OSMOSIS PREVENTION & REPAIR GUIDE
REACTIVE RESINS manufacture a complete range of advanced epoxy products to repair and fully protect your boat.
We can advise you on the best way of saving both time and money and ensuring that your investment is protected. The
following guide has been written to help you with the identification and treatment of osmosis. See Page 5 for a full list
of Reactive Resins’ Osmosis Prevention Range.
WHAT IS OSMOSIS?
Osmosis is the name given to the degradation of polyester resin in the hulls of GRP boats. Water that has diffused into
the hull causes the ester molecular links in the polyester resin to hydrolyse and degrade, to form a hygroscopic residue
which attracts more moisture into the laminate. Over time, the moisture pockets become pressurised, enlarge and form
blisters on the surface of the laminate. Unchecked, osmosis can work deep into a polyester laminate causing extensive
damage and weakening the structure.
PREVENTING OSMOSIS
Osmosis will eventually occur in any polyester laminate exposed to moisture unless it is treated from new to prevent
water penetration. Modern gel coats are very moisture resistant, however being polyester based they will never resist
moisture completely. The only effective long-term solution for preventing osmosis is to apply a barrier coating.
There are a number of factors that will contribute to the rate at which osmosis will occur. The quality and type of gel-coat
and resin, workshop conditions at the time of lay up and the quality of the hull lay up are important. Additionally, the
length of time the boat remains in the water, and the water temperature will impact the rate of osmosis. (e.g. is she
dry sailed or hauled out during the winter months?)
A point to remember is that water can penetrate from inside the boat as well as out, therefore keeping a dry boat down
below is important.
New craft and those with a low moisture reading and showing no signs of osmosis should be sanded to a mat finish,
degreased with Synsol solvent and given three coats of Safeguard EA or TSF followed by one coat of Easyfair SEU.
HOW DO I KNOW IF MY BOAT HAS OSMOSIS?
A good DIY check for determining if your boat is beginning to be damaged by osmosis is to carefully examine the bottom
of the boat looking for the existence of blisters. This is best done in the half-light of early morning or evening after the
hull has been thoroughly cleaned and allowed to dry. Any large blisters will be readily apparent. In the half-light, any
slight dimpling of the hull indicating the beginning of blistering can be detected. Mark any suspect areas and then
remove any bottom paint to ensure that the hull is affected and that the blistering is not merely due to poor adhesion
of the bottom paint. If in doubt get a surveyor to inspect the hull. The surveyor will generally remove some sections of
the bottom paint and check the hull laminate with a moisture meter. This will enable him to detect the presence of
moisture in the laminate, indicating the presence of osmotic activity, before the osmosis has caused any visible damage.
When detected at this stage, prevention against further damage can be done at minimal cost.
TREATING OSMOSIS
The treatment of osmosis depends on the severity of the damage to the laminate. The primary defence against the
continued development of osmosis is the prevention of moisture entering the laminate. Safeguard, our osmosis
prevention range are a unique combination of low solvent or solvent-free epoxy resin and solid ceramic micro-beads
giving the toughest protection available. Safeguard’s properties make it suitable for DIY application and so minimises
the cost of treatment.
The three main stages of osmosis and its treatment are detailed below.
1
Osmosis is indicated by the presence of high moisture levels in the laminate and there is no visible damage to
the laminate or gel-coat. Remove existing bottom paint over the area to be treated. Abrade the gel coat to a
matt finish. The hull must be thoroughly dried. Recommended moisture content less than 5%. Degrease with
Synsol solvent. Apply 5 coats of Safeguard EA or TSF followed by 1 coat of Easyfair SEU.
2
A few blisters are found or blistering is limited to one or more specific areas. This is generally indicative of
minor, localised defects in the original laminate. Practical experience indicates that localised treatment of
these areas, as outlined under stage one, and applying Safeguard EA or TSF over the remainder of the gel
coat will provide protection against further damage. Always make sure the laminate is dry and has been
checked with a moisture meter before application of Safeguard coatings.
3
If osmosis has advanced to the stage where extensive blistering has occurred over large areas of the hull and
damage to the underlying lay-up is apparent it will require complete osmosis treatment. The following sections
provide a step-by-step guide to the complete process, indicating the various options available to the boatyard
or DIY owner.
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Remove the old gel coat.
Blast the laminate to etch the surface and remove soft areas.
Inspect the laminate to ensure that no damaged areas remain.
Remove any remaining damaged laminate
Pressure wash several times preferably with hot water to remove salts and contamination.
Dry the laminate to below 5% moisture.
Replace any damaged laminate and prime with Safeguard LVP.
Fair the laminate with EASY FAIR filler and sand to a smooth finish.
Apply of 5 coats of Safeguard TSF or EA.
Apply of 1 coat of Easyfair SEU.
Sand to a smooth finish.
Application of Safeguard TC and Antifouling
DOES THE HULL NEED TO BE UNDER COVER?
The boat does not need to be undercover, however work must be carried out in dry conditions. It is beneficial to have
the boat under cover if such facilities are available then work may proceed regardless of the weather. An economical
and effective alternative is to ‘tent’ the hull with plastic sheeting from the sheer down after removing the gel-coat. This
will allow subsequent work to proceed in wet conditions.
Safeguard coatings, as with most other Reactive Resins epoxy products, do not require the hull to be under cover for
proper application. The hardeners enable the epoxy to be applied in a wide range of temperatures in high humidity
without blooming.
PREPARING THE HULL
Prior to treatment the skin fittings should be removed from the hull. This is important otherwise moisture can get under
the Safeguard where it adjoins the fittings. This also provides the opportunity for a thorough inspection of these fittings
on older boats.
The rudder should be unshipped to allow complete access to it and the surrounding hull.
The inside of the hull should be clean, free of all dirt, grease and oil. All gear and cushions should be removed and the
inside of the hull thoroughly rinsed to remove any traces of salt. The bilge should be sponged dry and the water tanks
drained.
The boat should be left open to allow the free circulation of air to assist in drying the laminate. A dehumidifier can be
used to assist with the drying. This is important, as moisture will penetrate the laminate from inside the hull as well as
outside.
REMOVING EXISTING GEL-COAT
The existing gel-coat, including bottom paint and any other previously applied protective coatings must be removed.
This is done to expose the underlying laminate from at least 50 mm above the waterline down. If blistering extends
above the waterline, the gel-coat should be removed to a minimum of 50 mm beyond the area affected. It is generally
a good idea to remove the gel-coat either to the bottom or the top of any existing boot – top stripe as this provides a
good visual break for stopping the Safeguard. In addition this extends the protection above the waterline.
There are three primary methods for removing the gel-coat: grinding, peeling / planing and grit blasting.
Sanding off the gel-coat with an angle grinder is suitable for DIY work, especially on small hulls. Some skill is required to
get a smooth surface, but the depth of cut is readily controlled and thorough removal of all the old gel-coat is no problem.
Furthermore, any areas of damaged laminate can be removed during the process. The disadvantage of this method is that
in unskilled hands, a grinder may not leave a smooth surface, requiring a large amount of filling when fairing the hull.
Protective clothing, mask and goggles are required.
Peeling/Planing off (“stripping”) the gel-coat with a purpose-made power tool is the method most commonly used today.
This leaves a smooth, uniform surface that generally requires little fairing prior to the rest of the treatment. It is very good
for all cases of osmosis damage. There are specialist firms who will quote for the job and then come and strip the bottom
on site at your yard. This method is excellent when performed properly with the right equipment and a skilled operator.
Grit blasting the hull to remove the gel-coat is one way of removal. It will remove all the gel-coat as well as any ‘soft’ or
suspect areas of laminate. However, it can leave many craters of various sizes, which may require a lot of filling and fairing.
Grit blasting has the benefit of leaving a slightly rough surface with ‘tooth’. This ‘tooth’ aids in drying the laminate and also
provides an excellent surface for the Safeguard to adhere to. The process is generally done by specialist firms (like the
stripping). If you choose to have the gel-coat removed by a specialist firm, your local yard should be able to assist you in
finding one.
Best results are obtained by peeling followed by sand or slurry blasting.
INSPECTING THE LAMINATE
Inspect the laminate at this stage to ensure that all damaged laminate has been removed. A healthy laminate is a uniform,
translucent colour and the reinforcing glass strands are faintly visible. Areas that appear snowy white or in which the
reinforcing fibres show white, but are otherwise dry and firm to the touch, are termed “resin-starved” and indicate the
fibres were not thoroughly saturated with resin during the lay-up. The fibres will have a tendency to absorb water. This
condition is serious but shallow areas can be effectively treated after drying by saturating the area thoroughly with
Safeguard LVP. This is a low viscosity epoxy material that will penetrate porous laminate displacing trapped air.
Extensive areas of deep resin-starved lay-up, deep pitting, soft laminate, apparent de lamination of the underlying layers
of reinforcement, or the presence of any fluid seepage indicate significant damage to the hull structure. If any of these
conditions are found, consult a professional surveyor experienced with GRP construction for advice. These areas will have
to be removed with a gel planer or by grinding and replaced with new epoxy laminate before application of Safeguard.
RINSING AND DRYING THE LAMINATE
After removing the gel-coat and any damaged laminate, it is essential to thoroughly wash the hull several times with fresh
water to remove any salts formed by the osmosis. This is best done with a high-pressure hot water washer. If any salts
remain in or on the laminate, they will continue to attract moisture from the atmosphere and the hull will never dry
properly. The washing process should be carried out several times during the first week after removal of the gel-coat. After
washing, the hull must be left to dry. This can be done in the open and may take several weeks to several months.
The moisture level should be monitored each week. A moisture reading of under 5% is desirable. If the hull gives readings
in excess of this amount, it generally indicates that salts are still present and further rinsing is required. Check too, that
the inside of the hull is thoroughly clean, dry and salt-free if high moisture readings persist. The use of heat may be
required to achieve low moisture readings. However, having the hull under cover may speed up the drying process and
make the following steps less dependent on the weather.
PRIMING AND REPLACEMENT OF DAMAGED LAMINATE
Prior to any repair work, any resin starved areas should first be thoroughly saturated with Safeguard LVP. The hull should
then be primed with one entire coat of Safeguard LVP to provide a sound base for application of Easyfair epoxy filler.
Any additional repair work, such as adding extra layers of laminate to replace damaged laminate removed in severe
osmosis cases, should be completed before application of the filler. Areas with minor surface pitting and isolated deep pits,
especially around the turn at the top of the keel and skeg, indicate where minor voids may have occurred in the lay-up.
These should be ground back to sound laminate prior to priming the hull.
FAIRING THE HULL
Fairing the hull is required following repairs and prior to the application of the
Safeguard range. This allows Safeguard products to be applied to a smooth, even
surface. Any low areas, nicks or gouges should be filled with Easyfair filler. This is
sanded smooth after curing and the process repeated as necessary until a smooth
bottom is achieved. Any sharp edges should be slightly rounded at this time. This
prevents thin areas of Safeguard on the edges.
APPLYING SAFEGUARD
Choice of system. Use Safeguard TSF (totally solvent free) coating if you want to
apply each coat in quick succession without waiting for each coat to dry. Use
Safeguard EA (easy application) low solvent coating if you wish to apply one coat a This yacht has been peeled, blasted,
day in winter or two coats a day in hot summer conditions. Safeguard products are washed and allowed to dry and is
ready for coating
intended to be applied by roller or brush. Spraying is possible but it is recommended
that a professional undertake the task.
5 coats of Safeguard TSF or EA should be applied to achieve a total cured thickness
of approximately 600 microns. To ensure that the correct thickness is achieved, use
the full amount of Safeguard that has been calculated for your craft, even if more
coats are required.
Apply the first coat. Successive coats of Safeguard TSF may be applied as soon as
the previous coat has set sufficiently to prevent sagging. Successive coats of
Safeguard EA must not be applied until the solvent within the coating has evaporated. Both products must be over- coated before they have cured so that chemical
bonding occurs between the coats. Details of minimum and maximum over-coating
times are contained in the relevant product literature. Alternate coats should be of
different shades to ensure even coats are applied.
Sound laminate
For best results when using a roller, it is suggested that the last coat be lightly brushed
smooth after rolling. The remaining brush and roller marks can be removed by
applying one coat of Easyfair SEU matt finish epoxy undercoat. It is easy to sand to
a perfectly smooth finish ready for the antifouling.
After the osmosis treatment has been finished this is the perfect time to apply
Synergy long-lasting metallic copper antifouling. Synergy gives excellent protection
against fouling and will eliminate the annual chore of antifouling.
Porous laminate
The finished coatings should be left to cure before immersion for at least 7 days at a
temperature not less than the minimum curing temperature of the hardener.
QUANTITIES OF MATERIAL REQUIRED
In order to calculate how much material will be required it is necessary to know the
underwater area of the hull. Bottom areas of 200 types of craft and a bottom area
calculator can be found in the ‘Articles & Guides’ section of our web site.
APPLICATION INSTRUCTIONS
More detailed application instructions are available in the product data sheets which
are available upon request or they can be downloaded from www.reactiveresins.com.
Large holes require priming with
Safeguard LVP and filling
The laminate darkens as the low
viscosity resin soaks in
REACTIVE RESINS
The Safeguard range of products have been developed to repair damaged GRP laminates and to provide a complete
moisture barrier to keep the laminate dry. Safeguard offers outstanding performance as an abrasion resistant moisture
barrier. New boats can be protected from the day of launch and existing boats can be treated and protected at any time
during their lives.
SAFEGUARD LVP is a clear, low viscosity two component epoxy primer for peeled GRP. It will penetrate resin starved and
porous areas of laminate. It contains additives that promote the displacement of air and aid bonding of the new coating to
the existing resin and reinforcement.
EASY FAIR fillers are two part, low density epoxy fillers that are easy to mix and apply. They cure quickly and are easy to
sand. It is available as a trowel-able or spread-able filler for a range of filling applications.
SAFEGUARD EA is our original easy application osmosis prevention coating which has been developed for amateur use.
It is an economical, two part low solvent epoxy coating that is easy to apply and produces excellent results. Because it
contains a small amount of solvent it has good pot life, but minimum over-coating times must be adhered to in order to
avoid solvent entrapment. Only one coat can safely be applied per day in cool conditions but two coats can be applied per
day in warm weather.
SAFEGUARD TSF is a totally solvent free two part epoxy water barrier coating which has been designed for professional
use. It is available with several hardeners. A fast hardener will enable the skilled applicator to apply up to five coats per
day while a slow one will provide a good over-coating period that is useful when working on larger craft. As the material is
totally solvent free there is no fear of solvent entrapment.
EASY FAIR SEU is an epoxy undercoat that dries to a matt finish. It is applied over the last coat of Safeguard EA or TSF
to fill the brush marks and roller stipple. It is easy to sand and can be over-coated at any time after it has cured. It provides
a good base for conventional anti-fouling paints.
SAFEGUARD TC is a low viscosity primer sealer used as a primer for Synergy.
SYNERGY is a new long life copper antifouling that has taken four years to develop and perfect. It has all of the advantages
of epoxy-copper antifoulings but by using a new water-borne thermoset resin binder, it avoids the problems of unreliable
performance and occasional failures that often beset epoxy bound copper anti-foulings.
For more information on each of the products above please see the individual Technical Data Sheets
HEALTH & SAFETY Please see Safety Data Sheets for full information. All users should ensure appropriate
protective measures are adhered to when applying our products.
DISCLAIMER Customers are advised to thoroughly read and adhere to the instructions provided to ensure the
products' optimum finish and performance. All information is based on results gained from experience and tests
and is believed to be accurate but is given without acceptance of liability for loss or damage attributable to reliance thereon as conditions of use lie outside our control. Any deviation by the user to these instructions may affect the products performance and is therefore not advised. In this circumstance, Reactive Resins will not be held
responsible and will be unable to offer any product replacement. Users should always carry out sufficient tests to
establish the suitability of any products for their intended applications. We aim to ensure consistency of colour in
production (where applicable), however small variations in shade may occur from batch to batch.
Please visit our web site at www.reactiveresins.com for details of our other products.
They include resins and coatings for marine, industrial and flooring applications.
33 Normandy Way, Walker Lines Industrial Estate, Bodmin, Cornwall. PL31 1HA
Tel +44(0)1208 264999 e-mail [email protected] www.reactiveresins.com
Reactive Resins is a trading division of EP Resins Limited.
Registered in England No. 07348986. Registered office as shown above.