Damp, rendering and insulating external walls

VfM4meplse

I have heard different stories from different traders and am getting confused, so some impartial advice from this board would be appreciated!

I have some damp coming in from cracks in my external rendering. Its not a huge problem but nor will it resolve itself, so something needs to be done about it. At first I thought I would ask a damp specialist to sort this out for me, which would involve chipping off the render outside, the plaster inside, allowing it to dry, ?injecting the brickwork with something?, and then making good the damage. So far, so simple.

But the plan was to re-render the external fascia anyway, so would chipping off the render, allowing the wall to dry and then rendering save any "damp treatment" and the hassle of having inside work done? The position of the walls is such that there will always be a risk of water ingress, but by using a waterproof (silicon / acrylic) render and ensuring the bottom of the wall has a ledge to drip over (as opposed to a way of letting water in) this solution seemed to make sense. I don't know whether foregoing the damp-proofing work would be a false economy and that is where some experience would be very welcome.

Finally, it was suggested to me that while I was having the walls rendered, I might like to consider having the walls insulated from the outside with panels of some description and then rendered on top. This was music to my ears because the house is brick constructed with no cavity wall that would be amenable to insulation. In theory its a grand idea because its no secret that I find my house a chilly place to be in for much of the year, but because I have heard of insulating disasters (internal condensation, difficultly in removal etc) and didn't think there was an alternative to cranking up the heating in my home I am sceptical. Am I right to be?

FreeBear

Solid brick walls should be rendered with a lime product, not cement, acrylic, or other modern material. Once damp, heat will quickly travel through the wall, and a waterproof coating will stop the brickwork from ever drying out.

If you remove the external render over 25% of the walls, building regulations require insulation to be added (although there are get out clauses). Due to the nature of your walls, it would be advisable to look at cork or wood wool insulation finished with a lime render. Have a look at some of the products here - https://www.mikewye.co.uk/product-category/natural-insulation/ - Then have a chat with their technical team.

snowcat75

Internal insulation is better as a rule, you can create a tank with an air gap, witch will stop any damp bridge and give damp or condensation some ware to go.

Free bear is quite correct there have been as many problems created with sand and cement render it can lock damp in, force it else ware even in the worst case cause movement. Hydraulic lime mixes are better as they allow damp out as well as in.


However having restored old buildings id still go for an internal insulate to allow the building to what it always has.

VfM4meplse

Thanks for your responses but I'm now even more confused! Is "traditional" rendering lime, or sand / cement?

What has really confused me is that my neighbour has gone for silicone, the rest of the street "traditional".

FreeBear

VfM4meplse wrote: »

Is "traditional" rendering lime, or sand / cement?

Traditional render is a mix of lime and sand. No cement added.
Modern renders are a mix of cement, sand, and other chemical additives.
Then there are modern acrylic & silicone renders which are a mix of chemical binders and sands.

A problem with a lot of builders that say they use "lime renders" is that most of them will add cement to the mix. This is not a "traditional" lime render, and is unsuited to solid brick houses.

snowcat75

VfM4meplse wrote: »

Thanks for your responses but I'm now even more confused! Is "traditional" rendering lime, or sand / cement?

What has really confused me is that my neighbour has gone for silicone, the rest of the street "traditional".

As free bear says.

One of the problems is render (sand and cement) was used as a cheep fix on a lot of Victorian era brick house with damp popular to do in the 50s and 60s. It only partially worked as damp can come from any ware from an old chimney breast to rising from (if any) the old slate DPC. As many times as it worked it did no more than lock in the damp.

Personally I think the only way to solve many of these problems in these old buildings is to completely remove the render bring it back to brick/repoint, then insulate and tank from the inside. However that of course is expensive.

VfM4meplse

snowcat75 wrote: »

Hydraulic lime mixes are better as they allow damp out as well as in.

Was I being overly optimistic in thinking rendering a dried out wall would prevent further damp problems?

I can see evidence of a damp course being installed previously, and the house has further records of damp treatment in certain spots. Its clear that water will always penetrate it over time (albeit at a very slow rate) and this was in part why silicone seemed an attractive option.

snowcat75

VfM4meplse wrote: »

Was I being overly optimistic in thinking rendering a dried out wall would prevent further damp problems?

I can see evidence of a damp course being installed previously, and the house has further records of damp treatment in certain spots. Its clear that water will always penetrate it over time (albeit at a very slow rate) and this was in part why silicone seemed an attractive option.

It might it might not, damp as I said can come from any ware even something as simple as changing a path laid against outside walls to permeable surface can stop it.


Personally id be tempted to make good the render, then insulate a room at a time as you decorate with an air gap to tank, done right its the cheapest most effective way to both insulate and prevent damp, only disadvantage is you will make your rooms slightly smaller.


Many of these wonder products and quick fixes tend to be part snakeoil. Not all but I certainly research well before parting with the hard earned.

VfM4meplse

snowcat75 wrote: »

Many of these wonder products and quick fixes tend to be part snakeoil. Not all but I certainly research well before parting with the hard earned.

Don't I know it! But its difficult to dismiss out of hand the advice by people doing the work day in, day out.


Ok, so another thick and how-long-is-a-piece of string question from me how long does it take for brickwork to dry out thoroughly, assuming it is warm and dry? It bleeps red on the damp meter but there are no obvious signs / smells of damp inside.

snowcat75

VfM4meplse wrote: »

Don't I know it! But its difficult to dismiss out of hand the advice by people doing the work day in, day out.


Ok, so another thick and how-long-is-a-piece of string question from me how long does it take for brickwork to dry out thoroughly, assuming it is warm and dry? It bleeps red on the damp meter but there are no obvious signs / smells of damp inside.

Those doing the work everyday however are normally getting paid to do so, and don't have to live with consequences 5 or 10 years down the line, many of these problems were created in prior decades by people doing the work day in day out. I'm not saying all are wrong but pick the advice carefully.


as for dry out It does depend the slowest could be 1mm per day so on a solid 9" wall over 200 days!!! but its likely it would be much quicker what you have to remember even now in summer a solid wall will create some damp as it will condensate between the warm and the cool.... Its why really these old houses need to breathe.

VfM4meplse

The comment about consequences is so right and in part why I'm dithering so much. Also, the more I learn, the more I seem to be changing my mind! I've been reading around a little, and found this article, which was helpful to a degree.

Lime plaster seems the most appropriate solution, but the pictures I have seen of it suggest a "lumpy" appearance. None in the 2 facing rows of same-style houses have this appearance, I can see that they have all strived for smooth (they are in various states of repair). So can lime render give an even finish?

Things that worry me:

FreeBear wrote: »

If you remove the external render over 25% of the walls, building regulations require insulation to be added

The article seems to corroborate this (it says 50%, but I want it all off) so that any underlying damp patches can dry out. It seems like a lot of faff for what is primarily a cosmetic procedure.

[QUOTE=snowcat75;76036203]Internal insulation is better as a rule, you can create a tank with an air gap, witch will stop any damp bridge and give damp or condensation some ware to go.

Free bear is quite correct there have been as many problems created with sand and cement render it can lock damp in, force it else ware even in the worst case cause movement. Hydraulic lime mixes are better as they allow damp out as well as in.


However having restored old buildings id still go for an internal insulate to allow the building to what it always has.[/QUOTE]The first article is advocating insulation if any rendering work is being done, but seems recommend external slab insulation as being standard. I can see both perspectives, but want neither the hassle of internal work, or damp problems associated with these panels. On balance, living with a cold home and spending on heating seems preferable!