Lime render requested, builder mixing in cement?

19 Dec 2009
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United Kingdom
Hi-my elderly mother is having an exterior wall re-rendered on her bungalow. The reasons are cracks in original sand and cement mortar but also internal damp/condensation. The wall is old, brick, with no cavity. The property was extended some 25 years ago and they retained some of the really old walls (for grant reasons as I understand it).

All I have read is that sand and cement render will not allow a wall to breath and therefore moisture will not escape, hence the condensation/damp inside. After doing some research and speaking to a couple of plasterers they said either Lime render or K Rend. We decided on Lime and got quote for that and builder has started (yesterday).

Builder applied scratch coat yesterday but when I went around last night noticed bags of lime but also cement (as well as sand). He was due around today to finish but it's raining so is coming back tomorrow. Anyway, spoke to him on the phone and asked why he was mixing cement in. He said that was right for scratch coat and would be a stronger lime mix (but still with cement) for top coat with waterproofer (PVA I assume). All he seems to be explaining is ways to keep the rain from soaking in but the problem we have is moisture unable to get out.

My problem is, what do I know? So looking for some advice please? They did suggest K Rend as well, but we wanted lime render-my understanding is this should just be a lime and sand mix and needs to be left a decent length of time to dry between coats? Also some cracks in the scratch coat but the builder said that was normal too? Not huge, maybe 1 mm at absolute max.

Any advice appreciated-will meet with builder tomorrow.

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All I have read is that sand and cement render will not allow a wall to breath and therefore moisture will not escape, hence the condensation/damp inside

Thats not the case, unless the whole house has been built with lime mortar and otherwise requires lime render due to the construction.

Cement render will not cause internal dampness and certainly not condensation. You need to determine the actual cause, and if you have a condensation problem lime render will not help at all with that, you will need to deal with the cause.
As you are upgrading the external finish you should of improved it thermally under building regulation.

It's a shame you did not take advantage of eco when it had funding you could of got EWI for free.
It's a shame you did not take advantage of eco when it had funding you could of got EWI for free.

There were grants, but it was never free, at least not in the Kent area. And oddly enough, I got the impression that the prices went up when they introduced the grants, and the prices came down to only a few hundred with the grants, than they were charging before.

As Woody has said, Poddy, most condensation problems are due to lack of ventilation in the property, or the heating not being kept on long enough as well. As you've got solid walls, they are always colder than double skinned ones, and so benefit more from external wall insulation.

The builder very likely using a 1 cement 1 lime, and 6 parts sand for the mix, and the lime gives it a bit more flexibility, but it still won't "breathe". Do a google search on Lime Render, and then have a chat with the builder on what you were expecting, and what he's giving you - there appears to be a bit of missconception on your part, and a missomunication with the builder.
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check out the lime centre Winchester for info.
what lime is he using?
cement render can in fact trap moisture in the fabric .
it will not cause condensation but it wont help things either.
The truth is peoples knowledge of using lime is limited.
if lime render is specified then zero cement should be used.
while its not unheard of to add hydrated lime to a sand cement mortar mix it is usually to influence finished colour and aid plasticity
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You was in negotiations with plasterers and ended up getting a builder? You do not use lime and waterproofer in the same coat I expect he's using hydrated lime with the cement this do not constitute a lime render the lime will just give it more flexibility as said above, proper lime renders use lime like nhl 3.5 or 5
Pva is not a water proofer. It should never be used on wet walls or with render.

IMO, a 3:1 sand & lime mix makes the best of the traditional renders.
The lime powder bags are typically stamped with a large NH.

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