Repair of exterior cement render and flaking masonary paint

[Cheltonian]

A Victorian villa has been rendered with cement and then painted with masonary paint.

While the render is sound in most areas, there are craters a few mm deep (many less than 1 foot square) of render.

Is there any way that this can be reliably repaired to re-instate a reasonably smooth finish without stripping back to the brick and starting again?

While the paint is sound in most areas, (including the craters) in others it is either
1. Peeling
or
2. Pitting and trapping dirt leaving a blackened finish

What is the best way to clean and prepare this ready for repainting?

Chelteonian

 

[Gervase]

As you don't want to remove the cement-based render (which, to be honest, would be the best approach for the house, but would take time and cost a fair bit), the best way to patch would be to give the holes in the render two coats of 1:2 PVA:water mix and then use a stiffish cement mix to fill. Try to match the aggregate to the existing stuff if you can - in terms of particle size rather than colour as you'll be overpainting it.
Use a float to level the new with the old, and before it takes a full set use a wet paintbrush to feather the fresh cement onto the older stuff.

As for the masonry paint, if it's the plastic sort so often used these days it's an absolute b*gger to sort. You end up peeling off great sheets of it trying to find a sound area. The stuff that's cracked needs to be taken off too - use a heavy duty scraper - and the stuff that remains needs to be given a key for the new paint. Either use a stiff wire brush or some coarse grit sandpaper, and be prepared for aching arms and a heck of a lot of dust!
But, as with all painting, the finished article reflects the amount of preparation you put into it.

 

[NT]

> While the render is sound in most areas, there are craters a few mm deep (many less than 1 foot square) of render.

> Is there any way that this can be reliably repaired to re-instate a reasonably smooth finish without stripping back to the brick and starting again?

If you do mean a few mm,
a) I'm surprised youre bothering
b) you cant use a cement mix, as you likely know
c) epoxy mortar is the better option, tile grout the not as good option.

Whether doing this at all is the best option is open to debate.


NT

 

[Mark]

craters a few mm deep

Does that mean that an older coating has been overpainted? We have some shallow (1 or 2 mm) patches on the front of ours and it is down to some thick 'weatherproof' coating applied years ago and overpainted by the previous owner. I have just painted over the lot of it because I am not interested in stripping off all the render at this point.

 

[Cheltonian]

Yes the craters are a few mm thick and around 25cm square in area, in several places around the wall.

It looks like the render was left unpainted for several years as it had stucco 'blockwork' lines drawn into them, until some masonry paint was then slapped on without first repairing any of aforementioned decayed areas.

Other areas of the render have 'blown' from the wall and are larger in area (~ 1m square) - so these will necessitate some more substantial remedial action before repainting.

Cheltonian.

 

[NT]

Cheltonian:

>Other areas of the render have 'blown' from the wall and are larger in area (~ 1m square) - so these will necessitate some more substantial remedial action before repainting.

I trust youll be doing these in lime, not more brick-damaging cement.

NT

 

[BMcD]

I trust youll be doing these in lime, not more brick-damaging cement.

Bear in mind that if it's a Victorian villa then there's a good chance it may be original render since from at least 1850 portland cement was being used to render the facades of many grand buildings and lots of not so grand ones and by the late Victorian period it was widely used for external works.

 

[L1zzy]

Just thought I'd pitch in - I have an 18th C cottage .It consists of rubble stone elevations to half way up then brick - at some stage it too has been rendered with what I'm prety sure is concrete and then coated with a cream/buff coloured substance which contains sparkly crystals - on top of this has been painted at least 2 coats of plastic paint - Pink and then white. YUUUUKKKK I too have teh problem you describe and cannot afford and not sure I would wish to sandblast the render off (I figure it would do much more harm than good) My own plan is to Lime Wash over the areas where I've been tempted to pulls off the plasticky paint so it looks presentable - then next year take off all the paint by hand ,scraper whatever but mainly my own hard work and then lime wash .As any concrete render blows and falls off I will patch it with Lime Mortar and eventually I hope to have a mainly lime rendered cottage in about 50 years time! Thats my plan after much thought and discussion and given my financial constraints.

 

[dmcquade]

If you do patch in lime due to the vastly different properties of the two materials you will get cracks at the joints. Also limewash may not take to a cement render.

All the best.

David

 

[biffvernon]

Sounds a good plan to me Lizzy. I always favour solutions that cost about nothing and look a bit ragged round the edges.

 

[NT]

I trust youll be doing these in lime, not more brick-damaging cement.

Bear in mind that if it's a Victorian villa then there's a good chance it may be original render since from at least 1850 portland cement was being used to render the facades of many grand buildings and lots of not so grand ones and by the late Victorian period it was widely used for external works.

Also bear in mind that 1850s cement was weak compared to todays opc, so whereas the original coating may not have pulled bits off the bricks, a strong modern cement layer generally will.

OPC is not the best stuff to use outdoors btw, if you must use cement.


NT

 

[NT]

My limewash has taken to my render happily enough, but I cant speak for someone elses render, as mixtures can vary.


NT

 

[L1zzy]

Phew ..........thanks NT I was thinking about the Limewash stickability problem at 3am (sad I know) and thinking well heck i'll just try the Lime Wash and see what happens - you see PPUK is teaching me to be a 'have a go' heroine!!! I figure try it and then if doesn't work and steadly drips off the wall then go to plan B .......given of course that I'll have thought of a plan B by then!!

 

[Lynn]

I have had good luck with lime wash or white wash (I think it is the same thing from this conversation) over cement stucco. I also tried putting it on a 2 square foot patch someone did in that new material (fiberglass spit on the wall) and after a year the color is still sticking. That was an experiment, but since it was on the wall I was painting I decided one color would be better. I'm not sure how long the wash will last there since it is an impermeable surface, but from my reading about it I gather we will need to white wash the place every few years anyway.

Don't loose sleep over it anyway.

 

[Gervase]

If you're worried about the 'stickiness' of your limewash, whisk a cup of linseed oil into every 20 litres. It will stick handsomely then (and smell rather nice, too, which is more than can be said for casein or tallow).

 

[BMcD]

Also bear in mind that 1850s cement was weak compared to todays opc, so whereas the original coating may not have pulled bits off the bricks, a strong modern cement layer generally will.

OPC is not the best stuff to use outdoors btw, if you must use cement.

This is absolutely true and I was mearly suggesting that it is not inconceivable for the original render to have been cement based and if you plan to restore to original then it's something to think about

 

[L1zzy]

Gervase - Hey great tip ....I'm such a fan of Linseed oil now I'll try it with anything and I know just what you mean about the smell .You know what they say 'one instinctively knows when something is right!' well every time I wash my paint brush out in Linseed Soap a la Holkham I think why on earth would anyone use modern paints and spirits when this simple solution works so easily.