Polybond Ltd

Polybond Q19 On Ferroconcrete Hulls Decorating Damp Walls & Problem Areas for over 40 years. Over the years the development of Ferroconcrete boat construction has declined mainly because of the dictates of fashion and the apparent cheapness of the mass-produced GRP market. However Ferroconcrete has never gone away and it still remains an excellent, cheap very strong alternative to steel and GRP when used for manufacturing ocean going cruising vessels and workboats etc. In the area of finishing much has been done over the years to improve the coating systems for concrete. In the early days of Ferroconcrete construction builders and owners had to make do with a number of paint systems 'borrowed' from other industries, the resulting finishes being less than satisfactory. In some cases this was another reason for putting people off going for Ferroconcrete as a boat building material. This has now changed with the availability of Polybond Q19 Water Based Epoxy System that has been especially adapted and improved for use on Ferroconcrete surfaces. Moisture Sensitivity One the main problems for builders of this type of hull has been finding a compatible, long term paint system which will perform satisfactorily in marine environments. Although some paint systems have been applied with some success ie. Chlorinated Rubbers and Epoxies both solvent and solvent free with Polyurethanes used as finishing coats, most tended to fail after a short time. The major problem being the moisture and concentration of salts which form in the skin at the time of application. One method used to try and overcome the problem was to acid etch prime. This process eats into the hard surface of the cured Ferroconcrete opening and at the same time neutralising alkali salts that are present. This process does allow conventional solvent based paints to penetrate but not sufficiently to ensure long term performance. In addition the waiting period for drying can be lengthy. The dried film adhesion is therefore suspect and any moisture left in the concrete will tend to push the paint system quickly off the surface, particularly around the boot-top. Should the paint film be broken at any time, particularly if the boat is in the water, a lateral breakdown will result as water moves under pressure across the hull surface. This can be described as 'sheeting' or severe delamination. Adhesion to Wet Surfaces The Polybond laboratories looked into the problem of painting damp and wet porous surfaces, initially on building structures and then with Ferroconcrete hulls in sea water and came up with some interesting results. It was obvious that to overcome the adhesion problem you would need a water based product off some kind which when applied to 'green', damp surfaces offered excellent adhesion to the ferroconcrete despite the moisture and salts present. The coating would also ideally cut down on the normal protracted waiting times. Only one product proved to work up to 98% successfully and that was the modified Polybond Q19 system primarily developed to seal, waterproof and protect building surfaces above and below ground. Waterproof & Vapourproof - Helps control curing Polybond Q19 Clear Sealer diluted with 10% fresh, cold water applied to Ferroconcrete in a two coat system will form a waterproof and vapourproof seal to a 'green' surface. It was also found that when applied immediately to a freshly plastered shell ie. within 24 to 48 hours, it allowed a certain amount of control over the curing process, perceptibly slowing it down, avoiding the need to 'water cure'. After painting, the deck framing can be covered over with polythene to inhibit evaporation inside the hull, dampening down should be continued inside every couple of days. Compressive strength of up to 597.38 kg per cm² (8500 lb per square inch) can be achieved using this method after a 28 day curing period. This eliminates stress cracking and the need to physically control drying on the external surfaces. Polybond Q19 helps to reduce the problems of accelerated drying and at the same time has advanced the painting process. Using the above method can cut ferroconcrete drying times substantially even though the water based epoxy system takes a little longer than conventional coatings to dry out & cure. The factors controlling the drying are as follows: 1. The humidity in the atmosphere. 2. The level of moisture in the Ferroconcrete. 3. Air temperature ( Time of the year, Geographical location etc.) 4. Ventilation. The coating whenever possible should be applied in dry weather conditions & undercover. Polybond Q19 contains no solvents and can therefore be safely used in confined areas. The use of artificial drying aids is not recommended. Cleaning & Removing Surface Salts Surface salts can quickly, safely and effectively be removed from the surface of ferroconcrete using an acid etch solution like our Polybond Concrete Cleaner or similar mild acid based cleaning products. Once the solution has been safely washed off the surface Q19 can be applied immediately. The use of strong Hydrochloric and other concentrated acids is not advisable. If they are used the performance of the Q19 may be affected. Please contact our technical department for further details of our Concrete Cleaner. Polybond Q19 diluted with 10% cold water covers approximately 8m² per litre on surfaces of average porosity. In our experience higher figures can be achieved and it is possible to get up to 10 or even 12m² per litre when working on 'green' ferroconcrete. Please refer to the table below. Coverage Skinning Another important aspect in the protective values of Polybond Q19 is found when 'skinning' existing boat hulls. The same drying problems occur when applying a ferroconcrete skin on to metal or wooden hulls. The acceleration of drying can be worse in this instance as there is little or no where for moisture to go on the interface between the concrete and the surface to which it is applied. The Q19 can be applied in the same way to control the movement of moisture out of the skin and prevent stress-cracking etc. It is important to remember two things however. 1. Do not apply more than one coat within 3 days of each other. 2. Make sure that your skin is not over wet at the time of application of the paint. Relating to item one, the application of a second coat within 3 days can create an effective seal too quickly. This can be patchy and there is a possibility of a higher degree of moisture being trapped tan would be desirable at this stage. An even application of the Q19 is essential and spraying is normally employed to achieve this. As regards the second point, an over wet hull would almost certainly retard the Q19 cure and risk trapping excess moisture within the skin. Note: Under no circumstances can a hull with a single coat of Q19 Primer be immersed in water until a full paint system has been applied ie. after a minimum of 28 days. Concrete can be immersed in water without protection but if this is done, not only the hull would suffer by absorbing salt or contaminated water, the damage could well be reversible. Methods of Finishing 1. Complete Hull Apply two coats of Q19 Clear Sealer diluted with 10% clean, cold water to the hull within 24 to 48 hours of plastering. After application of the initial coats the controlled drying procedures should be continued on the inside of the hull as per normal building practice (see above). 2. Keel below Boot-top Once the hull is reasonably dry ie. one to two weeks depending on the weather and air temperature etc. an Epoxy Primer such as Polybond E Primer should be applied to the Q19 plus a minimum of 2 coats of Epiglo solvent based epoxy undercoat to prepare for the application of antifouling. All tin free and 'hard' types perform well on the Epiglo Undercoat. These should be applied between 8 hours to 24 hours after the final Epiglo coats. 3. Top Sides Surfaces can be finished using Q19 Colour systems, within one week of applying the second coat of Q19 Clear Sealer. This is to ensure that follow on coats key in satisfactorily. Apply a second and final coat of the Q19 colour (Spray recommended) within 24 hours of the first. If you decide to overcoat with other systems such as a conventional Polyurethane, epoxy gloss, marine gloss or Alkyd paint then use the Polybond E Primer before overcoating and finishing. A minimum of two coats of Q19 sealer will be required. Allow 24 hours before overcoating especially in cold wet weather. 4. Decks Proceed as for the keel. As an alternative to the standard finish an excellent long term non-slip surface can be obtained by casting Polybond Non Slip Aggregate into the first coat of Q19 Colour. Allow this to dry overnight then brush off and apply a second coat of Q19 to finish. To obtain a more flexible surface use a final coat of Polybond Chlorinated Rubber Paint as your finsh coats. Please ask for details. 5. Bilges If the external hull surface is sealed with Q19 it is advisable not to paint the bilges until the concrete is completely dry and cured. Allow at least 3 to 4 weeks. The system is so waterproof that there always a risk that of trapping moisture within the hull creating a sandwich effect. Subsequent damage can cause corrosion of reinforcing wire. Lower areas nearer the keel can be treated when dry with our Epoxy Coal Tar finish to prevent bilge waste contaminating the concrete. 6. Bulkheads & Interiors etc. The Q19 system provides an excellent decorative finish for concrete bulkheads and boat interiors. Normally a three coat system is advisable on concrete as per Top Sides. The product is not recommended as a wood finish Please contact Polybond for technical advice. Repairs Should the Q19 ever be damaged, repairs are easy to make. The surfaces should be rubbed down and washed thoroughly with fresh water and patch primed using several coats of Q19 Sealer. Then re-coat as for Top Sides. If the surfaces appear very smooth and dense then use our Polybond Concrete Cleaner before application. General Note: Some curing aids used in ferrocement construction can cause problems when painting. Care should be taken before using any artificial curing aid to determine its affect on paint systems. If in doubt always try a patch test and contact our technical sales department.

Polybond Ltd. Unit 6, William Street, Northam, Southampton, SO14 5QH Tel: 02380 988350    Fax: 02380 988355

The claims in this leaflet were believed to be correct at the time of publication and made in good faith, based on exhaustive tests carried out over a long period. Polybond Ltd and their agents cannot, however accept any responsibility for the behaviour of the material(s) in any individual case. Potential users are advised to check that this information is still applicable and that the product(s) are suitable for their intended use.