FIBREGLASS What is Gelcoat?
A moulded fibreglass structure is designed (in most cases) to have a colour impregnated into the outer matrix of the resin and
reinforcing This is commonly referred to as a GELCOAT, which is a geli-fied resin (thickened) coating to which a pigment or
colouring has been added The gelcoat product is then applied to the inside of the mould as the first layer so that when the structure is removed the surface is already "coated" with a smooth coloured finish. The reason for the thickener being added, is to prevent the coating from running, or sliding down the mould during the lay-up process which would otherwise leave a less than solid looking finish :
After the gelcoat has been applied, a matrix of clear polyester resin and glass fibres are applied which then fuse to the sticky
gelcoat The more layers of clear resin and glass fibre that are applied, the thicker (and the more rigid) the structure becomes
The number of applications are directly related to the size of the finished article and its intended use.
When the determined number of layers are completed, the inside will have a clear sticky surface. All of the resin applications to this stage have been made with unwaxed polyester resins (including the gelcoat) to ensure that all layers bond together perfectly This is because the unwaxed resins leave some un-reacted sites or "hooks" for the next coat to adhere to. To complete the process a further coat of waxed resin is then applied to the inside. This is called "FLOWCOAT" .The addition of the wax solution bridges the partially undercured layer and gives a crisp hard finish to the inside. As a rule pigments are usually added to the fiowcoat to give a colour and provide a completed colour scheme.
When a fibreglass structure is exposed to weather, it is like all other surfaces, it starts to degrade. Depending on the colour this degradation can become apparent in as little as 18 months from manufacture For example a white boat with a red deck will show significant loss of gloss and colour on the red area whilst the white portion will still look new by comparison. This degradation is retarded by light reflection. White reflects 97% of all light, whereas black reflects only 3%. The greater the reflected light the less UN (ultra violet radiation) is absorbed The cooler the surface the slower the deterioration When this fading occurs, the normal tendency is to cut and polish the surface. This abrasive action removes the oxidised film and leaves the remaining surface with a reduced layer of pigment and rouged (polished) resin. However, this restoration is only temporary. The more the area is treated in this manner, the faster it will deteriorate, this is obvious. If a faded area is left untouched, the oxidised film will form a protective skin over the surface and retard further ultra violet attack. Unfortunately, the visual appearance is so unattractive that the tendency is to clean it off and apply some polish to brighten up the finish. Eventually this constant abrading reduces the finish to such a porous state that further "polishing" is no longer viable Now replacement of the coloured surface is essential In selecting a suitable replacement, it would seem obvious to regelcoat a mistake!!! Gelcoats are, as previously stated, thick stodgy coatings which do not lend themselves to refurbishing by anyone other than a professional applicator Even these people will recommend a sprayed finish of polyurethane, rather than more gelcoat. The reason is obvious when it is pointed out that polyurethane paints (urethanes) have much better handling characteristics and in fact give far more protection against ultra violet, than any other coating.
What about compatibility? Well urethanes have a compatibility with gel coats and fiowcoats NORTHANE for instance is a polyester polyurethane and is the perfect choice for refurbishing a fibreglass structure.
Selecting other types of paint coatings for this job will NOT be satisfactory due to their relatively poor adhesion (by comparison) and will not provide the chemical and water resistance required. NORTHANE does all this and more. For example, the gloss level and long term durability will far exceed that of the original gelcoat, as well as providing better chemical resistance.
Why then is NORTHANE not used in the original construction? The answer is simple, Polyurethanes are not compatible with
polyesters in the lay-up stage and therefore cannot be used in a moulded construction phase. Some manufacturers lay-up in clear gelcoats and then finish with sprayed urethanes, to provide the ultimate finish and durability
In most cases fibreglass refurbishment is only contemplated when the original surface has deteriorated beyond polishing
Where this is the case, it is not enough to just respray with NORTHANE because the surface will be so porous and pitted that some cosmetic rebuilding will be required before finishing can take place. When the oxidised gelcoat has been sanded and
partially removed, the surface will be cratered and have minute voids (or pinholes) in the structure. These have to be filled before the finish coats of NORTHANE can be applied Achieving this can be difficult (and frustrating) because these tiny holes are vessels for retained solvents, moisture, loose dust particles and silicone polish solutions
Any (or all) of these contaminants will create an ongoing problem with the refurbishment
Applying a thick coating over this area will NOT fill the voids because the coating will bridge the holes initially but the air pressure within the holes (as the paint settles) will cause the paint to contract leaving them open again A thin coating will do much the same and still resist filling the pin holes. The net result is the problem remains. What is really required, is a liquid coating than can be physically forced into these areas to fill the voids. This product is SHIPSHAPE PRIMER UNDERCOAT
1. Scrub the area to be treated with a cream cleanser such as JIF or similar domestic product using fresh water to remove contaminants and oxidised gelcoat making sure that the surface does not dry off in the process, (caked residues of cleanser and pigment will clog the pores unless flushed off with clean water). When completed, lay a slow running hose on the surface to thoroughly wet the surface down If this table of water forms a solid uniform layer, the area is then deemed to be clean If the water "breaks" it indicates that contaminants such as silicone polish remain. These areas must be circled with a pencil and re-treated as above Finally wash down with NORGLASS WAX & GREASE REMOVER as specified. NOTE: ANY REMAINING PRESENCE OF SILICONE WILL HAVE DISASTEROUS RESULTS ONCE PAINTING BEGINS Read the following carefully
Silicone Contamination (Fish-Eyes)
Silicone presence alters the surface tension of applied coatings For example a polished car (when wet) will not allow a layer of water to sit evenly all over the surface and will force the water to "bead" or push up into droplets. The water will then "ball-up" and run off. Conversely a car that has not been polished for some time will allow the water to "sheet" and lay evenly over the whole area.
When a coat of paint (of any description) is applied to a surface that has silicone on it, the silicone pushes the coating away from the affected area. Because the behavioural pattern of paint is unlike water, it cannot separate and "ball-up", instead it creates a crater by pushing the paint away from where the contamination is. This is called a "fish-eye" effect. Multitudes of tiny circular craters will immediately appear in the wet coating as the silicone pushes the paint away from the contaminated spots.
At this stage it is too late (short of washing all the coating off before it dries and starting again). If the paint is allowed to dry and then recoated, exactly the same result will occur again and again and again. Therefore it is imperative that all traces of silicone are removed before coating commences. Repeat the cleaning down as described previously until you are sure that the surface is thoroughly clean.
2. Wet sand the area with medium to fine paper making sure that all the residue of sanded material is washed off before it dries. Also ensure that the water "sheets" as described above. If in doubt repeat 1 above.
3. Inspect the surface for defects. Deep scratches or depressions in the gelcoat should be dried off with a hair drier (or hot air blower) and filled with NORGLASS NORFILL EPOXY FILLER. Do not overfill the NORFILL as no shrinkage will occur involving unnecessary sanding. When cured, lightly sand the area and dust off. Minor filling can be done by using a proprietary polyester filler, or bog, as it is commonly referred to
4. Filling pinholes in porous gelcoat. If the surface condition does not have these imperfections continue on to Undercoating (see 7). Where pinholes are present, circle these with a soft pencil as a means of identifying the areas to be treated. A hand held magnifying lens is ideal for identification as pinholes can be hard to detect with the naked eye.
5. Mix up a small quantity of SHIPSHAPE PRIMER UNDERCOAT (200mls maximum) 150mls Base and 50mls Hardener (3.1) Stir well and allow to stand for 10 minutes. Apply to the affected area with a small brush and immediately follow up with a stiff
rubber squeegee, forcing the SHIPSHAPE into the holes. Wipe off the excess paint and repeat the process until all of the hole have been filled
6. Allow to cure overnight and wet sand the residue to a fine finish. If any pinholes still remain repeat stage 5 again. In some cases, this second application will be necessary due to shrinkage and/or missed areas.
7. Mix up sufficient SHIPSHAPE PRIMER UNDERCOAT to cover the area at 10 square metres per mixed litre per coat. If spraying, multiple coats can be applied using a "wet on wet" technique. Brush and roller (short nap) applications must be left overnight to cure before repeating Where more than 48 hours elapses before recoating a light sanding is essential to promote subsequent adhesion
Note: All chemically cured products are solvent resistant and as such are resistant to themselves or other coatings... when left beyond their recoat period. The proposition of applying SHIPSHAPE is to act as a filling mechanism for the surface profile, not to enhance adhesion. For instance, if the overall condition of the surface is good, the finish coats of NORTHANE will adhere positively to the prepared gelcoat area. However, the NORTHANE will mirror any defects in the surface so the decision to paint or fill with SHIPSHAPE, must be made once the preparation stage is completed
8. When the SHIPSHAPE has been applied and allowed to cure, the surface will be seen to have a semi-gloss white finish This is because SHIPSHAPE has an unusually high balance of resin to pigment ratio to maximise adhesion. This also has the benefit of providing a visible indicator for remaining surface defects that are to be sanded smooth before the final finishing coats are applied.
Where a tinting of the SHIPSHAPE is desired to change the colour (from white) NORGLASS PIGMENT PASTE can be added at the mixing stage to improve coverage, (50g per mixed litre). Alternatively decorative tinters may be added in small quantities For a mirror finish fine sand to remove all traces of gloss
Note: NORTHANE can not be applied over a wet film of SHIPSHAPE, as they are incompatible in this condition. The SHIPSHAPE must be allowed to cure before continuing.
9. Mix up sufficient NORTHANE Gloss to cover the area at a rate of 10 square metres per mixed litre, per coat. If spraying, multiple coats can be applied using a "wet on wet" technique. Brush and roller (short nap) applications must be left overnight to cure before repeating Where more than 48 hours elapses before recoating, a light sanding is essential to provide adequate adhesion. If this is not done, the next coat of NORTHANE will not adhere satisfactorily to the previous one
The use of yellows and oranges are notoriously difficult to obtain coverage when applied over a less than uniform
background. Any patchy areas will still show through after several coats of NORTHANE or WEATHERFAST enamel. This is a problem with all yellow and orange lead free pigments regardless of manufacturer. The only solution is to make sure the background colour is completely uniform before painting i.e. uniformly white, grey, blue etc.
NORTHANE like all other chemically cured polyurethanes will give a fast "set up" time However, the finish will still be very
susceptible to atmospheric moisture for some 6 hours after the final application. Therefore, it is essential that the coated area is adequately screened away from dew for at least 8 hours after the job has been completed. When applied in the open,
NORTHANE should be left to obtain a dust free stage (usually 2 hours) then a tarpaulin or cover must be erected to protect all
surfaces that are less than vertical otherwise the impinging moisture laden air will affect the gloss and turn the finish flat For surfaces that are to be immersed in water, 72 hours should elapse before immersing
* Where NORTHANE is brushed and rolled it will "set up" very quickly. To avoid delays in application all areas should be suitably masked up to reduce the work time and to minimise the strokes required by brush or roller NORTHANE should be applied (in these circumstances) as a full unadulterated coat with as few strokes as possible-
* Where dust or other deposits stick to the finished job, allow the coating to mature for 48 hours before carefully removing the
imperfections. Use only a cutting compound such as toothpaste as any coarser abrading of the surface will reduce the gloss level below that of the rest of the job No amount of polishing can restore the area to that of the original NORTHANE finish If cutting and polishing is carried out a whole panel must be done otherwise the difference will be noticeable.
* Where two or more colours of NORTHANE overlap each other use only fineline masking tape or allow 48 hours to elapse before using conventional masking tape, otherwise imprinting of the tape may result. Note: NORTHANE must be handled carefully for the first 48 hours.
* Brush or roller applications of NORTHANE do not present the same health hazards as for the sprayed finish (in well ventilated areas) and therefore only require normal good housekeeping techniques and sensible precautions being used-
By definition OSMOSIS is a permeation through a membrane. This is a natural phenomenon created by pressure trying to equalise the concentrations of two solutions through the membrane. In the case of fibreglass boats the cause begins at the time of manufacture. Glass fibre stacked or stored in an environment that does not have a humidity controlled facility runs the risk of transferring moisture contaminated strands into the moulded matrix. When these strands become encapsulated within the glass structure the moisture settles into convenient voids created by the random distribution of the mass (See fig. 1.) To understand this process observe what happens when warm breath meets a cold glass mirror. As the condensed vapour mixes with residuals of the polyester it produces a pocket of concentrated solution
At this stage Osmotic pressure is created. Within the moulded matrix there are pockets of very concentrated solutions whilst on the outside, the seawater (also a solution) is trying to equalise this force. Where these moisture "cells" are close to the outer surface or able to "wick" down glass strands to reach the gelcoat layers the reaction starts to take place. (See fig. 2)
Because the concentration of the solution is greater within the hull, the direction of pressure is outwards into the seawater When the pressure exceeds the containment by the membrane (gelcoat), the bubble bursts and equalises the force. (See fig. 3). At this point the reaction is over. However the seawater is now able to permeate the mass in the same "wicking" action and could theoretically find other "sites" for further osmosis cultivation The potential for this is of minor concern and should be put into perspective. The Polyester resin crosslinking process is waterproof and structurally sound. This mass (surrounding the reinforcing fibres) ensures the integrity of the structure. ..In other words the "matrix" of resin and reinforcing cannot be compromised further. The waterproofing property and adhesion to the glass reinforcing fibres is not compromised and therefore does not represent a structural weakness. In a nutshell osmosis is a cosmetic condition.
It is a waste of time, money and energy trying to build an impervious barrier against osmosis. Any "shield" layer of extra
reinforcings, clear epoxies and the like, are normally a waste of money, because they do not take into account the practical day to day usage. Once this "shield" is broken or damaged the potential for osmosis reappears, immediately. The obvious answer is to provide a coating structure that does not impede the force of osmotic pressure but does act as a non-return valve. This means allowing the permeation of pressure vapour to pass through the membrane unimpeded but creating a barrier of resistance against the ingress of water We call the product SHIPSHAPE PRIMER-UNDERCOAT. The coating that allows the surface to breathe
Where osmosis blisters are detected the treatment should be as follows.
1. Chisel out any convex blisters with a cold chisel to produce a sound fibreglass matrix (usually 3mm minimum). Any dark acidic residue should be flushed clean using a clean cheap paint brush moistened with acetone. Whey dry NORGLASS
NORFILL should be applied to repair the indentation, followed by SHIPSHAPE PRIMER UNDERCOAT OR ANTI-FOULING
2. If the quantity of blisters appears considerable a thorough drying out process may be necessary prior to affecting the repair. After opening up and cleaning out the blisters, the remaining gel coat should be sanded off and then the hull be placed on a concrete apron with some black plastic film attached by tape just above the waterline. This should run the full length (both sides) and be tied out at 45 degrees to create a "tent" effect, with both ends open to stimulate air movement. Periodic readings with a moisture meter will determine the rate of drying. In extreme cases this can take many weeks.
3. Fill each blister as described in 1. above. DO NOT apply NORFILL or any other product in an attempt to cover the whole area. By restricting the filler to only the blisters, any ongoing osmotic pressure will bypass the treated areas and dissipate through the SHIPSHAPE.
4. Sand all the filled blisters to a smooth finish and apply 2-3 coats of SHIPSHAPE followed by the selected anti-fouling.
NORGLASS ADVISORY SERVICE Ph: (02) 97082200 or Fax: (02) 97963069 Email: norglass @ bigpond.net.au www.norglass.com.au