Form Finish Repair for Concrete - Sack-rubbed finish for Air bubbles, voids and irregularities etc.
a) Thoroughly wet the surface and allow it to dry such that it is just moist but not wet.
b) The mortar used for sack rubbing should consist of one part of cement to two parts by volume of sand passing through 1.18 mm IS sieve. Add enough water so that the consistency of the mortar is that of a thick cream/paste.
c) Spread the mortar thoroughly over the area with a clean sack to fill the voids, air holes and irregularities.
d) If matching of colors is also important, white cement to the extent of 2 to 5% may be mixed with the usual grey cement. Trial patches should be made, cured and allowed to dry for comparison.
e) Rub the dry mix of mortar in the same proportions over the partially-set finished surface. This serves to stiffen the plastic material in the patches and solidify the mortar.
f) Remove the excess mortar by scrapping and rubbing after the finishing surface has stiffened adequately to prevent smearing.
g) After final sack rubbing , spray a light fog to the coated surface , to keep the surface damp without allowing the water to drip or run down the surface. If a smooth finish is required, instead of the final sack rubbing , the final finish may be done by floating using a wooden float with a neat cement slurry of about 200 gms cement per litre of water.
h) Keep the finished surface continuously damp for atleast 3 days (or) until the completion of curing period for the concrete.
i) The finished surface should not have abrupt irregularities, like offsets, greater than 5 mm in the direction parallel to the direction of flow and 3 mm in the other direction. Gradual irregularities, like bulges, should not exceed 5 mm.
j) It is advisable to delay the finishing until near the end of the project. If all surfaces are finished in a short period of time, there is a better change of achieving a uniform appearance. Also, the chance of discoloration caused by subsequent construction operations is eliminated.
k) Do not use steel trowel for finishing formed surfaces because it will produce a smooth surface which will not blend with the surrounding concrete.
a) Thoroughly wet the surface and allow it to dry such that it is just moist but not wet.
b) The mortar used for sack rubbing should consist of one part of cement to two parts by volume of sand passing through 1.18 mm IS sieve. Add enough water so that the consistency of the mortar is that of a thick cream/paste.
c) Spread the mortar thoroughly over the area with a clean sack to fill the voids, air holes and irregularities.
d) If matching of colors is also important, white cement to the extent of 2 to 5% may be mixed with the usual grey cement. Trial patches should be made, cured and allowed to dry for comparison.
e) Rub the dry mix of mortar in the same proportions over the partially-set finished surface. This serves to stiffen the plastic material in the patches and solidify the mortar.
f) Remove the excess mortar by scrapping and rubbing after the finishing surface has stiffened adequately to prevent smearing.
g) After final sack rubbing , spray a light fog to the coated surface , to keep the surface damp without allowing the water to drip or run down the surface. If a smooth finish is required, instead of the final sack rubbing , the final finish may be done by floating using a wooden float with a neat cement slurry of about 200 gms cement per litre of water.
h) Keep the finished surface continuously damp for atleast 3 days (or) until the completion of curing period for the concrete.
i) The finished surface should not have abrupt irregularities, like offsets, greater than 5 mm in the direction parallel to the direction of flow and 3 mm in the other direction. Gradual irregularities, like bulges, should not exceed 5 mm.
j) It is advisable to delay the finishing until near the end of the project. If all surfaces are finished in a short period of time, there is a better change of achieving a uniform appearance. Also, the chance of discoloration caused by subsequent construction operations is eliminated.
k) Do not use steel trowel for finishing formed surfaces because it will produce a smooth surface which will not blend with the surrounding concrete.
