Cement Rendering - method ?

[Nick]

I have a small patch of swimming pool wall to render and paint with the Butyl Rubber paint.

The wall behind is brick that has had frost damage and popped the old render off - I will remove what loose stuff I can but there is a good key for the new render

Can someone tell me the mix and additives that should be used for a sticky and impervious coating that will set quickly ? Part will be continuously submerged after repairs done.

Thanks,

Nick

[Weatherlawyer]

Six to one should be adequate. Use plastering sand if you can get it. If you have to use brick sand, make it 5 to one. If it is a small patch, you won't need Feb (plasticiser) but without the plasticiser you must work quickly. Slap it on aqap. You can scratch it off level at your leisure.

You had best make certain the rest of the surface is sound. Tap it all to listen for hollow sounds. Give any suspect parts a sharp rap with a wooden club or stick. If it dents or falls off you will have to scrape as much off as is required.

Take it back to where removing it is hard work.

[Weatherlawyer]

Thanks for the reply - I do have Feb in stock and was thinking of using a stronger mix (4:1) and have plastering sand also to hand, unless there's a reason NOT to use Feb or a stronger mix ? I am only talking of patches in a strip approx 12" wide top to bottom and a few feet long, so not big areas.. *******

The reason I said not to use Feb is that it will be stronger. Feb makes mortar more malleable without the danger of making it bubbly as would be the case with using detergent. A lot of brickies use washing up liquid but it is a mistake to .

I believe the mix will be strong enough at five or six to one. It is the preferred ratio on sites for all sorts, although the text book for brickaying is or was 8:1.

With four to one you stand the risk of the mix going off too quickly and introducing small cracks. You already hae that problem along the joins which I suggest you paint some pve along to help bond.

In fact paint a dilute coat on all the bricks to be patched.

Brick sand grains are smaller then plastering sand and tend to be less sharp. That's why I suggested a different ratio for them. I don't know if you will be better off without the Feb. I would guess so because there is less chance of trapping air in the mix. I don't really know. You certainly don't need much -a couple of soup-spoons would be enough for a full mix in a smallish mixer.

[meow2222]

fwiw I tried 7:1 on blockwork once, was short on cement. I thought I'd get away with it but the result was useless. After more than enough days to fully cure I could get my fingernail into it without much difficulty, and most of the mortar joints had cracked up. Taking it out with the grinder was like cutting through a pile of sand, virtually no resistance at all.

So I reckon whoever wrote that book must be a major bodge merchant.

NT

[Nick]

Thanks for the replies - I will try the suggested method and keep the fingers crossed !

Nick