arch crack created stucco crack

[leckig]

Re: arch crack created stucco crack

I shimmed all stucco cracks open with small nails while the oven was hot. After it cooled down, I filled them with a very fine, sieved stucco mix and covered with a think stucco. Next fire, the same cracks opened up.
I will do it all once more, but this time I will add maybe 1/4 inch of the surface bonding concrete, maybe this will hold the stucco from cracking.

[Tscarborough]

Re: arch crack created stucco crack

There are 2 methods for preventing the mirroring of cracks through stucco:

The first is to provide a slip plane between the cracked layer and the new layer. The size of the slip plane depends upon the movement of the crack, but in general will be around 6 inches for a hairline up to 1/16th inch crack. The slip plane is normally composed of 20 to 40 mill poly, but this may not withstand the heat. Teflon sheeting or may work. Basically, you are providing enough surface area that the new layer is able to absorb the amount of movement without cracking. For relatively small cracks, say 1/8", this is rather large, on the scale of a 12-18" slip plane.

The second is to either fill the crack or cover the crack with a material that has a high enough modulus of elasticity to bridge the crack and also to shrink back to it's original size. Elastomeric coatings are one way, forming a proper joint and using a sealant is another. For small cracks, elastomeric coatings are best, for anything over 1/4" a properly formed sealant joint is the best answer.

[leckig]

Re: arch crack created stucco crack

nice! I was just thinking last night about sealing this crack with high temp silicone and spreading the silicone about one inch on either side of the crack. Looks like I was on the right track.

I think I will do the silicone and put a 3 inch wide aluminum tape over it. Slip plane, I like it, thanks!