Air trapped when rendering

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bryon

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Just rendered the infill on a garage today. All went well until I rubbed it down. Any advice welcomed on the following problem:

Rendering with 4:1 mix to blockwork (B&Q plastering sand! and Lafarge general purpose cement). PVA'd blockwork twice and then rendered. Intention was to do a 10mm scratch and 5mm finish.

Render took ages to pull in and as I was rubbing it up I found an area seemed to have delaminated. I ended up with air trapped behind which just made things worse. I've ripped it all off to do again.

So why did it delaminate?
1. Maybe I shouldn't have PVA'd blockwork?
2. I suspect I was also rubbing up too early as I was just moving render around on the lower section.

Any advice? on whether to PVA and when to rub up?

Cheers
 
Sounds like you killed the suction and lost the bond/key between the blocks and the render , also trying to float up to early move the render around unnecessarily and the float can pull the render off the wall , sometimes you can trap air behind the render but it rarely causes to many probems over mixing the render will not help .
 
church said:
Sounds like you killed the suction and lost the bond/key between the blocks and the render , also trying to float up to early move the render around unnecessarily and the float can pull the render off the wall , sometimes you can trap air behind the render but it rarely causes to many probems over mixing the render will not help .
Click to expand...

Spot on as usual Church.
 
I'll keep my float well away this time until right near the end.

Yep definitely seemed to have killed the suction. So if I re-render tomorrow what's the best way to get the suction back? go over with a wire brush?

I presume PVA'ing for the final coat once this damn's things stuck would be inadvisable as well?
 
If the blockwork is un painted just put a 4-1 coat over it about 10mm thick max get it flat as you can take any lines out and run a scrafier though it lightly forget it for a couple of days , then put a 5-1-1 coat over it rule it off and fill in any hollows wait for it to pick up float it up and run a sponge over it the suction should be even and controllable.
 
If the PVA is still on the blocks you could try running a nail float (as in mono scratcher) over the blocks to break the surface and allow the suction to come back and then do as Mr Church says.
 
why are using pva dampen the walls that should be enough i somtimes put a bit of waterproofer in top coat aswell
 
church said:
If the blockwork is un painted just put a 4-1 coat over it about 10mm thick max get it flat as you can take any lines out and run a scrafier though it lightly forget it for a couple of days , then put a 5-1-1 coat over it rule it off and fill in any hollows wait for it to pick up float it up and run a sponge over it the suction should be even and controllable.
Click to expand...

u make it sound so simple
 
Dont PVA clean masonry just give it a drink some need more than others, i wouldnt put waterproofer in top coat as has been said before on this site can cause problems prohibiting the scratch coat drying out and causing delamination.
Lucius.
 
Move on Mur , its over between me and you, uks was fine for a while but now im into tats. Deal with it
 
church no matter what happens ........we might shag eachothers girlfriends and have the odd tiff ........i like to call you my friend ......forever mate i love you maaaaaaaaaaaaaaaan ;D
 
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