There are a number of phases to the treatment
- preparing the surface
- fire-protection treatment
- finishing treatment (where required)
Preparing the surface.
The first operation is to make a careful inspection of the structure and the area subsequently to be protected from fire by applying an intumescent varnish. It is necessary to verify the general state of the structure, its solidity, the presence of any contaminants, the emission of water vapour, chemical attack, etc.
The preparation varies according to the type of surface to be treated. More specifically:
- New raw timber surfaces must be cleaned of any impurities, particularly if they are made of exotic wood, and washed down with paint thinner or acetone to eliminate any resin. Particular care should be taken to check the moisture content of the wood, which should be around 12%, the optimum value for varnishing operations, and to the roughness of the surface to be treated. For the best aesthetic result, it is advisable to apply the varnish to wooden surfaces that have been planed and sanded down with 180-grain paper.
- Old, previously varnished wooden surfaces should be thoroughly sanded down to remove paint residues that are not perfectly anchored to the surface. Only if the old varnish cannot be completely removed it is necessary to do a chemical compatibility and adhesion test for the products to guarantee perfect adhesion, an essential requirement in its behaviour in fire.
The quantity of intumescent paint to be applied to the various surfaces to be protected depends on a number of factors.The fire reaction or fire-resistance rating required
- The section of each element (for resistance only)
- The type of timber used (for resistance only)
- The load conditions (for resistance only)
- The conditions in which it is exposed to fire (for resistance only)
The protective treatment is applied using a spray, paintbrush or roller. It is essential that reactive/intumescent systems must only be applied to a properly prepared, compatible surface. We advise against applying the protective coating in unfavourable environmental conditions and to read the product technical specification very carefully. The thickness of paint to be applied in order to achieve the required protection is obtained by applying multiple coats, ensuring the correct amount of time has elapsed between coats. Remember that measuring the thickness is more difficult on wood than on other surfaces because of the amount of product naturally absorbed by the wood and that cannot be accurately measured. It is therefore very important to calculate the quantity of varnish to apply before starting, also taking into account any waste and to check that all the material has been applied.
N.B. During application, transparent wood varnishes can react in the presence of high levels of moisture. We would like to stress the importance of following the instructions carefully to avoid the varnish turning white or peeling off.
Finishing treatment. In order to obtain certification, some protective treatments require a finishing coat to be applied in order to guarantee the system’s effectiveness over time. For other systems, when the coating is to be applied in other than indoor environments or if a coloured surface is required, it is necessary to use a specific protective finishing coat, or use the product designed for outdoor use. We recommend consulting the technical documentation of the chosen product.