How to repair a crubling window sill made from cement i think !?

use resin and fibre glass as if fixing a small dent in a car. this can then be painted with exterior paints quite well. I fixed mine 7 years ago and still ok. I had tried fixing with sand cement renders but they always pop off, as the two compounds expand and contract at different rates. even recasting a face on will result in failure. the only way is to completeley remove old sill and replace with new pre cast one !! very expensive or try resin!! it realy does work .

Mike

Mike
March 2007

Very difficult. I tried float rendering mine as the surface was crumbling through past owner neglect and frost damage. I rendered them but it lifted after 2yrs as the stonework is difficult to get rendering coats to stay on them. I've moved since. You could try removing all loose bits and coating with 4 parts water to 1 part Unibond or similar adhesive. Allow it to dry and then coat with 1 water 1 Unibond mix allow to become tacky and render with rendering sand and cement at 3 sand 1 cement.
Lightly rub over the cement in a circular motion surface with a block of 1" x 2" x 3" long smooth/planned batten and this tightens the cement closing all air pockets. The difficult part would be replacing them. Shuttering can easily be supported on the downstairs sills but the upstairs presents a problem.
Look at how angled supports hold up a porch that's what you will have to do on the upper floor sills.
If you replace them watch what area they support and only cut out up to about 2" from each support ie: clolumns or piers. Preferably you need on site advice before attempting renewal as cutting back at the wrong place could cause the column/ Pier to float forward.

bob
June 2005