Cracks in a New House in Thailand: Normal, or a Warning Sign?

Cracks After Moving In: Something Almost Every House Gets

Cracks appearing after you move in are something nearly every new homeowner meets during the first year, and nearly everyone is equally alarmed by them. The reality is that concrete and cement render shrink naturally as they dry, and different materials expand at different rates under sun and rain, so a certain number of small cracks will appear even in a well-built house.

What you need to separate is which cracks are a matter of the surface finish and which are a signal coming from the structure. The two look different, appear in different places, and call for completely different responses. The first can be filled and painted over; the second needs an engineer.

This article works through the crack types seen most often in houses around Korat, Roi Et and Khao Yai, with simple ways to judge which can wait, which cannot, and what you should record before you call the contractor.

Render and Material-Joint Cracks: The Group Not to Worry About

Fine hairline cracks spreading across a wall in a web pattern, usually called crazing or map cracking, come from cement render shrinking as it dries. They are most common on walls that take strong sun, such as west-facing walls. These cracks are shallow, do not reach through to the brickwork, and do not widen over time. The repair is to rub the surface back, fill it, and repaint.

Straight cracks running along the joint between two different materials, such as where a brick wall meets a concrete column or where a door frame meets the wall, come from two materials moving by different amounts. These run vertically or horizontally along the joint line rather than diagonally, and they usually appear in the first year and then stay put.

Short diagonal cracks at the top corners of doors and windows belong in this group in most cases, because the corners of openings concentrate stress in the wall. If the crack is no longer than the width of a hand, less than a millimetre wide, and not getting longer, it is a surface crack. If the same crack runs all the way to the floor or the ceiling, read the next section.

Which Cracks Mean Calling an Engineer Straight Away

Long diagonal cracks that step through the mortar joints from a lower corner of a wall to an upper corner are telling you that the wall is being pulled or pushed by uneven settlement of the foundations. This kind of crack is typically wider at one end than the other, and several of them often appear at once in the same house. It is not a crack to fill and paint over.

Cracks on a concrete column or beam itself, whether running across a column, diagonally on a beam, or spalling the concrete until the reinforcement shows, need an engineer the same day. Columns and beams carry the weight of the whole house, so cracking in the structure is a matter of safety rather than appearance.

Signs that appear alongside cracking and help confirm a structural cause are doors or windows that used to close flush and no longer do, a floor that feels sloped when a marble consistently rolls one way, floor tiles cracked in a long line, or a gap opening up between the floor and the skirting. If you find diagonal cracks together with any of these, do not sit and watch.

Cracks in Slabs and Around the House Come From the Fill, Not the House

Most houses built outside the cities stand on land that has been recently filled. Fill keeps consolidating for months or even years afterwards. The house itself sits on piles and does not move with it, but anything cast directly on the ground does: parking slabs, paths around the house, laundry yards and fences. The result is a split between the external paving and the house, or slabs that crack in long lines.

These cracks look frightening because they are sometimes a centimetre or more wide, but they are not a structural problem with the house. The giveaway is that the split sits exactly at the joint between what rests on soil and what rests on piles, and the house itself shows no diagonal cracking and no sticking doors. Houses around Roi Et, where plots are often filled high to stay clear of floodwater, show this most clearly.

The fix is to wait until the fill has settled before making a permanent repair, which may mean waiting into the second year. In the meantime, seal the gap with a flexible sealant so that water cannot run down and wash out the soil beneath the slab. Breaking out and recasting the paving in the first year usually ends with the same crack in the same place.

How to Watch a Crack and Tell Whether It Is Moving

The best tools for this are a pencil and a calendar. Draw a line across each end of the crack, write the date next to it, and photograph it with a coin or a ruler in the frame for scale. Repeat every two weeks. If the crack runs past the lines you drew, or its width visibly increases, it is still moving.

Width is an easy measure to use. A crack that will not take a credit card is narrow, one that will take a card is worth watching, and one wide enough to see through or let light past needs attention now. The other thing worth noting is timing: a crack that opens in the hot season and closes in the rains is telling you the soil around the house is shrinking and swelling with moisture, which happens on some of the clay plots around Korat.

These records are what an engineer wants to see, far more than a spoken account. A crack that has been stable for two months and a crack that lengthens every week lead to different conclusions, and the notes are evidence you can use in a warranty discussion without either side arguing from impressions.

How Far the Warranty Covers Cracking, and How to Report It

A standard construction contract splits the warranty in two. General work such as render, paint and finishes is usually covered for about one year, while the main structure is covered for far longer, with Thai civil law setting liability for structural defects in a building at five years. Render cracks should therefore be reported within the first year, structural cracks can be raised over a longer period, and both should be reported the moment you find them.

Always report in writing. Send a Line message or an email with photographs, the date you found the crack and its location in the house, and keep that message. A phone call proves nothing about when you reported the problem. Ask the contractor to come and look at the site before any repair is carried out, rather than sending a worker to fill it immediately with nobody diagnosing the cause, because closing a crack without knowing where it came from only hides the symptom.

Houses handed over by the OBILIS team include a scheduled inspection of cracking and settlement around the property during the first months of occupancy, so that surface cracks which can wait for a single combined repair visit are clearly separated from anything an engineer should look at. Whoever you build with, ask before you sign whether there is a post-occupancy inspection and which kinds of cracking fall under whose responsibility.

To get a rough budget before you talk to anyone, try our house price calculator, or contact the OBILIS team to talk through your plot.

Related reading: House Inspection Before Handover in Thailand: Full Checklist

Frequently Asked Questions

My new house has fine crazing on the walls. Should I be worried?

In most cases, no. Crazing is render shrinking as it dries and is most common on walls in strong sun. It is shallow, does not reach the brickwork, and does not widen. Mark it and record it, and if it is stable after two months it can be filled and painted during the first-year warranty repair round.

Which cracks mean stopping everything and calling an engineer?

Long diagonal cracks stepping through the mortar joints, cracks on columns or beams themselves, spalled concrete exposing the reinforcement, and any crack that comes with doors that will no longer close or a floor that feels sloped. These say the foundations or the structure are moving, and they should not be filled or painted over before someone has diagnosed them.

The parking slab has pulled away from the house. Is the house settling?

In most cases it is not. The parking slab rests on fill and settles with it, while the house rests on piles and does not, so the split opens at the joint between them. If the house shows no diagonal cracks and the doors still close flush, seal the gap against water and wait for the soil to stabilise before making a permanent repair.