Hair­line plas­ter-wall cracks may be se­ri­ous

Winnipeg Free Press - Section G - - HOMES - ARI MARANTZ

QUES­TION: Thanks for your weekly col­umn. I find it in­ter­est­ing and very in­for­ma­tive. I live in a 1,000-square-foot bun­ga­low in River Heights that was built in 1948 with plas­ter walls and ceil­ings. I am seek­ing ad­vice on the best method to re­pair hair­line cracks in the walls and ceil­ings, prior to paint­ing. What method and prod­ucts would you sug­gest? I am sure the an­swer would be of in­ter­est to many Win­nipeg­gers who are think­ing of ren­o­va­tions. Thank you in ad­vance. Leanne Pauch.

AN­SWER: While I rarely ad­dress ques­tions of a purely cos­metic na­ture, this is one that may of­ten go deeper than what ap­pears on the sur­face. Some­times this type of re­pair is sim­ple and only su­per­fi­cial in na­ture, but other times re­quires more ex­ten­sive ren­o­va­tions to pre­vent a quick re­oc­cur­rence.

Crack­ing in old plas­ter walls and ceil­ings is in­her­ent, as any­one who lives in a home built be­fore the 1970s can at­test. Of­ten, th­ese small cracks are sim­ply the re­sult of the older sur­face layer or plas­ter dry­ing out and los­ing its flex­i­bil­ity. When this hap­pens, any small move­ment in the home or sea­sonal changes in tem­per­a­ture and rel­a­tive hu­mid­ity can cause the old walls to crack. Other times, the sub­strate be­hind the sur­face plas­ter can be­come loose or dam­aged due to mois­ture or ex­ces­sive move­ment and it will cause cracks to oc­cur time and time again.

The first thing to de­ter­mine be­fore de­cid­ing on whether your cracks are se­ri­ous or just cos­metic in na­ture is to de­ter­mine the com­po­si­tion of dif­fer­ent lay­ers be­hind the thin sur­face plas­ter.

If your home was built in the 1950s or early ’60s, like many homes in your neigh­bour­hood, it’s likely that you have long, nar­row sheets of gyp­sum­based plas­ter lath be­hind the plas­ter top­ping. This ma­te­rial is quite durable and may be cov­ered with a thin mor­tar layer be­fore the plas­ter, or it may have the top coat ap­plied di­rectly to the sur­face. This can of­ten be de­ter­mined by re­mov­ing a re­turn air reg­is­ter in a wall or looking for any dam­aged or cut wall sec­tions. If this is the sit­u­a­tion in your home, looking at the di­rec­tion and length of the cracks is your next step.

If the cracks are thin, short and rather ran­dom in na­ture, th­ese are likely cos­metic in na­ture. Th­ese can of­ten be re­paired by chip­ping or sand­ing off any loose paint or plas­ter and patch­ing with typ­i­cal plas­ter patch or dry­wall com­pound. The patch­ing com­pound should be ap­plied in sev­eral thin lay­ers and fin­ished by sand­ing with fine-grit sand­pa­per. If the cracks are long and very straight, this may be an in­di­ca­tion of loose plas­ter lath and fur­ther re­pairs will be re­quired be­fore patch­ing.

Be­cause most older plas­ter lath was at­tached with sim­ple nails, the sheath­ing can be­come loose from the studs or ceil­ing joists over time. If this oc­curs, reat­tach­ing the wall or ceil­ing sheath­ing to the fram­ing with dry­wall screws will be nec­es­sary to pre­vent fre­quent re­oc­cur­rence of the cracks. Th­ese dry­wall screws can be in­stalled right through the sur­face of the old plas­ter, but pre-drilling small holes with a ma­sonry drill bit will en­sure the screws don’t snap when in­stalling.

Once the plas­ter lath sheath­ing is se­cured, proper patch­ing may re­quire re­moval or coun­ter­sink­ing of older loose nails if they pop through the sur­face of the plas­ter.

The other type of plas­ter sub­strate is in older homes, typ­i­cally built be­fore the end of the Sec­ond World War. This is com­prised of older wood lath cov­ered with lay­ers of mor­tar and plas­ter. This wall and ceil­ing cov­er­ing is very durable but is prone to var­i­ous sever­i­ties of cracks de­vel­op­ing due to shrink­age and move­ment.

Once older wood lath pulls away from the studs or fram­ing be­hind, there is not much that can be done to fix it. The best way to en­sure a lon­glast­ing re­pair is to in­stall new dry­wall di­rectly over the old plas­ter with long dry­wall screws. This will re­quire a bit of ex­tra work in lo­cat­ing the fram­ing be­hind the old plas­ter, but this is crit­i­cal in en­sur­ing proper se­cur­ing of new dry­wall over top of the old plas­ter walls and ceil­ings.

Once new dry­wall is in­stalled over top of the old, de­te­ri­o­rated plas­ter, typ­i­cal dry­wall com­pound and tape can be used to cover the seams and screws, which should be ap­plied in suc­ces­sive lay­ers. Once the fi­nal layer is ap­plied, it can be sanded smooth be­fore prim­ing with dry­wall primer paint. Fi­nal touch-ups are still pos­si­ble af­ter prim­ing to en­sure an ex­tra-smooth sur­face be­fore ap­pli­ca­tion of fin­ish paint or wall­pa­per.

Wall and ceil­ing cracks in older homes are not nor­mally of ma­jor con­cern, but may re­quire sub­stan­tial re­pairs to en­sure a long-last­ing fin­ish. Determination of the dif­fer­ence be­tween su­per­fi­cial, cos­metic cracks and se­ri­ous dam­age may re­quire the ex­per­tise of an ex­pe­ri­enced painter or con­trac­tor, but re­pairs should be pos­si­ble no mat­ter what level of dam­age has occurred.

If your home has pre-Sec­ond World War plas­ter-on-wood-lath walls such as shown, and the plas­ter is merely cracked, the best re­pair is to in­stall dry­wall over top us­ing

ex­tra-long dry­wall screws to fas­ten di­rectly to the studs be­hind the lath.

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