|Lime rendering done by Welsh Lime Works in Cardiff|
Lime rendering is a specialist trade (not to be confused with lime plastering or cement rendering!) and as such it takes time served craftspeople to do it well and it also takes more time to do. These two factors mean that many people who need to have their houses re-rendered choose the cement route. Using cement, of course, represents a higher long term cost. The render will crack and, most likely, damp will be re-introduced to the walls. This will need to be addressed again in the future, whilst a lime render should last the lifetime of the building.
A customer of ours choose cement render over lime due to the cost, however within 8 months the cement had failed, the wall was still wet and she has had to do it again. So the difference in price has already been negated due to failure.
However, this article is about what to do if you cannot afford at the moment to replace the cement with lime.
My recommendations (in general) would be as follows:
- Keep the existing cement render on
- Regularly check the walls for failed render (tapping the walls will audibly indicate where the render has become separated from the wall)
- Repair any cracks (even the small ones, especially if facing the prevailing winds and rain) and any blown areas of render
- When replacing blown areas, it is better to cut around the render to be removed so that the process of removal does not dislodge any of the surrounding render
- Use cement render to replace / repair
- Check for failure of seals around doors, windows, pipes etc and repair as necessary
- Save up and when you can afford it, replace the cement with lime.
|Enlarging cracks allows for a better repair as the new render will fit into it|
The rationale behind this recommendation is that where you have a structure that has been altered to try to keep water out then as long as this philosophy is being maintained then it will have a better chance of working than when it is not. Cement render and masonry paint is designed to keep water out and as long as it is doing this then it will provide some protection from wind driven rain, however it needs to be uncompromised. So maintenance of its integrity is really important. The more water that gets behind it, the worse the wall will perform and the more likely damp issues become.
This patching and maintaining is really important to allow the wall to perform as well as it can before the ultimate solution of the lime render is applied. So don’t waste your money on putting a new coat of cement render over your pre 1919 solid wall house, repair what you have and save your money up so that you don’t waste it on an unsustainable, and still quite expensive, piece of cement based sticking plaster!
If you have a ‘rising damp’ problem (this is rare to occur in most untreated houses, but can be caused by the introduction of cement based renders and plasters onto a breathable wall) then another cheaper option is to remove the cement render up to around 1m above ground level. This wall might then need to be repaired using lime mortar (re-pointing) or it could be lime rendered. Doing this at ground level means that there is no need for scaffolding and the area involved is much less, thus keeping the costs down. You will need a good drip above this so that any water running down the upper wall is not fed directly into the lime or onto the exposed wall.
If you need to put up expensive scaffolding to do the repairs then this brings an extra dimension as the lime rendering becomes more cost effective in the longer term. So any initial repairs to the cement are best done off of a tower scaffold or ladders.
I have written at length before about lime rendering, but it is worth re-iterating at this point the things to remember when looking for a good lime renderer.
- Use a company that both supplies and installs the render (this can get over the issue of where, if there is a problem with the final work, you are not inbetween a rock and a hard place where the installer blames the manufacturer and the manufacturer blames the installer!)
- Remember that rendering is not the same as plastering. So use an experienced renderer.
- Ask for references and a good portfolio of completed works
- If it is new company then you will need to ask about the experience of the tradespeople and where they served their time. You can then investigate this company.
- Read up about lime from trusted sources like CADW, Historic England, Historic Scotland etc (depending on where you are)
- Ask about the mix that they will use and the finish that will be applied. I am a believer in aggregate being really important. I think that the aggregate needs to be a mix of sizes and also that it contains a high proportion of permeable stone.
- The finish needs to be appropriate. So a lime putty and permeable stone mix can be easily covered with a lime wash, a less breathable combination of NHL lime and sand will probably work better with a mineral paint.