External Lime render

[mlf1973]

Hi everybody. Pleased to be enrolled onto this forum. We have recently bought an old building and I am looking for some specific advice on lime render. Let me outline the reasons for its use to see whether it is a worthy option. The exposed gable end has many weathered bricks beyond repair and the pointing is in good need for redoing. Inside we seem to be getting a lot of damp and mould on the walls (this may well be down to moisture within unable to escape but hoping the rendering will at least help)
On the exterior I need a coating to help protect the gable end from further deterioration and feel that a render would suit the building ,(We already have 1 side of the building rendered) My main question is what would be the best materials to use (including mixing ratios) i am thinking of using a nhl 3.5 with sand??? Or are there any breathable ready mixed renders on the market suited to older buildings.
The building dates back to the 1750's although there are various later adaptations. This property is not a listed building. Just want the best advice before I begin the work. Many thanks in advance Matt

 

[TheSpid]

Ty Mawr do ready mixes - we are using one of theirs for internal plastering and it is saving so much time I would def recommend looking at their website. https://www.lime.org.uk

 

[steveb]

Hi Matt

Where are you in the world - pre-mixed lime (we used tonnes of it from "heritage cobb and lime" in North Devon) is certainly available in many different mixes, grades and qualities but due to the bulk and weight is likely desirable to pick a local specialist. This is not really mail order stuff

-Steve

 

[Flyfisher]

Agreed. I buy lime products, including ready-mixed from Anglia Lime Company in Sudbury, Suffolk, but who knows if this is helpful to the OP?

Inclusion of an approximate location in one’s profile or posts is always helpful.

 

[mlf1973]

Hi and thank you for the replies so far I will investigate each one for practicalities and price. Good point on location. We are in the East Midlands near Derby to be precise so companies that deliver here for a reasonable price or local manufacturers would be great. Nice to know there are companies producing the ready mixed lime products that will take out the guesswork of making my own and getting each mix as exact as possible. On the off chance I can't get hold of ready mixed is there anybody who has made their own lime render and have a good long lasting product out there (again with aggregate type and ratios in mind) thanks again for those taking the time for tge responses so far.

 

[mlf1973]

Ty Mawr do ready mixes - we are using one of theirs for internal plastering and it is saving so much time I would def recommend looking at their website. https://www.lime.org.uk

Many thanks for this link I have emailed them for advice

 

[88v8]

....lime render.

Hello and welcome.

Well, it will do no harm.
NHL 3.5 or 2.0 would be fine, needs to be mixed with a sharp sand. Sharp, not soft that is to say not 'Building Sand'.

There is a good guide to rendering and plastering here https://www.periodproperty.co.uk/shop/acatalog/plastering_with_lime.html

Trad Lime also sell ready-mix http://www.traditionallime.co.uk/products/traditional-lime-products/lime-renders and they sell suitable sand if you prefer to mix your own.

As regards the damp and mould, built in the 1750s the building would have had no dpc nor dpm, so the internal moisture level will inevitably be higher than in a modern building. If modern builders have been at it with non-breathable materials such as cement or gypsum plaster, if the walls have been painted with modern plastic paint, if there have been half-baked attempts at 'damp proofing', if the fireplaces are sealed up, if the doors and windows do not have a nice little draught coming through them, if there is no extractor fan in the kitchen and bathroom, if the external ground levels are high in relation to the floors, then all this conduces to damp and mould.

With a couple of rh meters you can see what you've got. Anything over 70% relative humidity is a potential problem.
https://www.amazon.co.uk/Habor-Thermometer-Hygrometer-Temperature-Replacement/dp/B07GWL6ZFV/ref=sr_1_7?keywords=hygrometer&qid=1554107826&s=gateway&sr=8-7

Currently in our C17 cottage, we're about 50%, that's as low as it goes. We have two dehumidifiers and two woodburners. When we stop lighting the woodburners, the rh will creep up until it hits about 70% and it will stay that way until autumn when we light up again.
Our entire upstairs has been painted with vinyl paint, and in our coldest room we have some mould.

A dehumidifier in your worst room may help with the symptoms, while you work on the causes. We have two of these Ebac 2650
https://www.ebac.com/dehumidifiers/2650e-18-litre-white-dehumidifier-dd695wh-gb

Anyway, yes, external render will protect the bricks. After the danger of frost has passed, now would be a good time, before the summer sun gets up and creates drying problems. Lime render needs to dry slowly.

Ivor

 

[mlf1973]

Igor many thanks for a detailed and comprehensive review. Yes my property sounds similar! Unfortunately the house is plasterboarded in various locations and we are finding rh hitting the 70% Mark in winter. I had purchased a dehumidifier which really does help. The problem with renovating an old building that has seen many occupants and more worrying lots of tradesmen who don't understand older buildings is that it's virtually impossible to undo all the bad things. That is why I am opting for the lime render on my gable end.
So far this is what I have been advised:
Using a hydraulic lime nhl 2.0 with aggregate as base with a fibre in
Then a top layer hawled on for a rough finish weaker than the base.
I am struggling to understand how I would bead this. What would be the best way to finish the edges to keep it long lasting, looking good for the age of building and stopping edges getting damaged. I assume the metal or plastic is not used
Cheers

 

[mlf1973]

Igor many thanks for a detailed and comprehensive review. Yes my property sounds similar! Unfortunately the house is plasterboarded in various locations and we are finding rh hitting the 70% Mark in winter. I had purchased a dehumidifier which really does help. The problem with renovating an old building that has seen many occupants and more worrying lots of tradesmen who don't understand older buildings is that it's virtually impossible to undo all the bad things. That is why I am opting for the lime render on my gable end.
So far this is what I have been advised:
Using a hydraulic lime nhl 2.0 with aggregate as base with a fibre in
Then a top layer hawled on for a rough finish weaker than the base.
I am struggling to understand how I would bead this. What would be the best way to finish the edges to keep it long lasting, looking good for the age of building and stopping edges getting damaged. I assume the metal or plastic is not used
Cheers

 

[88v8]

I am struggling to understand how I would bead this. What would be the best way to finish the edges to keep it long lasting, looking good for the age of building and stopping edges getting damaged. I assume the metal or plastic is not used

Yes, it can be hard, undoing the bodges of the past.

Beading, mmm , if the render doesn't have a recess to sit in, you really need to create one by a timber surround. Think 1920s mock Tudor.
At the bottom you can create a drip, if you have the skills (I don't) so no bead needed.

A picture?

Ivor

 

[livias]

You dont need beading. Make a rounded curve like this ...
.

 

[mlf1973]

Cheers again for the responses. On the latter response the rounded finish does look good. However if it is just the gable end I am rendering then it will be a corner. 1 side will be the rendered side and the other is brickwork finish. So I wouldn't be able to round a finish??
I will post a couple of pics
Cheers matt

 

[mlf1973]

Here are a few pics of my 2 gables I am planning to render and brick condition etc

 

[Flyfisher]

Having now seen the photos I'm not sure that rendering would be my first thought.

Yes, there are some spalled bricks and some areas of poor pointing but overall it's a rather lovely brick building and I'm not sure that rendering would improve its looks.

I'm wondering if it might not be better (e.g. quicker and cheaper) to carry out some appropriate repairs to the affected bricks rather than take the fairly drastic step of rendering the whole wall and giving yourself (or some future owner) a lifetime of limewashing maintenance?

Spalled bricks can sometimes be removed and 'reversed', depending on how easy it is to remove the mortar on the internal face. This can be an almost invisible repair because the brick match would be perfect. Alternatively, replace with a a closely matching brick - brand new or reclaim depending on which side of that argument you lie :wink:

I appreciate you're also considering the internal 'damp and mould' but you've already suggested that could be internal condensation (common mould likes freshwater rather than water moving through brickwork and picking up salts on the way), so external render might not help anyway.

You don't say how recently you moved in but if it is very recent, eg a few months, then I'd be tempted to live in the house for at least the rest of the year before rushing to render the exterior, just to see how the house adjusts to its new occupants.

 

[TheForge]

I agree with Flyfisher.

Rendering those gables to my eye would ruin the look of the building. Repointing the areas where the mortar is clearly failing and checking for damage where the slate roof abuts would be a better investment for the same result.

Where is the damp on the inside? Again I’d tend to agree with Flyfisher that it is likely the result of condensation.

Rendering over cement pointing will be counter productive as moisture within the fabric will still migrate through the bricks.

Those bricks have withstood the elements for 270 years and a few have spalled likely due to recent cement over pointing. I really doubt they’ll deteriorate much during your time in the house, especially if you remove the cement pointing.

 

[mlf1973]

Thanks for the opinions guys, appreciate the honest assessments. If I went down the repointing route does anybody know how to go about filling some of the very very small gaps between some courses?I gave done some repointing in the past with lime mortar. Generally using a sharp sand aggregate and using the pointing knives down to around 5mm blades. Some of these gaps are 2-3mm and I am worried that trying to point these will a) end up with mortar on the brick faces and
b) not able to get the mortar in to the joints.

 

[TheForge]

I’d be surprised if brick joints were only 2-3mm wise, that’s narrow for high quality ashlar work.

In any case the edge of a point iron or an adapted/ground down iron or screwdriver will be fine. A good, reasonably dry mix, with appropriately graded sand will be needed and any mess wiped off the face as you go. Joints that small will need an aggregate with grain size less than the width of the joint, not the normal, genetically banded about ‘sharp’ sand.