Correct use and Application of Paint:
- Incorrect paint for the surface type
- Poorly prepared surface
- Poor application method (although application is simple a few golden rules must not be broken)
Scroll down to read about each of the following:
- Which paint for which surface?
- Surface preparation
- The use of primers
- The use of sealers
- Paint storage
- External conditions when painting
- Safety, Environment and Health
Bastion Paint will usually be dry to the touch within 30 minutes, ready for a re-coat after 4 hours, able to get wet after 10 hours and reaches full strength after 2 weeks (depending on substrate, temperature, number of coats etc).
Which Paint for Which Surface:
Modern acrylic paints, and those manufactured by Bastion Paint, can be used over a range of surface types. Obvious rules must be applied such as Exterior Paints for exterior applications, Roof Paints for roof painting and you cannot just use any paint in a spray application. Normal interior applications do not require the high degree of UV radiation resistance that a good exterior paint has while stain resistance is usually more of an interior requirement.
Depending on taste it may be preferable to varnish or stain wood rather than to paint it. Modern varnishes are designed to penetrate deeply below the surface so multi-layers of varnish rather than a paint primer are required.
For specific preparation and primer requirements of masonry, metals, wood, chalky, flaky, highly permeable and other surfaces just read on.
Surfaces that expand and contract a lot require especially flexible paint. Good acrylic paints have a fair degree of flexibility but get advice if abnormal substrate movement is expected.
The first steps in surface preparation involve cleaning and drying. In almost all cases the correct and thorough application of cleaning and drying will greatly improve the life of paint that is subsequently applied.
Loose paint must be removed from previously painted surfaces. This may require the use of scrapers, sandpaper or even chemical paint stripper. If paint is generally poor then strip the old paint off completely and treat the surface as new.
Cleaning includes the removal of salt, grease, grime and dust.
Caution: Many older paints contain lead. Sanding of these paints is hazardous to your health so wear a dust filter.
Some special requirements for surface preparation are covered below:
Masonry surfaces require cleaning whether previously painted or not. See below if the surface is chalky. If there is any evidence of loose paint it must be removed. Fill defects with an appropriate filler. Fresh plaster and cement require 2-4 weeks to dry prior the application of a primer or bonding liquid. Both fresh plaster and old paint outside near the coast should be sprayed down with a hose to remove salt deposits before painting. These salts will significantly reduce the life of acrylic paint if not removed first as they dissolve in the paint when it is applied.
Galvanized surfaces require a special pre-treatment that involves the application of special cleaning chemicals and washing these off with water before using a specialized "Galvanized Iron Primer". Galvanized surfaces that are not properly treated and primed usually exhibit a white powdery corrosion product (or rust).
Other metal surfaces must always have corrosion products removed as far as possible by sanding down to shiny metal. Any corrosion removal chemicals used must be properly cleaned off prior to the application of a primer.
PVC surfaces such as gutters and drain pipes need to be roughened up with light sandpaper prior to painting. Use an exterior paint with high adhesion characteristics if not using a suitable primer first. If in doubt test the adhesion of the paint by applying a small paint sample first. Plastics usually have a lower surface energy than PVC and special paints and application methods are required.
Enamel Surfaces must be sanded to a matt finish. Any pits in enamel need to be specifically treated. Glossy paints are also referred to as enamel paints. These may require roughening to a matt finish by sanding first. You can check just by painting a very small area and checking the adhesion with sticky tape the following day.
Wood: Knots should be sealed with a special knot sealer and the wood must be sanded smooth prior to the application of a primer.
Roof painting: Clean the roof first with medium to high pressure water or hose pipe and broom. Take care not to damage old underlying paint layers with too high pressure and not to remove any surface treatments by scrubbing with a steel brush. If any fungal growth (mould, lichen etc) is visible use a fungal wash and follow Fungal Wash directions. High quality roof paints such as Ultimate Roof can be applied onto new concert tiles or cement fibre sheets without a primer being applied first but it is may be useful to quickly spray on a clear Bonding Liquid to reduce surface permeability and thus paint usage. Other surfaces such as galvanised steel definitely require a primer first. Any roof which has a paint layer that may have turned chalky definitely requires the use of a Bonding Liquid first.
Smooth surfaces cannot all be roughened. Glass and glazed surfaces are examples and they require special paints with high adhesion.
Chalky and friable (flaky) surfaces require brushing and cleaning. If the surface remains chalky after brushing with a steel brush then bonding with a bonding liquid will be required before painting. Walls previously painted with cheaper paint and exposed to sunlight always become chalky if not painted over soon enough.
Highly permeable and absorbent surfaces: Defect fillers are highly absorbent and regularly cause paint failure outside as they absorb the paint binder. (They also cause the same problem as regular chalky / powdery surfaces.) Avoid the chalky type of defect filler outside and if used apply a bonding liquid before painting over. Roof tiles, old asbestos and cement fibre sheets are highly porous and hence a lot of paint is used. One option is to prime these surfaces first and only when a very high quality 7-year guarantee paint is used is priming not essential.
Allow surfaces to dry: Generally dry is better. Cement plaster must dry for 2-4 weeks before applying a first coat; the longer the better. If this is not done even alkali resistant primers will get broken down by the initial high alkalinity of fresh cement.
Surfaces that are continually or frequently wet from beneath the paint layer will peel. Address the problem first by applying a quality sealant or preferably remove the source of the moisture. Allow the structure to dry and then paint as normal. Moisture beneath the paint layer will cause the paint to de-bond from the substrate and flake or peel off. Try to avoid painting retaining walls that have one side below ground level as these normally suffer form this problem.
The Use of Primers:
Primers should only be applied after correct surface preparation has been completed and not too long afterwards (especially on metals).
Primers are required for various reasons. Corrosion resistance, achieving adhesion to difficult surfaces, penetration bonding and sealing against moisture are common functions of primers. In the case of masonry surfaces, primers need to create a seal against water and penetrate below the surface to bond up loose particles. Surfaces such as crack filler and gypsum plaster tend to be troublesome as they are highly porous and the primer should serve to bond them up. The priming of masonry is more critical on exterior surfaces where sealing against moisture is important whereas for interior surfaces a good quality acrylic is often sufficient as a first coat. Primers used on cement / cement plaster need to be alkaline resistant. It is also advantageous if the primer offers a good hiding power and good smoothing characteristics.
When you see the name "Universal Primer", check which surfaces it is actually suitable for.
Masonry Primers and Bonding Liquids
Always allow cement plaster and other masonry surfaces to dry for at least 2 weeks (preferably 4) before priming. If this is not done the alkali nature of plaster will attack the primer and render it chalky.
Always wash cement plaster off with a hose shortly before priming. This removes salts that have formed during drying/curing as well as sea salt that may have been deposited near the coast.
Alkyd / solvent based binders still dominate the masonry primer market in SA. In Europe, where environmental issues are taken more seriously, customers are prepared to pay for high quality water based primers.
Alkyd primers are usually called ARPs (Alkaline Resistant Plaster Primers). Many can function as bonding liquids too, but generally a bonding liquid is clear (very low hiding power) while Primers are opaque with reasonable hiding power.
A good water based primer will be far more health and environmentally friendly and will often give superior hiding. Always make sure that the first coat on cement plaster is alkali resistant. Remember that alkyd primers are broken down rapidly by UV radiation and should be painted over within a few days. In SA water based primers definitely have a place for interior priming of cement plaster. Avoid the use of cheap Acrylic/PVA paint directly onto cement plaster as peeling after a few years will be inevitable.
Always apply a bonding liquid over gypsum plaster and crack filler before painting. After the bonding liquid has dried these surfaces should not be at all chalky if rubbed with the hand. As a rule, apply a bonding liquid to all chalky surfaces before applying normal paint.
The Use of Sealers:
Sealing vs. waterproofing
When we refer to "sealers" we refer to the prevention of moisture ingression when water is intermittently applied e.g. during rain or washing of the surface. This is quite distinct from waterproofing which is applicable to permanently wet areas, joints, repair of leaks etc. Sealing an external wall cannot prevent rising damp.
What should be sealed
All cement and stone paving should be sealed as this makes it easy to clean, helps keep mould and algae away and prevents the colours from fading. Around a pool the use of sealers helps protect paving against chlorine attack.
Walls that allow damp through from rain or from garden sprinklers can be simply sealed by application over existing exterior paint.
Tile grout can be sealed by simply painting a sealer over it. This will prevent moisture penetration the grout and ending up under the tiles (even from activities such as mopping).
Face brick can be sealed to protect colour of brick and integrity of cement.
Parapet walls are best sealed over existing paint as are all horizontal painted surfaces e.g. tops of pillars.
It is actually quite cost effective in the long term to apply sealer over all exterior paint work to prolong its life. Although seldom performed in SA it is always an option.
What type of sealer?
The best sealers are probably solvent based combinations of silicon and acrylic binders with some special chemistry such as silanes. In SA, water base silicon and acrylic binder sealers are common as they are more cost effective (acrylic sealers are usually a white liquid while silicon sealers are usually clear. Both are clear after application).
- If the area being sealed will ever need to be painted over then definitely select an acrylic sealer.
- Acrylic sealers are usually harder wearing and thus better for paving and driveways (check with the manufacturer before taking a chance).
Glaze coat sealers impart a glossy appearance. Glaze coats are normally high quality sealers that will last well.
Sealers are not normally primers or bonding liquids although they will bond dusty stone etc. Good plaster primers provide new plaster with a sealing function (don't use sealers for this).
Good water based acrylic sealers should utilise a small particle size pure acrylic binder (pure acrylic for UV resistance and small size for penetration). Bastion Paint products utilise a binder called Primal AC339 which gives very good results. Very good water based sealers can be expected to last 5-7 years.
Poor storage can damage any paint. Bastion Paint requires only that it does not freeze and that it is stored with the container lid sealed. Most paints in SA cannot recover to normal if frozen once. Store in a cool dry place as warm environments reduce the paints life. No paint can be stored forever so don't buy more than you need and don't keep any paint for many years. The recommended maximum storage time is normally 1 year.
External Conditions When Painting:
Temperature – avoid too low temperatures.
Take note of the temperature at which paint can be used. If this is not stated then as a rule don't use it below 10°C. The temperature stated applies both to the paint and the surface to be painted. All Bastion Paint paints can be safely used down to 10 degrees and are actually fridge tested.
At low temperatures (below the MFFT or mean film forming temperature) the paint binder becomes immobile and cannot move into the best position when the paint dries. Orientation of the binder molecules and bonding between them suffers. This orientation and bonding is known as "coalescence". Better coalesced paints are more flexible, less prone to cracking and last longer.
Obviously low temperature paints can be manufactured. Nobody ever painted an igloo (that we know of) but some areas in the world require low temperature paints. The coalescing agents used in these paints are normally very expensive or environmentally unfriendly due to their release of VOCs and are not used in our paints. New technology is replacing these coalescing agents with plasticizers and innovative binder chemistries.
Direct Sunlight – avoid painting in strong direct sunlight and on warm surfaces.
Direct sunlight and hot surfaces will lead to the drying rate of paint being too rapid. If drying is too rapid the binder molecules don't have time to coalesce fully resulting in a weaker, less flexible paint film.
Allow hot surfaces to cool first.
Areas that receive strong direct sunlight should rather be painted during cooler periods. As a rule the surface should be below 30°C or preferably below 25°C.
Painting warm surfaces may also result in uneven colour of the dried layer as the temperature gradient within the paint film leads to unwanted movement of certain additives towards the surface.
Rain – watch the weather when painting outside.
This may sound obvious but remember that paint will simply wash off if it is wet immediately after application. 3-4 hours of rain free time is reasonable for acrylic paints while alkyd paints may require longer. Paint goes through a variety of curing and drying processes and usually only reaches maximum strength after a week or two. You may know from leaving your paint brush out overnight without cleaning it that paint is already rather water resistant by the morning.
Very rapid drying paint is available but expensive. Road marking paint often has to be applied to fairly hot black surfaces and needs to dry fast due to traffic requirements anyway. Unfortunately such paints are expensive and frequently not very environmentally friendly.
Always think about safety. Basics must be thought about at all times. A child can get their head stuck in a can or bucket, some solvents and paints are flammable (fortunately not a risk with Bastion Paint) and paint should not be swallowed or ingested. Be responsible!
In the event of ingestion seek medical advice and inform the medical practitioner of the type of paint swallowed.
Acrylic paints are not highly toxic to the environment but they make a mess and will colour water even at low concentration. No fish could ever live long in even the most environmentally friendly paint. Washing of brushes etc. does not put a significant amount of paint down the drain but spills and discarding of un-required paint will be harmful. We manufacture responsibly so please use our products responsibly. Rather return unwanted paint to us than throw it down the drain. If paint must be discarded then allow it to dry fully and dispose of it as solid waste.
Fortunately Bastion Paint only makes paint with fairly low odour and VOCs (the two are closely related). Gone are the days when you need to ventilate rooms well for days after painting, unless you choose old paint technology of course. Areas being painted must still always be well ventilated with at least windows and doors open while you are painting. If there is no draft then the use of a fan will help.
Stop immediately if you should develop nausea or a headache and go outside.
It is interesting that in SA very high odour solvent paints are still used. People smell the odour for 2 weeks afterwards and even sleep with it after painting their bedrooms. We can really do much better for our own health.