29 March 1996

Repairs better sooner rather than later

POTENTIAL problems with two silos at New House Farm, Forden, Powys, were spotted during a routine pollution audit.

ADAS buildings consultant Rees Williams told milk and beef producer Philip Benbow that damaged seals would eventually allow silage effluent to leak. Though there was no immediate pollution risk, he suggested it would be wise to carry out repairs sooner rather than later. Mr Williams warned that existing serious surface corrosion of silo floors, the lower parts of walls, and an effluent collection channel, would get worse.

The most severe damage has occurred in the newer of the two clamps, constructed only five years ago using highly recommended RC 40 concrete. A sloping floor ensures effluent drains from the 27m x 12m (90ft x 40ft) building to be collected in a concrete channel that empties into a tank.

"Clearly effluent ponds are forming on the floor area close to the channel, which is becoming severely roughed up, as is the channel itself," Mr Williams says. "The seals between different areas of concrete have also disappeared in some parts, allowing effluent in to start corrosion."

His advice is to use a grinder to get rid of all the damaged concrete on the edge of the joints before re-sealing them. If the roughed up surface is not tackled, any approved polyurethane sealant could be used. But should Mr Benbow decide to re-surface, the silo damaged seals could be cleaned and filled with new concrete.

"Something has to be done to ensure that effluent does not escape through damaged seals, but I advise resurfacing using 50mm of rolled asphalt. Such surfaces have been down for 10 years on some farms. The only snag is that machinery should not be parked on them because of the risk of damage by leaking oil or fuel."

Surface corrosion is more extensive in the second 27m x 13.5m (88ft x 44ft) 20-year-old silo. For the first three years the walls were not lined with plastic before filling and an acid additive was used.

"We also made wetter silage then," Mr Benbow claims. "Because we are not self feeding and there is no chance of damaging the feet of cattle, I had not considered re-surfacing."

Mr Williams is concerned about the absence of sealant in the butt joints between the different areas of concrete making up the floor, and about corrosion between walls and the floor. "The silo has an excellent effluent collection system, but I would like to see it pressure washed, the butt joints cleaned and sealed, and the area surfaced with hot rolled asphalt."

He also advises corrosion where walls meet the floor is removed and the joint sealed with epoxy resin before asphalt is laid.

Robert Davies

Resurfacing the silos would cost £8 to £9/sq metre, or a total of around £6000.

Robert Davies

&#8226 Remove corrosion where walls meet the floor.

&#8226 Seal joint with epoxy resin.

&#8226 Lay asphalt.

&#8226 Resurfacing cost is £8-9/sq metre.

For the latest research on clamp and silo maintenance see our Focus on Forage supplement.

Rees Williams – corrosion where silo walls meet floor should be removed.