 SACKING CONCRETEOften you will need to fix the concrete once poured.. it is easy to screw up.. a tie snaps, a waler cracks, someone overvibrates, you don' t fill under a window buck properly... with concrete you list it.. it can go wrong... and even if everything goes perfect there are always bug holes... the small holes that appear from vibrating the concrete ..forcing the air to the outside trapping it in little bubbles on the finished surface So if you have a bulge.. that you cannot live.. with or a cold joint seam or a spread corner... it has to be fixed... start with a mid size concrete chipper... you have to be careful if concrete is still green you can blast it apart... for most repairs I go straight for the bush hammer bit, a square bit with knurls on face, it is designed to take off the face layer of concrete, chip away the bulged area until you are lower than the face that you are trying to match.. note any little piece of aggregate that is above this face area will give you grief.. so make sure the whole area is done before you start patching Now you are going to use a patching mortar to cover and bring back the face to smooth.. if it is exposed wall (in plain view) you will want to try to blend the colors... I use a patching mortar called star patch... it is a very fine powder (texture of baby powder or a bag of Portland cement)... and if you cannot find it... remember that the texture is one of the keys to a nice finish.. many mortars have a sand base and are just too gritty..be selective in your choices Some patching mortars need a bonding glue to be spread on the patch area before the mortar is spread ... (an example is plaino for levelling floors) these are called : bonding compounds ... read the bag... it gives directions You will need for tools: a foam rubber trowel foam is red with big pourous holes... not the same as your tiling trowel... and either a chunk of extruded styrene foam insulation( preferred) or a burlab sack, a bucket of water and a bucket for mortar mix and abucket for dry powder mortar Mix your mortar.. add
mortar to water
prevents lumping... your are looking for a consistency of cake icing...
although it sets up fairly quickly and you use a wet sponge.. so
a little dryer does not hurt -clean patch area slope sides slightly inwards ..steel brush to sound material.. wet area thouroghly .. apply bonding if called for... now if repair area is deep use several thin layers to reach your desired levels use your sponge trowel load it up and spread it on.. use a circular motion spread it smooth... if you are putting on a thin layer re: first layer in a deeper fill do not leave any peaks that are higher than the face you are trying to match.... let dry between coats... overnight until: you have reached the final smooth coat... this coat is applyed and you let it set up about 1/2 an hour now take your styerfoam block and starting at the outside edges of your patch ... using the finished wall face as a quide.. blend in the patch ..rub your patch smooth as you work load up the styerfoam block with powdered mortar and rub it into the freahly set mortar...working inwards from the face you are matching to the centre of patch (some finishers use the burlap sack to rub in the dry powder thus the term sacking) if so the mortar has to set up until quite hard before you apply the sacking finish repeat this process until you get the look you want... if the wall is small I will often sack the whole wallsacking
bug holes:
-mortars like star patch mixed 50 /50 with
#10 Portland dry no moisture -
presoak patch area and keep wet -
use a concrete sponge float damp with water
dip in mortar mix
and smooth over entire surface let dry until well set up strike off
wall with steel trowel |
