Painting the base/skirt of a rendered timber-framed house

[Suffolk_tyke]

Newbie on the forum, be gentle....
I have a timber framed grade-II listed house, c.1650. It originally had exposed beams, but was rendered in the 1980’s, apparently (TBC) with cement render, “to protect studwork that is at present exposed”. Listed building consent was given...

The bottom 2 feet or so is painted black. The paint is wearing away in some spots, and just “looking thin” in others, so I need to do something. I think the generally accepted advice is to use limewash on buildings of this age, but I’m not sure that’s necessary.

My questions are:
(1) is there such a thing as black limewash? If not, what alternatives exist?
(2) if it is a straight cement rendering, will it matter if I use a modern paint?
(3) If so, any suggestions? Current front runner looks to be Dulux Weathershield which claims to be water based http://www.dulux.co.uk/advice/questions/faq/faq_050.jsp but also acrylic (?) and to be a breathable and flexible, see http://www.dulux.co.uk/products/info/weathershield_smooth_masonry_paint.jsp.

Finally, somebody suggested that the existing finish is black bitumen paint – sounds horrible, any comments?
All constructive advice gratefully received.

 

[Gareth Hughes]

It is likely to be black bitumen paint. Traditionally the treatment would have been tar.

If the cement is sound, then at a purely technical level and as far as the cement is concerned, painting in "modern" paint won't make any difference.

However, I would be very concerned about what may have been going on under the cement in the 25 years since it was put on to "protect" (ie hide, out of sight and out of mind) timbers which presumably were already showing some signs of distress (otherwise why suddenly want to "protect" them?). In Suffolk they would, almost always, have been lime rendered or at least lime washed for most if not all of their lives, (possible exposed in the 1930s or 1950s to look pretty?) but cement isn't lime.

Others will no doubt be along shortly to provide the appropriate horror stories, but this is one case where I really wouldn't advise doing nothing and hoping for the best.

 

[Penners]

Welcome Suffolk Tyke - there's a few of us South Folk on this forum.

The first question that probably needs asking is this: do you have damp problems on the inside walls? If not, then on the principle of "if it ain't broke, don't fix it", you may not need to do anything too radical. Although I echo what Gareth has said - it's possible that there could be problems inside the walls, particularly with the sole plate. But it's up to you whether you want to pursue that.

I take it from your post that the house is rendered right down to the ground, and that the bottom couple of feet of this render is painted black. If, as you say, the render is cement, then frankly it doesn't make too much difference what you paint it with - it's not going to be breathable. So you pays yer money and takes yer choice.

However, if you do have damp problems, then we need to talk about more extensive action. So please post back on this point.

 

[Flyfisher]

Yes, welcome to the forum. I can't really add anything to the good advice above except to say you're certainly not alone. The black paint around the bottom of our house (part timber frame, part chalk) looks very much like bitumen-sort-of-stuff and, yes, the rendering over the timber frame was at some time replaced with that new cement mortar 'wonder material'. :roll:

Our plans include the eventual replacement of the cement render with a lime render and, until then, I'm just keeping everything crossed that there is not too much damage being done to the underlying timbers by trapped water. If everything is dry underneath then things should be OK, but we won't know for sure until it all comes off.

As for 'protecting' your beams by covering them up, I'm afraid to say that 25 years of being wrapped up inside cement mortar might possibly have done them more harm than simply being exposed to the elements. We have some exposed timbers about 450 years old and although they are fairly gnarled they are also rock solid. Of course, I don't know their entire life story, but I'm pretty sure they've never been covered in cement mortar and they look good to me for another few hundred years.

So, the good news is that it doesn't really matter what you paint over your cement render, the more cautious news is that Gareth's concerns are very real. Oh, and as a newbie to the forum, you may not be aware that Gareth is a professional in these matters, so his concerns are very, very real.

 

[MdB]

Welcome from me too.

Some of us here like myself are non experts (unlike Gareth) and have learnt things as we go along. One thing I can totally agree with is that wood encased in cement can rot completely as had happened here:

It can be fine, if the damp doesn't get in but if it does, the wood will rot.

 

[Penners]

A god thing that you photographed that wood when you did, MdB. It looks as though it was probably dust a few hours later.

 

[robgil]

same boat here , you should expect a few bad sill plates and perhaps the lower half of your studs to perhaps need attention.

is the cement cracked? if not you might be lucky. for the timbers to rot you need moisture , cement or no cement if your timbers remained dry then they should be ok. can you see them from inside the house? are there any signs of damp anywhere?

as Gareth said your house probably would have been originally rendered with a lime render , a mix of chalk , lime putty and water has been found on a few 16c +/- houses around walsham , in fact my own house shows signs of this type of plaster although it also shows signs of originally being daubed on the outside which i think is more likely.
has any of the render on your house blown?
and most importantly , how about some pics?

edit -most paint is breathable to a certain extent , but how porous are they really? and how porous a paint do you need for a particular set of circumstances? (i dunno smiley)

 

[Suffolk_tyke]

Thanks all. The degree of skill and amount of experience on these forums is very impressive.

I take Gareths point - given that the cement is the determining factor anyway, the type of paint will make minimal difference. I hate to think what’s behind the concrete, especially after seeing some of the pics.

The good news is that there are only a few hairline cracks in the render (would be covered by a good paint job), and no sign (or smell) of damp inside the house (where the beams and sole plate are exposed). There’s no “blown” render, its all very secure. Since I can’t realistically afford the time or the money to strip off the rendering and replace it, it’s going to have to be a simple paint job.

I contacted Dulux re the paint and got the following response:
“I can confirm that our Weathershield Masonry range is suitable to be used on Lime render as its water based. The formulation is designed with high performance acrylic resin that provided total protection against extreme weather conditions. The paint is designed to be porous so the paint film is breathable which is an advantage therefore moisture being released.”

So – it looks like Weathershield (BTW, the B&Q equivalent is no cheaper).

 

[Suffolk_tyke]

Post script to this.

The local council were helpful, and looked up the original LBC. Associated with their file was a letter stating that the "rendering is to have a smooth finish and comprise of an undercoat mix of five sand, one cement and half lime, the top coat to have five sand, one cement and one lime, giving a total thickness of between 3/4 and 1".

Any comments on just how advisable this was or wasn’t?

 

[Flyfisher]

Do you know the date of the original LBC? Opinion seems to have changed over the years.

 

[MatthewC]

Post script to this.

The local council were helpful, and looked up the original LBC. Associated with their file was a letter stating that the "rendering is to have a smooth finish and comprise of an undercoat mix of five sand, one cement and half lime, the top coat to have five sand, one cement and one lime, giving a total thickness of between 3/4 and 1".

Any comments on just how advisable this was or wasn’t?

My experience of a listed church with a similar render is that the resulting surface is impermeable, which isn't what you want, is it? We only had a few problems as most of the inside was done with lime plaster and, I think, the lack of moisture inside the church meant that the walls were still able to breathe sufficiently. I would guess that in a house the average volume of moisture per unit area of wall would be considerably higher (especially given how draughty most churches are!). That church was done in 1993, and understanding of lime and dampness has come a fair way since then, so if your LBC was granted a while ago then it is probably irrelevant.