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Poops 08-28-2011 08:49 PM

Rendered Dome Finish - Waterproofing
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Hi All

Looking for some advice on the finish for my dome. I have insulated the dome with vermiculite/cement 10:1 and a single coat (so far) of 3:1 standard plaster sand/cement render. I have another coat of render and then a final finish coat which I was planning to colour using oxide powder.

My question is whether a standard 3:1 render will provide adequate protection from the elements during the winter months (Adelaide Hills, South Australia). I don't want water getting through and soaking the vermiculite between the dome and brick outer skin, or soaking the render enough for it to steam up and crack during firings,

Has anyone used any of the waterproofing additives around, or painted the rendered dome? Still early stages of curing for me, so don't know how hot the outer skin is going to get yet.

Appreciate any advice.

brickie in oz 08-28-2011 09:12 PM

Re: Rendered Dome Finish - Waterproofing
It looks like the way the oven is at the moment that it will catch all the water, you still have to do some work I take it?

The waterproof additives work just fine, but you wont be able to paint the dome with water based paint after if you use it.

Poops 08-28-2011 11:12 PM

Re: Rendered Dome Finish - Waterproofing
That's right, still some work to go. The photo is not the best angle, but the brick skin has been filled with vermiculite around the dome to within about an inch of the top of the last course. The first coat of render is flush with the top course, and was a rough coat to hold the vermiculte insulation onto the dome.
I still need to finish the render, which will direct any rain down the sides (hopefully ....)

Mike D 08-31-2011 09:10 PM

Re: Rendered Dome Finish - Waterproofing
I am at about the same spot as you and plan on asking the same question for my roof. I was thinking of using an acrylic modifier (or they call it white glue). I used this stuff for a skim coat to fill the holes on my concrete counter. But I don't know if that is what one is supposed to use. I will look forward for someone else to jump in.


woodfried 09-01-2011 03:59 AM

Re: Rendered Dome Finish - Waterproofing
Hi mate , It looks like your building an enclosure? or are you going half brick dome top which would be pretty unique. Have you covered the bricks in ceramic blanket before covering with vermiculite?.
As Far as waterproofing render I would use Bondal Silasec Ive used it to build ponds for years and it works well as a waterproof render
cheers James

david s 09-01-2011 05:36 AM

Re: Rendered Dome Finish - Waterproofing
If you add a waterproofing agent to the outer shell you risk locking in the moisture as well as keeping it out. This can result in the steam creating pressure in the insulating area and cracking the outer shell. I prefer to dry the whole thing out, about 10 decent firings, then add an acrylic elastomeric product, which can handle the expansion and also make it waterproof. you can paint over this in any acrylic exterior paint.

Forno Gator 09-02-2011 04:04 AM

Re: Rendered Dome Finish - Waterproofing
The outer layer of my dome is clay brick. I picked up a brick sealer from the company that sold me the refractory brick. I sealed the dome after firing it a number of times. The sealer is solvent based so I needed it to dry a couple of days before firing it... the water now beads on the bricks. Some sealers for natural stone may also work because on the label they say they can be used for brick and mortar. I'd pick up the sealers from an independent stone/slate tile company. Big box stores have the cheaper/poorer sealer products.

Has anyone any tips for protecting a brick dome for winter.... ie a winter with lots of snow and cold temps?

Poops 09-05-2011 12:13 AM

Re: Rendered Dome Finish - Waterproofing
Hi All

Yes the pic is as high as I'm going with the brickwork, with the top of the dome exposed. The rendered top has the profile of a bell really, with any water then directed over the sides of the brickwork.

The dome itself is insulated only with vermiculte (mixed about 12:1 with cement) over the top of about a 1" thick fireclay render (hope that will be okay!)

I've now completed all but the final coat of render, which I was planning to colour with brown oxide power. I've had four curing fires so far with another couple to go before the final render coat. Hopefully most of the moisture will be out by the weekend.

I have some of this stuff which I was planning to add to the render, although I'm not entirely clear on the ratio to use added to a 3.5:1 sand cement mix

I'm not used to mixing by weight ..... (any advice is appreciated). :confused:

Will post some updated images after the weekend (flue going on this weekend too).

Getting close now!

david s 09-05-2011 01:29 AM

Re: Rendered Dome Finish - Waterproofing
Hi Poops,
I think you should cover the finished render coat for a week to keep the moisture in it so that it cures nice and strong. Probably then wait a few more days for it to dry out before firing may also want to consider adding lime to the render mix as it increases flexibility. A render with cement and sand only is more brittle and does not have any flexibility.

cobblerdave 09-06-2011 04:48 AM

Re: Rendered Dome Finish - Waterproofing
Hi poops
My dome was sealed with a coloured render problems there.
The brick entrance however was not and in the wet summer was to porus for the conditions finally used a "bondall" sealer which works can see the water "bead" on the surface. It darking the colour only a little bit and doesn't make the surface glossy

Regards Dave

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