What to do about 'blown' areas ?

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countryman

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We're having the front of our house re-rendered. The wall was prepped, cracks filled and a coat of waterproof PVA and sand to give a good key to the scratch coat.

What to do about 'blown' areas ?

What to do about 'blown' areas ?

What to do about 'blown' areas ?

However when he started to put the finish coat of render on, he struggled the first day because the plastering sand was quite fine and he was finding that as he was trowelling off the finish coat was starting to pull away from the scratch coat. The next day he brought some sharp sand along to mix in with the plastering sand and that made a huge improvement.

I was up on the scaffolding today and discovered quite a few 'blown' areas especially where he had the first days' problems - some of them circled in the photo below.

What to do about 'blown' areas ?

Now my dilemma is this. Do I get him to remove the blown areas and re-re-render. The trouble with this is that I'm concerned that these patches will then stick out like a sore thumb thus defeating the whole object. Or do I keep my fingers crossed that some good coats of paint will keep the moisture out and that the blown areas won't fall off six months down the line.

Appreciate any thoughts. TIA.
 
I tapped it with my knuckles and it had a hollow sound. You can also tell when tapping with fingernails. Completely different sound to where it's solid. At least that's my interpretation.
 
He's probably overworked the top coat and its pulled from the scratch. Needs knocking off and re doing. Can be patched but it's difficult to do perfectly. Especially if there's spots all over the place.
 
i wouldn`t try to patch it, knock it back down and re render the lot. If you try to patch it it will stand out. Try to come to a mutual agreement instead of just demanding things so it would benefit both of you. He can keep his customer and you won`t have to put the work onto someone else to fix others mess and be seriously out of pocket. I would doubt it that he would take the lot on the chin, so work something out. that would be my bet advice.
Nice pad by the way.
 
Looks like a case of cheapest is best?! If hammering holes into the old render is supposed to be a key he definitely doesn't know what's going on!
 
First mistake as Marshy pointed out was using pva instead of SBR.A good coat of scudding with sharp sand is a must for any sand and cement job I do.Looks like a bit of a cowboy set up to be honest.
 
Scratch coat doesn't look very deep and looks like a lot of smooth areas in in the scratch, did he put waterpfrooer in the scratch coat?, did he give the scratch a light dampening down?
 
In all fairness I have replaced render that has been put on pva 30 years ago and survived but of couse other pva jobs have failed. It is down to good luck with that stuff.

This job has been painted so even sbr might not have worked. This is where the modern render systems involving Parex Parinter or microgobetis comes in and fully meshed with the mesh pinned back. Probably trying to explain this to the OP would sound double dutch!

Get is hacked off and get a render specialist in using the latest methods. Be prepared to pay and get the scaffolding right as well.
 
It has blown because of either an inadequate key or failure to control suction. Either way, It needs to come off and be redone. If it is poor keying then the scratch coat might need to be redone too or expanded metal lath applied to problem areas. failing that patch the blown areas then tyrolean the lot. Problem solved!
 
By the looks of it you get what you pay for unfortunately.
To cut it short sand and cement will never stick to existing paint even with a good key. The pictures say it all in my opinion. It's never nice to knock someone's work but that looks a job done by someone who's either a novice with no clue or a skimmer with no rendering experience.
As Rigby says Parinter or micro is the only stuff I'd use over paint or maybe rend aid but it would need a good key with a grinder and full mesh and pin.
You've got a nice house so why spoil it with a cheap repair job?
 
Pva is for skim.
Skim is gypsum and lightweight.
Painted surfaces will stop the sand and cement from sucking into the substrate so it drys on it instead of into is the easy way of explaining. So the weight of the render is hanging on the paint and this is why its hollow.
 
Thinking about what I said above about pva? I did a hack off recently that was done in 1988. He used pva, primed the bricks, applied the pva then applied a mix of building sand, cement and pva on at about only 5mm thick then painted it.

This was one the hardest renders I have had to hack off! It knackered me up that much getting this stuff of I was so knackered the next day I crashed the Cabstar. Thats going to cost me when I renew the insurance.
 
Rigsby said:
Thinking about what I said above about pva? I did a hack off recently that was done in 1988. He used pva, primed the bricks, applied the pva then applied a mix of building sand, cement and pva on at about only 5mm thick then painted it.

This was one the hardest renders I have had to hack off! It knackered me up that much getting this stuff of I was so knackered the next day I crashed the Cabstar. Thats going to cost me when I renew the insurance.
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Diluted PVA on high suction brickwork outside to kill the suction no problem, although I'd rather use Diluted SBR as it's quicker. PVA would probably need more coats. The problem comes when people use PVA as a bonding coat onto Engineering bricks or Paint.

Load of b*llocks you can't use it outside it just depends what your going onto.

I've used Micro on several jobs now over sound paint, not going on thicker than 15mm with no problems whatsoever, Micro sticks to paint like sh*t to a blanket. Saves a packet on expensive basecoat.
 
FreeD said:
Diluted PVA on high suction brickwork outside to kill the suction no problem, although I'd rather use Diluted SBR as it's quicker. PVA would probably need more coats. The problem comes when people use PVA as a bonding coat onto Engineering bricks or Paint.

Load of b*llocks you can't use it outside it just depends what your going onto.

I've used Micro on several jobs now over sound paint, not going on thicker than 15mm with no problems whatsoever, Micro sticks to paint like sh*t to a blanket. Saves a packet on expensive basecoat.
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Are you using sand and cement over the micro?
 
Traditional sand and cement isn't recommended for going over micro. Thin coat, OCR, mono only really.
 
I would still like to know what happens when wet render is appled to this dry filmhow the two adhere to one another?

One of these days I amgoing to do a test panel and see how well it sticks.
 
Rossi46 said:
Are you using sand and cement over the micro?
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Yes mate, it sticks like sh*t. I'm using 4-1 with Sika waterproofer (concentrated) quite a wet mix at under 10mm, then mono on top.

Never had a problem, have done it over sound paint to.

If brickwork is sound we go straight on, micro first no matter what brand mono, had enough of Rend Aid.
 
FreeD said:
Yes mate, it sticks like sh*t. I'm using 4-1 with Sika waterproofer (concentrated) quite a wet mix at under 10mm, then mono on top.

Never had a problem, have done it over sound paint to.
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Existing render .... Paint ..... Micro .... 4-1 s and c ...... Then mono ?!?!?
 
No, paint, micro, 10mm beads dabbed on, mono

or if brickwork is bad, micro, dub out sand cement, 10mm beads, mono

or good brickwork, micro, 10mm beads dabbed, mono
 
FreeD said:
No, paint, micro, 10mm beads dabbed on, mono

or if brickwork is bad, micro, dub out sand cement, 10mm beads, mono

or good brickwork, micro, 10mm beads dabbed, mono
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Make sure you sort me out when you make your first million ;)
 
FreeD said:
Make sure you sort me out when you make your first million ;)
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I meant over paint? You said you use micro, sand and cement at 15mm on top of a painted surface.

Ahh f**k it who cares. You said it's fine. I personally wouldn't sand and cement over paint with micro but each to their own.
 
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