Saturday, 31 March 2012

Hole in the wall

Dear Joe,
How do you patch a large sized hole in drywall and make it smooth and look like the paint was done at the same time as the rest of the wall? 

Angela,   Port Alberni, BC

Sent via FaceBook.

Thank you for the great question.   First thing we have to know is how large is large.  Tiny is like a nail hole up to about ½” diameter, small is ½” diameter or larger, medium about the size of a doorknob or larger, and large would be bigger than a dinner plate.  Tiny holes can be filled with a couple coats of drywall compound or spackle applied smoothly and sanded.  No other steps required, just prime and paint.

Small and medium holes can be patched easily with a small piece of drywall  of any thickness.   First  square off the hole with a drywall saw.  Now cut a patch  2 – 3 inches larger than the hole.  On the back of the patch, scribe the dimensions of the hole with equal spacing all the way around.  Now cut the back paper along the lines, fold and peel off the gypsum core.  This should leave you with a patch the perfect size which has a paper flap all around the front.  Now you simply apply drywall compound around and inside the hole and apply the patch.  Large holes will require some bracing using a plywood strip along each edge.  Simply screw it to the back of the drywall and allow it to overhang by half.  Now cut a patch to fit inside the hole and screw it to the braces.  Now you can cut the patch in the same fashion as above with the paper flap or you can use drywall tape to mend the edges.
Now after the first coat has dried apply a second coat over the entire patch expanding out 8 -10 inches all the way around.  Third coat will be expanded out another 8 – 10 inches .  This is where the blending is really going to make the difference between the patch you can see and the invisible patch.  We can pretty well detect any deviation in the wall over 1/8” to the foot so keeping the patch tight with a lot of pressure on the trowel and using as little compound as possible is very important  and will result in a much cleaner finish.  Once everything is dry sand and be sure that you feather the patch around all the edges.   Do this by shining a light oblique to the wall. This will illuminate any high spots that will become apparent when the wall is painted.  Sand them smooth and wipe down the dust.
Now when you prime you want to expand out another foot or so all the way around.  Now your baseball sized patch has grown to about three feet but should be invisible if you have done everything right.
Painting is now straight forward provided you have some left over from the last time you painted.  If you do just paint two coats over your patch and you should be good to go.  If you don’t, then you will have to have more mixed to the same recipe as the old color.  The problem with that is the newly tinted color, even though the code is the same as the last, will not match the old paint exactly.  So to overcome this you will  have to paint the entire wall, from corner to corner.  The color will be close enough that you won’t be able to tell that it changes at the corner but stopping in the middle of the wall will leave obvious color, gloss, or texture differences.

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