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Mixing Your Varnish

By January 14, 2016 Boat Varnishing Tips

Not all varnishes need to be stirred (read the instructions carefully before use). Any product that does need stirring should be mixed thoroughly using a flat stirrer (a cheap wooden rule is ideal) making sure that any solids that have settled to the bottom are mixed in. Stir along the sides lifting frequently to be sure all contents are mixed thoroughly. Pour the mixed varnish into a separate clean container; never use the varnish direct from the tin as you stand a good chance of contaminating the lot with dirt etc. Pour just enough to cover the immediate area especially if the weather is hot. Allow the mixed varnish to stand for about ten minutes so any bubbles caused by mixing can dissipate before brushing or rolling.

Do not be tempted to mix by shaking as this will aerate the mix even more and the bubbles will mess up the surface. Follow the supplier’s recommendations & add thinners only if necessary. Some suppliers recommend adding up to 50% thinners for the first coat over raw timber, while others recommend no more than 5%. When using a two pot varnish, measure the exact quantities recommended into a clean container & thoroughly mix. These mix ratios are generally based on volume. The supplied pump will give most exact quantities. Alternatively use a parallel sided can with a measuring stick (the school rule) to determine the exact ratio. Do not use a can with a rounded base or tapered sides as you will finish up with the wrong ratio. If using a measuring cup, add the required quantity of resin then top up to the correct ratio with hardener before mixing.

Two-pot lacquers begin to react as soon as they are mixed in the container & have a limited life (pot life) before they begin to harden & become useless. Spray Bloxygen Finish Preserver into the original varnish can & then close the lid on tight, & spray Bloxygen Finish Preserver into the catalyst container & close the lid on tight, to prevent the product from hardening. By using Bloxygen Finish Preserver you will be able to use the entire contents and not just the first half. As soon as the varnish & catalyst are mixed they will begin to harden. This depends on the temperature of the mix. chemical reactions work quicker as they heat up, doubling their activity for each 10 degree increas in temperature (at 20 degrees, the reaction takes half as long as at 10 degrees; at 30 it will halve again). Some mixtures give off heat when reacting (exothermic). The heat raises the temperature causing the mix to react faster giving off more heat – a chain reaction. This speeds up the setting process even more, especially when concentrated in a small container. Retarders can be used during hot weather. Pour out only enough mixture to use it up completely before it begins to gel. Coverage is shown on the container & varies (from 9 to 15 square metres per litre) depending on the surface roughness & thickness of the varnish.

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