K rend

[bookemdanno]

Guys, i'm going to K-Rend soon.

Have any of you that have K-rended, experienced any crackings when render touches any twin walled flue or the brickwork near chimney or entrance arch?

I've yet to get a fire into my oven since fitting the twin wall, so i don't know how much heat actually makes it to the outer skin.

I do know that the brickwork of the entrance arch gets warm, not hot, but possibly warm enough to induce cracking.

I could set a break at these areas and back fill with mastic later, but i don't want to if its not really necessary, as it'll stick out like a sore thumb really.

Thanks for your views and help.
Danno

[kstronach]

hi danno, i may be wrong (and i hope i am) but i think you might be the first! i'm planning on it but haven't fully decided yet and i have a few issues to sort first! i'll post them on my thread at some point when i get round to it! anyway as for the flue ive installed a twin wall and at full firing the maximum temp i recorded was 52 degrees if my memory serves me correctly but over the whole firing and cooking process i would say the average temp was around 40 degrees. personally i am going to leave a gap on all points touching either flue or bricks and fill with mastic as you say, i'm not sure its worth the risk not doing but thats just my choice. i would probably say though at least leave a gap around the flue even if its only 5mm and fill that and it wouldn't be too noticeable there would it? as there may be more expansion at that point and it will probably be your hottest point. did you leave a thermal break between your dome and landing arch bricks i didn't and wish i had now!

keith

[bookemdanno]

Hi Keith! Thanks for the reply. You sort of point me in the direction i know i need to, but i suppose i was just hoping that i didn't have to use mastic. Hate the stuff!

I did have a break between the landing and dome, which i wish i left as a full gap, but its pointed with a vermiculite mortar, so some heat bleeds through. Not a lot though.

Thanks for the help, and i'm off to look for some nice coloured mastic...

[cannyfradock]

Danno

I have recommended the use of K-rend ....but in all honesty I haven't yet used it. I was hoping to use it on my latest build, but the client wanted a housing around his dome so I couldn't trial it...



Full details....http://ukwoodfiredovenforum.proboards.com/index.cgi?board=pompeiiovens&action=display&thread=1230

To protect inner and outer dome from heat transfer I have used differing methods....I used 6mm fire rope on my latest build for a community....

...full details...

ukwoodfiredovenforum.proboards.com/index.cgi?board=pompeiiovens&action=display&thread=1031

.....this would have to be sealed with fire-proof mastic.

Terry

[bookemdanno]

A Guinea Piggin i shal go then!

I think all our efforts to Thermal break, really only attempt to keep the higher temps in the oven. The actual hot gasses and smoke rolling up and into the vent heat the entrance bricks up sufficiently to cause issues with the render. I have a plan though!

[kstronach]

A cunning plan my lord? A plan so cunning you could put a tail on it and call it a weasel?

[bookemdanno]

Wasn't really thinking of finishing off the oven today...


But i did!!!

Now, that K-Rend...
really liked it!

Set some old bits of upvc cover strips to create a mastic break between what might be hot bits and the render.
The K-rend mixed very easily in a large bucket, and using the 4-5ltrs per 25kg ratio, and giving it a mix up with my drill mounted whisk for a couple of mins slowly, then letting it sit for five before another fluff up produced a lovely cakey, fluffy, easily spreadable render. I found that half bag mixes worked best for me. Two and a half litres into a bucket, then add the powder, stir, whisk, wait, whisk again and get spreading!
I liked the gritty nature of it, and the first coat went on in around 45 mins. I didn't really spend much time playing about with this first pass, and once it was on, gave it a light key. I've found it best to use a hawk, but rather than a plastering trowel, my gauging trowel worked best. Still using the back of it, in the usual plastering technique. The plastering trowel held too much mix across its width, for the shape of the dome.
It started to tighten up quite quickly, probably due to the mature and very dry Vermicrete underneath, although i did give it two good mistings of water before applying the first pass.
It wasn' t long before it felt right under the thumb.
Straight into the second coat, which i mixed for a little longer on the second fluff up, and ever so slightly wetter, went on again very easily. So sticky, and very easily spread about.
A cuppa was needed after that, and was all that was needed before getting into the task of curved trowelling off to tighten it up, get the shape right and the final finish.
An odd spray from the hand pump, circular motions with the curved trowel moved the render about nicely, created the shape and showed the flat spots which could be filled with a little of the left over mix from my bucket and trowlled off again. The wooden float kept the texture nice and gritty and open. If i'd used a metal trowel, it'd probably be more polished. The gritty-ness of the render produced a lovely open texture to the final finish, which was a mist spray of water and a light handed circular motion again with the curved trowel.
All done in around four hours. This was achieved mostly due to how quickly the mix started to go off.
I'll pop some photos on here tomorrow.

All in all i can recommend K-rend as a really easy to use product, but you need to be prepared, have everything to hand, and a decent time window available to go from start to finish. I really felt the pressure to make sure i wasted nothing and didn't leave myself short, as its not that readily available around here. Also, at £12 a bag, i didn't want to go over a bag quantity by a small amount. 3 bags bought, and i have around a third of a bag left over for any repairs. Mine isn't a full dome render, so 3 bags would be perfect with very little to spare on a full dome render job. As Alex Feguson would have said "it'd be squeaky bum time" towards the end. I chose the Ivory colour to try to keep it like the Lime Render i had before.

I'd use it again, if i had the choice.
Time will tell if it will stand up to heat cycles and harsh winters on a pizza oven dome.

[kstronach]

Congratulations on finishing the oven off sounds like it all went very smoothly indeed. Can't wait for the pics!

[bookemdanno]

Photos of the K-rend, as promised...



Geeky close up one too...

[petec]

I like it a lot - lovely finish Danno.

When it comes to repair time in a year or two I will go K-Rend too i think.

Rgds
Pete

[alun]

Does anyone know where you can source K Rend from? I'm in SE London

[alun]

I managed to find some at CCF in Wandsworth. Though you have to love either white or ivory. Ended using 6 bags on my dome based on trying to achieve a 20mm depth and this calculator www.calculatorsoup.com/calculators/geometry-solids/hemisphere.php (high school was a long time ago)

[markhuse]

did you apply the K-rend onto the bricks, any prep or insulation you had to apply? or just simply throw it straight on?

[alun]

I applied it directly to the blocks on the base, and over the vermiculite on the dome. Both seem to had been fine - no extra keying layer needed.

[tim1989]

Sorry to highjack the thread but when talking k render I have found two types a mixed and none mixed one is there any difference? Other then price lol


m.builderdepot.co.uk/k-rend-silicone-tc15-white-25kg-tub.html

m.builderdepot.co.uk/k-rend-25kg-silicone-ft-textured-white-render-coat.html