Rendering a Besser Block Wall

[srohara]

Hi

I am about to render a besser brick retaining wall, i am going to use the pre mixed Render It product from Cement Australia. I am not sure on how damp to have the besser blocks. I am worried that if they (besser blocks) are to dry it will draw out all the moisture from the render and cause it to crack. If it is to wet it will make the render to wet and fall. When i core filled the bessers if they were dry they caused the concrete to shrink. i just dont want to have the render crack. should i hose them down so they are wet and let the dry a bit then render. If anyone has any idea happy to hear them.

Cheers
Scott

[brickman]

It wouldnt hurt to dampen the wall down a bit prior to rendering , just a light flick of water of a paint brush or hand broom is all the renderers use . The corefill in the wall shrank because it is a very wet mix and the shrinkage is the water drying / evaporating.The most important thing to prevent cracking is to keep the wall damp in at least the next 24 hours after initial cure , if not 48 hours . In hot weather that can even be started the same day as the render is applied , just a fine spray of the hose at regular intervals e.g 2 - 3 hours , regards

[myla]

hello,

if possible look for a different render, I find all those pre-mixed brands which are sold at bunnies etc are too cement rich

if you can find some unitex or quikcote you will have an easier time at it and not have to worry about wetting wall

if warm weather start early in morning and go till around midday, do 2 passes if dont want to see blockwork

thankyou

myla

[Bleedin Thumb]

Don't worry about having the wall too wet, its almost impossible. get it as wet as you can. If the water is not running on the surface you are OK.

You will soon know if the wall is too wet and the render mix is slideing off, then just wait 10 minutes and you should be good at this time of the year anyway.

[Stringy]

Completed rendering 80square m of besser blocks about 6 weeks ago. An ex-brickie mate came and had a look at the job before I began and gave me good advice;

nail battens to 2.6m high wall to screed off against. I had some 9mm HMR double sided melamine that I cut into 40mmx2400mm strips and lightly nailed approximately 2m appart. After the first coat I just ran the trowel down the sides and top of the battens so they would not become stuck. Removed immediately after screeding the top coat (again run a cut with the trowel around them so not to take chunks of render as you pull them out) and fill the 40mm wide slot left behind.

Use 2 coats; 1st coat about 3mm below screed level, this can be fairly rough as long as it leaves enough room for a top coat, run screed over to check and remove any high bits. let this dry before top coat. I had to remove one wall of render due to it becoming "drummy" because the coat underneath was not set enough and I disturbed it when applying the top coat! Near the end of the job and was becomming confident!

Use sand/cement/lime mix, I could not use this as the sealant (Davco K11) underneath does not recomment using lime products, so used 3sand/1cement. sharp beach sand, GP cement.

Why sand cement and not a pre-packaged product; brickie mate said I would get just as good a job with a huge difference in material costs. I have never rendered or used any other product before but was going to use that same one as you have mentioned! Had no problems with the sand/cement mix and have a good finish in a mainly internal area. If you are paying someone to render then the labour will far outweigh material costs but when DIY material becomes the cost and obviously your time!

Keep the cats outa the sand.

Don't worry how much falls on the ground as it can be picked up and reused. Try not to tilt the hawk back towards yourself as a heap of render down the neck of your shirt will eventually work it's way into your undies (personal experience).

Wet the walls and floor, as Bleedin says I could'nt get them too wet, if they were dry then the render would fall off.

Finish with a foam trowel. I found judging "when" a bit tricky at first and doubt I could explain!

Went to buy a hawk, $99.99. Did'nt buy a hawk, used a piece of 9mm HMR double sided melamine with a handle underneath and a ring of expansion joint foam to go between hand on handle an underside of board.

Wear gloves, the sharp sand cuts the ********* out of your hands and lets the cement in and takes ages to heal.

My walls are seperated into bays from 4 to 5m which made the job easier due to the issue of not being able to let an edge dry and start again on the top coat.

There is probably more. I had never had a go at rendering before and am happy with the job.

[rmartens]

yes you do move the hawk towrds yourself at the same time pick up the mortar with your trowel this is centrifical force. I may have a video of this skill to start just get enough on your hawk for one trowel and as you pick up your skills put more on your hawk.
Besser block are a very hard product so the formular if you follow specification from manufacturers the harder the product. the more cement you put in.
Yes wet the walls but not to soak too much depending on how much the bricks will absorb concrete holds a lot of moisture. But depends if you do your work in the sun.
And if possible do two coats as this gives a more consistent finish.
You may find before you can screed it will stay wet for a long time

[Jacksin]

sharp beach sand

I thought thats one sand you couldnt use because of its structure and high salt content? Or did you mean sharp plastering sand?

[Stringy]

Jacksin,

This is just what my local suplier called it. I told them what I was using it for and checked with my brickie mate, who calls it sharp sand and told me that the regular sand for bricklaying is too "fat" and has a high percentage of clay.

I would guess that this sand is washed and has no salt, wait, just went and had a lick of said sand and, no salt, could do with some though and probably a bit of pepper.

Sharp plastering sand may be another name for the same stuff. I don't know!

I was hoping that the pro renderers would step in and debate the following;

Sand/Cement (with and without lime) mix versus Pre Mixed products.

Using battens to screed off.

An explaination of how to get a good surface finish.

Cheers,

James

[pawnhead]

I was hoping that the pro renderers would step in and debate the following;

Sand/Cement (with and without lime) mix versus Pre Mixed products.

Using battens to screed off.

An explaination of how to get a good surface finish.

Cheers,

JamesYour description sounds pretty good.
The pros I've seen, most often use Plastermaster instead of lime, they don't usually use battens, but they do sometimes use straight edges on external corners. When cutting back, you have to do it at just the right time, which depends on the substrate/temperature/humidity. They usually test it by pressing their fingers into it to gauge its stiffness. When sponging they flick a bit of water on with a renderer's brush to liven up the surface.

Around these parts, renderer's sand is often called 'Sydney Sand'.

[rmartens]

You did pretty well Stringy and no doubt will improve your plastering skills.
In Perth I found using the normal cement is better than the mortar mix stronger.
For external work on the second coat you can add a water proof in the render.
What you can try to do simular to stringies method of the battens to make the walls straight is apply a band of render on the corners just a trowell width vertical.
About 12mm thick wait till the mortar (render hardens test with your fingers for right hardness)
Using a box rule and level screed back and plumb wall on band. dont go too deep fill in slacks (hollows) screed again till all filled in. Do this on both sides. Run your straight edge across ways to make sure nowhere it touches brick and carefully screed out highs on verticle bands. Let dry. come back the next days and fill in middle.
Like pawnhead mentioned after screeding using water with a float to bring the water to the surface using a figure 8 or circular motion to close all the render.
I use a garden hose with a fine mist spay on the end of the hose bringing a consistent finish to the work. After floating with a wood float i use a sponge float and use the same method as with the wood float apply water to the wall and rub the sponge float in a circular motion bringing the sand to the surface not too much otherwise you make the wall too bald. If too wet too streaky so sometimes you have to wait a little and hit again. On two coat sometime it is so wet not requiring too much water.
Sand cement lime is a good mix I usually use a higher content of lime and this really makes a nice finish and with a high lime content you cant go wrong. Lime has been around a very long time.

Oh with pre mixed products I think that comes down to taste personally I dont tlike them because they generally are paint products they have good ingredients and may not crack as much or claim not to crack. But if any of it gets damaged then it will be close to impossible to repair or match where as the conventional way done well you you can repair and extend then only needing paint to match up