I'm encoutering a problem with the finish-out of my rastra walls: we covered the rastra inside the house with dry-wall mud, than paint. I recently noticed that spider cracks have appeared almost everywhere; they seeem to be a print-through of the blocks. The exterior stucco doesn't show distress at this point. My GC doesn't have a clue . I would appreciate so much everyone's opinion. 

Dry wall mud looks like that if it was to thick and it drys out slow.
I think that is what you are seeing here.
Did you use a bag mix first or just out of the pail mud. pail mud shrinks like that.
You did not use dry wall?
 I have never seen this one be for.
Dry wall mud is NOT the same as plaster, you need to use it on dry wall only and in thin coats.
 May be I am wrong, I just think that what it sound like.
Hope that this helps.

I agree with woulfcc, drywall mud is for thin applications and shrinks in thicker apps.. The proper finish would be a plaster. This would be a good opportunity to use an earth plaster such as American Clay. I believe that it could be applied directly over your drywall mud and paint with a little surface prep., but I would check on the proper application on their web site.

I heard at a seminar that this technique has been used on similar type blocks in Texas and hairline cracks can  be a problem, but the cracks were reported to be more random. While it may work if perfectly applied, I am a bit skeptical of the application.  Elastomeric paint may solve the problem.

Did you ever get your leaks traced?

Bruce

Maybe you should contact the people who make the rastra and talk to them. I have the name and number of the company in Arizona

Look up plastermax ICF from Gigacrete. www.gigacrete.com I would recommend this product on the block, but am not sure about putting it on the drywall mud since the drywall mud when put on thick like that will tend to collect moisture and if this happens, it loses all strength in bonding to both the rastra and the other finish materials such as the plastermax. Ian with ICF Builders www.ICFResource.com

Drywall mud cracks if applied over 1/8" thick.  Normally, the first coats cracks are covered up with a thinner second or third coat of mud.  Or, it can be re-wetted with a sponge and the cracks covered just by moving the sponge over them.  Sounds like you've already painted, which will make the fix more difficult. 

Drywall mud is not plaster.  I just did a project where I used drywall mud over the entire drywall surface, no sanding, to give a semi-smooth hand-trowelled plaster look.  First, it looks okay, but it doesn't look that much like plaster.  Second, it is very soft, much softer than plaster and softer than the underlying drywall.  If bumped by a chair or something, the paint scuffs off and shows the skim coat of mud.  Not too practical for many areas or with kids.  I used real plaster in the bathroom and am much happier with that area.

Rastra has a rough surface that definately requires more than 1/8" thick in places, so you'll have cracks.  I would think that the block seams would be the most common place for thick mud, just like you would get cracks in drywall panel seams if there's no tape. 

I've seen an earthen clay finish also crack when applied thick on Rastra.  Clay cracks can be fixed with either another coat of clay, or with consolidation of the clay as it dries, sort of like with real plaster.  It can also be re-wetted and sponged like drywall mud.   Rewetting was what they did on the cracked project that I saw and it looked okay a few months later.  I assume that the cracks never came back.  The walls were left unpainted, so it could easily be fixed if they did.  The owners had kids, so I'd really like to see how unpainted clay held up.

I've seen manufacturer's claims that earthen plaster can be applied over paint.  You might contact one to see if it's a possible solution.

I'm getting ready to start a Rastra project and would like to hear more about your thoughts and experiences.  You can email me directly.

Mark Fleming

Thank you for your supprt.
Well, I still live with my spider cracks, which slightly increased over time. You must be right about the drywall mud having been applied to thick, I ended up having this problem even with my inside drywall, the crew did a shameful job all over the place.
Another factor is probably the water, it rained a lot in Tx last spring while the house was built, so the wall must have been too wet when they applied the finish and it migrated inside (and cracked the finish) during heating season. Still wainting for the builder to measure the water content with a hydrometer and redo the finish...( from smooth we go to hand troweled and a lot of paint) And hopefully it won't migrate to the outside and crack the stucco during cooling season. By the way, we are very happy with the energy efficiency and feel of the house.
Mark, I would gladly share my learning experience with you, but how do I contact you directly?