Painting a 20-yr old rendered wall. Preparation?

I plan to paint the rendered gable end of my house for the first time. It was rendered 20 years ago. Is there any preparation I need to do, to maximise the durability of the planned paintwork?
TIA
Al
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AL_n wrote:

Check the rendering's still attached. Then, if it is, thoroughly clean it.
I had what looked like perfect rendering on my flat three years ago, which had been applied a couple of decades earlier, which turned out to be sort of attached in places, but was mostly staying up due to not having the energy to fall down. 90% of the tap tests had that horrible hollow sound.....
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Tciao for Now!

John.

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On Fri, 22 Jul 2011 13:22:43 +0100, John Williamson wrote:

That is exactly the description of what I found on one of the gables here last summer. With the exception that a few square yards had found the energy to fall off in the previous winter.
Got proper scaffolding put up and put a chisel behind it, it would come away in great chunks. I never really worked out why it had been rendered in the first place, the pointing was 99% good and the stones in good condition. I suspect it failed as who ever put in on didn't remove the paint that was there first so when the paint's bond to stones or render failed...
I pressure washed the entire wall with an ordinary domestic pressure washer and "dirt blaster" jet. That removed most of the old paint, algae and anything else loose. Found a few weakness's in the pointing. Patched that up and painted with Dulux Trade Smooth Masonary Paint, it's surived one winter and looks pretty good.
--
Cheers
Dave.




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AL_n wrote:

Id pressure wash it to get lichen off, and then put onb a 50-50 thinned coat of whatever it is you are using.
Think mines done in Dulux exterior. That worked well and is holding up 10 years later.
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On Fri, 22 Jul 2011 11:53:19 -0700 (PDT), harry wrote:

Yep.
The test for "powdery" is doe you end up with the old paint on your fngers if you rub it gently. Even then I'm not convinced that a stabilising solution is any better than a slightly diluted first coat. IIRC the first coat I used last year (and this when I've finished the patching) was about 10:1 paint:water.

Brush is damn hard work if there is any texture to the surface and tedious in the extreme. Rollers work but you need a decent one. Dulux Trade Heavy Duty Woven Sleeve(*) worked and lasted well, two and a half two storey gables with two full coats on smoothish pebble dash and stone. The dilute first coat was brushed. I don't think that roller was quite dead but was starting to moult a bit quicker than at the start. Give a new roller, no matter the make, a good washing and scrubing before use to get rid of any loose pile.
(*) Be aware that roller is a 1 3/4" core the sheds sell frames for rollers with smaller cores...
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Cheers
Dave.




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On 22/07/2011 21:34, Dave Liquorice wrote:

I found if painting textured render (i.e. like stipple finish or roughcast), those small 4" wide rollers can be good. Often you can't get enough force onto a full width one to work the paint into the texture, and the small roller works faster than a brush.
--
Cheers,

John.

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Thanks to all for the tips. I followed the advice about pressure cleaning and then using a diluted coat. It all seems to make good sense.
They say that a lick of paint hides a multitude of sins. Well this paint job actually seems to have shown up a load of sins - like what a amateurish rendering job it was. I think I may have to apply a coat of really thick textured emulsion to try and disguise the patchiness of the cement rendering.
Al
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