Before You Paint
Good results from paint application depend on 6 factors:
- Proper planning
- Proper working conditions
- Microclimate/environmental conditions
- Surface preparation
- Correct choice of application method
- Operator skill / workmanship
HEMPEL paints are very tolerant to varying application conditions. The drying/curing rates and overcoating times quoted here are calculated (unless otherwise stated) assuming:
- temperatures of 10oC and 20oC
- a relative humidity (RH) of 60-65%
- a well ventilated working area
As painting can take place over a wide range of temperatures, you may need to adjust the drying and curing times quoted. A good guide is to double the drying/curing time with a drop of 10oC and halve the time with an increase of 10oC (adjust accordingly between these temperatures).
Paint properties change with temperature variation. At lower temperatures paint thickens and may need thinning (always note the correct/maximum thinner ratios and take care not to add more than is recommended). Avoid painting above maximum recommended temperatures as the faster drying/curing rates of the paint reduce the flowing properties which can result in visible application marks; this can also occur when painting in direct sunlight where the surface has a much higher temperature than the ambient (surrounding) temperature.
Check minimum application temperature of the paint you are using as the paint will not cure below this, which will result in poor film formation, poor adhesion between coats and unsatisfactory gloss finishes.
Ideally relative humidity should not be above 65% (this is measured with the use of a hygrometer). A good test is to moisten the surface to be painted and if it dries within 10-15 minutes, it should be all right to paint. Outdoor painting should not take place too early or too late in the day when there is a risk of condensation or dew.
Make sure there is plenty of ventilation to allow the paint solvents to evaporate and the paint to cure properly and avoid blistering.
Choose a day with calm weather to minimise the risk of dust pollution on the paint surface and to allow solvent based paints to flow out naturally, which will improve the final finish.
Make sure you have suitable protective clothing to wear, including gloves and glasses.
Removing old paint
Removing old paints and antifoulings can be made easier with the use of Paint Stripper.
Paint Stripper is a highly effective solvent based paint remover which can be used on most painted or varnished surfaces. Apply liberally by brush or roller onto a dry surface. Leave to work for 15 to 30 minutes until the paint coat dissolves or lifts. Shortest duration for antifoulings, alkyd paints and varnishes, longest for silicone and epoxy. Use with caution on glassfibre and plastics (may harm some thermoplasts). It is recommended a small test patch be performed prior to application and the duration of treatment required is noted. Avoid treating too large an area in one step. It is recommended to place aluminium foil over the treated area to avoid excessive evaporation of the active solvents. Scrape off old paint and clean with hot water and Boat Shampoo. Old or thick coatings may need a repeat treatment.
If you do not wish to use a chemical remover, then:
- a paint scraper is an excellent means of removing paints and varnishes (not antifoulings).
- hot air guns can be used to remove paints and varnishes but not antifoulings. Care should always be taken not to damage/burn the substrate.
- abrading is a good method for removing all paints and antifoulings – for larger jobs it is worth considering employing a contractor! Choose the coarsest grade paper to remove coatings, taking care not to damage the substrate.
Paint coat film thickness is measured in microns (a micron = 1/1000 mm). A wet film thickness gauge can be used when applying the product if coating depth is critical, but normally the surface area to be coated is calculated and the recommended amount of product is applied.
The solvent and solid content varies between products. A coating applied at a wet film thickness of 100 microns will cure to a dry film thickness of between 35-65 micron per coat (depending on the product) as the solvents evaporate. (High Protect is a solvent free product, therefore the wet film thickness is equal to the dry film thickness as no solvent evaporation takes place.)
To help you to get the correct amount of paint on to the surface, our specifications list the literage required per square metre to allow you to calculate quantities needed for the area you will be painting.
Do not try to apply more than the specified amount of product for one coat as this can cause you problems with curing and solvent entrapment which may result in coating failure.
The film thickness of each coat depends on:
- Surface profile – An irregular surface has a larger surface area and will therefore require more paint.
- Surface porosity – Some surfaces absorb more paint than others.
- Temperature – In cold conditions the paint becomes thicker and more difficult to distribute evenly.
- The addition of thinners
- The application method – the table below shows the wet film thickness levels (microns) that you can expect to achieve using various application tools per coat
|Tool / method||wft|
|plastic foam roller*||40 – 80|
|felt roller*||65 – 120|
|mohair paint roller||40 – 100|
|brush*||70 – 110|
|conventional spray||75 – 150|
|airless spray*||60 – 500+|
NOTE: High Protect can be applied at 200 microns+ with application tools*
- Always use a good quality brush which is as large as possible for the job you are doing.
- Avoid using a new brush for a final coat as new brushes have a tendency to shed bristles.
- For best results use a crisscross technique on an area that is manageable. This involves brushing from side to side, followed by up and dow
- Continue until the paint is evenly distributed over the area, with the final strokes being very light (‘laying off’) and in a vertical direction (see Paint Pad below for an alternative way of laying off).
- Paint with the brush at an angle of 45o to minimise brush marks.
- During painting, the paint will start to cure on the brush, cleaning the brush every 30 minutes (approximately) will ensure consistent performance.
- Applying paint with a roller is a fast method of covering larger areas and the use of the appropriate roller head can produce excellent results.
- Where speed of application is more important than surface finish, a short pile mohair roller can be used.
- To produce a better quality finish, small diameter felt and closed cell foam rollers are recommended.
- In all cases use the same crisscross technique as above to distribute the paint evenly.
- After applying by roller, laying off the paint with a brush or pad will give you an improved finish.
- Before using a new felt or mohair roller, wrap masking tape around the roller and then pull off, this will remove any loose fibres.
- Paint can be applied directly with a pad, but it is most effective for laying off paint which has been applied by brush or roller.
- Use the pad immediately after the paint has been applied.
- Draw the pad in one direction only, using vertical strokes to avoid a paint build up which may sag.
- This technique will eliminate almost all application marks and give you an excellent finish!
- It is generally accepted that paint applied by a spray gun will give the best results.
- Where possible the job should be carried out inside a shed to ensure a steady temperature with low humidity.
- A full air fed mask should always be worn when spraying two pack products.
- If you do not have the skill and the necessary spray equipment, it is advisable to leave spray application of paint and varnish to a professional!
For most applications we offer two types of Hempel coating systems to choose from – a Single Pack (Conventional) and a Two Pack (High Performance) system.
It is very important to choose the system which will best suit your requirements and a little time spent before starting could save you a costly mistake.
You should consider the following before making your choice:
Any existing coating
A two pack product should only overcoat another two pack system, whereas a single pack product can overcoat either a two pack or a single pack system. If you decide to change from a single pack to a two pack system you should remove the single pack system first to avoid any risk of incompatibility.
Substrate construction & flexibility
In general two pack systems should only be used on structures where substrate movement is minimal. It is not advisable to put a two pack system on to carvel or clinker built wooden hulls as they require the benefits of the greater flexibility of a single pack system.
Experience of applicator
A two pack paint needs to be mixed thoroughly before use and can then be applied in exactly the same way as single pack paint, giving consideration to the more critical temperature and overcoating times.
Usage & Durability
What usage is the finished surface going to be put to? A two pack finish will withstand a good deal more wear and tear than a single pack.
Length of service
A two pack finish will last, on average, twice as long as a single pack finish