External house painting

dairbhre

Folks,
I'm planning to paint my house on the outside within the next 5/6 weeks. It's a fairly plain standard 3 bed bungalow, but a lot of the paint work has been discoloured by moss. There are old trees in the adjoining property and hence the green mossy problem on one gable in particular.
Before I paint I plan to Power wash the lot, but should I apply anything to the existing paintwork before I start to paint on the new emulsion?
Is there any solution I should apply after I have finished to reduce this problem for the future?

Dairbhre

air

I did a big job on roof slates a few years back & I used some anti fungal wash on them after power washing & before the sealant coat. You basically paint (well I sprayed it on with power washer ) it on and leave it dry & then wash it off a day or two later before you put on the first coat.
Might help in your case.

mad m

Well to reduce or even stop the problem from happening in future is to find out exactly why its happening, and then do something about it.I would apply a Fungicidal Wash Link
And then use either Dulux weather shield or Sandtex exterior emulsion.

GreeBo

I dont think power washing is recommended, thats a hell of a lot of water hitting your walls at force.
You'd want to leave it for a week to dry out I reckon.
To be honest I just wouldnt do it at all.
I used a scraper and a wire brush to remove any moss and loose paint.
The painted dilute PVA over the areas that were down to the render (or close) and then 2-3 coats of Dulux Weather Shield.

narommy

GreeBo wrote:

I dont think power washing is recommended, thats a hell of a lot of water hitting your walls at force.
You'd want to leave it for a week to dry out I reckon.
To be honest I just wouldnt do it at all.
I used a scraper and a wire brush to remove any moss and loose paint.
The painted dilute PVA over the areas that were down to the render (or close) and then 2-3 coats of Dulux Weather Shield.

PVA will do nothing for the problem.

THe people who advise a fungicidal solution are right. Use plenty of it. I power hosed a house i did a long time ago and it didn't cause any problems but the house would have been damp anyways. Drying it out mightn't be a bad idea.

Make sure that the paint you use has a fungicide in it. I used a paint by Circle.

If you can chop those trees down.

GreeBo

narommy wrote:

PVA will do nothing for the problem.

The PVA wasnt for the moss, its to seal the exposed render/plaster/concrete.
Id still defnintely not recommend a power washer, yeah it will certainly clean off most anything from the house, but it will probably take off paint and a layer of render and I think thats just too harsh for the house.
Better use some elbow grease imo...

tred

GreeBo wrote:

The PVA wasnt for the moss, its to seal the exposed render/plaster/concrete.
Id still defnintely not recommend a power washer, yeah it will certainly clean off most anything from the house, but it will probably take off paint and a layer of render and I think thats just too harsh for the house.
Better use some elbow grease imo...

We powerwashed our home house a couple of years ago. it was in a bad way one gable end with red mossy type stuff. we applied a fungicide. Power washsed it off, it ran off it, and then let it dry for a a few days. just make sure power wash gun is not on a very narrow full power setting as i have seen them take the plaster off the wall. Have gun a bit away from wall. Tahts 5 years ago, and you know it never came back.

rooferPete

Hi Greebo,

A little off topic but take care using PVA (polybond) on external walls, while it does stop water soaking into the plaster finish it also stops the wall from breathing.

By that I mean any moisture that rises from under the foot path level in or behind the plaster can be trapped by the PVA, causing damp in the wall or cavity.

.

Steve

I'll second that - do not under any circumstances put PVA on exterior walls. At best you'll be watching all of the paint peel off in 6 months - worst you'll end up with a damp problem.

PVA has it's uses -
1. sticks plaster to walls and reduces suction...
2. sticks bits of wood together.
3. seals concrete before putting carpet down

do not use it before painting, tiling, anything else you think you need to "seal" the surface.

if you're worried about paint adhesion, the best thing is to prime with a 50/50watered or thinned coat of the paint you're applying.

PVA forms a barrier - it does not soak in, when it's subsequently exposed to moisture it re-activates and turns into a semi-liquid state happily releasing any paint or tile that is stuck to it.

GreeBo

Good point Pete, however I only use the PVA on the areas where the paint was right off and down to the bare wall.
I wouldnt advise "painting" your entire house with it.

stevec, I dont think thats quite true.
I use a very, very diluted form of PVA for this purpose and have always found it to be a good job. I can tell that it has soaked in and dried off, the mix is only about 20% PVA its not like Im just painting glue to the wall.
I've had no problems with Paint peeling off in areas that have been treated in this manner.
It's advised to use it before tiling as it will stop the undersurface sucting at the tile cement.
Im not sure why you have such a problem with it...

Steve

Sorry if that sounded aggressive, not intended.
I was really surprised to read the following, before which I would have probably given the same advice as you did.

Have a read and see if it changes your mind:
http://www.diynot.com/forums/viewtopic.php?t=33645

GreeBo wrote:

It's advised to use it before tiling as it will stop the undersurface sucting at the tile cement.

He's saying the opposite - the adhesive maker won't guarantee the product if used over PVA

I've also read the same arguement about using PVA before painting - and - I've previously fallen into that trap with the paint in my kitchen - couldn't work out why it was peeling - turns out it was the PVA undercoat. What the Pro's do is use a proper primer or use a watered coat as a primer.

I'll post the link to the painting discussion if I can find it.

GreeBo

stevec wrote:

Sorry if that sounded aggressive, not intended.
I was really surprised to read the following, before which I would have probably given the same advice as you did.

Have a read and see if it changes your mind:
http://www.diynot.com/forums/viewtopic.php?t=33645



He's saying the opposite - the adhesive maker won't guarantee the product if used over PVA

I've also read the same arguement about using PVA before painting - and - I've previously fallen into that trap with the paint in my kitchen - couldn't work out why it was peeling - turns out it was the PVA undercoat. What the Pro's do is use a proper primer or use a watered coat as a primer.

I'll post the link to the painting discussion if I can find it.

No worries, none taken...
Im still not sure, I wouldnt have used it on a plasterboard wall that I was going to paint but would before tiling, in fact I am about to on my bathroom wall (gipsum) and floor (ply) and kitchen floor (concrete)

At a guess I would say it very much depends on the quantities used and the mix ratio, as I said, I havent seen any problems on the exterior walls where I used PVA (just on patches, not a whole wall wash)

<edit>
ahh interesting, the last post on page 3 of that thread says the same thing I just did,
I think the problems occur when you have too much PVA and you end up with e layer of glue on the wall, which, as you say when gets mixed with wet cement can turn back to goo.

dairbhre

Thanks everyone, so its,
1. Fungicide
2. Power wash off dead moss after 24 hours
3. then paint on good quality paint prefferably containing fungicide also.

Thanks.

mad m

Personally I would of never have used Pva on a wall before painting,have only ever used Pva on a hole that was dusty and about to be filled.THe only thing I would suggest on outside walls would be Stablising solution.This acts as a sealer to dusty flakey walls prior to painting.You can get this in either water/oil based solution.

Goodluck to OP with outside of house.

rooferPete

Hi mad_m,

Spot on use it to help prepare the surface.

.

narommy

stevec wrote:

PVA has it's uses -

do not use it before painting, tiling, anything else you think you need to "seal" the surface.


PVA forms a barrier - it does not soak in, when it's subsequently exposed to moisture it re-activates and turns into a semi-liquid state happily releasing any paint or tile that is stuck to it.

The amount of time and misery PVA has caused me is horrific.
Bought a house, started to repaint inside walls. the paint started peeling off and brought a layer of the skim coat off as well.

Definitely do not use it to prime walls, especially if the skim hasn't hasd time to dry out properly