Pointing and wooden frame windows

Thu 4 Apr 2019, 14:11

Interesting discussion on mortar and its variants.  This is actually for my son who lives in a period cottage which needs re-pointing which is why I thought it should be lime based for the stone in the wall.

Anyway thanks for the information

Wed 3 Apr 2019, 22:01

As Ian has already said, using a cement-based mortar on the type of stone building that we have here in Charlbury is a really bad mistake.  However, there is an alternative to using lime putty to make up a mortar that is suitable for building and pointing this type of stonework - natural hydraulic lime, which is actually easier to use while still providing the soft, breathable mortar that is needed.  It is a completely different product from "builders' lime" (hydrated lime), which is what Hans has mentioned in his 6:1:1 mix, and which does not do the same job.

In a nutshell, repointing Cotswold stonework with a mortar containing cement is asking for trouble, sooner or later.  Stone walls need to breathe, to get rid of any damp, which is what lime mortars allow them to do.  Cement-based mortars are hard and impermeable, so prevent walls from breathing.

And while we're on the subject, the other thing to remember is that, being hard with a polished surface, modern gypsum-based plasters don't allow stone walls to breathe inside a house either.  This can lead to the surface blistering and plaster falling off (often around the bottom of walls) as damp from inside the wall tries to escape.  Again, plastering using lime is the answer. Lime plasters can breathe.  Gypsum plasters can't.

Wed 3 Apr 2019, 21:56

My builders used that 6-1-1 mix for my extension last year. I experimented with re-pointing parts of my house (I am that way) and can report it's soft. And much softer than the stone. 

Wed 3 Apr 2019, 20:57

Ian’s comments no doubt assume that you do indeed have a property with cement free lime mortar. In my experience of properties in Charlbury, it is more realistic that Hans’s advice is appropriate.

If in doubt of the lime content of your existing pointing, test it with spirit of salts. If it is cement based, it will fizz. If lime based, you will get a very vigourous  exothermic reaction

Wed 3 Apr 2019, 20:40

A builder experienced with old period houses should be able to use lime putty and sand to make lime mortar. Please dont be fooled by talk of cement mortar with some lime, it is not the same and is very bad for old buildings being stronger than the stonework and waterproof and non-breathable and will eventually lead to damp problems and breaking up of the stone/brick. Look for a conservation builder,  I have seen a few specialists around the town working on some of the older buildings.

Wed 3 Apr 2019, 18:46

Builders no longer use lime mortar, they use a mix they call 6-1-1, that is six parts sand, one part cement (Hansons is good) and one part lime. Any bricklayer can do that.

For the windows I can recommend Jonathan Hitchcock Woodworks http://www.hitchcockwoodworks.com/ he's done three sashes and three casements for me and they are superb. 

Wed 3 Apr 2019, 16:43

Can anybody recommend a local firm that can re-point a wall in lime mortar and also ?one that can fit good timber framed double glazing ?