Waterproofing WFO dome

[Ben & Relle]

Hi Guys,

I have had my oven up and running now since NYE last year and all has been going well... until this weekend.

I noticed that the floor was a tad damp when I went to light the fire, and when I got it up and running, there was steam coming from the floor and it was struggling for temperature.

Then after about an hour, I noticed water seeping out from the exterior base and through some of the small cracks that have appeared in the vermiculite/concrete insulation.

Obviously with all the wild Melbourne weather we have been having, the water is getting in and I need to stop it before I do some damage.

I haven't yet been able to 'pretty up' the oven with render and such, and now before I do, I would like some advice on the types of waterproofers you guys have used that have been successful.

I have seen some bitchumen based membranes, but assume they will not handle heat to well? Also, some of the water based 'clear coats' seem to me to be a bit light weight.

Any suggestions and advice will be greatly appreciated.

Cheers guys,

BEN

[Neil2]

Re: Waterproofing WFO dome

I used an acrylic stucco. This has some flexibility to handle the expansion and contraction you get during the heating cycle.

[scottz]

Re: Waterproofing WFO dome

Another idea is to build a patio over the oven...might be more expensive, but with summer on the way over here...it stops you getting roasted while cooking in your oven. Also allows you to cook in the winter without your wet weather gear on

[Johnny the oven man]

Re: Waterproofing WFO dome

I,m with Neil2, go for an acrylic render for waterproofing your oven. You can add oxides to get the colour of your choice.

[Ben & Relle]

Re: Waterproofing WFO dome

Thanks guys. I am looking at using a tinted roll on acrylic render, but I wasn't sure if I Would need any kind of supplementary waterproofing under the render.

I have a simple spray on waterproofer at home that I might use for a quick coat before the render goes on top.

I am a bit worried that the Cal Sil board base has got a bit wet though - do you think I should just give the oven a steady burn at a moderate temp for a full day to dry it out before rendering?

[david s]

Re: Waterproofing WFO dome

I think it is really important to make sure that there are no cracks between the base of the outer shell and the floor. If water gets into that vermicrete it's like a sponge. Use an acrylic stucco/render that is flexible, but make sure the oven is really dry first otherwise you are just locking the moisture in and it's even harder to get it out.
On colouring I prefer to use acrylic exterior paint over the top of the acrylic render. Just use the colour of your choice. It is difficult to achieve the same colour on any subsequent patch up work if you mix in an oxide to the render coat. The outside will often get quite dirty with soot falling from the flue cowl and another coat of paint will clean it up and looking new again.

[Johnny the oven man]

Re: Waterproofing WFO dome

Thanks guys. I am looking at using a tinted roll on acrylic render, but I wasn't sure if I Would need any kind of supplementary waterproofing under the render.

I have a simple spray on waterproofer at home that I might use for a quick coat before the render goes on top.

I am a bit worried that the Cal Sil board base has got a bit wet though - do you think I should just give the oven a steady burn at a moderate temp for a full day to dry it out before rendering?

Cal Sil should dry out fairly quickly.

[Ben & Relle]

Re: Waterproofing WFO dome

Thanks again for all your suggestions guys. In the last few days while it hasn't been raining, I spent an afternoon firing the oven and kept it at a steady 400 degrees celsius for about 5 hours and didn't notice any of the water seepage I saw last time.

I have also filled a few small cracks with a thin coat of the high temp brick binding mortar I used during the build and also added a ring of it around the base.

After this dried I applied a simple spray on waterproofer I have in the garage that is uses to sealing terracotta pots and such. I have yet to see any more rain to check if it has worked, but I think this will keep the moisture at bay until I can get the final render coat on in a few weeks.

Also, the long term plan is to build a cover over the oven as it was also built with a prep bench and bbq in the same platform - but, funds are in short supply at the moment with a baby on the way.

Cheers all.

BH

[v6passat]

Re: Waterproofing WFO dome

I think it is really important to make sure that there are no cracks between the base of the outer shell and the floor. If water gets into that vermicrete it's like a sponge. Use an acrylic stucco/render that is flexible, but make sure the oven is really dry first otherwise you are just locking the moisture in and it's even harder to get it out.
On colouring I prefer to use acrylic exterior paint over the top of the acrylic render. Just use the colour of your choice. It is difficult to achieve the same colour on any subsequent patch up work if you mix in an oxide to the render coat. The outside will often get quite dirty with soot falling from the flue cowl and another coat of paint will clean it up and looking new again.

whats the best way to seal the metal chimney flute where it meets the external render coat? Thanks in advance.

[david s]

Re: Waterproofing WFO dome

This is a problem area where the hot expanding flue is likely to cause cracking and lead to water entry. If you use vermicrete it has some elasticity and a high temp silicon where that meets the flue will do the trick. I have two terra cotta collars that allow the inner parts of the oven to breathe. It works very well, but for a one off this would be impractical to make.

[sjmeff]

Re: Waterproofing WFO dome

I want to second David's suggestion of high-temp silicon caulk. I left a small space between my double-walled metal chimney and the acrylic stucco, which I filled with the high-temp caulk. So far it's worked very well.

[Neil2]

Re: Waterproofing WFO dome

In the end, there is truly nothing that is "waterproof". Water resistan maybe all you will achieve. I put a tarp over mine during the heavy rains and go thru a mini "curing session" every spring.