Render Problem

[jamjar]

Hello,
I have etched my exterior brick wall with Hydrochloric acid then applied Bond Crete. I have since tried to render using a pre-made sand cement mix and Bond Crete as an additive. Although application was easy, I found that the brick work was no longer porous, therefore, the render did not want to adhere. I have tried to etch the wall again with Hydrochloric acid, but water still seems to bead and roll off. How can I make the brick work porous again, or get the render to stick, thank you.

[scooter]

No experience with rendering, so take my comments with a few grains of salt, but I'm under the impression that you don't seal masonry with bondcrete before rendering, I think you just wet it down beforehand with water so the rendering isn't weakened by the brickwork pulling the moisture out of it.

Need to remove the bondcrete would be my guess, pressure washer maybe?

Wait for some knowledge to drop by this thread.


Cheers...................Sean

[Cliff Rogers]

On the bit that I have done I didn't use bond crete either, just sprayed the concrete with water from a trigger spray bottle.

Where I got into trouble was if the render went on thicker than 10mm, it just sagged & eventually fell off the wall. :cool:

I reckon rendering is a bit like mustering cats. :D

[journeyman Mick]

....................I reckon rendering is a bit like mustering cats. :D


Easy enough with a pump action shotgun:o :q


Jamjar,
the bondcrete sealer on the wall is the problem. Not sure how you would remove it. You may be able to soften it if you could soak it in water. On a vertical surface that might entail hanging or pinning wet bags to it un til it's softened and then hitting it with a high pressure jet. Try just a high pressure jet first though, you might get lucky.

Mick

[jamjar]

Thanks for the response. FYI, I called Bondall today and they confirmed that Bond Crete would become soft when hot water is applied. So there goes my Easter, cheers

[scooter]

Jamjar, if you can get access to a steam cleaner, such as some workshops use to clean greasy engines & the like, could be the go to soften & remove the Bondcrete.

Another idea could be to put the inlet hose for the pressure washer in a bucket of hot water, that should work fine too. Probably worth trying first.


Good luck................cheers.....................Sean

[schwerdty]

Buy bagged render in 20-25kg bags and mix with water. Too many people think rendering is about nailing in battens and screeding etc. Go to a rendering outlet, buy the product (its cheap) and the correct applicators and ask them to tell you how. I learned from some professionals and now run a little weekend trade in it. If you want more precise info on application, just let me know. Rendering is about applying thin layers (two to three) in which each is flatter and smoother than the previous. First layer, about two millimetres, next two layers about one to two mills at most. Apply with steel Trowel thinly. It will stick easily. Even upside down on a roof. Home made render blends are much too difficult. Bags cost between 11 and 20 dollars and do a fair bit of a wall.

[Joister]

i'm with schwerdty,

i was mixing my own render up and have just go with pre-mixed bags

definitely go for the few coats - what i've been doing is using the first coat to fill holes, old traces (pipes, conduits, etc..) and repointing bricks (filling in broken away mortar)

i usually run a few scratch marks between coats to give a key for the next coat

apart from a steel trowel what is also handy is a mud board so that you can 'push' the render off the board and on to the wall and a long straight edge to level out your job - usually doing the last step once the render has firmed up a bit

you can also run a wet sponge over the job once it's firm if you want to change the texture

if you want to mix your own what i found worked well was 6 washed sand to 1 lime to 1 cement (for interior) - for exterior dropped the lime down quite a bit and made it a 5 to 1 regards sand to cement

hope this helps

[Joister]

forgot to mention about keeping the wall moist - a must i reckon - one of those pump up garden type sprays works pretty well otherwise a hand spray

on a hot day i've also given the render once on the wall a mist spray of water now and again