Painting a peddle dashed/plastered wall

[clivejo]

Just a thought that been going through my head just wanted to ask for some expert opinion.

If you have a peddle dash or plastered wall which can soak up moisture, would it save energy to paint the wall so that water couldnt penetrate it?   I was reading that water evaporating from a surface has a cooling effect and is basically robbing the heat from the wall.  Would it be considerable to justify the expense of painting?

[A.L.]

hello,

first do nothing that will prevent water vapour from escaping from inside the house,

second, dry brick has a greater thermal resistance than wet brick, an uninsulated brick/ventilated cavity/brick wall has a U value of 1.72 when averagely wet and 1.58 when dry

the effect on a cavity filled wall would be insignificant - U-value 0.55 to 0.54

[skyewright]

If you have a peddle dash or plastered wall which can soak up moisture,

??
I could be wrong but I was under the impression that the harling (pebble dash) used on walls in exposed areas such as up here was there to help keep water out! It is certainly the practice to paint it, and nowadays that's almost invariably done with products like "WeatherShield".

[offthegridandy]

I think you'll find that it depends on the type of construction.

Old stone buildings with no DPC in particular need to "breathe". As such (ideally) pointing and rendering should be done using lime products that breathe naturally allowing the release of water vapour. Lime based paints for internal use are also available.  For best advice on lime based products speak to Nigel or Joyce at Ty Mawr Lime (Brecon)
 http://www.glaster.org.uk/  I don't have any commercial relationship apart from that of satisfied customer.  Our barn/home is bone dry. 300 Mtr high on Welsh mountain. Walls are unrendered but all pointed with lime.

Modern Harling on modern cavity wall constuction can be painted with Weathshield type products. Modern construction should deal with internal water vapour/moisture through planned ventilation.

 Around here old properties are often clad in slate or tin on North and West elevations as that creates a physical break between the wet and the wall.

Andy

[djh]

I could be wrong but I was under the impression that the harling (pebble dash) used on walls in exposed areas such as up here was there to help keep water out! It is certainly the practice to paint it, and nowadays that's almost invariably done with products like "WeatherShield".

I don't know if it matters but I don't think pebble dash and harling are quite the same. AIUI in pebble dashing, the render is applied to the wall and then pebbles are added (a.k.a. drydash). In harling the pebbles are added to the render and the whole lot is then applied to the wall (by throwing = harling) (a.k.a. wetdash).

To my mind, harling seems like a better technique from the point of view of weather resistance and also less likely to suffer from pebble dandruff.

[dhaslam]

Quote from A.L.
an uninsulated brick/ventilated cavity/brick wall has a U value of 1.72 when averagely wet and 1.58 when dry

You really need to save up the pennies for an insulation job.   

[Ivan]

I hate pebble-dash - it constantly rains debris, which needs clearing up. The thrown-render looks ok - great for covering up uneven walls (I thought that was the main reason for using it). But, and I speak from experience, it will take something like 4x the amount of paint that a standard rendered finish will require for repainting. My Dad tells me that painting a house regularly is a good idea because the paint fills the very small cracks which would turn into larger cracks which then get expanded by frost causing the render to start coming away from the wall.

[clivejo]

My Dad tells me that painting a house regularly is a good idea because the paint fills the very small cracks which would turn into larger cracks which then get expanded by frost causing the render to start coming away from the wall.

Well that makes sense.  I wish the local Roads Authority listened to this advice!

[knighty]

if you do paint it....

mix the first coat 50/50 paint to PVA glue

it stops the paint being soaked up by the wall

do it that way the the 2nd coat will cover it



if you just use paint you'll need up needing 3 or more coats of paint to properly cover it :-(

[clivejo]

if you do paint it....

mix the first coat 50/50 paint to PVA glue

it stops the paint being soaked up by the wall

do it that way the the 2nd coat will cover it



if you just use paint you'll need up needing 3 or more coats of paint to properly cover it :-(

Surely the more paint 'sucked' up by the wall the better water proved it would be?  In a long term point of view

[offthegridandy]

I was told by the guys that rendered our old house to apply unibond (PVA) diluted part water to 1 part PVA first. Slap it on with 8 inch brush.  Lovely job for a summers day!! Otherwise you'll need 3 coats of expensive paint.

Andy

[knighty]

Surely the more paint 'sucked' up by the wall the better water proved it would be?  In a long term point of view

I thought about that.... and it probably would help.... but painting walls like this is long hard work...

after seeing you're first 2 coats disappear into the all (and maybe the 3rd) you soon start adding PVA to the paint !

[Ivan]

I've used PVA on concrete and on plaster prior to painting or tiling. It's amazing how even the PVA gets sucked into the wall.

[knighty]

I had a breeze block wall built at work just before Christmas... I was in work over Christmas painting it...

first coat was a (rough) 50/50 pva to white gloss

right near the end with 4 blocks left to do I ran out of the mix... and figured just gloss would do and I could give that little bit an extra coat....

the stuff which was covered with gloss and pva first time took 1 more coat to cover it and make a nice job of it

the bit without the pva took 4 coats and still looks a bit lighter than the rest


painting fresh breeze blocks is a long boring thankless job.... I hadn't realise how much easier the existing wals are to paint once they have 40 years of paint on them to start with....


I spent about £140 on blocks/cement/sand, £170 for the bricky.... and then just over £200 on paint

I was expecting the paint to be the cheap bit... but it needs decent stuff... there's a lot of steam etc.. in our place and last year when I tried cheap b+q gloss it went yellow inside a week so I had to do it again