What is the cement render mix ratio for external concrete block walls?

Answer 1

A good mix for rendering is 1 part lime 1 part cement and 6 parts sharp sand(1:1:6).

To ensure a good even mix the materials should be measured in buckets rather than shovels, this will ensure consistency throughout the job.

Water should be added in small quantities to the mix, the consistency should be just stiff enough to stand on the trowel. The area to be rendered should be brushed down with a stiff brush, then doused with a hose pipe to remove the rest of the dust and prevent the surface 'sucking' the moisture out of the render.

Always start at the top and work your way down and protect the floor with with boards or sheets as it is quite a messy job. It is advisable to apply in two coats, the first coat should be 'combed' before it begins to set.This is done with a special rendering comb. The second coat can be a little weaker, i.e 1:1:8. Dont worry about any imperfections in the finish as these can be scratched off the following day with a trowel to achieve a lovely even finish ready for painting.

Its my opinion to use a ratio of 4 sharp washed sand to 1 part cement, Bycol added to the water to aid in the flow of the cement but its not that important once your skill level is up there. Lime is not necessary and 1:6 is far too weak. 2 applications of render should be avoided at all costs. No you cant scratch it off the next day. Secrete/float the walls 1-2 hrs max after its applied. When floating the walls make sure the surface is sprayed with a fine mist to keep it moist. Small Golf ball size blobs of render mix can be thrown on to fill any low spots whilst floating. And use a Teflon float not a trowel.

Be sure the wall prior to rendering is paint free & hosed down. the more water on the wall the better and if in direct sunlight work in small sections...2x1 mt

Answer 2

THE MIX add your waterproofing and plasticiser to your water butt and fill with water then stir thoroughly add approx a bucket full of this mixture to your cement mixer the cement mix should be consistant and mixed to the following specs parts: cement : 4: soft washed sand :10: sharp sand :2: this gives a ratio of 3-1 a strong mix, you could use a 4-1