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Common Problems with Polyurea Coatings

Due to the installation process of a polyurea coating looking so fast and simple there is a common misconception it does not take much skill to apply. This is not true. To get all the benefits a polyurea coating must be installed by an accredited waterproofing specialist. If not some of the common problems of a polyurea coating are likely to occur.

Incorrect Mix

An extremely frequent problem with a polyurea coating is an incorrect mix before waterproofing commences. If this step is not carried out properly the application which has been coated will suffer from a multitude of problems Below we will look at these common problems in more detail.

Two-component products must always be mechanically mixed, preferably with a continuously adjustable mixing machine or drill.

Use a suitable mixer or whisk of the correct size. As a guideline, the diameter of the mixer or whisk must be at least 1/3 of the diameter of the container in which the product is mixed. First, mix the base component and the hardener together.

Pour some of the mixed material back into the hardener container and mix it in the container until all the hardener has been used.

Next, pour this mixture back into the base component container and mix it again until a homogenous mixture is obtained. When combining partial containers, both components must be carefully stirred and weighed.

Not Adhering to the Substrate

Due to polyurea having an extremely fast curing time it is extremely unforgiving if any mistakes are made. The areas in which mistakes are most often made in relation to adherence include, priming, coating, surface preparation and mixing. Because of the excellent tensile strength of polyurea it will not chip and flake like other liquid systems if adherence is not achieved. Instead it will pull away from the substrate in one large sheet.

Poor Surface Preparation

With a polyurea coating the surface of the substrate must be prepared correctly. It is very frequently the case with non-specialist polyurea coating specialists to see the preparation stage rushed and for a multitude of problems to follow. The most common of these problems are non-adherence as mentioned above or blistering. Below we will detail the correct preparation for a polyurea coating for various substrates.

Surface Contamination

Contamination is a common problem when applying a polyurea coating. This ties in with poor surface preparation which we covered above. If the substrate has been correctly prepared but not correctly cleaned the polyurea will start to pull away from any dust, oil or grease in contact with it.

The degree in which the polyurea pulls away from the substrate will depend upon the amount of contamination. The effects of contamination can also result in the coating blistering. Thermal contraction can accelerate the effects of contamination.

The Conditions When the Polyurea Coating is Applied

Although polyurea coatings perform better than nearly every other system across a wide range of weather conditions and temperatures. It does have some limitations which are not often mentioned. Polyurea is sensitive to moisture if the substrate is within 3 degrees of dew point.

Any polyurea coatings which are applied to a substrate which is within 3 degrees of dew point is likely to result in a failure. The coating will in most cases pull away from the substrate in one large sheet. To avoid this happening do not risk applying a polyurea coating to a substrate which is within 3 degrees of dew point.


As mentioned above blistering in the Polyurea Coating is a common problem. This phenomenon can be caused by several defects. If blistering is identified in a polyurea coating it is important to diagnose the cause to prevent it reoccurring.

Once a blister is identified you should cut it out of the coating and analyse it. If the back of the underside of the blister is smooth. The likely cause is moisture or substrate contamination. If moisture is the cause the blister occurs as the moisture tries to escape the roof.

And if contamination is the cause the blister is caused as the polyurea coating pulls away from the substrate. To fix a blister with a smooth underside the substrate should be thoroughly cleaned. Then re-primed. And finally, the polyurea coating should be reapplied.

If when you inspect the blister the back is rough this is an indicator of either moisture being present between the coating and substrate or the polyurea being isocyanate rich. To rectify this situation, you must ensure the substrate is dry. And check your spray machine if the coating is spray applied.

Once you are sure there is no moisture in the substrate or in the spray machine you can apply primer and a new polyurea coating. If you do find no moisture in either the spraying equipment or the substrate the cause of the blistering is from a poor mix of polyurea.

If the underside of the blister feels gummy upon inspection, this indicates a problem during the mixing process or the primer not curing correctly. It is important to ensure the primer has cured not only dried before applying a polyurea coating. If this blistering is caused by a poor mix of the polyurea, the cause is due to the mix containing too much resin. To fix this problem re-apply a correctly cured primer and apply a properly mixed polyurea resin.

Pinholes in the Polyurea Coating

A polyurea roof can suffer from pin holing. The reason for this is most often when the polyurea is being spray applied to a roof or any other application with a porous substrate which has not been correctly sealed. The process of hot polyurea being spray applied to the substrate causes any trapped moisture within the substrate to outgas and push through the wet freshly applied polyurea coating before any film is formed.

If you notice this problem on your polyurea coated surface the best course of action is normally cheapest to apply another coat of primer to seal the surface completely. On smaller areas, the holes can be filled with polyurethane mastic and resprayed with polyurea once cured.

During summer months, a precaution you can take when applying a polyurea coating is to apply it in a falling temperature rather than a rising one.


Cavities can form when a polyurea coating is applied to thickly around the details on the application which is being waterproofed. These cavities look like melted candle wax along the sides of a candle once it has melted.

The best way to avoid any cavities forming is to apply the polyurea coating to the details of the application prior to coating the main surface.

Blow Holes

Blow holes are most often seen when applying a coating to a concrete substrate. Small hole can be present in the concrete due to trapped air being forced against the shutter as the concrete is poured. To prevent blow holes forming prior to priming the concrete substrate should be filled with an epoxy or cementitious resin. Once dried the surface should be thoroughly cleaned with a jet wash then primer should be applied prior to the application of a polyurea coating.

However, if you notice the blow holes when the polyurea coating is being applied. You should stop and fill in the area which is suffering from the blowholes with polyurethane jointing compound, then re-apply the polyurea coating. It is important to stop as soon as you notice the blow holes as if this problem of blow holes is across the whole roof, you will have many holes to fill. And by the time this is done the recoat window may have shut.