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Drying Out

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Drying Out

Once you have pumped out all the standing water you can begin to dry your property out. In cases of severe flooding it can take weeks or months to dry out the fabric of a building.

There is argument amongst experts about the best strategy for drying out flooded buildings. There are three competing methods:

  • To open all windows and doors and create a flow of air through the building
  • Add heat to the flow of air
  • Or close the building and employ dehumidification

Obviously, the deeper the flood and the longer it has been in contact with the structure the more moisture it will have absorbed. Stone, brickwork, plaster, concrete, wood and block work are all porous to some extent.

Ideally buildings should be dried out by the central heating system where possible, with the thermostat at 22°C or above. If possible use heaters, fans and dehumidifiers to aid the process.

Good ventilation of the building will aid the drying out process, open as many doors and windows as possible. On dry days keep all doors and windows open. On wet days leave windows ajar - the inside of your house can only dry if moisture can get out. If you can, use fans to help to circulate air and to draw humid air out of the building. Fans are more beneficial than heaters - they speed up the drying process by increasing airflow and the evaporation rate within your house.

It is possible to determine whether a building has dried out or not by using a meter, which can be obtained either via building specialists or via a tool hire shop. A lack of condensation may also indicate that a building has dried out. The length of time that a building takes to dry out is extremely variable and will be affected by a number of factors, including the severity of the flood and the type and thickness of the building materials that have been in contact with the flood waters. You should be prepared for the process to take months rather than weeks in the case of acute flooding.

Chimneys should be dried out carefully, starting with only small fires before moving on to larger ones, in order to avoid expansion of water to steam (and therefore damage) within the structure.

Drying Out Flooring

The floor surface, whether boarding or concrete, should be exposed as far as possible. Carpets, sheet vinyl floor finishes, tiles and similar should be removed and the floor area sufficiently ventilated.

In the case of suspended wooden floors, some boards should be lifted away and any water present in the cavity should be removed. This can be achieved by draining through air-bricks; cutting holes in the perimeter walls or using a pump, however do get advice (from expert builders or damp-proof experts) before cutting holes in walls.

Spaces beneath suspended concrete floors should naturally drain and dry out through existing air bricks or drain holes, though forced ventilation may be needed.

Wet mineral wool insulation and pipe insulation should be removed and replaced and aluminium/metal foil around the insulation should be punctured to drain off any water.

Floor joists showing signs of rot should be replaced and the surrounding area treated to prevent any spread. Distortion or twisting of joists can be prevented by stiffening the joists with struts or battens. Electrical connections and junction boxes must be checked by an electrician.

Floodwater will seriously damage most chipboard and there is the added problem that contaminants can get into the wood. Chipboard should be replaced if you think that the floodwaters have made contact with it or it appears swollen, distorted or damp. Where you cannot replace it (e.g. under partitions) provide extra support with struts.

Heaved floors are those that have not returned to their original level or have cracked badly. The floor may have to be removed and a new floor constructed. If a floor is badly cracked, but has returned to its original level, a new floor may be placed over the old one.

A vapour barrier should be added between the two floors and the new floor should be at least 2 inches thick.

The best way to tell when the flooring is dry by using a humidity meter, which will give a percentage humidity reading. This reading should generally be under 24% between October and May, and 22% between June and September.

Generally it is best to get advice before undertaking these kinds of repairs, either from surveyors or expert builders.

When you are replacing floorings, consider using materials that are less vulnerable to damage from flooding or that are more easily moved following a flood warning (e.g. rugs rather than fitted carpets).

Drying Out Walls

Any area of concern is best discussed with a surveyor or other building expert, who should be able to identify and assess points of weakness and rising damp in the wall, and give advice on how best to deal with them. If walls have sediment or debris piled high up against them (over 1-2 feet) this will exert a force upon the wall (a loading); take care when removing loadings. Try to remove loadings in stages and seek to maintain levels inside and outside of walls if loaded on both sides.

Walls built of traditional brick or concrete block with mortar joints will in general dry out well. Some types of lightweight block may begin to lose strength following a period of standing in floodwater. Have these checked by a specialist.

Signs of buckling include horizontal cracking and areas that have moved out of vertical alignment. When this condition is minor, you need not repair the wall immediately. However, any noticeably buckled wall will eventually collapse from normal ground pressures and seasonal temperature changes. When buckling has seriously weakened the wall, the damaged parts should be rebuilt immediately. Vertical reinforcements may need to be constructed into walls over 15 feet long.

Settled walls and footings are indicated by vertical cracks either in small areas or throughout the structure. Repairs are difficult without special equipment. Contact a reliable contractor for this work.

Regularly check walls for cracks and rising damp, and consult a specialist if concerned. Record any de-lamination (splitting into layers) and joint expansion, in order that the damage to the building can be fully assessed.

Wash and disinfect all contaminated surfaces and remove all loose decorations (e.g. wallpaper or tiles). Remove any low-permeability internal finishes such as vinyl paper, ceramic tiles and gloss paint, which will slow down or prevent drying out. Hose and scrub down external walls.

It is important to drain away or remove standing water in cavities (both external and internal walls) as soon as possible. Inspect cavities either by getting a specialist to use an optical probe or by carefully removing bricks and identify the internal conditions. Remove any water, mud or debris from within and replace any corroded wall ties and insulation. In the case of wall ties it is advisable to bring in an expert to repair or replace them, and you will find that some builders will specialise in this field.

Dry brush off any efflorescence (growth of salt crystals) that forms on walls as they dry. The salt content of walls can be assessed, but generally it is best to bring in an expert in this case.

Anti-moisture sealants can cause significant problems. It is very difficult to give advice on how to deal with such substances, as they can be very variable in structure, how much they allow the wall to breathe and how long they last. Again, the best course of action is to bring in a professional who can assess whether removal and replacement will be necessary.

Check that all airbricks in the walls are clear for ventilation. Put in vents at about one metre intervals all round the building at damp proof course level at each floor level and at the top of cavities behind masonry cladding to speed drying.

See also: You have been flooded.