wanted; recipe for render mix

[Helen888]

Have horrible breeze block wall facade to a barn and would like to render it. I dont think crepi alone will be anough to cover all the lumps and bumps! Would be really grateful if anyone knows what to put in the mix! Should i use something with lime.

 

Best Regards

Helen

[Nick Trollope]

A cement render would be suitable for concrete/breeze blocks, I doubt if you would gain anything by using a lime render (which are much more flexible than cement & "breathe", neither of which are important on blocks).

I'd use 3 parts soft sand, 3 parts sharp sand & 1 part cement. Although you can't always find soft or builders sand around here...

[Helen888]

Thanks Nick!

[Hindhaugh]

Re sand, we have a cottege in Indre(36) and I wanted some standard builders sand, the sort you would have delivered in the UK for cement mix / brickwork. Our local builders merchant in France only appears to stock sharp sand in bulk or very find sand for filters in bags (similar to that sold in the UK for brushing over block drives). I have wandered around the large stockyard but fine sand does not appear to exist as I know it. I bought one of those massive cement pointing guns - looks like a mastic gun on steroids. This requires fine sand but as I say cannot find any - suggestions?

[Nick Trollope]

Neither can I (find soft sand), as I alluded to above, so if anyone can source some in the Dinan area, I'd like to know, too.

For Helens render, 100% sharp sand will do, but produce a coarser finish (not as coarse as crapi, however).

[Ianhaycox]

Have you tried the sabliere up near Bretagne Materiaux for soft sand ?

[The Riff-Raff Element]

We are using a product called PARAX Monocouche, made by Lafarge. I've never seen it in a brico, but it is stocked by builders merchants. Although the instructions imply that this can only be used for machine applications it applies very nicely with a trowel. You will need a mixer though - it is waterproof, and mixing by hand is virtually impossible. It looks pricey at first glance (about 13€ for 30kg) but coverage is good and it is really easy to get a good finish. Its also available in a range of colours. Use a "semolina pudding" consistency for render, "cream cheese" for pointing. I've no idea how long this stuff has been around, but its clearly becoming very popular with our local building types.

[Blondie]

Hindhaugh I don't know where you are in Indre but we get our sand from a M.Piot at Angles sur L'Anglin which is about 10k from Le Blanc, it is not quite as soft as you get in England but is much softer than any other sand we have seen around this area and we get along fine with it. In case you want to give him a try his tel. no. is 05 49 48 61 17.

[Jackie]

Bricomarche near us in Deux Sevres do 5 or 25Kg bags of Fine or Very Fine sand by SB Mercier, I think, and I have used this for thin internal render on breeze blocks. I used a wet mix of 3:1 and the blocks sprayed with water first. Sprayed it twice a day with a fine mist for the next few days. After a few weeks, and when dry, gave it a coat or two of white crepi. Seems to be ok.........John not Jackie 

[builderbloke]

Helen

I am a builder, registered with the Chambre de Metiers, and have just finished rendering a thirty metre stretch of barn, exactly like yours.  Took me three days to do the job

Here is my advice for what its worth.

If the surrounding barn and you house are lime rendered or built from a lime based stone, then using lime render will help the finished building blend in.  The colour of the render will depend on the colour of sand that you use, plus any additives that you consider (dyes, or if you like a traditional look, the odd handful of mud!)  If your house is modern, then use a modern cement mix.

Mix should consist of three to one (sand to cement/lime).  I usually use batidol chaux.  I also highly recommend that you use a fine sand such as sable d'enduit, whcih is readily available from my local suppliers (all of them).  If you do not use fine sand, you will have a very rough finish which will also be more liable to crack in the coming years.

If possible leave the job until spring, as the render will dry much more quickly and you will reduce the risk of the wet render freezing overnight (if you are in a frosty part of the country), and cracking.

For a large area, hire a cement mixer, the put a big load of mix on a mortar board and using a large trowel, e.g. 22cm, throw it with a flick of the wrist against the wall.  Build up a rough cover of a half metre or so and then smooth it out with the back of the trowel.  Repeat until finished.

When the render is nearly dry, you really should scratch the surface with a small trowell or nailboard to avoid a shiny finish when it eventually dries.

There should be no need to mist the wall, nor to apply crepe afterwards, but then again i hate crepe, so I would say that.

Finally, if you mess it up, just hack the dry render off and do it again.  Can't do any damage to the barn.

good luck.