Why does my render always crack??

Joined
17 Jun 2008
Messages
43
Reaction score
0
Location
Warwickshire
Country
United Kingdom
Hi all.
I'm a plasterer by trade and lately have tryed some small rendering jobs

3 fireplaces ready for wood burners and a small porch.
All done 5:1:1 scratch coat and 6:1:1 top coat. Prob between 7 and 9mm thick for each coat.
Finish up the jobs and they look great and I'm very happy with them but pop back the following week with a invoice to always find hairline cracks. It's never sounds blow or hollow. they just appear to be on the very top surface.

What am I doing wrong?
Thanks.
Ian
 
Sponsored Links
Joined
2 Aug 2007
Messages
4,757
Reaction score
718
Location
Moray
Country
United Kingdom
What are you rendering onto, (brick, block etc) and what's your method, prep etc?
 
Joined
17 Jun 2008
Messages
43
Reaction score
0
Location
Warwickshire
Country
United Kingdom
All have been onto blockwork.
Plastering sand from travis perkins.
From reading different forum I get the impression most like to just soak the blockwork rather than pva so that's what I have been doing.
Mix scratch coat and lay on wit my mt stainless trowe, rule off, re-trowel and then scratch with my mt scratcher. Porch was left a week before top coat and the fireplaces 3 days In between coats. Top coats mixed and applyed with same trowel and when starting to turn rub down with plastic float and then into sponge float for nice finish.

Is there any steps that I'm missing?

There is a large house that I have been doing regular jobs on the the past 3 years. They had a small extention around 5 years ago that got rendered. The chap that has done it had made it look a rite mess, it's looks hideous but it has zero cracks. It gets to me every time I see it as by looking at his work he was no tradesman and had zero pride but had a bash and it was crack free. Im a tradesman that's very proud of my work but still can get it rite.

Thanks.
Ian
 
Joined
2 Aug 2007
Messages
4,757
Reaction score
718
Location
Moray
Country
United Kingdom
Well,, reading that Ian, it couldn't have been done any better. You did it the way most of us would have done it. Did you wet the scratch coat too before you top coated, and did the finished render dry out and cure "slowly"? You can get cracking it it dries out too quickly as you probably know. Sometimes too, the sand, although plastering sand, can be a little too fine on it's own, and can shrink, causing light cracking in the render. Mixing in some "clean" sharp sand can help. Not much else to say really, maybe the other guys on here will have some thoughts on this too. You sound like a good thoughtful tradesman, and i hope you get what you're looking for on here.
 
Sponsored Links
Joined
17 Jun 2008
Messages
43
Reaction score
0
Location
Warwickshire
Country
United Kingdom
Thanks roughcaster.
Yes scratch coat was well water before top coat, again just water rather than pva. Am I correct using just water?

The porch dried quite quickly and may have been to problem but both fireplaces dried a lot slower. To me the crack looks more like shrinkage rather than movement. As its not blown can the cracks be successfully filled or do I need to start from scratch? Tbh I think the paint would pretty much hide them.

Thanks.
Ian
 
Joined
2 Aug 2007
Messages
4,757
Reaction score
718
Location
Moray
Country
United Kingdom
Hard to say what to do with the cracks Ian. Take it off and start again?? depends how bad it looks, plus it might get worse once the woodburning stove is up and running.
 
Joined
28 Oct 2005
Messages
31,283
Reaction score
1,996
Country
United Kingdom
My guess is you are mixing too sloppy to counteract the suction. It's defo shrinkage and that is the only cause that I know of.
 
Joined
6 Oct 2007
Messages
2,883
Reaction score
504
Location
Bedfordshire
Country
United Kingdom
Chimneys and flues being what they are( ie designed to draw air up and create a draught) perhaps it is a case of drying too quickly as well.

If it's a flue, can you block it temporarily, or if a larger fireplace some sheeting across it to allow the render to cure rather than dry?
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Top