External wall insulation

David_Aldred

Hi donmaico,
If the original brickwork is at all recoverable and you are not insulating externally then I would tend to stick with the original brick finish rather than rendering over it to a severely exposed property. Rendering will reduce evaporation outwards from the property increasing the risk of dampness internally and if the cavity wall is clear then the whole point of the cavity wall is that penetrating damp from wind driven rain should not reach the inner leaf of the cavity wall. You might want to look at what type the original mortar is (not any re-pointing that followed after) and if it is a breathable lime mortar then stick with this for any re-pointing works which should include for raking out mortar beds 25mm deep prior to re-pointing.

Cement mortar re-pointing of original lime mortar beds reduces evaporation outwards through the mortar beds making the brickwork wetter so more prone to freeze / thaw damage. In addition if the pores of the brick contain water instead of air they are colder and if they are colder they are more prone to condensation within them thereby increasing the moisture resevoir within the wall which again is not desirable.

The same thing that applies to cement mortar re-pointing also applies to rendering and if you are going to render then again I personally prefer true lime renders which are far more breathable than cement renders. When lime renders crack they tend to self heal such cracks as rainwater passes over them in the same way stalagmites are formed. This does not happen with cement based renders and once cracked they stay cracked allowing water ingress which once behind the render freeze / thaws spreading detachment of the render often taking the outer face of the softer substrate with it.

The product you mention in your post above sounds tempting and the company are one of the market leaders in renders and concrete repair systems. You might do well to read the small print of their specification regarding substrate preperation and application to coastal properties and in addition it remains a cement based system. One of the biggest issues you are likely to have will be heavy chloride contamination of the substrate to such a coastal property from sea salts in the air giving the property a battering over the years and this can play havoc with cement based mortars and renders even with good substrate preperation.

The Building Research Establishment (BRE) recommends three coat work for rendering exposed properties and this is a one coat quick application system. In addition cement rendering systems are heavy and need to physically hang onto the wall rather than attempting to stick it on with SBR or similar and the recommendation for this is to rake out all mortar beds at least 15mm deep to provide this function which a builder will often fail to do. Remember 1 square metre of render at only 2 coat work weighs approx 40kg (88lbs).

You pays your money and you takes your choice - kindest regards, David Aldred Independent damp and timber surveyor

donmaico

thanks David , a lot to think about there.
my main concerns were about the genral condition of the brick faces because the house i lived in before the front elevation bricks spalled badly so we ended up have a textured coating sprayed on it to protect it.
The surveyor we used on this property didnt seem too concerned about that but felt there were areas where the pointing could be replenished, the paintwork redone and wall ties possible replaced.I t was only this other fellow i know who was in the building trade and he seemed to think the bricks were quite soft and suggested rendering.
Presumably lime pointing is different colour and would be quite easy to rake out the loose stuff.
I take your point about rendering although there are heck of a lot of houses round here that have been rendered,Guess they must all have lime render.What would be the best mix - 1-3 lime sand or 1-1-6 lime cement sand?

knowloads

Not read every post on this subject, but there are some grants available for external insulation currently 000's of homes (council stock) being EXI'd with brick or stone finish that is durable. Mobile / static homes getting 80% grants through Blue Flag in Halifax, had some dealings with Frank , but can't find his number. The systems have been devloped for all the issues mentioned here.

iamcornholio

David_Aldred wrote: »

Hi donmaico,
Any property within 8km of the sea is classed as severe exposure

I think you will find that for the purpose of full fill cavity insulation, the BRE class severe exposure as parts (not all) of the west coast of the UK and southern Cornwall and parts of Devon and Dorset, and some inland area of the northern counties.

Exposure is rated based on prevalent wind driven rain, not just being by the coast.

It is generally accepted that the ability of the face of the wall to resist moisture penetration together with its location (taking into account local conditions) is the key factor in determining how susceptible the wall is to water penetration to the cavity

Now add the fact that the passage of moisture to the internal leaf of a full fill cavity wall, is determined by the type and thickness of insulation.

This all means that the chances of moisture wicking to an internal leaf is determined by the location, type of insulation and cavity thickness.

It also means that even in coastal locations, full fill cavity insulation can be perfectly acceptable and lead to no internal damp issues.

As to external insulation systems in general ....

One of the biggest problems with external insulation systems, is the fact that it completely hides the structure behind it. Whenever I survey a property with external insulation I have to flag it up as being impossible to give an assessment of the structure. Now, if the property is in an areas of known ground movement potential, then this is a worry - as is when old drains or large trees are nearby

Its an enormous risk for a homeowner or potential buyer to live in a property where you can't see what is going on on the external walls. Add the increased maintenance costs - including very costly repair of proprietary systems, and this leaves a property which should be kept at barge-pole distance

The sales brochure tends to tell you how well the insulation works and how nice it looks when completed. After that, the rep has got his commission and the problems are passed to the homeowner

donmaico

David_Aldred wrote: »

Hi donmaico,


Cement mortar re-pointing of original lime mortar beds reduces evaporation outwards through the mortar beds making the brickwork wetter so more prone to freeze / thaw damage.

what would be the best mix David, 1 part lime to 3 of sand ?I dont suppose a masonry mix of 1:1 :6 would be suitable would it?

donmaico

iamcornholio wrote: »

As to external insulation systems in general ....

One of the biggest problems with external insulation systems, is the fact that it completely hides the structure behind it. Whenever I survey a property with external insulation I have to flag it up as being impossible to give an assessment of the structure. Now, if the property is in an areas of known ground movement potential, then this is a worry - as is when old drains or large trees are nearby

Its an enormous risk for a homeowner or potential buyer to live in a property where you can't see what is going on on the external walls. Add the increased maintenance costs - including very costly repair of proprietary systems, and this leaves a property which should be kept at barge-pole distance

The sales brochure tends to tell you how well the insulation works and how nice it looks when completed. After that, the rep has got his commission and the problems are passed to the homeowner

musdt admit my surveyor has very strong reservations about them too.Same with textured paint

darich

donmaico wrote: »

musdt admit my surveyor has very strong reservations about them too.Same with textured paint

In my line of work (structural engineering) we NEVER specify anything to cover a wall. Roughcasting can hide so many problems. Generally not so much an issue in a house to make sure the walls are stressed/cracked but the principle is the same.
I once had to inspect a damaged wall that was roughcast and decided that we needed to remove a fairly large area because the roughcasting was hiding potentially more problems.

To clarify, I've nothing against roughcasting on a house (mine is roughcast) but adding it retrospectively isn't always a wise choice.

donmaico

darich wrote: »

In my line of work (structural engineering) we NEVER specify anything to cover a wall. Roughcasting can hide so many problems. Generally not so much an issue in a house to make sure the walls are stressed/cracked but the principle is the same.
I once had to inspect a damaged wall that was roughcast and decided that we needed to remove a fairly large area because the roughcasting was hiding potentially more problems.

To clarify, I've nothing against roughcasting on a house (mine is roughcast) but adding it retrospectively isn't always a wise choice.

thats a good point but if your bricks are spalling what do you do?I have seen several incidents of that taking place here.My neighbour had the the whole outside skin on his walls facing replaced:eek:I dont want to have to do that

darich

donmaico wrote: »

thats a good point but if your bricks are spalling what do you do?I have seen several incidents of that taking place here.My neighbour had the the whole outside skin on his walls facing replaced:eek:I dont want to have to do that

Bricks can be taken out and replaced. We did it recently on a wall where numerous bricks were badly slapped and weathered. It's cheaper than taking the wall down and rebuilding it. Don't take too many out in the same area at once for obvious reasons!!!

donmaico

darich wrote: »

Bricks can be taken out and replaced. We did it recently on a wall where numerous bricks were badly slapped and weathered. It's cheaper than taking the wall down and rebuilding it. Don't take too many out in the same area at once for obvious reasons!!!

that seems the best idea, thanks!