Things You'll Need
Fiberglass repair kit
Septic tanks come in a variety of materials, shapes and configurations, although, they are all functionally the same. Older tanks are metal and require replacement once corrosion sets in. Newer tanks are concrete or fiberglass with access covers or risers with lids for inspection. Regardless of the configuration or material, repairing a lid is more cost effective than purchasing a new one.
Clean loose debris from damaged area of concrete lid. Use a wire brush to rough up the area. This improves the surface for better adhesion to the new concrete.
Mix enough concrete in wheelbarrow to repair the lid in a single batch. After emptying the sack of quickrete into the wheelbarrow, add water with a pitcher or bucket instead of a water hose. It is easy to add too much water when using a water hose, leaving the concrete too soupy and ultimately weak. Mix until concrete forms a heavy mud consistency.
Apply concrete mix to damaged area of tank lid with a wide trowel. Fill the area until level full and shape the concrete with the trowel. Allow concrete to cure for 24 hours before moving the tank lid.
Remove the fiberglass lid from the septic tank and cover the hole with a large sheet of plywood. Clean the fiberglass lid with mineral spirits or paint thinner in order to remove all dirt, grease and build-up. Once clean, dry the lid with an old towel or shop rags.
Cut the fiberglass cloth with a pair of household scissors. Overlap the cloth at least two inches beyond the damaged area. With the cloth cut to size, set it aside on a clean surface.
Screw a piece of plumbers strap across any split areas on the tank lid. Self tapping screws driven with an electric drill will work fine for this. Immobilizing a part of the lid split in two will allow the resin to cure more evenly.
Shake the can of resin for about a minute before pouting a small amount into a container. Use an old paint brush to paint liquid resin onto the repair area of the lid. Allow for the over-size fiberglass cloth by spreading the resin a couple of inches beyond the damage. Lay the fiberglass cloth onto the tank lid. Maneuver it into place so that it covers the damage completely. Remove any air bubbles or wrinkles from the fiberglass cloth before applying a heavy top coat of resin with the paint brush.
Brush on a heavy top-coat of resin and allow 24 hours to cure. Once curing is complete, remove temporary plywood cover of septic tank, and install the fiberglass lid.
Allow concrete to adequately cure before placing atop the septic tank.
Wear latex gloves when working with fiberglass resin.
Do not leave septic tank uncovered if hole is large enough for a pet or child to fall into.