be tested in advance – best on a sample area. In addition the old layer must adhere firmly: if it comes away in the adhesive tape test or sounds hollow when tapped, it has to come off.
Not sure which system suits your surface? Give us a call: Baustoffheld, Lindenstrasse 56, 47623 Kevelaer, +49 (0) 2831 - 916 77 03.
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