What is the Right Way to Skim Coat?
I have heard that there are many different definitions of “skim coating” for plaster walls. I am meeting with contractors and I would like to know (from somebody with experience) what the correct way to skim coat plaster walls is so that superficial cracks will not re-appear. I know it is very expensive so I…
I have heard that there are many different definitions of “skim coating” for plaster walls. I am meeting with contractors and I would like to know (from somebody with experience) what the correct way to skim coat plaster walls is so that superficial cracks will not re-appear. I know it is very expensive so I want to make sure it is done properly. Any tips on what to ask the contractors are most appreciated. Thanks!
Hi I see you got a lot of good suggestions. I am a second generation Irish plasterer. I would not use sheetrock over the existing walls for many reasons. One being it adds inches to the walls and can mess up the lines where the baseboards start. Also it just does not look as good as plaster.
I also would not use straight joint compound, if you use joint compound you want to do a mix with plaster added. This is a little tricky, and it takes a while to get the mix right. This allows for faster drying between coats, and also being able to work, and smooth the plaster more easily. It generally takes me 3 to 4 coats with the mix and then a polish coat to finish.You may also find inside, outside corners, and angles tricky. There are very good corner tapes out now that help a lot with outside corners, and angles. You can also use diamond plaster that gives a much harder surface but is much more labor intensive. Most contractors in N.Y.C. use the compound mix.
The wall should be prepared by removing all the loose plaster and opening any cracks. Large, deep areas should be filled first with structalite, then Plaster weld and fiberglass mesh tape that is available in 4′ roles should always be used.
Skimcoating is something that takes a while to “get the knack of” and if not done right requires a lot of sanding. I avoid sanding as much as possible as the fine dust can be a real problem. Make sure the contractor is on top of dust control and does proper prep, and clean up, plaster work gets messy.
I would be happy to answer any questions you might have.
Dee Finley
email me at deefinite@gmail.com
The right way to have it done is to do as mopar above stated. The pink stuff is called plaster weld. After doing the patches you can also do a full coat of plaster over the whole wall to get a nice smooth wall. My husband is very skilled at plaster he uses a different brand which is better than other brands sold in NY. If you are interested in maybe getting a quote he would be happy to do so!
He has a few plastering recommendations here on the site.
Willian Jr and Aida at 914-562-2706/774-955-3804
http://www.pratesplastering.web.officelive.com
Why not add a layer of 1/4″ drywall, containing the weak and crack prone plasterwork, and get a smooth clean finish? We did this on our parlor floor and hid a 100 years of irregularities.
This is very tricky and although I’ve done it and seen a lot of it done in my house, I am not sure I know the answer.
You must scrape away all the loose bits first before applying the new coats. All cracks must be taped. Apply three coats, sand well between each one. Whether you use joint compound or a mix of joint compound and plaster depends on the weather.
If you have big pieces coming off the wall and the keys are gone, as the above poster says, you either have to use washers, patch with drywall, or this weird pink stuff (I forget the brand name) that basically glues the parts together.
We have a few places in our re-done walls where problems are showing up again. I suspect most of them (hairline cracks) are because the loose bits weren’t completely scraped away during prep. There is another section (bigger cracks) that I know was caused by loose keys and they only taped instead of anchoring. Then there are some buckling areas caused by a not-very-talented fellow who didn’t tape where he was told to tape. We had another guy who was much more talented, and his work has held up well so far.
The mesh is critical if the plaster is cracked. The next issue is what medium to use. The quickest is to use pre-mixed buckets of joint compound. It is predictable and goes on smooth but you can easily dent it later on since it is weak. I would not accept this method if I were you. Better is Easy Sand dry joint compound that is mixed with water on site. It is stronger but the contractor has to spend time every half hour mixing up a new batch. The strongest and original way to skim coat is using lime based powder that is mixed on site. The Home Depot contracting crowd is not familiar with this method and people who use it cost more.
Skimming by itself is only for an uneven, mildly cracked/alligatored surface. As Eman points out, fiberglass mesh stabilizes, it comes in 36″, 60″ or wider rolls and self adheres, so it’s relatively easy to use. If the keys of the plaster are broken (the back part of the plaster that oozes out between the lath is called “keys”), then mesh alone probably won’t keep it in place and you should use plaster washers as well (thin metal discs with holes punched into them and a dimpled middle so the screw head is recessed)
when skimming plaster walls it often behooves you to apply fiberglass mesh over the surface and skim over it…that stabilizes the dried out grey coat that is breaking up and cracking