rendering over an old scratch coat

[matt9714]

At some point within the last 12 months or so some one began rendering the front of the property i've just purchased. They got as far as putting on a scratch coat, which still looks in a reasonable condition. Am i best off going over the top of this with a fresh 1st coat or will it be good enough to just apply the final top coat.

 

[roy c]

The only problem here is that you dont know what mix was used for the scratch...If it is not too big an area I would be tempted to hack it off and start again from scratch (excuse the pun), That way you will know what is in the coats that you apply and have peace of mind. I have seen a couple of plasterers come on to a job after a house was scratched, and the plasterers weren't paid so they left the site.I said to them aren't you going to hack the scratch off and start again? He said No! and carried on and floated it all out, and I am not lying , in 2 weeks most of the render had "blown" and was coming off the wall in sheets....So be careful what you do, You could put a 5-1-1 mix on or a 6-1-1 mix after you have controlled the suction with SBR , as I shouldn't imagine they would of scratched weaker than that, but you must kill the suction as they might not of put W/proofer in...Good Luck....
P.S. I have got the back of my house scratched and I haven't touched it for 4 or 5 years, but I know what the mix was and I put W/proofer in the scratch so there wont be a problem when I do finally get around to floating it