I am using softwood which contains a high number of knots and am worried about these knots staining the paint finish – what could I use?

This is a very common problem that needs to be carefully considered when deciding upon what coating system to apply. Obviously using timber with “no knots present” is a preferred option, but in instances where the use of timber without knots is not possible the following coatings solution is recommended.

  1. The use of a two component polyurethane primer such as Remmers Induline ZL-550 to minimize and slow down the onset of knot staining is a solution.
  2. Another option is to Auger the knot/s just below the substrate surface, overfill with 2 pack filler allow to dry then sand back flat and smooth.

Note: In extreme circumstances where there is a lot of resin present in a knot, knot staining can still occur there is no 100% guarantee against knot staining if they are present and over-coated.

Why do I get what appears to be a pink or yellow discolouration of the Top Coat finish when applied to hardwood?

This is because many of the common hardwoods used in the UK joinery industry contain water soluble tannins. When coated these tannins can then migrate from within the timber and into the water based coatings causing the resulting discolouration of the finish paint, which is particularly noticeable on lighter coloured finishes. In order to prevent this from occurring it is important to isolate any tannins that may be contained within the timber. A specialist coating such as Remmers Induline ZW-400 mid coat is able to perform this isolation task.

Why am I getting bubbles appearing in my dry paint finish?

Coarse grain timbers often have pores in the surface and when the paint does not fill these pores air from them escapes through the drying film causing bubbles to appear. Try using pore filling primers such as Remmers Induline GW-306/360 and mid coats such as Remmers Induline ZW-400. These products flow into the pores replacing the air pockets.

How can I prevent the apparent ‘patchy’, visual appearance of translucent coatings on my joinery items?

In the first instance, the selection of good quality timber and attention to surface preparation using the correct initial sanding procedure will help to prevent this from occurring.

It is still possible however that a variable degree of surface porosity will cause uneven absorbency of the translucent basecoat stain resulting in a ‘patchy’ appearance.

The use of a clear impregnation such as Remmers Induline SW-900 which is a timber conditioning product is a good solution as this product takes up some of this variable absorption.

My coatings seem to take far longer to dry in the cold, wet weather – particularly in winter. Do I just require direct heat to help dry the coatings or is there a better method of drying?

The ambient conditions in any joinery production facility can have a very significant effect on the final finished quality of the coatings. With the majority of high quality coatings now being water-borne it is important that the water contained within them is able to dissipate into the surrounding atmosphere in a controlled and efficient manner.

After the initial period of drying when the coating should be allow to flow out of humid and still conditions, the perfect drying conditions are good air movement and a degree of warmth. Cold conditions allow the air to hold high levels of humidity so the use of heaters to elevate the temperatures in the drying areas is a key issue. Avoid heaters that directly burn fuels producing additional moisture. The simplest rotary ceiling mounted type fans are often very effective as they create air movement but also drive warm air (that has a tendency to rise to the ceiling) back down to floor level.

Why is my translucent finish going milky in appearance when it rains?

Water-borne top coats often contain a small amount of solvent (called coalescing solvent or co-solvent), to help them form smooth films when drying. If the coating is not sufficiently dried or an appreciable skin forms before the coating underneath has had time to dry the co-solvent remains in the finish. This co-solvent goes milky when water gets into the surface of the film. Try to ensure coatings are dried properly in the factory before putting them out in the rain. In most cases the co-solvent will dry out of the coating film over time and the effect will start to dissipate and eventually not reoccur.

I still experience timber movement even though I have put a full coating system on my joinery?

Timber movement is usually caused by a large change in the moisture content of the timber or the use of a timber that is unstable to moisture related movement. Joinery being coated too dry and then being put in UK wet weather is often a cause of movement. Try to coat joinery between 13 and 16% moisture content if possible.

Joinery being placed in a very wet environment with no ventilation is another common reason for excessive movement, try to avoid leaving windows and doors closed on new build sites where there are wet trades present as the moisture from the drying material has no place to go apart from into the timber.

Finally ensure the timber coating is properly cured before sending joinery out on site. For Induline DW-601 Aqua Stop, 48-72 hours is enough time to dry the coating sufficiently to protect the timber from excessive water uptake through the non-cured coating. Some acrylic primers can take as long as 14 days before they can be placed in wet weather conditions otherwise severe moisture uptake can be the result.

Is there a clear coating system available for treating timber in an external location? If so how long is it likely to last?

Clear coating systems are available but they only have limited durability.

Under exposure to ultraviolet light from the sun clear coating systems have a tendency to become brittle. Additionally, as a result of the exposure to UV the surface of the timber is also damaged, although this may be difficult to see with the naked eye. This then results in the surface of the timber becoming de-stabilized which in turn may cause the clear coating to lose its adhesion and thus become detached on a localized or widespread scale.

It is possible to prevent this from happening so quickly by introducing clear UV light absorbing additives into the coating so that they can delay the onset of the inevitable break down of the coating, this can extend the life to perhaps 2 or even 3 years but the cost of such additives can make the clear coating system prohibitively expensive.

For further information on the possible clear coating options we recommend you talk to one of the Remmers technical sales consultants.

Why do pigmented coatings last longer than clear coatings?

The pigments used in exterior coatings are able to absorb and reflect UV light and reduce or slow down the damage to the surface of the timber.

This presence of these pigments in an exterior coating, effectively results in a more durable system with a much longer lifespan of up to 10 years before re-decoration in many cases. As a general rule, the more pigment that is in the coating the longer it will last. The exception to this is very dark coatings which can age prematurely because of solar heat gain. Light coloured opaque coatings do not suffer from excessive solar heat gain and tend to be the most durable of all.

Light translucent coatings are the least durable because they do not have sufficient pigment to absorb high amounts of UV light, never use Clear Translucents externally they do not work.

How do I treat the end grain of my joinery sections?

The end grain section is the most vulnerable area of any joinery item. The absorption of moisture is many hundreds time greater through the cut end grain sections than through the face of the timber. When problems are experienced on exterior timber constructions they are frequently observed near to end grain sections due to moisture uptake. Good sealing of these areas is one of the best forms of joinery protection. Exposed end grain that will be present at the end of sashes and door leaves need to be specially protected by using end grain sealers. The spray coating requires this supplemental assistance. Remmers offer a brush applied coating called Induline SW-910 which is a water tight product especially formulated for sealing the exposed end grain. It is applied between the base primer/stain and the mid coat layer by brush and dries quickly to allow for subsequent spraying.

I am interested in installing some spraying equipment in my production facility – what type of equipment should I use

For efficient spraying of joinery products it is necessary to use a pneumatic pump to apply the products. Environmental Coatings (U K) Limited recommend the use of an air assisted airless spray pump made by WIWA of Germany these pumps can deliver sufficient quantities of paint or woodstain to coat joinery items in a matter of minutes, the use of conventional systems such as gravity fed guns or pressure pots for large quantities of Joinery is not recommended, while these systems may be ideal for lower viscosity products used in the furniture industry they do not deliver product fast enough to coat large items quickly and efficiently. They also struggle to atomize some of the higher viscosity paints and stains used for exterior windows and doors.

For further advice on the most suitable spray pumps and guns contact us at:

Environmental Coatings Technical Sales on: 01623 634281
Email: [email protected]