Building kitchen - 90 degree in the corner

[jeric.cire]

Hello! I have a charming old house from 1929. As you can understand, not much is perfectly straight.

I'm going to build a kitchen with only lower cabinets - so any slope on an individual wall (between ceiling and floor) doesn't really matter to me. I've already framed this wall and made sure it's level (horizontally).

However, I'm a bit puzzled about how to ensure it will be 90 degrees between the two walls - meaning the corner is 90 degrees. I might be missing the forest for the trees. But how do I easily ensure it's 90 degrees?

What I'm currently thinking is that I could use an OSB board and place it in the corner of the room (can I trust that it's 90 degrees?).

Follow-up question: If the corner is not 90 degrees, how do I best correct this? One wall is already fixed. The other will get new surfaces (OSB + gypsum), so there's an opportunity to make adjustments before I install the OSB. But how?

Thanks in advance and sorry for the dumb and "simple" question.

 

[Slunken]

Hi, I dare to say that there are probably no corners that are E X A C T L Y 90 degrees anywhere.

However, I didn't understand if you are going to build another wall or if the corner already exists and you just want to know if it's 90 degrees?!
Edit: OK, read it again, it's half-finished.

A board sounds excellent to use as a template, provided it is fresh/unmodified.

 

[KnockOnWood]

What does it matter if the corner isn't exactly square, or 90°?
That's part of the charm with old houses.
And it's easy to cut a countertop at the angle the corner has.

 

[Slunken]

If you have a sketch or pictures, I think you'll find it easier to get help.

 

[jeric.cire]

Hi, I dare say there probably aren't any wall corners anywhere that are E X A C T L Y 90 degrees.

However, I didn't understand if you were going to build another wall or if the corner already exists and you just want to know if it's 90 degrees?!
Edit: OK, read it again, it's half-finished.

A sheet sounds absolutely perfect to template with, provided it's fresh/unmodified.

The corner already exists! I'm going to fix a new surface on one wall, so I have the opportunity to correct it to be 90 degrees. Thanks for the reply, I'll use an OSB board (newly purchased).

If there's a slight difference - what can I put behind OSB+plaster to adjust?

 

[Stuff]

Use the 3-4-5 method (based on Pythagoras' theorem)
Measure from the corner and out on one wall and make a mark at 3m. Measure from the corner and out on the other wall and make a mark at 4m. Then measure the diagonal between these points. If the angle in the corner is right, the diagonal should be 5m.

 

[jeric.cire]

What does it matter if the corner isn't exactly perpendicular, or 90°?
It's part of the charm with old houses.
And it's easy to cut a countertop at the angle the corner has.

That's right, if you cut your countertop! Harder when it's a countertop in kalksten ;-)

 

[Rickard.]

Use the 3-4-5 method (based on the Pythagorean theorem) Measure from the corner and out on one wall and make a mark at 3m. Measure from the corner and out on the other wall and make a mark at 4m. Then measure the diagonal between these points. If the angle in the corner is right, the diagonal should be 5m.

Adding here that this method can of course be adjusted to any measurement if the kitchen happens to be smaller than the incredibly suitable 3,4,5. Just Google the Pythagorean theorem if you need to refresh your memory.

 

[KnockOnWood]

If it differs a little - what can I put behind OSB+gypsum to correct?

That's right, if you saw your countertop! Harder when it's a countertop in limestone ;-)

Oh, it's easy to saw limestone! The Egyptians managed it back in the Pharaoh's time.

But putting up a new wallboard on top of the existing wall, supported by a couple of strips/filler boards shouldn't be too hard to do, right?

 

[major_tom]

if there is a slight difference, a gap between the wall and the countertop can be concealed with both tiles and a trim