Patching and Plastering - Plaster Repair needed

I need to repair the plaster on some walls that are water damaged in my church. The building was built in the early 60's in Florida and has a medium sand finish. What do I use to repair this and what techniques are needed?

Thanks

How much damage is there?

Setting compounds like durabond usually work fairly well when repairing plaster.

The damage areas in most cases are small from water intrusion (roof leaks, windows leaks etc.) the largest is an area about 1 foot wide wide and 7 feet high.

I'd scrape off any damage, [prime the area if it's chalky/dusty] and repair the areas with durabond. You will need to use an oil base or pigmented shellac primer to seal any water stains so they won't bleed thru the paint.

Is the sand texture like the kind that's added to paint? or is it in the plaster?

I'm just a painter with a bit of drywall experience but hopefully one of our plaster pros will chime in later with better advice.

Was the water damage from a leaky roof or windows that now have been fixed?

How much repairing do you have to do, out of curiousity?

Are you the church's maintenance man?

Matching the texture, so you can't hardly see it, will be the biggest challenge. There may be a rough surface, that you call sand, that may have been painted over many times after the sand additive. When you stir in sand additive and it dries , it resembles if somewhere were to have flung sand at a wall that was tacky and it stuck - as compared to a many-times painted-over sand texture, that will have the sand peaks more rounded off, due to the paint. If so, you will have to duplicate that by painting the patch areas several times.

Also, I'm not sure if you or someone else will be doing the painting? Are you going to try to just touch-up paint?, or paint entire wall sections? If you just touch-up paint - if the repair area is up high enough where natural light can reflect off it, often the sheen of the paint will be noticeably different, and will be noticeable even if the color match is dead-ringer. With flat paint, this effect is less noticeable. But if you already have the walls painted in say an egshell or satin, that is when recoating can increase the sheen. However, if you wisk out the paint with the brush, beyond the repair area - to feather out with brush or roller, your repair will not stand out, reflect the light as noticeably, in the way if you were to simply touch up paint heavily on the repair area without doing this.

As far as how to do the patching - if you read up on some of the recent posts here regarding Durobond, and mesh tape, that will help you with that aspect.

Yesterday, I had to scrape and gouge out water damaged plaster next to bathtub and under bathroom wallhung sink. The plaster was applied over a gypsum board. In areas, I am 1/2 inch deep down to the gypsum board. I scraped off all the paper from the gypsum board down to it's chaulk and then used Zinsser paint to prime-seal the chaulkiness, and also the crumbly plaster edges around it, as marksr already suggested. Today I wil be applying more Durobond. I will forego any tape, as I do not feel it is necessary in my application of this type- of a fill-repair over old stable material. The Durobond will lock into and almost become one, fuse, with those plaster edges I prepped good.

If anytime you have large repair areas where you have to take out a lot of plaster to a depth or 1/2 inch, then you might want to consider cutting and piecing-in some sheetrock first. And/or you can actually screed the Durobond over wide areas, to cut down on uneven waves of mud, from just troweling it on, in the same way how concrete flatwork is done (except you don't have to work the screed back and forth - just pull it). I have done this several times and this works out quite slick. You just trowel on the mud relatively evenly and then screed off the excess with a straight edge, making sure that the outer edges of the screed are held tight up against the original wall areas.

It's probably worth noting that durabond is extremely hard to sand! It's easier to apply an extra coat and pull it tight than to have to sand off any excess. I often use joint compound for the final coat because it sands easy :D